Abstract: 1. Floristic Part (1) Natural Environment (2) Distributive Types of Genera (3) Eco-Geographical Distribution of Species (4) Analysis of endemic Species (5) Compare with Adjacent Flora (6) Floristic Characteristics and Areal Area 2. Systematic Part (1) Index to the System (2) Gramineae (3) Key to The Genera (4) Subfam.1.Oryzoideae (5) Subfam.2.Arundinoideae (6) Subfam.3.Pooideae 3. References 4. Index Kunlun Mountains general situation
Abstract: Foreword:
National Range and Pasture Handbook
The National Range and Pasture Handbook (NRPH) constitutes Natural
Resources Conservation Service (NRCS) basic policy and procedures for
assisting farmers, ranchers, groups, organizations, units of government, and
others working through conservation districts in planning and applying
resource conservation on non-Federal grazing lands throughout the United
States. This handbook may also serve as a general reference for grazing
lands resource information. It was prepared primarily for NRCS use, but
others who are interested in grazing lands conservation may find it useful.
The NRPH was developed by NRCS grazing lands specialists using their
experience and many textbooks, scientific publications, manuals, and other
references. The authors of the National Range and Pasture Handbook thank
the many authors of these references for their work and contribution. The
NRPH does not use scientific reference notations or citations in the text
unless a direct quote is used. It does list references in a reference section.
This format was chosen to make the NRPH a resource manager, field-user
friendly, easy-to-read handbook and reference.
There are 634 million acres of non-Federal (privately owned, state and local
publicly owned, and tribally owned) grazing lands in the United States. Non-
Federal grazing lands are in every state. These rangelands, pasturelands,
haylands, grazed forest lands, grazed croplands, and naturalized pastures
constitute about half of the total lands on which the NRCS provides technical
assistance, through conservation districts, at the request of the cooperator
(the owners or managers of these lands). This technical assistance
provides a source of expertise to guide cooperators in solving resource
problems and in sustaining or improving their grazing lands resources and
operations. Guidance for developing conservation plans with cooperators
on grazing lands is based on current NRCS policy relative to consideration
of all soil, water, air, plant, and animal resources, as well as, the
cooperator’s objectives.
This handbook replaces the National Range Handbook (1976), which was
only applicable to rangelands and other native grazing lands. In addition to
providing guidance for rangelands, the NRPH includes information and
guidance for pasturelands, haylands, grazed forests, grazed croplands, and
naturalized pastures. The ecological principles used in the former handbook
are updated, and new ecological principles have been added. New
technology is included for enterprise diversification and grazing lands
hydrology. Technical guidance for livestock husbandry, nutrition, and
behavior science, as well as wildlife habitat management has been expanded.
Economic analysis tools and their interpretations are explained.
This handbook, along with other appropriate NRCS technical and policy
guidance manuals and handbooks, contains information to assist the NRCS
conservationist in providing technical assistance to cooperators in all
phases of the planning and application process. The NRPH deals with the
policy and procedures for the study, inventory, analysis, treatment, and
management of the grazing lands resources.
Abstract: This book is the happy result of a collaboration between scientists working in Australia and China. It combines taxonomic and descriptive skills with computer methodology, automated key making and databass applications. China has a rich grass flora – some 213 genera and 1124 species, according to the researches of one of authors, Mr. XU ZHU – so that this account of the grass genera of China, employing automated descriptions and keys, will be major contribution to the literature and a useful tool ofr both pure and applied plant scientists. It constitutes , in effect, part of a series of account of grass genera of different parts of the world in the preparation of which Drs Watson and Dallwitz have been engaged.
Abstract: Ethnobotanical information relevant to the management of savanna vegetation was obtained through interviews with 57 elderly villagers living near Delta du Saloum National Park, Senegal. Local people had observed a change in the local environment from forest to savanna during their lifetime and considered it primarily a result of frequent intensive fires and declining rainfall. Most people preferred the woody vegetation to be dense. In particular, nine woody species were useful for construction, 10 for protection in agricultural fields, 19 for medicine and 10 for livestock fodder. Some of the locally highly preferred species were also considered to be declining in the local environment, they included Cordyla pinnata, Pterocarpus erinaceus, Daniellia oliveri, Parkia biglobosa, Khaya senegalensis and Pericopsis laxiflora. Highly preferred and declining species were characteristically large trees, non-thorny, with edible fruits and of Sudano-Guinean to Guinean affinity. The study furthermore identified a close coincidence between the interest in conserving tree species diversity in protected areas and the priorities of local people which included preservation of plenty of large trees (including many fruit trees), maintenance of a variety of species, improvement of woody regeneration, and reduction of fire intensity and frequency. Focusing management strategies on increasing populations of such declining and highly preferred species, by active fire protection for instance, would enhance the natural resource value considerably and thereby the quality of life for the local people.
Abstract: Relationships between soil characteristics, various forms of soil organic matter, microbial biomass and the structure of phytoparasitic nematode populations were investigated in six fallow fields aged from 1 to 26 years in the West African Savanna (WAS) belt in southern Senegal. Soil sampling was performed along two transects in each field. Herbaceous biomass and soil physical, chemical and biological characteristics were studied with principal component analysis (PCA) and the relationships between the parameters were extracted with co-inertia analysis. Soil properties (mainly calcium, magnesium and total carbon contents, and cation exchange capacity) slightly improved in the upper soil layer (0-5Â cm) during the succession of vegetation. In constrast, in the 0-10Â cm soil layer, microbial biomass and total soil organic carbon content showed no clear pattern of change over time, while highest charcoal stocks were found in older fallows where bush fires are frequent. In the 0-40Â cm layer, living root biomass increased and herbaceous biomass decreased through the chronosequence. Evidence is presented here for particular relationships between some of the carbon components and the structure of the nematode community. Pratylenchus and Ditylenchus species were associated with the grass vegetation of the youngest fallows. In contrast Helicotylenchus and Scutellonema were present in old fallows. The multiplication of the latter appeared closely related to the presence of woody fine roots, whereas, that of the former seemed to be favoured by the presence of the coarsest roots of trees. Xiphinema had a higher density in soils with higher bulk density. Microbial biomass was not affected by fallow duration and was not correlated with the abundance of non-phytoparasitic nematodes. These results suggested that the management of crop pests such as nematodes in the soils of the WAS could be exerted through stump protection and tree plantation (improved fallow, agroforestry) during the crop-fallow cycle.
Abstract: The Tool for Exploratory Landscape Scenario Analyses (TELSA) is a spatially explicit model of vegetation succession, natural disturbances, and forest management activities. TELSA is a strategic planning tool designed to support adaptive management by projecting the consequences of alternative scenarios at the scale of landscape units (i.e. 10[punctuation space]000-200[punctuation space]000 ha) over time frames of decades to centuries. Scenario combine user-specified assumptions about natural disturbances and management activities, and can include [`]no action' or historic disturbance scenarios. The simulation model is at the core of a set of tools that also includes a geographic information system, databases, and several user interfaces for scenario definition, data analysis, spatial analysis and the display of results. Spatial characteristics of landscapes, such as fragmentation, patch-size distribution and connectivity are largely determined by management actions and their interaction with natural disturbances. The TELSA toolbox includes a tool for the automated design of management units (i.e. harvest cutblocks), based on user-defined criteria and scenario objectives. TELSA easily evaluates strategic alternatives regarding the size range of management units, their spatial aggregation, the use of adjacency constraints, and the application of different silvicultural systems. TELSA represents vegetation succession as changes in species composition and structural stages of stands, thus projecting landscape conditions in a format that is relevant for the analysis of wildlife habitat and many other resource indicators. Succession pathway diagrams define the transition times between successional classes and, for each class, the probabilities and impacts of disturbance by insects, fire or other agents. These diagrams also define the impacts of management actions on stand structure and vegetation composition. Diagrams can be defined for forests and other vegetation types such as shrub and rangelands. Wildfires and other natural disturbance events that affect vegetation dynamics are inherently unpredictable. The model can use multiple stochastic simulations of each scenario to provide estimates of the mean, range and variability of selected performance indicators.
Abstract: Estimates of the value of carbon sequestration services provided by a savanna ecosystem and of the value of water for the supply of a number of environmental goods and services are developed in a Zimbabwean case study using an ecological-economic model that captures the interactions between ecological and economic processes. The estimated values of carbon sequestration, in both the woodlands of the Communal Area and the State Forest, are substantial, but slightly lower than the value of converting these lands to individually held agricultural land. This, and the lack of markets in which individuals can be compensated for maintaining some land under woodland as a store for carbon, creates strong incentives for households to convert woodlands to agriculture. There is a high value for additional water availability, associated with the supply of wild foods, firewood, crop production and carbon sequestration, suggesting that efforts towards conservation in this eco-region can have high economic returns.
Abstract: This paper describes an adaptive agent model of rangelands based on concepts of complex adaptive systems. The behavioural and biological processes of pastoralists, regulators, livestock, grass and shrubs are modelled as well as the interactions between these components. The evolution of the rangeland system is studied under different policy and institutional regimes that affect the behaviour and learning of pastoralists, and hence the state of the ecological system. Adaptive agent models show that effective learning and effective ecosystem management do not necessarily coincide and can suggest potentially useful alternatives to the design of policies and institutions.
Abstract: Since attainment of independence, almost every country in East and Southern Africa has introduced some kind of land reform aimed at reconciling indigenous land tenure practices and those introduced by colonial regimes. The reforms have centred on modification of tenurial rules on access, ownership, administration and transfer of land rights coupled with land redistribution and/or restitution in some countries. With the exception of a few countries, such as Botswana, land reforms have largely remained on statute books with little to show on the ground. The paper gives an overview of land reforms in East and Southern Africa, taking Botswana as a case study. It notes that although Botswana has largely been successful in implementing land reforms, it is currently experiencing land tenure problems, especially in peri-urban settlements and inner city low-income areas, despite government's enhanced control over local land administrative structures. The paper ends with suggestions on how to contain the current problems.
Abstract: A preliminary investigation was carried out to evaluate the nutritive value of six forb species widely used as feedstuffs in West Africa. The study examined four legumes (Crotalaria senegalensis, C. goreensis, Alysicarpus glumaceous and A. rugosus) and two non-legumes (Cassia mimosoides and Ipomea eriocarpa). Field observations on gross phenology of these forbs illustrate their potentials in increasing the range of native forages for use in pasture development or improvement. All species sustained growth on residual soil moisture into the dry season providing green forage when most associated forages had dried up. Results of chemical analysis reveal that the species have properties in terms of contents of protein and some mineral elements that could be advantageously employed to balance animal ration or improve the quality of standing hay of tropical pastures. The species had mean values of 14-18% CP, 3.5-7.0% Ca and 40-58% DMD. Levels of Ca was high and more than 10 times the standard requirements for ruminant production in the tropics. While levels of P, K, Mg and Fe were sufficient, Mn and Na were low, and apparently deficient. The high levels of Ca resulted in unusually wide Ca : P ratios of 16 : 1-33 : 1 among the species. The implications of these findings on uses of the forages in ruminant nutrition and the need for intensive studies on the observed results are discussed.
Abstract: The Universal Soil Loss Equation (USLE) was used to predict soil erosion hazard in the Upper Ewaso Ng'iro North basin of Kenya using data from erosion plots and reconnaissance surveys. The R-factor (rainfall erosivity) was determined by extrapolation from the rainfall amount-erosivity relationship, using data from autographic records. The K-factor (soil erodibility) was determined using data obtained by laboratory analysis of soil samples collected from 83 test sites in the basin. The LS-factors (slope length and steepness) were determined from a digital elevation model (DEM) of the basin, while the C-factor (crop and management) was determined from vegetation cover data, obtained from SPOT imagery and field surveys. The P-factor (conservation practice) was estimated from maps of soil conservation, obtained from the Ministry of Agriculture. A raster-based Geographic Information System (GIS) was used to interactively calculate soil loss and map erosion hazard. The results obtained were comparable to measured soil loss values from erosion plots. About 36 percent of the Upper Ewaso Ng'iro basin was predicted to have high risk of erosion, most of this land being in the overgrazed rangelands. Land use and management were the major factors associated with soil erosion, and -- to a lesser extent -- the topography. Due to the reconnaissance scale of this study there were limitations in determining reliable LS, C and P factors for the USLE. In addition, there is a need for research to determine appropriate P-factors for local soil conservation practices, such as trash lines, fanya-juu terraces and stone lines.
Abstract: A number of methodological approaches to understanding and quantifying the potential impacts of changes in macroeconomic and sectoral policies on the natural resource environment have been developed in recent years. However each has its limitations, resulting in policy change still being implemented without due attention to environmental impacts. Two key drawbacks of those methodologies that do attempt to model these impacts are that they are generally static in their approach, thus may not alert the decision maker to the often quite different long-term implications, and that they attempt to generate rather specific sets of indicators, making them difficult to use and/or interpret outside case study applications. In this paper we expound a framework for addressing these limitations in the context of the agriculture sector. In developing countries in particular the dynamic dimension is critical given the twin pressures of population growth and rising incomes associated with economic growth. In light of the second drawback, it is the propensity of policy to impact upon the natural resource environment via its effect on the type of farming practice adopted that forms the focus of the paper. A methodology is first developed to facilitate the tracing of likely impacts of both price and non-price reforms, via both the incentives and constraints to increased food production. By separating out the impacts on environmental indicators associated with extensification and intensification of agriculture, it is possible to determine which of these indicators are most likely to be affected by policy changes, and to what degree in both the short and longer term. The framework is then applied to case study data from the South African agriculture sector to demonstrate how consideration of the risk of natural resource degradation earlier in the policy dialogue process could result in the implementation of more effective complementary measures.
Abstract: Many introduced plant species rely on mutualisms in their new habitats to overcome barriers to establishment and to become naturalized and, in some cases, invasive. Mutualisms involving animal-mediated pollination and seed dispersal, and symbioses between plant roots and microbiota often facilitate invasions. The spread of many alien plants, particularly woody ones, depends on pollinator mutualisms. Most alien plants are well served by generalist pollinators (insects and birds), and pollinator limitation does not appear to be a major barrier for the spread of introduced plants (special conditions relating to Ficus and orchids are described). Seeds of many of the most notorious plant invaders are dispersed by animals, mainly birds and mammals. Our review supports the view that tightly coevolved, plant-vertebrate seed dispersal systems are extremely rare. Vertebrate-dispersed plants are generally not limited reproductively by the lack of dispersers. Most mycorrhizal plants form associations with arbuscular mycorrhizal fungi which, because of their low specificity, do not seem to play a major role in facilitating or hindering plant invasions (except possibly on remote islands such as the Galapagos which are poor in arbuscular mycorrhizal fungi). The lack of symbionts has, however, been a major barrier for many ectomycorrhizal plants, notably for Pinus spp. in parts of the southern hemisphere. The roles of nitrogen-fixing associations between legumes and rhizobia and between actinorhizal plants and Frankia spp. in promoting or hindering invasions have been virtually ignored in the invasions literature. Symbionts required to induce nitrogen fixation in many plants are extremely widespread, but intentional introductions of symbionts have altered the invasibility of many, if not most, systems. Some of the world's worst invasive alien species only invaded after the introduction of symbionts. Mutualisms in the new environment sometimes re-unite the same species that form partnerships in the native range of the plant. Very often, however, different species are involved, emphasizing the diffuse nature of many (most) mutualisms. Mutualisms in new habitats usually duplicate functions or strategies that exist in the natural range of the plant. Occasionally, mutualisms forge totally novel combinations, with profound implications for the behaviour of the introduced plant in the new environment (examples are seed dispersal mutualisms involving wind-dispersed pines and cockatoos in Australia; and mycorrhizal associations involving plant roots and fungi). Many ecosystems are becoming more susceptible to invasion by introduced plants because: (a) they contain an increasing array of potential mutualistic partners (e.g. generalist frugivores and pollinators, mycorrhizal fungi with wide host ranges, rhizobia strains with infectivity across genera); and (b) conditions conducive for the establishment of various alien/alien synergisms are becoming more abundant. Incorporating perspectives on mutualisms in screening protocols will improve (but not perfect) our ability to predict whether a given plant species could invade a particular habitat.
Abstract: Livelihood security in Eastern and Southern Africa is strongly dependent on rainfall distribution and land management practices among smallholder farmers. Over 95 % of the land used for food production is based on rainfed agriculture. The major challenge for the rural communities, representing up to 80% of the population in certain countries, is to improve the productivity of the arable land and the available water resources. This paper gives an outline of the hydrological challenges facing smallholder farmers with focus on water scarce areas. The importance of rainfall partitioning rather than rainfall totals is discussed. The main focus is on the management of rural water using low-tech practices, both for domestic purposes and for crop production. Case studies from Eastern and Southern Africa are presented, showing the potential of stabilising the water supply over time both for livestock, household use, and for crop production. The challenges facing research and extension of introducing water management on different scales (household, community, catchment) is discussed.
Abstract: Climate change is a reality and will affect the poor in developing countries in many ways. The effectiveness of global change research could be substantially improved by linking International Geosphere-Biosphere Programme (IGBP) study with Consultative Group on International Agricultural Research (CGIAR) centres based in the tropics. These centres are carrying interdisciplinary research and development on how to achieve food security and reduce rural poverty through the innovative management of natural resources. A CGIAR intercentre working group on climate change (ICWG-CC) identified joint opportunities that take advantage of the comparative advantages of both institutions. CGIAR centres will focus on adaptation and mitigation research in developing countries. A natural resource management research approach is suggested, which consists of six steps: (1) identifying and quantifying the extent of food insecurity, rural poverty and resource degradation; (2) conducting technological and policy research on economic and environmental functions; (3) optimising the trade-offs between global environmental benefits and private farmer benefits; (4) extrapolating and disseminating results, including research on policy implementation; (5) assessing impact and (6) providing feedback. Two examples of current CGIAR research illustrate this approach. Agroforestry alternatives to slash and burn (ASB) agriculture at tropical forest margins were identified and the trade-offs between carbon sequestration and farmer profitability provided options to policy makers. Land tenure problems were resolved with participatory policy research. Agroforestry practices sequester an additional 57Â Mg C per ha, three times that of croplands or grasslands are able to do. Soil nutrient capital is being replenished in subhumid tropical Africa through improved leguminous tree fallows, rock phosphate and biomass transfers of Tithonia diversifolia, helping farmers to attain food security. Afterwards, when farmers shift to high-value tree or vegetable crop production, poverty is reduced. The transformation of low productivity croplands to sequential agroforestry is estimated to triple system carbon stocks in 20Â years.
Abstract: The scale "jump" in hydrology and agriculture from the small scale at which individual processes such as infiltration, soil water redistribution, evapotranspiration, soil loss or crop development/yield have been studied, to the global scale at which climate change impacts and international trade in agriculture manifest themselves, has presented agrohydrologists with conceptual as well as practical problems of scales and scaling. In this context, selected scaling issues are, therefore, identified and highlighted. The paper discusses why scaling problems arise, defines concepts and types of scales, poses what are considered key questions with regard to upscaling and downscaling, as well as to dis-aggregation to homogenous landscape response units (HLRUs) and to re-aggregation. Examples from southern Africa are then given of space/time scaling approaches, ranging from country to local-scale levels, followed by an evaluation of types of errors associated with scaling. The paper concludes by identifying what, in the author's perception, some of the challenges are which relate to scaling applications of the "real world" and which hydrologists and agriculturists face in the next few years.
Abstract: The value of ants as bioindicators of incipient environmental change in rangeland condition was assessed on a local scale in the South Australian arid zone. The sensitivity of ants to intense pulses of unsustainable grazing was tested, in order to identify species, functional groups or community variables that could be used as indicators of more typical grazing pressure. Genera represented by the largest number of species were Iridomyrmex, Melophorus, Camponotus andMonomorium . A significant decrease in captures of Rhytidoponera metallica was recorded on swales, whereas theIridomyrmex sp.(bicknelli) group increased on dunes relative to controls following grazing. The Generalized Myrmicinae functional group increased on swales, and Hot-climate Specialist ants increased on dunes, after grazing. Several other species and functional groups responded qualitatively but not significantly. However, neither overall ant abundance and richness, nor the abundances of most of the common species and functional groups responded significantly to grazing in this local scale experiment, which rendered ants of limited use as early warning indicators of unsustainable management. The use of ants for this purpose is constrained by a lack of knowledge of the ecology of individual ant species, particularly of the less common and more localized species that are likely to be most sensitive to disturbance.
Abstract: New South Wales (NSW) can be regarded as one of the more "data-rich" parts of the world but its detailed biological data sets, like others elsewhere, are localised. These data are therefore not useable over large geographical areas for consistent reviews of established protected areas or future conservation priorities. In this sense, the constraints of data are similar to those in other parts of the world, including global biodiversity hotspots. We describe here the development of a new classification of landscapes at a scale of 1:250,000 across the whole 802,000 km2 of NSW. The classification is derived mainly from abiotic data and, in conjunction with new data on native vegetation cover, has allowed the first quantitative State-wide review of protected areas and future priorities at a scale approaching that of decisions about land use. We also describe methods for measuring biases in the coverage of reserves in relation to land use potential, mapping numerical conservation priorities across extensive areas, and producing quantitative profiles of priorities for the remaining native vegetation on private land relative to that on other tenures. The same or similar approaches to developing the landscape classification and analysing biases and priorities are feasible for many other jurisdictions or natural regions. We found that most of the 1486 landscapes in NSW are poorly reserved relative to an indicative conservation target of 15% of the total area of each (the baseline target in recent national planning for forest reserves). In the eastern 60% of the State, gaps in the reserve system are related to the concentration of reserves on land with high ruggedness and low potential for intensive land use. We measured the relative priority of landscapes to indicate the urgency of conservation action to prevent conservation targets being compromised (or further compromised) by clearing of native vegetation. Mapping of priorities shows large differences within and between natural regions and land tenures. More than 9% of private land is occupied by high-priority native vegetation and, across the whole State, about 85% of high-priority vegetation occurs on private land.
Abstract: The grazing behaviour of two mixed flocks of sheep and goats on a Sahelian rangeland was observed in the Far North Province of Cameroon. The area was dominated by thorn shrubs and a herbaceous layer made up of annual grasses. The study ran for 9 months, covering the rainy (June-September), post-rainy (October-December) and cold dry (January-March) seasons. A simple method was adapted for estimating the dietary preference of goats and sheep, and variation in plant biomass. Observation on the vegetative cycles of some browse species was also done to see whether this influenced dietary preference. It was noticed that sheep and goats possess a certain degree of nutritional wisdom and that contrary to what most people might think, no amount of feed scarcity could force them to feed on some undesirable forage species. Browse species with high preference indices were Acacia seyal, A. senegal, Pterocarpus lucens and Ziziphus mauritiana. Goats spent 75% of their grazing time browsing, while the reverse was true for sheep. Maximum plant biomass was noticed in the month of September and high preference indices in the rainy season were seen to correspond to stages of maximum foliation of the browse species. The fruits, blossoms and pods produced by some of the browse species made a reasonable contribution to the diet of both goats and sheep, particularly in the dry season. Given the reputation of goats as highly-selective feeders, range management programmes should aim at preserving plant communities that are highly diversified in botanical structure as well as ensuring the survival of the tree species that are highly browsed by herbivores.
Abstract: A reliable estimation of primary production of terrestrial ecosystems is often a prerequisite for land survey and management, while being important also in ecological and climatological studies. At a regional scale, grassland primary production estimates are increasingly being made with the use of satellite data. In a currently used approach, regional gross, net, and aboveground net primary productivity (GPP, NPP, and ANPP) are derived from the parametric model of Monteith and are calculated as the product of the fraction of incident photosynthetically active radiation absorbed by the canopy (fAPAR) and gross, net, and aboveground net production (radiation-use) efficiencies ([epsilon]g, [epsilon]n, and [epsilon]an); fAPAR being derived from indices calculated from satellite-measured reflectances in the red and near infrared. The accuracy and realism of the primary production values estimated by this approach therefore largely depend on an accurate estimation of [epsilon]g, [epsilon]n, and [epsilon]an. However, data are scarce for production efficiencies of semiarid grasslands, and their time and spatial variations are poorly documented, often leading to large errors for the estimates. In this paper, a modeling approach taking into account relevant ecosystem processes and based on extensive field data was used to estimate time variations of [epsilon]g, [epsilon]n and [epsilon]an of a shortgrass site in Arizona. These variations were explained by variations in plant water stress, temperature, leaf aging, and processes such as respiration and changes in allocation pattern between above- and below-ground compartments. Over the 3 study years, averaged values of [epsilon]g, [epsilon]n, and [epsilon]an were found to be 1.92, 0.74, and 0.29 g DM (MJ IPAR)-1, respectively. [epsilon]g and [epsilon]n exhibited large interannual and seasonal variations mainly due to changes in water limitations during the growing season. Interannual variations of [epsilon]an were much less important. However, for shorter periods, [epsilon]an exhibited very contrasting values from regrowth to senescence. The calculation of ANPP seems less prone to errors due to environmental effects when computed on an annual basis. When estimating GPP and NPP, better results are expected if water limitations are taken into account. This could be possible through the estimation of a water-stress factor by using surface temperature or other indices derived from thermal infrared remote sensing data. The limitations due to temporally varying efficiencies, shown here for shortgrass ecosystems, are also relevant to all drought-exposed ecosystems, particularly those with abundant evergreen or perennial species.
Abstract: Using normalized difference vegetation index (NDVI) imagery, we examined changes in vegetative cover across Tanzania and found that overall greenness increased over 13 years from 1982 to 1994. We then assigned 8 km pixels to different habitat types using a vegetation map compiled from Landsat satellite imagery between 1978 and 1982. We found that woodland and forest pixels increased in greenness but that swamp pixels showed a marked decline in vegetative cover. National parks and game reserves, which have heavy restrictions on resource extraction and on-site patrols, both showed increases in vegetative cover, particularly for woodland pixels. Forest reserves, which are explicitly designed for forest protection but do not have on-site patrols, did no better than lands under no legal protection at all. Game controlled areas, which allow for settlement, cattle grazing, and hunting, suffered worse habitat degradation than areas with no legal protection, with bushlands, grasslands, swamps and "other lands" pixels faring worse than baseline measures. These results show that complete protection and on-site policing are key elements in enhancing vegetation health in this region of tropical Africa, paralleling results for mammals in the same area.
Abstract: Entire sub-Saharan Africa and pockets of Asian population is at risk of starvation. The problems and possibilities are however quite different amongst the two regions. Africa with its less than 8% of land irrigated, 3% or more population growth rate, continues to practice only rudimentary, nonscientific form of agriculture. In Asia where input use is high, farmers are approaching economically optimum yield levels, making it difficult to sustain the same rate of yield gains. While efforts to improve long-term productivity on small scale farm must be accelerated, more emphasis must also be placed on research that will help farmers and governments better cope with expected increases in risks resulting from climatic fluctuations, use of limited water resources, poor market integration and other problems. Finally we believe that all appropriate scientific tools including advanced weather forecasting, information technologies such as models, decisions tools should be mobilized to help solve the problems facing small-scale farmers in developing countries. Due to lack of financial support, the network of meteorological stations do not adequately cover various agrometeorological zones to meet user needs. The general lack of confidence in the reliability of weather forecasts has caused farmers not trust and use the weather forecasts. Training opportunities for meteorological services staff in the use of modern tools like computer simulation modeling, remote sensing, geographic information systems as well as electronic instrumentation is needed.
Abstract: Mapping the abundance of 13C in leaf-wax components in surface sediments recovered from the seafloor off northwest Africa (0-35°N) reveals a clear pattern of [delta]13C distribution, indicating systematic changes in the proportions of terrestrial C3 and C4 plant input. At 20°N latitude, we find that isotopically enriched products characteristic of C4 plants account for more than 50% of the terrigenous inputs. This signal extends westward beneath the path of the dust-laden Sahara Air Layer (SAL). High C4 contributions, apparently carried by January trade winds, also extend far into the Gulf of Guinea. Similar distributions are obtained if summed pollen counts for the Chenopodiaceae-Amaranthaceae and the Poaceae are used as an independent C4 proxy. We conclude that the specificity of the latitudinal distribution of vegetation in North West Africa and the pathways of the wind systems (trade winds and SAL) are responsible for the observed isotopic patterns observed in the surface sediments. Molecular-isotopic maps on the marine-sedimentary time horizons (e.g., during the last glacial maximum) are thus a robust tool for assessing the phytogeographic changes on the tropical and sub-tropical continents, which have important implications for the changes in climatic and atmospheric conditions.
Abstract: Small ruminant production systems vary widely, from high producing dairy goats to suckling ewes on rangelands. However, in all environments feed characteristics influence animals' motivation to eat, dietary choices and ultimately nutrient intake. This review highlights the common feed factors that influence feeding behaviour and intake, although their expression and consequences depend on the environment. The main characteristics of feeding behaviour are described in terms of the satiation process and motivation to eat. The main feed factors that influence intake are then reviewed. The relationship between the nutritive value of forages and their voluntary intake is well established. The relationship between nutritive value and palatability of feeds is discussed in the light of recent work on how feed characteristics are learned. At pasture, ease of prehension of the sward influences rate of intake and dietary choices. On heterogeneous resources, animals graze selectively and choose a diet of higher quality than that on offer. Recently more effort has been made to model intake and foraging decisions. Management of the grazing circuit has become an important factor in a heterogeneous environment. In conclusion, modelling and predicting intake for small ruminants in different environments are briefly discussed.
Abstract: Abstract Embedded in species-poor grasslands, fairy circles are circular or sub-circular patches devoid of any vegetation. Characteristically, the circumference of each circle shows a band of more densely packed taller tussocks within a shorter, more sparse grassland matrix. The average diameter of the circles is between 58 m. Restricted to sites showing deep sandy deposits, in Namibia, fairy circles occur in a broken belt in the pro-Namib from southern Angola to the Orange River (Republic of South Africa). The distribution of fairy circles is significantly limited to areas with an average of 50100 mm of annual precipitation. Based on remote sensing methods and expeditions, a map of the distribution area of fairy circles in Kaokoland (NW Namibia) was drawn up. The map indicates that fairy circles are more widely spread over the western parts of Kaokoland than previously reported. The two different active biological hypotheses of the fairy circles' origin comprise 1. the allelopathic interaction between Euphorbia damarana and the contemporary herbaceous vegetation (Theron 1979) and 2. the involvement of harvester termites (Moll 1994). Both hypotheses are discussed and a model about the origin and dynamic of fairy circles is presented. This model includes the foraging behaviour of the harvester termite Hodotermes mossambicu s which is the prime causal factor in forming the fairy circles of Kaokoland.
Abstract: Abstract Pollen data from 18,000 14C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present-day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south-western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.
Abstract: Major problems are experienced in South Africa due to the invasion of non-indigenous or alien species of terrestrial plants in several catchments. Alien invaders are estimated to use approximately 6,7% of the estimated mean annual runoff of water over the entire area of South Africa and as high as 15,8% in the Western Cape Province. The impacts are significantly higher, on a percentage basis, during drought periods as the riparian invaders still have free access to water. Rural and urban communities with limited storage capacities for water supply that depend on the flow of water in the river are particularly affected by the reduced flow of water. The invasion of alien plants in catchments is influencing the total water resources system and affecting all sectors. The nature and extent of invasive alien plants, the effects thereof on available water resources, the threat to ecological environment and impacts on society, need to be understood to ensure the success of the integrated approach to control the spread of invasive alien plants. If properly managed, the programmes to control invasive alien plants can provide the stimulus needed for an active participatory approach in integrated management of catchments in South Africa to deal with water scarcity and to ensure sustainability of the environment, land use and water.
Abstract: Increased public awareness of resource management issues and new attitudes toward resource conservation have led to great interest in the subject of the apposite use and management of natural and environmental resources in the American West. This paper analyzes this subject from an interdisciplinary ecological-economic perspective. Four salient issues concerning the study of the West's ecological-economic systems that remain inadequately understood are identified and then discussed. A research agenda is proposed to answer some key questions concerning the functioning, health, and management of the West's ecological-economic systems.
Abstract: Conservative land-use over the past few decades has converted the Montseny Biosphere Reserve (Spain) from the original open, patchy landscape to almost continuous woodland. Small ruminant grazing is virtually the only major remaining utilisation activity yet little is known about its role in the changing vegetation of the Reserve. This study was undertaken to determine the effects of current grazing practice on its main vegetation components. Three flocks, composed of sheep and goats, that graze yearlong on three separate ranges in the Reserve were selected for study. The ranges represent the wooded slopes and the shrubby upland (altiplano) in the area. Biomass consumption by the flocks was estimated by calculation of normative requirements for observed production and the botanical composition of the livestock diets over a whole annual cycle was determined by micro-histological analysis of the faeces. Production of herbaceous vegetation was determined by clipping sample quadrats, the production of the woody vegetation was derived from previous work in the Reserve. It was found that grazing removed a very small proportion of the dominant Holm oak (Quercus ilex) on the slopes, and a moderate fraction of the shrubby and herbaceous vegetation on the altiplano. Only the heath tree (Erica arborea), an edible shrub in the woodlands, was relatively heavily grazed. It is concluded that grazing alone is not enough to maintain the open, diverse landscape with its many natural values. As in other northern Mediterranean countries, under-utilisation of these woodlands is becoming a serious problem that is also increasing the fire hazard. Maintaining landscape diversity in the region is a complex challenge that land managers should recognise.
Abstract: We investigated the effects of changing fire regime on the stocks and isotopic composition of soil organic carbon (SOC) in a tropical savanna ecosystem at Matopos, Zimbabwe. Vegetation plots from both sandy and clay-rich soil types at this location have been subjected to fire frequencies ranging from annual burn to complete protection for the last 50 years. Gross variations in 0-5 cm SOC stocks and the [delta]13C value of SOC were predominantly related to soil texture, with carbon densities at the sandy sites being consistently 35-50% lower than those at comparable clay sites. Average 0-5 cm carbon densities for all the burnt plots were approximately 100 mg/cm2 and 50 mg/cm2, at the clay site and the sandy site, respectively. In both cases, lower fire frequencies had resulted in a ~10% increase, while higher fire frequencies had resulted in a ~10% decrease from these average values. Plots from which fire had been excluded experienced a 40% to 50% increase in carbon stocks in the 0-5 cm interval, compared with the average for the burned plots. There was a linear relationship between carbon density and [delta]13C value at both sandy and clay sites. This is controlled by the rate of delivery of C3- and C4-derived carbon to the SOC pool, by the differences in residence time for C3- and C4-derived carbon in the SOC pool (in turn controlled largely by fire frequency), and by soil texture. The distribution of carbon and 13C between size fractions is also controlled by soil texture and fire frequency. Increasing fire frequency results in a relative increase in fine particulate SOC and an increase in the [delta]13C value of SOC in all size fractions. Soil texture, on the other hand, controls the magnitude of the increases in both the abundance and the [delta]13C value of SOC in all size fractions.
Abstract: Palaeoclimatic estimates of mean annual rainfall in the equatorial highlands of Central East Africa have been established for the last 40 kyr. The values are inferred from nine fossil pollen sequences, collected from six peat bogs located between 2° and 4°S latitude, in the forest belt, from 1800 to 2240 m a.s.l. The transformation of pollen data into climatic parameters is achieved by the best analogues statistical method, using a modern pollen data set of East and Central Africa and calibration by meteorological data. The climatic reconstructions are first performed for each individual sequences. They are transformed into time-series using 88 of the 125 available radiocarbon dates (including 41 AMS dates). The synthesis of the results is presented as a single curve, illustrating the precipitation values obtained for 682 dated stratigraphic layers plotted on a radiocarbon timescale. The precipitation changes are presented at about a century resolution during the Holocene, and about a millennium for the glacial period. The most characteristic feature of the synthetic curve is the changing variability through time. During the last glacial period (30 to 15 kyr BP interval), our results indicate a ca. 450 mm/yr (32%) precipitation decrease relative to the present. Two maxima decrease periods are registered at ca. 19 kyr BP (700 mm/yr, ca. 45%) and between 18 and 16 kyr BP (608 mm/yr, ca. 42%). Several abrupt positive peaks of higher precipitation are noticed pre 35 kyr BP and ca. 22-20 kyr BP. During the lower Holocene (10-7 kyr BP), the mean calculated precipitation estimate is 30 mm/yr (2%) below the present-day value, with several abrupt positive shifts; the maximum at ca. 8 kyr BP reaches 600 mm/yr (42%). Great variations between low and high precipitation values are expressed post ca. 4 kyr BP. These results are discussed in light of other climatic indicators extracted either from the same sedimentary record, isotopes, microfauna, or from other geological palaeoclimatic proxy in the concerned region, and pattern of the monsoon record in marine cores. Anthropogenic disturbance on past vegetation, as well as humidity signal as a better response of forest to climatic forcing, and possible CO2 effect need more investigation in the future. We feel confident that the greater variability at the century scale registered in the equatorial highlands provides a good explanation for increased aridity in the desertic region of Sudan and Egypt during the last 4 kyr. The possibility that such greater variability could be induced by high variability or instability of the Atlantic Ocean or global sea surface temperature instability should be explored.
Abstract: The grazing behaviour and diet selection by Dorper sheep, as well as other related aspects (pasture intake, walking habits and trampling) is reviewed. It was clear that Dorper sheep are less-selective grazers, compared to Merino-type breeds. Dorpers utilised shrubs and bushes to a greater extent, but grass to a lesser extent in relation to Merino sheep. The Dorper also utilised a larger number of different plant species than Merinos. Dorpers walked less to select food, or a suitable spot to graze, which consequently led to a shorter grazing time and less separate grazing periods. Dorpers consumed less herbage per metabolic size compared to Merino-type sheep. No uniform pattern in the walking distance of Dorpers was observed when compared to other sheep breeds. The relative trampling factor for Dorper sheep was less than that of evaluated Merino-type sheep. The review revealed a lack on information on the grazing behaviour and diet selection of Dorper sheep under more intensive grazing conditions. There is also a total lack of scientific information on other behaviour aspects of this unique breed.
Abstract: Following germination, the ontogeny of white clover is characterized by two distinct morphological growth phases, a seminal taprooted stage followed by a clonal growth stage. Death of the seminal taproot and primary stolon initiates a process of fragmentation of the taprooted plant into a variable number of independent clonal fragments (plants) which comprise the initial population of the clonal growth stage. The objective of this study was to characterize the plant morphology of field-sown white clover populations from germination through to established clonal populations. Populations of eight white clover cultivars were assessed when sown with perennial ryegrass or tall fescue in pastures established under a common grazing regime for 16 months prior to imposition of continuous or rotational grazing treatments. One year from sowing, taprooted plants attained maximum size, with a mean plant branching order of 3·35, stolon DW of 460 mg and lateral spread of 250 mm, with some individuals having 6th order branching, 3·5 g stolon DW and 1m lateral spread. These taprooted plants were 4–5 times the size of plants in the subsequently formed clonal population. Nine months after sowing, the first individual taprooted plants fragmented into clonal plants. Twelve months from sowing, fragmentation processes were occurring at a linear rate, eliminating 6% of the original taprooted population each month. This resulted in a 12–15 month transition period when the white clover population comprised both taprooted and clonal plants. During this transition period, the initial clonal fragments produced from taprooted plants were large, and this maintained a larger mean plant size in the clonal plant proportion of the transition population than measured in the later fully clonal population. This process was also considered to act to prevent the development of the expected differences between grazing managements, as it was not until the third year when all taprooted plants had disappeared that the clonal populations developed characteristics reflecting the expected influence of grazing management. Variation due to white clover cultivar and companion grasses was minor. The substantial differences in plant size and branching structure between taprooted and clonal populations has significant implications for the evaluation of breeding lines.
Abstract: Abstract Aim Fires are an important landscape disturbance which interact in a complex way with land-use and land-cover change. The objective of this study is to understand the role of fires in vegetation-cover change and, conversely, the role of land use as a controlling factor of fires. Location The study sites are located in Mato Grosso, Brazil, in Central Africa and on the border between Kenya and Tanzania. Methods The role of vegetation fire is addressed through a landscape-scale analysis of the spatial association between maps of active fires and maps of land-cover change derived from remote sensing data for the different sites in Africa and South America. Results The empirical results of this study clearly support the idea that fires have widely varying impacts on land cover in savanna and forest ecosystems. Fires play different roles within the different components of landscape mosaics and at different times of the land-cover change trajectory. The impact of fires on vegetation is mainly controlled by land use. Conclusions There is thus a need to consider the socioeconomic purpose of biomass burning and the context in which such activities are undertaken. In forest ecosystems, a statistically significant relationship exists between the occurrence of fires and forest-cover changes. One could not conclude however, that fires are always the cause of the change in land cover, nor that fires are a reliable indicator of ‘hot spots’ of deforestation. Current low spatial resolution information on fire activity derived from remote sensing systems can be prone to inaccuracies due to a poor co-location of fire with respect to land-cover data, and temporal sampling problems affecting fire data.
Abstract: Floristic diversity was compared across boundaries where the trees have been cleared in semi-arid brigalow (Acacia harpophylla), gidgee (A. cambagei) and eucalypt (Eucalyptus populnea, E. melanophloia) woodland and forest in central Queensland. The cleared treatments included Exotic pasture (uncultivated, exotic grasses having more than 10% total cover) and Native pasture (uncultivated, not dominated by exotic grasses). An ordination of presence-absence data did not distinguish the floristic composition of the uncleared pasture and native pasture treatments, however, these treatment types were floristically distinct from the exotic pasture treatment in all three land types. Declines in species richness and diversity were substantial between uncleared and exotic pastures for brigalow and eucalypt lands. Differences were far less substantial for the same comparison in gidgee lands, and between uncleared and native pasture for all three land types. These trends reflected differences in most perennial lifeform groups and the species that show significant declines are identified. There was no significant relationship between native diversity and the age of clearing. This study draws attention to the negative impacts on plant diversity posed by deliberate and inadvertent spread of exotic perennial grasses in tropical forests and woodlands.
Abstract: The records of the LGM climates of tropical South America are still sparse compared to the vast region under consideration. Nevertheless, a number of records hold up to critical evaluation. Early attempts to reconstruct the LGM temperature and precipitation conditions for the LGM, around 21 14C ka BP, have suggested that relative to present, lowland temperatures were on average only a few °C cooler, whereas in the Andes the temperature depression was in the range of 6-8°C. These reconstructions further suggested that tropical precipitation was more limited in both the lowlands and in the Andes. Although recent pollen evidence supports significantly cooler tropical lowland temperatures during the LGM, additional (alkenone) evidence from sea-surface temperatures and model analysis are contradictory. The data from tropical South America suggest that the late Quaternary climatic changes of the lowlands as well as of the Andean mountains reflect a response (1) to environmental changes in the source area of the moisture and (2) to global temperature fluctuations. Based on glacial, periglacial and pollen evidence, a LGM temperature depression of 5-6°C can be assumed for both tropical lowland South America and the Andes. These LGM values for the cooling correspond with recent coral records from Barbados and the southwestern Pacific, ice-core records from Peru, noble-gas measurements in Brazil and ocean core records from the western equatorial Atlantic. No difference in the value of LGM cooling can be recognised between the tropical lowlands and the high mountains of South America. Furthermore, in all regions the LGM climates were more arid than the present-day climates. Terrestrial records have not yet yielded records of Younger Dryas age apart from the tropical Andes of Ecuador where the Younger Dryas time is characterised by a cooler and drier climate. Pollen evidence for cooler Younger Dryas conditions comes from the Bolivian Andes.
Abstract: asked Li Derong, the highest ranking official responsible for rangeland policy formulation in China. His question illustrates three points. First, it shows that on the way to becoming a market economy, after more than two decades China is still very much constructing, amending and reconstructing a viable and solid system for grassland management. Secondly, it is indicative of the growing awareness within the Chinese Ministry of Agriculture that rangeland policy as it emerged after the demise of the people's communes in the 1980s is ripe for revision. Finally, it suggests an interest in examining and learning from the experience of other countries, particularly in the West.
Abstract: An investigation was made during 1988 to test the hypothesis that ‘Grasslands Huia’ white clover (Trifolium repens L.) could be eliminated under close sheep grazing. The effects of grazing management, topography and fertilizer on the contribution of Huia plants to the white clover population in an 85 ha experimental upland pasture ecosystem in the southern North Island, New Zealand (lat. 40° 20′ S, long. 175° 50′ E, 125–350 m altitude) were quantified 11 years after oversowing. Replicated sampling sites (108 in total) were located on nine combinations of slope and aspect within grazing management treatments comprising rotational grazing with cattle (RC), rotational grazing with sheep (RS) and continuous grazing with sheep (CS), with high and low fertilizer treatments in each case. White clover occurrence, leaf area, phosphoglucoisomerase-2 (PGI-2) allele frequencies and the proportion of Grasslands Huia plants in the white clover population were determined at each site. White clover frequency was lower on steeper slopes. Aspect, slope and grazing management affected area of individual clover leaves. The proportion of Huia plants in the white clover population averaged 54·9, 49·0 and 33·6% for RC, RS and CS, respectively (P < 0·039, 5 D.F.). Fertilizer and topography did not affect the proportion of Huia. It was concluded that although Huia did persist after 11 years of close sheep grazing, its contribution to the total white clover population was unsatisfactory in some cases, and use of better adapted cultivars is suggested.
Abstract: Abstract * 1Areas burned annually in the United States between 1700 and 1990 were derived from published estimates of pre-European burning rates and from wildfire statistics of the US Forest Service. Changes in live and dead vegetation following fire and fire exclusion were determined for 18 types of biomes and added to a book-keeping model to calculate the long-term effect of fire and fire management on carbon storage. * 2Over the 290-year period, burning declined by an estimated 98%, first, because wildlands were converted to agricultural lands, essentially eliminating fire from 236 × 106 ha and, secondly, because wildfires were excluded and suppressed in the remaining forests and non-forests. * 3Adding fire and fire management to an analysis of land-use change (companion paper) reduced the emissions of carbon over the period 1700–1990 by 25% (8 PgC). Less carbon was released because fire reduced the average biomass of forests cleared and burned, and because fire exclusion led to an increase in carbon storage in forests. * 4The wildfire statistics of the USDA were insufficient for addressing two kinds of change: fire exclusion before 1926 and changes in the burning of non-forest ecosystems. We estimate here that as much as 4 and 12 PgC, respectively, may have accumulated in vegetation as a result of these changes, but the estimates are uncertain and likely to be upper limits. * 5The maximum rate of carbon accumulation attributable to all changes in land use, including fire management, was 300–400 TgC/year and occurred around 1980. Less than half of this uptake was in forests. Uptake by forests was constrained by the fact that most forests were already accumulating carbon in response to earlier harvests. Fire exclusion added little to this uptake.
Abstract: The Jornada Experimental Range (Jornada) in southern New Mexico provides a unique opportunity to use remote sensing techniques to study arid rangeland and the responses of vegetation to changing hydrologic fluxes and atmospheric driving forces. Research by the United States Department of Agriculture Forest Service and Agricultural Research Service at Jornada has been continuous since 1912. The Jornada has been a National Science Foundation Long-Term Ecological Research site since 1981. These long-term investigations have provided ground data on vegetation characteristics, ecosystem dynamics, and vegetation response to changing physical and biological conditions. To complement the programs of ground measurements, a campaign called JORNEX (JORNada EXperiment) began in 1995 to collect remotely sensed data from aircraft and satellite platforms to provide spatial and temporal data on physical and biological states of the Jornada rangeland. A wide range of ground, aircraft, and satellite data have been collected on the physical, vegetative, thermal, and radiometric properties of three ecosystems (grass, grass/shrub transition, and shrub) typical of the Jornada rangeland and of southwestern U.S. deserts. Spatial surface energy balance estimates were made from a combination of parameters and state variables estimated from aircraft and ground data. Landscape surface roughness was evaluated with the laser altimetry data and used to estimate aerodynamic roughness. Data from different platforms allowed the evaluation of the landscape at different scales. These measurements are being used to quantify hydrologic budgets and plant responses to change in components in the water and energy balance at the Jornada.
Abstract: A grassland formation has been subjected to pollution generated by the Ventanas copper smelter since 1964 (Puchuncavà Valley, central zone of Chile) with extensive damage to local vegetation and important changes in soil characteristics. The aims of the study were (1) to detect soil parameters that best explain changes observed in plant species richness and abundance and (2) to determine if pollution-derived stresses have also affected regeneration capabilities of plant communities from the soil seed bank. The grassland was quantitatively analysed in terms of physico-chemical soil characteristics, plant species diversity and abundance, and soil seed bank species composition and abundance. Results showed that a decrease in total soil nitrogen explained 13% of the changes detected in plant abundance while soil pH and 0.05 M EDTA extractable copper explained 10% and 7%, respectively, of the vegetation change. It was also found that the pollution has already affected plant species regeneration capabilities from the soil seed bank and the microsite distribution of the seeds in soils.
Abstract: Quantifying water balance components, which is particularly challenging in snow-fed, semi-arid regions, is crucial to understanding the basic hydrology of a watershed. In this study, a water balance was computed using 10Â years of data collected at the Upper Sheep Creek Watershed, a 26-ha semi-arid mountainous sub-basin within the Reynolds Creek Experimental Watershed in southwest Idaho, USA. The approach computed a partial water balance for each of three landscape units and then computed an aggregated water balance for the watershed. Runoff and change in ground water storage were not distinguishable between landscape units. Precipitation, which occurs predominantly as snow, was measured within each landscape unit directly and adjusted for drifting. Spatial variability of effective precipitation was shown to be greater during years with higher precipitation. Evapotranspiration, which accounted for nearly 90% of the effective precipitation, was estimated using the Simultaneous Heat and Water (SHAW) Model and validated with measurements from Bowen ratio instruments. Runoff from the watershed was correlated to precipitation above a critical threshold of approximately 450Â mm of precipitation necessary to generate runoff (r2=0.52). The average water balance error was 46Â mm, or approximately 10% of the estimated effective precipitation for the ten-year period. The error was largely attributed to deep percolation losses through fractures in the basalt underlying the watershed. Simulated percolation of the water beyond the root zone correlated extremely well with measured runoff (r2=0.90), which is derived almost entirely from subsurface flow. Above a threshold of 50Â mm, approximately 67% of the water percolating beyond the root zone produces runoff. The remainder was assumed to be lost to deep percolation through the basalt. This can have important ramifications in addressing subsurface flow and losses when applying a snowmelt runoff model to simulate runoff and hydrologic processes in the watershed.
Abstract: Miombo woodlands are crucial to the livelihoods of rural people throughout southern, eastern and central Africa. This paper describes a dynamic simulation model of key ecological processes in miombo and examines the ecological and economic impacts of various forms of management. The model shows that removing harvestable trees and reducing the level of grazing by livestock causes an increase in grass fuel loads and a corresponding increase in the frequency of fires. More frequent and intense fires in turn suppress woody regrowth, thereby adversely affecting harvestable tree stocks. Despite the marked ecological response to manipulating the level of grazing, the impacts on economic performance were minimal. The NPVs for Forestry Commission in particular remained relatively constant under different management regimes. Given these low potential returns, the advantage of applying some of the known silvicultural management treatments to miombo woodlands seems questionable. Varying the proportion of harvestable timber trees cut and changing the length of the cutting cycle might suggest that profits to the Forestry Commission or timber concessionaires could be maximised by harvesting as much timber as possible in a single cutting period. Under such a scenario, however, the woodland would be rapidly converted to bushland. There is a need to explore further the trade-offs between direct use values, as derived from harvesting and selling timber, and ecological service functions, such as carbon sequestration and modifications of the hydrological cycle.
Abstract: Livestock trails frequently evolve in pastures when plant growth or establishment cannot keep pace with vegetation disturbance. In some instances, man-made trails are established in rangeland settings to encourage uniform use of forages or facilitate livestock passage through dense vegetation or across rugged terrain. A long-term assumption has been that livestock establish pathways of least resistance between frequented areas of their pastures, but this hypothesis has never been tested. We mapped cattle trails in three 800+ ha pastures with global positioning units. A geographic information system (GIS) helped quantify characteristics of trails and the landscape and was used to plot least-effort pathways between water sources and distant points on selected trails in the pastures. Characteristics of the cattle trails and least-effort pathways were compared to test the hypothesis that cattle develop least-effort routes of travel in rugged terrain. The mean slope of the three pastures was 13.5%, and the average slope of the topography traversed by the cattle trails was 8%. The slope of the trails was reduced to 5.2% by selection of cross-slope routes. When we compared the characteristics of 10 selected cattle trails and least-effort pathways generated by our GIS, the cattle trails were 11% shorter (P=0.046) than the least-effort pathways, and the topography traversed by cattle had a gradient about 1% less than the least-effort pathways (P=0.02). The slope of the selected trails (5.5%) and pathways (5.6%) were similar (P=0.74), however. Analyses of values extracted from cost surfaces indicated that, on the average, 183 units of effort were needed to traverse the trails and 170 units of effort expended to traverse the least-effort pathways (P=0.07). These data support the hypothesis that cattle establish least-effort routes between distant points in rugged terrain and suggest that GIS software may be useful in designing systems of livestock trails in extensive settings.
Abstract: 13C/12C ratios in plants depend on factors like temperature, evaporation or seasonal moisture distribution. Fluctuations of 13C/12C in Procavia capensis (hyrax) dung samples from different vegetation zones and various ages over the last 20Â 000 years indicate variations in the amounts of C4 and CAM, or C3 plants consumed by these herbivores. Potentially they also indicate vegetation changes that may have occurred. 13C/12C values for a series of hyrax middens of Late Pleistocene/Holocene age, from a variety of biomes across Southern Africa, show that hyraxes favour mainly C3 plants in their diets but they do incorporate CAM or C4 plants under certain circumstances. In the eastern mountainous summer-rain area around Clarens with C3 woodland and unpalatable "sour" grassland consisting mainly of C4 grasses and fewer of the C3 type, hyraxes seem to avoid at least the C4 component of grass and rely mainly on leaves of the woody plants. Isotopic data for hyrax dung in the western Cape Cederberg region indicate diets composed almost exclusively of C3 plants during the last 20Â 000 years. Slight shifts towards more enriched values occur, e.g., around 420 and 2100 years ago, which may indicate slight increase in CAM or C4 plants. Interestingly no enrichment occurs during the Last Glacial Maximum when a shortage of atmospheric CO2 may have favoured C4 plants. During the late Holocene some CAM and/or C4-plant ingestion by hyraxes is suggested in the dry western and southern areas which receive more summer rains, probably reflecting the availability of some palatable (or "sweet") summer grasses. Although slight, a comparable pattern of isotope change is observed in three areas viz., the Cederberg, the Karoo and the Namib Desert, suggesting that plant cover is responding to regional climate mechanism ca. 2100 years BP. This does not necessarily imply similar seasonal rainfall shifts over the whole of this wide area.
Abstract: The densities of self-established non-indigenous prickly pears (Opuntia ficus-indica) in rangelands of the Karoo recorded on 3434 km of road transects, were on average 800 times greater below telegraph and transmission poles than away from poles, and 200 times greater next to wire fences along roads than in open rangelands. We suggest that this uneven establishment pattern is mainly due to the dispersal of Opuntia ficus-indica seeds by crows and other vertebrates (chiefly primates). Cape (Corvus capensis) and pied crows (C. albus) feed on fruits of Opuntia ficus-indica in the Karoo, and regurgitate pellets containing viable seeds of these plants below nest sites, roosts and occasional perch sites. Crows use man-made structures such as wire fences, telegraph and transmission poles and windmills for perching, roosting and nesting. Crow pellets, containing regurgitated bones and viable seeds of Opuntia spp., and other alien and indigenous plants, are most common around such perch sites. Crows are frequently associated with roads in the Karoo because they scavenge on road kills in the Karoo as well as feeding on fruits, insects and reptiles in road verges. We suggest that dispersal of seeds by crows is important for range extension and establishment of new Opuntia populations.
Abstract: Indicators of land quality (LQIs) are being developed as a means to better coordinate actions on land related issues, such as land degradation. Economic and social indicators are already in regular use to support decision making at global, national and sub-national levels and in some cases for air and water quality, but few such indicators are available to assess, monitor and evaluate changes in the quality of land resources. Land refers not just to soil but to the combined resources of terrain, water, soil and biotic resources that provide the basis for land use. Land quality refers to the condition of land relative to the requirements of land use, including agricultural production, forestry, conservation, and environmental management. The LQI program addresses the dual objectives of environmental monitoring as well as sector performance monitoring for managed ecosystems (agriculture, forestry, conservation and environmental management). The primary research issue in the LQI program is the development of indicators that identify and characterize the impact(s) of human interventions on the landscape for the major agroecological zones of tropical, sub-tropical and temperate environments. Core LQIs identified for immediate development are: nutrient balance, yield gap, land use intensity and diversity, and land cover; LQIs requiring longer term research include: soil quality, land degradation, and agro-biodiversity; LQIs being developed by other authoritative groups include: water quality, forestland quality, rangeland quality, and land contamination/pollution.
Abstract: Drawing on marine and terrestrial palynological data, vegetation maps of equatorial West Africa are presented for eleven time slices over the last 150,000 years. Long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle. Much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale. Temporal and spatial variation is revealed in relation to global patterns of climate change. Rain forest was widespread during Oxygen Isotope Stages 1 and 5, but strongly reduced during Stages 3 and 4 and especially during Stages 2 and 6 when open, grass-rich vegetation prevailed. Glacial rain forest refuges are found in the southwest of the Guinean mountains and along the eastern coast of the Gulf of Guinea. Miombo woodland of the Zambezian vegetation zone expanded during Stage 5, especially during the first half. Podocarpus forest had its largest expansion during Substages 5d (115 to 105 ka) and 5b (95 to 85 ka). The last occurrence of Podocarpus in the Guinean mountains is during Stage 5a. The distribution of mangrove swamps was extremely reduced during glacial times. During Stage 6, savanna and open dry forest covered large areas along the northern coast of the Gulf of Guinea. The southern Saharan desert reached far to the south and the Namib desert far to the north. The area of rain forest was restricted, mangrove swamps were strongly reduced, and the area of Podocarpus forest fluctuated. During Stage 5 large changes in the area of Afromontane forest, rain forest, dry open forest and savanna occurred. Rain forest was widespread and mangroves were extensive along the coast during the last interglacial (Substage 5e). Podocarpus forest area strongly extended during Substages 5d and 5b. In Substages 5c and 5a, rain forest reclaimed areas it had lost in the previous substages (5d and 5b, respectively). Mangrove swamps were less widespread in the later substages of Stage 5 than during Substage 5e. During Stage 4, the rain forest area was again strongly reduced, and recovered only slightly during the following Stage 3. Also the mangrove swamp area was reduced except along the Ivory Coast and along the northwestern coast of the Gulf of Guinea. Podocarpus forest only occurred in Angola and may be in Congo during Stage 4. Again forest was much reduced during Stage 2 and open vegetation types covered large parts of equatorial West Africa. Mangrove swamps must have been rare. At the beginning of the Holocene, mangrove swamps had recovered and reached their largest extension. Also the rain forests area increased in the early Holocene and Guinean and Congolian rain forests were probably not separated by a savanna corridor now existing in Togo and Benin.
Abstract: The development of the non-woolled Dorper sheep breed is briefly reviewed. Despite the large number of Dorpers in South Africa, precious little research results have been published on its nutrition under harsh, arid grazing conditions, especially since this has been an objective for creating and developing the breed. Results from the limited number of trials with free ranging Dorpers on natural pasture (veld) regarding diet selection, voluntary feed intake and rumen variables are used in conjunction with production data to create a nutritional perspective of the free ranging ruminant.
Abstract: Early-warning indicators of rangeland health can be used to estimate the functional integrity of a site and may allow sustainable management of desert rangelands. The utility of several vegetation canopy-based indicators of rangeland health at 32 Great Basin rangeland locations was investigated. The indicators were originally developed in rangelands of the Chihuahuan Desert. Soil resources are lost through wind and water-driven erosion mainly from areas unprotected by plant canopies (i.e. bare soil). Study sites in Idaho had the smallest bare patches, followed by sites in Oregon. The more arid Great Basin Sagebrush Zone sites in Utah had the largest bare patches. Several vegetational indicators including percent cover by vegetation, percent cover by life-form, percent cover by sagebrush, and percent cover by resilient species were negatively related to mean bare patch size and are potential indicators of Great Basin rangeland condition. Plant community composition and the range of bare patch sizes were different at sites in the three locations in Idaho, Oregon and Utah. Therefore, expected indicator values are location specific and should not be extrapolated to other locations. The condition of study sites were often ranked differently by different indicators. Therefore, the condition of rangeland sites should be evaluated using several indicators.
Abstract: Several high-resolution proxy environmental records have been obtained for the last 35 kyr from ODP Hole 658C, a well-studied site ca. 200 km off Cap Blanc, NW Africa. The collective assessment based on the marine proxies (U37K' SST, contents of TOC and chlorins, Upwelling Radiolarian Index and the percentage of Florisphaera profunda), surprisingly indicates that the last glacial maximum (LGM) was characterized by warmer sea surface temperature (SST), weaker upwelling, and lower marine productivity, compared with the preceding older glacial and subsequent deglaciation periods. Of the terrigenous proxies, the mean grain size of the non-carbonate fraction and the terrigenous alkane content indicate that wind strength and aridity were high. The weaker upwelling at the 658 site during the LGM may have resulted from changes in the strength and direction of the wind systems and/or shifts in the position and geometry of the upwelling cell.
Abstract: The debate about the sustainability and productivity of communal lands, especially in comparison with privately managed land, is far from settled. Emerging theories emphasize the spatial and temporal diversity of the environment, and are often in agreement with local opportunistic land management strategies. This study explores differences in variables such as plant species richness, composition, and abundance of the field-layer and woody vegetation, between sites with different soils and different histories of land use (communal, private ranch, and rested from grazing), for 2 years. The results indicate that, for the study area chosen, differences in land use have not caused any major differences in the vegetation. However, there were clear differences depending on soil type, and plant production increased strongly with a slight increase in rainfall. Although people and livestock have had a strong impact on the vegetation, most indicators of degradation were absent, implying that the land has not lost its productive potential.
Abstract: A sampling system was devised and used from 1992 to 1996 in annual grassland and open woodland of the south-west Kenyan Rift Valley. The monitoring was designed to detect vegetation changes consequent on the attempted removal of the tsetse vectors of trypanosomiasis in cattle during a simultaneous trapping programme. The sampled sites covered most vegetation-landscape types, and have led to a better understanding of processes within some. Although fluctuations in pastoralist use and occupancy have been observed, no change in vegetation can be attributed to increased grazing or browsing. Although there is high climatic variability some vegetation types seemed stable over the period studied, and some trends appear to be predictable. xD;Resume On a con 231;u un syst 232;me d 039; 233;chantillonnage qui fut utilis 233; de 1992 224; 1996 dans les prairies annuelles et dans les for 234;ts ouvertes du sud-ouest de la Rift Valley, au Kenya. La surveillance 233;tait con 231;ue de fa 231;on 224; d 233;tecter les changements de v 233;g 233;tation qui r 233;sultaient des tentatives d 039; 233;radication des mouches ts 233;-ts 233;, vecteurs de la trypanosomiase chez le b 233;tail, au cours d 039;un programme de pi 233;geage. Les sites d 039; 233;chantillonnages couvraient des paysages correspondant 224; la plupart des types de v 233;g 233;tation et ont conduit 224; une meilleure compr 233;hension du processus dans certains d 039;entre eux. Bien qu 039;on ait observ 233; des fluctuations dans l 039;occupation et l 039;utilisation pastorales, on ne peut attribuer aucun changement de v 233;g 233;tation 224; une augmentation du p 226;turage. Bien que le climat soit tr 232;s variable, certains types de v 233;g 233;tations semblent 234;tre rest 233;s stables pendant la dur 233;e de l 039; 233;tude et l 039;on semble pouvoir pr 233;dire certaines tendances.
Abstract: We develop a simple, analytical model for canopy resistance to canopy-atmosphere gas exchange that is well suited for incorporation into regional-scale land-surface parameterizations. This model exploits the conservative nature of canopy light-use efficiency (LUE) in carbon assimilation that is observed within broad categories of plant species. The model paradigm assumes that under standard environmental conditions, a canopy will operate at the field-measured LUE, but will deviate from this standard efficiency as conditions change. Effective LUE estimates generated by the model respond to variations in atmospheric humidity, CO2 concentration, the composition of solar irradiation (direct versus diffuse beam fractions), and soil moisture content. This modeling approach differs from scaled-leaf parameterizations in that a single estimate of nominal canopy LUE replaces both a detailed mechanistic description of leaf-level photosynthetic processes and the scaling of these processes from the leaf to canopy level. This results in a model that can be evaluated analytically, and is thus computationally efficient and requires few species-specific parameters. Both qualities lend themselves well to regional-and global-scale modeling efforts. For purposes of testing, this canopy resistance submodel has been embedded in the Atmosphere-Land Exchange (ALEX) surface energy balance model. The integrated model generates transpiration and carbon assimilation fluxes that compare well with estimates from iterative mechanistic photosynthetic models, and with flux measurements made in stands of corn, soybean, prairie grasses, desert shrubs, rangeland, and black spruce. Comparisons between modeled and measured evapotranspiration (LE) and carbon assimilation (Ac) fluxes yield mean-absolute-percent-differences of 24% (LE) and 33% (Ac) for hourly daytime fluxes, and 12% (LE) and 18% (Ac) for daily-integrated fluxes. These comparisons demonstrate robustness over a variety of vegetative and climatic regimes, suggesting that this simple analytical model of canopy resistance will be useful in regional-scale flux evaluations.
Abstract: This article describes a greenhouse gas (GHG) emissions scenario for a world that chooses collectively and effectively to pursue service-oriented economic prosperity while taking into account equity and environmental concerns, but without policies directed at mitigating climate change. After peaking around 2050 at 2.2 times the 1990 level of primary energy use, a number of factors lead to a primary energy use rate at the end of the next century that is only 40% higher than the 1990 rate. Among these factors are a stabilizing (and after 2050, declining) population, convergence in economic productivity, dematerialization and technology transfer, and high-tech innovations in energy use and supply. Land use-related emissions show a similar trend. Total CO2 emissions peak at 12.8 CtC/yr around 2040, after which they start falling off. Other GHG emissions show a similar trend. The resulting CO2-equivalent concentration continues to rise to about 600 ppmv in 2100. Present understanding of climate change impacts suggest that even in this world of high-tech innovations in resource use in combination with effective global governance and concern about equity and environment issues, climate policy is needed if mankind is to avoid dangerous interference with the climate system.
Abstract: The germination of seven common weeds and seven species native to south-western Australia was studied at three sites where they co-occur and in the laboratory. Under field conditions, final germination of the exotic species was much higher than that of the native species, and the number of days to reach 50 160;% final germination was lower. For some of the germination period, soil moisture was lower than expected after 48 160;h without rain, with one dry period lasting 10 160;d. Overall, germination rose with increasing wetness of the three sites, especially among the weeds. Most exotic species germinated under laboratory conditions needed less than 10 160;d to reach 50 160;% of final germination which was further delayed by 2 160;d when seeds were removed from their moist substrate and allowed to dry out (air-drying) for 48 160;h. Most native species took 10-35 160;d, with a mean delay of 7 160;d after 48 160;h of air-drying. Total germination of the weeds was close to 100 160;% and was little affected by periods of air-drying. Germination of the native species was more variable and greatly reduced by air-drying in two species. We conclude that water availability as it varies through time and space is significant in controlling germination even during the wet season. The quicker and greater responses of weed seeds to moisture may contribute toward the superior ability of weeds to colonise disturbed habitats. Differences in life form, seed size, flatness, presence of appendages, and ability to absorb or retain water only partially explain these results.
Abstract: Patterns of higher plant species richness and beta diversity were assessed using standard Modified-Whittaker plots in relation to landuse, slope position and mean annual rainfall across a rainfall gradient in the savanna areas of the Bushbuckridge lowveld, South Africa. In particular, comparison of communal areas with adjacent protected areas was important in showing the impacts of potential changes in landuse within an overarching catchment management plan. Although most of the protected areas considered preservation of biodiversity as their primary goal, they were characterised by significantly fewer plant species than the adjacent, highly utilised, communal lands, at both the plot and point scale. Slope position also had a significant effect on plant species richness, with eutrophic bottomlands having c. 30% more species than the dystrophic toplands. This adds weight to the need for greater public awareness for the judicious use and management of the sensitive bottomlands, which fringe the primary drainage lines that are vital for sustained supplies of good quality surface water in this semi-arid environment. The total number of species increased with increasing mean annual rainfall across the rainfall gradient. This suggests that, if the catchment management plan aims to identify additional areas for conservation, the higher rainfall areas should be the first to be assessed. Species turnover was greater along the rainfall gradient than the catenal gradient between toplands and bottomlands.
Abstract: Speargrass is a dominant, competitive and difficult weed to control in tropical Asia, Latin America, and some parts of West Africa. In West Africa, no information is available on the cropping systems and soils most affected by speargrass infestation; Farmers 039; perceptions of speargrass and common management strategies employed by farmers are unknown. Surveys were conducted in 1996 and 1997 in the coastal/derived savanna (Benin and Nigeria) and southern Guinea savanna (C 244;te d 039;Ivoire) to characterize farming systems, soils, and farmers 039; management strategies in fields dominated by speargrass. Twenty-one crops were found in speargrass dominated fields. Speargrass was ranked as the most serious weed in both agroecological zones. Besides speargrass, Commelina benghalensis L., Digitaria nuda Shumach, Cyperus rotundus L., Tridax procumbens L., Rottboellia cochinchinensis (Lour.) Clayton, Digitaria horizontalis Willd, Striga spp., and Euphorbia heterophylla were also considered as important weeds in major cropping systems. Speargrass was undesirable because it reduces crop yield and quality, limits farm size, causes injury to the skin, increases labour requirement and increases the presence of pathogens and insects of economic crops. Nevertheless, some farmers indicated that speargrass was an important source of cheap roofing material, animal fodder and medicines. Most farmers used labour intensive control strategies to combat speargrass due to, among other reasons, lack of capital. Speargrass occurred in soils with a wide range of chemical properties and particle size distribution.
Abstract: There is significant uncertainty about the effects of global change on the vegetation and animal productivity of pasture and rangeland ecosystems. This paper presents a synthesis of progress made between 1994 and 1999 in the Global Change and Terrestrial Ecosystems (GCTE) Pastures and Rangelands Core Research Project 1 (CRP1) network, a world-wide network of 83 full-time equivalent researchers established in different pasture and rangelands systems to reduce these uncertainties. The network focuses on key processes controlling forage and animal production at a paddock/landscape scale, in order to improve the ability to model animal production. To date, the network has resulted in a considerable reduction in the uncertainties about the effects of elevated CO2 on growth, and to a lesser extent composition and forage quality, of intensive pastures in cool, wet climatic zones. However, knowledge of other grazed ecosystems and processes is more limited. The greatest confidence is in predicting implications for vegetation production, with lesser confidence in implications for vegetation composition, animal production and adaptation options. Overall, the stimulatory effect of double ambient CO2 on grassland production averages about +17% in ecosystem-based experiments. This is less than previous estimates. Individual system responses to elevated CO2 can vary widely and are predicted to be higher in moisture-limited and warm-season grassland systems. Species composition change is likely to be an important mechanism altering grassland production and its value for grazing livestock, especially in drier rangelands with woody shrub invasion. On average, the legume content of productive grass-legume swards is increased by +10% due to CO2 enrichment. Leaf nitrogen reductions due to elevated CO2 are often observed but are generally modest compared with effects of other management factors. New data collection efforts should be focused in areas of the world which are most sensitive to food security issues and most subject to global change, in particular humid semi-arid margins and subtropical grasslands. There remains no good basis for extrapolating findings between different pasture and rangeland systems. This synthesis indicates that greater focus is required on the linkages between the biophysical, social and economic factors that will influence future changes in pasture and rangeland ecosystems and their implications for food security.
Abstract: During the last decade a [‘]new rangeland science 039; has emerged. One of the tenets of the new science is that pastoralists should not adhere to a single conservative stocking rate, but rather adopt an opportunistic strategy, where numbers will fluctuate widely in response to good and bad seasons. It is further argued that opportunistic strategies give higher economic returns compared to strategies based on conservative stocking rates. In the current paper we compare the economics of four cattle management scenarios. The analysis is based on a simulation model of the fluctuation over time of animal numbers, outputs and prices, using data from field surveys and the literature. Our results suggest that strategies based on conservative stocking rates would have higher net present values than strategies based on opportunistic stocking rates. Previous analyses have failed to account for losses due to drought and the costs of capital tied up in livestock, and the analyses have tended to compare commercial with communal production rather than considering different kinds of small holder production methods. To receive the full benefits of destocking, however, a decision to destock has to be made at the level of the community, as the benefits of improved outputs can only be achieved if the stocking rates of the communal grazing lands are reduced. Making collective decisions about managing numbers is a process with considerable transaction costs, and thus the likelihood of new institutions emerging are lessened. It is surprising that a tight tracking scenario (where numbers of cattle are managed by purchasing and selling so as to maintain numbers in equilibrium with the available feed resources) is being recommended in the most recent literature. Our results suggest that such a system would come with considerable economic losses. The costs of a current programme to reclaim small dams illustrate the environmental costs of the opportunistic scenario. A tight tracking policy is likely to further increase environmental degradation and its associated costs. We identify several serious flaws in the papers that elevate opportunistic pastoral systems as giving higher economic returns than other systems.
Abstract: The species composition of grazing lands can be influenced by livestock and grazing pressure. A study on manure seed bank was conducted in Ghinchi highland Research Site in Ethiopia between 1995 and 1997. The data on species composition and life-form of the plants germinating in pots receiving air dried manure were compared with species composition of experimental plots in natural grassland subjected to varying grazing intensity. There was significant difference among the species composition of grazed and non-grazed grasslands and the manure seed bank (p = 0.01). The life-forms of the species also showed variation. There were more families and species in the natural grassland vegetation than indicated in the manure seed bank. The manure seed bank had more annuals than the natural grassland vegetation. The species composition and life-forms in the manure seed bank showed variation with time and this corresponded with the seasonal variation in the grassland, which had a direct relationship with the rainfall pattern. The study showed that livestock play a major role in maintaining the biodiversity of grassland vegetation by spatial and temporal dispersion of readily germinating seeds in their manure. The use of manure to improve soil fertility should be weighed cautiously against the introduction of weeds into crop fields, although weeds are important feed resource for livestock in land-constrained areas. There is therefore the need for developing manure management practices so that the benefits can be optimised and the undesirable effects can be minimised.
Abstract: A vegetation survey of road verges along an urban to rural gradient in the Potchefstroom Municipal Area was conducted. Important applications of these studies include understanding of the role of indigenous (native) and exotic species in the overall synanthropisation of vegetation. The present study forms part of a research programme on spontaneous vegetation in urban open spaces in the North-West Province of South Africa. A numerical classification technique () was used as a first approximation and the classification was refined using Braun-Blanquet procedures. The result is a phytosociological table from which 13 plant communities and seven sub-communities were recognised. Although some of these communities and sub-communities are similar to previously described vegetation types in natural and disturbed areas, most of them were not described before in South Africa. Two ordination scatter diagrams show the distribution of the plant communities along gradients which were related to the depth of the soil water table, habitat type, trampling, soil compaction and percentage of gravel in the soil surface. Similarities between roadside vegetation in this study and those overseas are discussed, as well as the possible role of road verges as dispersal corridors between natural and disturbed areas.
Abstract: After the breakup of the Soviet Union, the republics of Central Asia began to restructure their agricultural sectors to achieve food security and to adjust to the requirements of a market economy. Although they encountered many common challenges, their agricultural policies differed significantly. For this reason, it is important to see the results of these policies and to learn lessons from them. This paper discusses the role of and the challenges facing rangelands and livestock production systems in achieving food security among the pastoral communities of Central Asia. It analyzes the trends in livestock development during the economic transition in Kazakhstan, the Kyrgyz Republic, and Uzbekistan, and derives policy directions for the sustainable use of rangelands and for the growth of the livestock sector in Central Asia.
Abstract: There have been several efforts to utilize satellite-based synthetic aperture radar (SAR) measurements to determine surface soil moisture (to 5Â cm) conditions of rangeland regions. The results have been mixed since the relation between the SAR signal and surface soil moisture is confounded by variations in topographic features, surface roughness and vegetation density. We designed an experiment to investigate the sensitivity of C-band SAR backscatter ([sigma]0) to surface soil moisture ([theta]s) in a semiarid rangeland and to test a data-fusion approach based on both optical (Landsat TM) and radar (ERS-2 SAR) measurements to improve regional estimates of surface soil moisture content. The data-fusion approach [Sano, E.E. 1997. Sensitivity analysis of C- and Ku-band synthetic aperture radar data to soil moisture content in a semiarid regions. Ph.D. Dissertation. University of Arizona, AZ] utilized the difference between dry- and wet-season SAR [sigma]0 to normalize roughness effects, and utilized surface reflectance in optical wavelengths to account for differences in vegetation density. We focused the study on three flat, uniformly vegetated sites of known surface roughness, monitored variations in surface soil moisture, vegetation density and SAR signal over time, and obtained eight optical/SAR image pairs throughout the dry and wet seasons. For these sparsely vegetated sites during this dry year (1997), we found that the SAR signal was not significantly attenuated by sparse green vegetation cover (greenleafareaindex<0.35) and dense standing brown vegetation cover (brown leaf area index up to 1.5). Consequently, the optical data was not required for this application, and the approach could be implemented by simply taking the difference between the dry- and wet-season SAR [sigma]0 ([sigma]0-[sigma]dry0). For a data set of eight dates at three study sites, we confirmed that the relation between ERS-2 C-band SAR [sigma]0 and [theta]s was weak (r2=0.27); yet for the same data set, that the relation between [sigma]0-[sigma]dry0 and [theta]s was strong and significant (r2=0.93). This study also raised two concerns: (1) the overall sensitivity of SAR [sigma]0 to [theta]s was relatively low, and (2) the approach required a high level of accuracy in the estimate of green leaf area level that may not be obtainable with standard optical remote sensing algorithms. In any case, the positive results from this study should encourage the use of a multi-temporal SAR and optical/SAR fusion for monitoring semiarid range conditions, and improving management of scarce resources.
Abstract: The Waste Isolation Pilot Plant (WIPP) is a mined repository for the permanent disposal of transuranic wastes. It has been constructed by the United States Department of Energy (DOE) in semiarid, sparsely inhabited rangeland in southeastern New Mexico. The disposal area is 655Â m below the land surface, in bedded salt of the Late Permian (approximately 255 million-years-old) Salado Formation. The extremely low permeability of the halite and other evaporite rocks provide the primary geologic barrier assuring long-term (10,000-year-plus) isolation of the radioactive waste from the accessible environment. Extensive geologic investigations during site characterization have provided information on the stratigraphy, structure, and natural resources of the region (including hydrocarbons, potash, and groundwater), and have investigated the potential for disruption by processes such as dissolution, salt deformation, tectonic activity, and climate change. Hydrogeologic investigations have documented the physical properties of the evaporite rocks, and have identified the Culebra Dolomite Member of the overlying Rustler Formation as the most transmissive water-bearing unit in the region. If the evaporite barriers are breached by accidental drilling intrusion, the Culebra would provide the most likely pathway for radionuclide transport away from the site. Although water in the Culebra is of poor quality and none is currently used for human consumption, groundwater flow and potential radionuclide transport in the unit have been studied in detail. Results of geologic and hydrogeologic studies of the WIPP region indicate that the geologic and hydrogeologic features of the site will provide effective long-term containment of radionuclides. Geologic and hydrogeologic information is used in the performance assessment that supported the DOE's compliance certification application to the United States Environmental Protection Agency.
Abstract: Agapeta zoegana is a Eurasian root-mining moth introduced for biological control of spotted knapweed, Centaurea maculosa, in North America. A study was conducted during 1992 through 1994 to assess the establishment of the moth and to make a preliminary assessment of the combined effects of the moth and grass competition on spotted knapweed plant structure and density at two nearby sites in western Montana. The moth was well established at a release site in 1992 where it had been previously released, and it became comparably well established at a check site, 140 m away, by 1994. Knapweed plants at the A. zoegana release site had less above-ground biomass (43%), fewer stems per plant (29%), and fewer capitula per plant (43%) and were shorter (18%) than knapweed plants at the check site, which may represent impact of the moth on the plant. However, a comparison of infested versus uninfested knapweed plants throughout both sites showed that infested plants had more stems (15%), more capitula (40%), and more above-ground biomass (112%), were taller (7%), had thicker roots (92%), and were older (22%) than uninfested plants, suggesting that the moth preferentially attacked older, larger knapweed plants. Numbers of A. zoegana larvae per root were positively correlated with root diameter. Incidence of attack by A. zoegana was significantly greater in bolted knapweed plants than in rosettes, but larvae showed no preference for bolted plants over rosettes when root diameters were similar. A. zoegana had no effect on knapweed rosette density, but appeared to reduce the number of bolted knapweed plants in plots with low grass density (10% grass cover) by 39% and increase the density of knapweed seedlings in the spring by 65%. Plots with high grass density (50% grass cover) contained fewer bolted knapweed plants (35%), fewer rosettes (38%), and fewer seedlings (50%) than plots with low grass density. The effects of A. zoegana and grass competition on bolted plant density were not additive.
Abstract: The investigation was conducted on an area covered by a dense stand of Hardwickia mopane (Leguminosae: Caesalpinioideae). Seven plots (65×180 m) were subjected to different intensities of tree thinning, ranging from a totally cleared plot (0%) to plots thinned to the equivalent of 10, 20, 35, 50, and 75% of the leaf biomass of a control plot (100%) with a tree density of 2711 plants ha-1. Thinning was completed during 1989 and the soil water study was conducted during the 1990/91 and 1991/92 seasons with the aid of a neutron water meter. The study area, before thinning, was characterized by the virtual absence of herbaceous plants with severe soil degradation in the form of surface erosion and crust formations. Increased infiltration of rainwater was measured in the thinned plots and this was associated with the establishment of herbaceous plants, mainly grasses. The soil water was predominantly held at a very shallow depth (<450 mm) and only in the totally cleared (0%) plot did the soil water content of the >450-900 mm soil zone show marked increases associated with specific rainfall events. Mean evapotranspiration water losses varied seasonally, but were generally much higher in the 0% plot (grass only plot), which confirmed that grasses use soil water more rapidly than the H. mopane trees. Evidence is presented that the roots of the H. mopane trees are able to utilize soil water at a matric potential lower than that of grasses ([psi]<-1500 kPa). This enables the H. mopane trees to compete successfully with herbaceous plants and to prevent their establishment at high tree densities.
Abstract: Dinoflagellate cyst and pollen records from marine sediments off the southwestern African coast reveal three major aridification periods since the last glaciation and an environmental correlation between land and sea. Abundant pollen of desert, semi-desert, and temperate plants 21,000-17,500 cal yr B.P. show arid and cold conditions in southwestern Africa that correspond to low sea surface temperatures and enhanced upwelling shown by dinoflagellate cysts. Occurrence of Restionaceae in the pollen record suggests northward movement of the winter-rain regime that influenced the study area during the last glacial maximum. Decline of Asteroideae, Restionaceae, and Ericaceae in the pollen record shows that temperate vegetation migrated out of the study area about 17,500 cal yr B.P., probably because of warming during the last deglaciation. The warming in southwestern Africa was associated with weakened upwelling and increased sea surface temperatures, 2000-2800 years earlier than in the Northern Hemisphere. Aridification 14,300-12,600 cal yr B.P. is characterized by a prominent increase of desert and semi-desert pollen without the return of temperate vegetation. This aridification corresponds to enhanced upwelling off Namibia and cooler temperatures in Antarctica, and it might have been influenced by oceanic thermohaline circulation. Aridification 11,000-8900 cal yr B.P. is out of phase with the northern African climate. Reduction of the water vapor supply in southwestern Africa at that time may be related to northward excursions of the Intertropical Convergence Zone.
Abstract: This paper explores the potential of a new method of reconstructing historical vegetation change in the Australian rangelands. Historical monitoring of rangeland vegetation has been so deficient that it is not possible to determine whether a long-term trend toward degradation has occurred (as is often assumed) or, indeed, if it is continuing to occur. Because long-term records are unavailable any attempt to monitor vegetation retrospectively must be based on proxy measures rather than direct observation. Where historical data are lacking an integration of palaeoecological, archaeological and ecological methods is required to reconstruct the past. Our research is based on a detailed analysis of sheep faeces deposited near a shearing shed in the semiarid rangelands of south-west Queensland between the late 1930s and the mid-1990s. The faeces in these deposits represent the diet of sheep in the days leading up to the property's annual shearing and as such are a potentially useful index to changes in vegetation. Results indicate significant changes in the diet of sheer since the late 1940s. The potential of this method, and its limitations, are discussed. Long-term records are critical in understanding issues of sustainability in land management and it is intended that this paper will stimulate further research into historical vegetation change in rangelands.
Abstract: This paper provides a summary of our current understanding of the key drivers of N2O emissions from soil in temperate and tropical, natural and agricultural ecosystems. These drivers are substrate supply, as N additions and mineralisation of organic N in soil, soil water content and temperature. They can exert synergistic or antagonistic influences on the emissions which can vary spatially and temporally. Such influences explain why emission rates often differ greatly from those based on current IPCC methodology. The latter only takes account of N inputs: direct emissions from agricultural soils are taken to be 1.25% of the N applied, while those from natural soils are taken to be 1% of the N deposited from the atmosphere, however, observed values range from 0.2% to 15%. Inadequate accounting for all sources affecting levels of soil mineral N (e.g. freeze-thaw cycles, ploughing, biomass burning, the first rainfall in wet seasons) and inter-annual differences in the size and timing of rainfall events in relation to land management practices are prime causes of the deviations.
Abstract: We present a remote sensing based vegetation mapping technique well suited to a heterogeneous, semi-arid environment. 10 structural vegetation classes were identified and described on the ground. Using Landsat-TM from two different seasons and a combination of three conventional classification techniques (including a multi-temporal classification) we were unsuccessful in delineating all of the desired vegetation classes. We then employed a simple textural classification index, known as the Moving Standard Deviation Index (MSDI), that has been used to map degradation status. MSDI measures spatial variations in the landscape and is calculated by passing a 3 X 3 standard deviation filter across the Landsat-TM red band. High MSDI values are associated with degraded or disturbed rangelands whilst low MSDI values are associated with undisturbed rangeland. A combination of two conventional multi-spectral techniques and MSDI were used to produce a final vegetation classification at an accuracy 84 %. MSDI successfully discriminated between two contrasting vegetation types of identical spectral properties and significantly strengthened the accuracy of the classification. We recommend the use of a textural index such as MSDI to supplement conventional vegetation classification techniques in heterogeneous, semi-arid or arid environments.
Abstract: Summary In savannas, degrading trends such as increasing woody cover are caused by livestock ranging. Hence, identifying sustainable utilisation intensities is crucial for range management. However, knowledge concerning herbivory effects on herbaceous vegetation and primary productivity, but also productivity of and foraging on woody vegetation (browsing) is incomplete. Consequences of these knowledge gaps for predictions of long-term herbivory impacts are analysed by exploring a set of herbivory models in the framework of a spatially explicit simulator of vegetation dynamics in a semiarid savanna. We distinguish herbaceous and woody vegetation, and two impacts of herbivory, namely on phytomass and on primary productivity. Herbaceous phytomass is consumed under all grazing models, which are distinct by effects on herbaceous productivity per unit ground area: none; direct effect on productivity; direct effects on productivity and survival. Browsing is either absent or present. Additionally, low and high spatial grazing heterogeneity are distinguished. For a time scale of 100 years, herbivory impacts were analysed in a simulation experiment over a range of low to high stocking rates. Without effects on primary productivity, herbivory showed no long-term impact on shrub cover. However, under higher stocking rates, mean herbage utilisation reached over 50% of herbaceous phytomass production, rendering the null hypothesis on productivity effects of herbivory unrealistic. When grass productivity was affected by herbivory, shrub cover showed a threshold response to utilisation intensity: at low subcritical intensities, shrub cover did not exceed the low initial values; above a threshold intensity, savanna vegetation was characterised by high shrub cover. The level of this threshold was affected by heterogeneity, browsing, and by the nature of the productivity effects, and also depended on the time span considered. Since sustainable livestock ranging is possible only at utilisation intensities below this threshold, its determinants are crucial for long-term assessments. Given the insufficient quantitative understanding of all three of the factors determining long-term herbivory impacts, our results suggest caution towards current predictions, and provide for a priority ranking in urgently needed further research.
Abstract: Abstract A new compilation of pollen and packrat midden data from western North America provides a refined reconstruction of the composition and distribution of biomes in western North America for today and for 6000 and 18,000 radiocarbon years before present (14C yr bp). Modern biomes in western North America are adequately portrayed by pollen assemblages from lakes and bogs. Forest biomes in western North America share many taxa in their pollen spectra and it can be difficult to discriminate among these biomes. Plant macrofossils from packrat middens provide reliable identification of modern biomes from arid and semiarid regions, and this may also be true in similar environments in other parts of the world. However, a weighting factor for trees and shrubs must be used to reliably reconstruct modern biomes from plant macrofossils. A new biome, open conifer woodland, which includes eurythermic conifers and steppe plants, was defined to categorize much of the current and past vegetation of the semiarid interior of western North America. At 6000 14C yr bp, the forest biomes of the coastal Pacific North-west and the desert biomes of the South-west were in near-modern positions. Biomes in the interior Pacific North-west differed from those of today in that taiga prevailed in modern cool/cold mixed forests. Steppe was present in areas occupied today by open conifer woodland in the northern Great Basin, while in the central and southern Rocky Mountains forests grew where steppe grows today. During the mid-Holocene, cool conifer forests were expanded in the Rocky Mountains (relative to today) but contracted in the Sierra Nevada. These differences from the forests of today imply different climatic histories in these two regions between 6000 14C yr bp and today. At 18,000 14C yr bp, deserts were absent from the South-west and the coverage of open conifer woodland was greatly expanded relative to today. Steppe and tundra were present in much of the region now covered by forests in the Pacific North-west.
Abstract: We examined the perceptions and realities of land degradation in a communal ranching area, Otjimbingwe, in arid Namibia (in south-western Africa). It is commonly perceived that large-scale degradation of Otjimbingwe has occurred due to a mixture of improper pastoral practices and pressures induced by a high human population growth rate. We sought to determine whether the inhabitants perceived land degradation to have taken place and whether their perceptions were consistent with empirical data on environmental quality. Furthermore, we wished to determine whether these pastoralists had management strategies to help them withstand the harsh environmental conditions in which they live. All respondents in our surveys perceived that the environment had become degraded. The claimed source of this degradation, a decline in annual rainfall, is inconsistent with long-term rainfall records (there was neither change nor cyclicity in rainfall over time). There is also little evidence of a decline in plant cover and soil quality in spite of the very high stocking densities. No overall pastoral strategy exists in Otjimbingwe. Options for management are extremely limited due to a variety of external and internal pressures such as a high human population growth rate, high immigration into Otjimbingwe, restricted water availability due to dams constructed upstream, and limited movement opportunities for livestock in drought periods.
Abstract: The effects of three fire regimes--(1) burning early in the dry season (June), (2) burning late in the dry season (September) and (3) not burning (protected from wildfires)--on the water quality, water yield and export coefficients of three intermittent streams, which flow between December and June, have been examined in a tropical savanna in northern Australia. The study was conducted over a three year period in Kakadu National Park, and employed a comparative catchment approach though without any pre-treatment data. The canopy cover, density of riparian vegetation, litter- and ground-cover of the catchment burnt early in the dry season (catchment E, stream E) and the unburnt catchment (catchment U, stream U) were similar. Fires lit late in the dry season (catchment L, stream L) however resulted in tree mortalities, and a lower canopy cover (50% less), riparian tree density (80% less) and litter cover, and increased amounts of bare ground; thereby increasing catchment L's susceptibility to erosion. This resulted in episodic runoff events from catchment L in November and December, before continuous wet season flow. These events, absent in catchments E and U, featured high concentrations of total suspended sediment (TSS), volatile suspended sediment (VSS), N, P, Fe and Mn up to 10 times those measured later in the wet season. During continuous wet season flow between December and June, baseflow water quality of the three streams were similar. Storm runoff concentrations for N and P were also similar, however stream L storm runoff concentrations of TSS, VSS, Fe and Mn were 2-5 times higher than those measured in streams E and U. Despite this, only the export coefficients for TSS from catchment L (average 61 kg ha-1) were significantly higher (average 2.4 times) than catchment E and U coefficients. This was attributed to the overwhelming influence of stream volume, relative to concentration, in determining stream load and hence catchment export coefficients (load/catchment area). The apparently negligible impact of the fire regimes on VSS, N, P, Fe and Mn export coefficients, and also the overall low sediment export coefficients for the three catchments which were up to 100 times less than that reported for other tropical environments, were ascribed to the low catchment slopes (average 0.5%), low soil fertility, maintenance of a protective surface gravel lag, the negligible impact of the fire regimes on water yield, and the sometimes lengthy (maximum 6 months) period between burning and runoff.
Abstract: Experiments were conducted to investigate: (1) tiller recruitment within the interior of Eragrostis curvula tussocks, with and without litter removal; and (2) effects of moderate defoliation on tiller recruitment within the interior of the clump. Tiller recruitment within the interior of non-defoliated plants was significantly (p<0·01) increased by litter removal. When field-grown plants were defoliated, the tillering rate was greater (p<0·01) in plants with litter retained than those with litter removed 91 days after defoliation. When the greenhouse-grown plants were defoliated, tiller recruitment was greater (p<0·05) in plants with litter retained than those with litter removed during the first 13 weeks after defoliation. Tillering in the non-defoliated plants was less (p<0·05) than in defoliated plants with litter retained. Litter removal or moderate defoliation stimulated basal tillering by opening up the canopy and providing more light available to the basal buds. Therefore, the central dieback is not simply a natural consequence of tillering pattern; resource depletion within the interior may be a contributing factor to this phenomenon.
Abstract: Abstract Anthropogenic natural habitat transformation presents the single most important threat to global biodiversity. Land cover data, based on Landsat Thematic Mapper (TM) imagery, were used to derive land use information for the Gauteng, Mpumalanga and Northern provinces of South Africa. The assessment integrated land use data with species presence data (15 × 15 minute grid cell resolution) for butterflies, mammals, birds and endemic vascular plants. The objectives of the present study were: (1) to identify areas at a regional scale where there is a possible conflict between biodiversity conservation interests and current land uses; (2) to investigate the influence of incorporating a land use constraint (LUC) into a conservation area selection algorithm, while taking cognizance of the existing reserve system; (3) to investigate the circumstances of species recorded within these conflict areas. Many grid cells identified as species richness hotspots, rarity hotspots or as part of the complementary network selected by the unconstrained algorithm were in reality largely transformed or modified. These areas should thus be avoided when striving to identify a viable conservation network. Although the LUC algorithm selected more grid cells to represent all species, it succeeded in increasing the percentage of natural vegetation within the selected conservation network and highlighted areas where potential conflicts should be thoroughly investigated at a local scale.
Abstract: Watering points in the semi-arid Kruger National Park, Klaserie Private Nature Reserve, Cleveland Game Park and four game ranches in the Klaserie district were studied. Herbaceous community composition and basal cover were measured in transects starting at, and radiating from the water. The community compositions were converted to herbaceous forage and fine fuel production potential scores and the extents of impact determined. A general linear model was used to analyse the extent of impact of indigenous large herbivores on these parameters at artificial watering points. Rainfall in the previous rainfall season, stocking rate and distance to the nearest neighbouring watering point had significant effects. Amounts of clay and sand in the A and B horizons of the soil were not important in determining the extent of impacts on herbaceous rangeland condition indices. Once watering points are placed at a density such that all areas on a property are within reach of foraging, water-dependent indigenous large herbivores, the effects of additional watering points are expected to be of little importance relative to those of rainfall and stocking rate. It is feasible to manage for reduced impacts on rangeland condition at watering points. A water provision system of clusters of watering points separated by large waterless areas is proposed.
Abstract: This paper discusses land use patterns of hunter-gatherers inhabiting arid grasslands of later Pleistocene East Africa, inferred from an analysis of raw material economy in five Later Stone Age (LSA) lithic assemblages from Lukenya Hill, southern Kenya. Later Stone Age lithic assemblages at Lukenya fall into two groups, one based predominantly on the use of quartz to manufacture scrapers and other flake tools, and the second using greater amounts of rarer chert and obsidian lithic materials to manufacture microliths. Aspects of raw material use, coupled with ethnographic data on how food and water abundance affects Kalahari forager land use, indicate that the first group of sites had longer occupations by groups with smaller home ranges. The second group of sites had shorter occupations by more mobile groups with larger home ranges. The paper compares the land use patterns of arid grassland LSA foragers, like those at Lukenya Hill, with those in woodland and forest areas of Central and Southeastern Africa. Improvements in the ability to procure food, such as the development of fishing and fowling technologies or better hunting projectiles, allowed grassland groups to become more mobile in the later LSA, while foragers in wetter parts of Africa, including woodlands, riverine areas, and lakeshores, seem to have intensified the procurement of fish and plant foods. The processes of economic specialization taking place in both grassland and woodland areas of Later Stone Age Africa may have parallels in other parts of the Old World.
Abstract: The conversion of grasslands and savannas to shrublands and woodlands by invasive weeds is a global problem confounding scientists and land managers. Since the 1960s, prickly acacia, Acacia nilotica ssp. indica, has substantially increased in density and range to become one of Australia's worst tropical rangeland weeds. Although the plant has been classified as a noxious weed for more than 30 years, relatively little research on its biology or ecology occurred until the late 1980s. A program of introducing biological control agents commenced in 1980 and resulted in the release of two insects: one failed to establish and the other has failed to exert any control. We suggest that studies of the population dynamics of a weed should occur prior to implementation of biological control programs. These can be valuable to identify weaknesses that can be exploited and to focus the search for effective agents, thereby enhancing the success rate of biological control efforts. We examine the life history and dispersal mechanisms of A. nilotica with a view to understanding the relative sensitivity of the population to reductions in each lifestage, understanding the vulnerability of each lifestage to biological control, and prioritizing potential control points in the lifecycle. Seedlings and juveniles appear to be the most susceptible lifestages to target for control. They are relatively easy to kill, and significant reductions in their numbers will reduce the overall weed status of the plant.
Abstract: Thatta Leghari rangeland in the Dera Ghazi Khan district of Pakistan covers an area of 1004Â ha. Its topography is undulating, soil is calcareous and low in organic matter and supports a native standing crop of mainly unpalatable herbaceous vegetation. Due to uncontrolled grazing the range has degraded from its productive potential. Between 1992 and 1993 the native range (1004Â ha) was not grazed. Then in 1992 and 1993, a 600Â ha area was reseeded with two introduced grasses, Gorkha (Lasiurus sindicus) and Buffel grass (Cenchrus ciliaris). Forage production on both the reseeded and native range was measured in 1992 and 1993 at the end of the growing season during October. Weather during these 2 years reflected the long term mean conditions with respect to temperature and distribution of precipitation. The reseeded area produced 10 times (4000Â kg/ha) more forage than the native range (425Â kg/ha) in 1992 and more than twice the forage (1250Â kg/ha vs 534Â kg/ha) in 1993, a year with 37Â mm less total rainfall. Proximate analysis of the forage harvested in 1993 was determined for both treatments. Buffel grass was higher in crude protein (7.8%) than Gorkha (6.2%) and chimber (5.9%; Eleusine flagellifera) a native grass. The native shrub, lana (Salsola foetida) had a higher energy value, 2.7Â Mcal/kg, than all of the other species. Daily goat and sheep diets consisted of 51% and 32% shrub, respectively, with grasses comprising the remainder. Forbs composed 35% of the sheep diet whereas, shrubs (51%) dominated the goat diets on the reseeded rangeland. Liveweight gain differed (p<0.05) between goats (34Â g/day) and sheep (14Â g/day). These preliminary results indicate that reseeding may be an important intervention for Pakistan rangeland improvement, for improving nutrition for small ruminants.
Abstract: Small mammal and bird assemblages were compared across fence-lines between one communal and three adjacent commercial range-lands in Namaqualand, South Africa. The communal area has twice the recommended stocking rate of sheep and goats, and has less perennial plant cover and more annual plants than neighbouring commercial rangelands. Commercial rangelands supported a larger and more diverse assemblage of small mammals and birds. Small mammal species composition on communal lands was a subset of that on adjacent commercial rangelands, with only one species equally abundant in both treatments. Diurnal mammals were scarce in communal rangelands, apparently due to the lack of cover for predator avoidance and herbivory. Management to maintain a diversity of small mammals requires a minimum level of effective cover. Bird richness and diversity was also reduced on communal rangelands, with many species, especially insectivores, less abundant. A few bird species, notably granivores, were more abundant on communal rangelands, probably because of the increase in annual plant cover. The absence of some large bird species regularly found in Namaqualand, but absent from both treatments (e.g., bustards), suggests that neither management practice is optimal.
Abstract: In this paper we review the effects of the provision of artificial sources of water on native flora and fauna in arid and semi-arid zones, with emphasis on Australia but drawing on information from other countries where possible. The effects of artificial sources of water are profound and are a rarely-cited aspect of change in arid and semi-arid zone rangelands. Direct effects of artificial sources of water include: (1) the development of wetlands that support native plants and animals; (2) the expansion of geographic range and increased abundance of native animals which need to drink regularly; and (3) the possible expansion of breeding ranges of invertebrates that require water for some stage of their life cycle. The major indirect effects of artificial sources of water are as a source of drinking water for domestic stock, and native and feral mammalian herbivores, and so they provide a focus for grazing. Recorded changes in vegetation in response to grazing around artificial sources of water are: (1) the development of a zone of extreme degradation around the water (up to 0.055 km) where soil crust is broken, erosion is high and unpalatable plants dominate; (2) an increase in the number of unpalatable perennial shrubs beyond the extreme degradation zone, particularly in semi-arid woodland and arid shrubland habitats; and (3) a decrease in abundance of palatable native perennial grasses due to selective grazing. Effects of grazing on native fauna are poorly documented but published accounts include: (1) a possible contribution to the recent extinction of some medium-sized native mammals in Australia, also assisted by those introduced predators which rely on drinking water; (2) the displacement of some ground-dwelling bird species from regions heavily developed for pastoralism, and geographic range reductions for many other species of birds; and (3) changes to the distribution and abundance of invertebrates such as grasshoppers, ants and collembolans. Artificial sources of water may also indirectly affect native wildlife by acting as foci for the activities of native and introduced predators.
Abstract: Analysis of a Landsat TM image from a rangeland near Peddie, Eastern Cape, revealed differences in two vegetation indices (normalised difference vegetation index, NDVI, and moving standard deviation index, MSDI) between communal and commercial rangeland. It was suggested that the difference in the MSDI reflected differences in rangeland condition. To assess whether or not any differences could be detected in the field, vegetation parameters were recorded (cover, species composition) along ten, paired 20-m transects. Based on species forage factors for commercial livestock production, the commercial grassland was in a significantly better condition than the communal land. The commercial farmland had a higher occurrence of palatable species while the communal land was richer in non-palatable species. A TWINSPAN classification and the NDVI and MSDI values confirmed the marked difference between the communal and the commercial land. Both the vegetative field survey data and the satellite imagery showed that the communal land was transformed in comparison to the commercial land, and this difference can be attributed to differences in land-use.
Abstract: The biodiversity convention aims at conserving biodiversity and guaranteeing fair and sustainable human use of biodiversity. The convention further requires that the causes of biodiversity decline are identified and evaluated, and that effective conservation and monitoring strategies are developed. Resolving these needs requires a different approach than those described in the last Global Biodiversity Assessment. This assessment tended to be descriptive and did not comprehensively attempt to describe future trends in biodiversity in relation to the major threats: habitat destruction, overexploitation, alien species, pollution and climate change. Integrated assessment modelling and scenario development have therefore not been introduced and applied to assess changes in biodiversity. These tools were originally developed for acidification and climate-change impact assessments but are also well suited to analysing other environmental problems. The implemented business-as-usual scenarios show the causes of biodiversity decline to differ regionally. Although complex patterns of causal factors and changes occur in many regions, a valid (but generalised) statement is that climate change causes biodiversity decline in industrialised regions, while in developing regions expanding land use is the major contributor. The scenarios further highlight that despite population growth contributing to the problem, rapidly increasing consumption patterns, rapid expansion of rangelands to support changing diets and too slow-moving technological innovations are major attributes of land-use change and biodiversity decline. Finally, it is concluded that scenario studies transparently highlight the complex systemic interactions and feedback between society and the other components of the earth's system. In addition, scenarios can contribute well to improving the understanding of changes in biodiversity at global and regional levels of assessment.
Abstract: This study investigated the composition of the soil seed bank and growing annual plant community in sheep-grazing exclosures. The effects of stock exclusion on annual plant community structure was slight, and was different in the seed bank and in the growing community because of little correspondence between the two. Stock exclusion favoured a few species, but never decreased the abundance of invasive species. It had little or no effect on species diversity. We conclude that grazing exclusion of the order of a decade is not enough to reverse changes produced by long-term grazing.
Abstract: Changes in tussock attributes and sward structure with time-since-fire were documented for the dominant tussock grass, Themeda triandra, at the Derrimut Grassland Reserve in southern Victoria, Australia. When the inter-fire interval exceeded 6 yr, the number of tillers per tussock and the total number of tussocks declined, and by 11 yr, few live tillers or tussocks remained in the sward. Below-ground biomass was also substantially lower at this time. With increasing time-since-fire, the canopy of live leaves was elevated high above the soil surface and dead leaves accumulated around and over the tussock bases. Productivity declined in long unburnt areas and by 11 yr without disturbance, the canopy "collapsed" upon itself, forming a thick layer of dead thatch over the soil surface. A single fire in an area previously unburnt for 12 yr did not immediately return the tussocks to a state more characteristic of a site with a 4 yr inter-fire interval burnt at the same time. Inter-fire intervals of [less-than-or-equals, slant]5 yr would appear necessary to maintain the health and competitiveness of Themeda triandra. These findings have important implications for the maintenance of faunal habitat and the potential for weed invasion into remnant grasslands.
Abstract: The overall effects of fire on ecosystems are complex, ranging from the reduction or elimination of aboveground biomass to impacts on belowground physical, chemical and microbial mediated processes. Since a key component of overall ecosystem sustainability occurs belowground, recovery is tied to the soil's physical, chemical, and biological functions and processes. Depending on several fire severity measures, changes in belowground components can be either beneficial or deleterious to the entire ecosystem. Low-impact burning can promote a herbaceous flora, increase plant available nutrients, and thin over-crowded forests, all of which can foster healthy systems. Severe fires can often cause changes in successional rates, alter above- and belowground species composition, generate volatilization of nutrients and ash entrainment in smoke columns, produce rapid or decreased mineralization rates, alter CÂ :Â N ratios, and result in subsequent nutrient losses through accelerated erosion, leaching or denitrification. In addition, changes in soil hydrologic functioning, degradation of soil physical properties, decreases in micro- and macrofauna, and alterations in microbial populations and associated processes can occur. The direct effect of fire on belowground systems is a result of the burning severity, which integrates aboveground fuel loading (live and dead), soil moisture and subsequent soil temperatures, and duration of the burn. The time for recovery of belowground systems will not only depend on the burning intensity and its effect on key ecosystem processes and components, but also on the previous land-use practices. Thus, the impacts of fire on belowground systems can be highly variable and may not be predictable. Our paper is a general review of the effects of fire on belowground systems with emphasis placed on the changes in physical, biogeochemical and biological properties of soils and the resulting consequences these changes have for ecosystem sustainability.
Abstract: Food security for the world in 2025 is possible and probable if the right set of things are done, starting now. But the task will not be easy. It is both a technology and a political/economic challenge. The challenge for sub-Saharan Africa is even greater. While other regions improved per capita food availability over the last 30 years, Africa's availability declined. But food security is about more than supply. It is also about access which means income generating employment is critical. Meeting future requirements in Africa and the world will require sustainable intensification of complex production systems, appropriate national and international policies and continued investments in agricultural research. Without these conditions and increased employment intensive growth, prospects for the future are less bright.
Abstract: Land-use practices can impact on bird populations. This study set out to explain why the helmeted guineafowl, Numida meleagris (Linnaeus 1766; Aves: Numididae) declined in the Midlands of KwaZulu-Natal, South Africa, an agricultural area where these birds were once abundant in savannas mixed with cultivation. Within the Midlands, the potential roles of land-use practices and pesticides were investigated. Using a grid cell approach, the distribution of 11 land-uses was mapped for 19 farms with different levels of guineafowl abundance. The edge distance between extensive and intensive agriculture was significantly associated with the presence of guineafowl. The presence of guineafowl was associated with greater land-use diversity, showing this species' preference for a mosaic of land-uses. Extensive agricultural areas were used for cover and intensive ones for food, but the adjacency of these land-uses affected access to these resources. Larger flocks (>=100 birds) were associated with pastures free of agro-chemicals, while smaller flocks (<100 birds) were associated with cereal lands where chemicals were used. The use of chemicals may reduce reproductive success by removing arthropods and weeds, which are critical food sources for female guineafowls and their keets during the breeding season. An inadequate grass cover for nesting may further reduce reproductive success. This study suggests that a combination of land-use spatial pattern and other factors, such as pesticide use, contributes to the decline in helmeted guineafowl populations in this intensively farmed area of South Africa.
Abstract: In the semi-arid open woodlands or savannas of eastern Australia banded vegetation is a common form of landscape patchiness. This banding can form relatively long strands or shorter stripes across the landscape, or small patches can occur in a stippled pattern. In degraded areas these patches can be completely removed from the landscape. This study addresses two related questions: does the type of patchiness (strands, stripes, or stipples) significantly influence how efficiently these semi-arid landscapes capture and store scarce soil resources; and how does this efficiency compare with landscapes that have lost all their patches? Results from a landscape simulation model, validated for a semi-arid woodland study site, demonstrated that the loss of landscape patchiness had the greatest influence on the capacity of the landscape to capture rainfall as soil water--reduced by about 25% compared to banded landscapes. This 25% loss of soil water reduced annual net primary productivity in these systems by about 40%. Banded patterns (stripes or strands) captured about 8% more rainfall as soil water than a stippled pattern; this increased their plant production by about 10%. However, these differences between banding patterns were relatively small compared to the impact of totally eliminating patchiness, which can occur with severe land degradation. This implies that preventing the loss of landscape patchiness is very important for managing savannas for production and conservation goals.
Abstract: While community-based natural resource management (CBNRM) now attracts widespread international attention, its practical implementation frequently falls short of expectations. This paper contributes to emerging critiques by focusing on the implications of intracommunity dynamics and ecological heterogeneity. It builds a conceptual framework highlighting the central role of institutions -- regularized patterns of behavior between individuals and groups in society -- in mediating environment-society relationships. Grounded in an extended form of entitlements analysis, the framework explores how differently positioned social actors command environmental goods and services that are instrumental to their well-being. Further insights are drawn from analyses of social difference; "new", dynamic ecology; new institutional economics; structuration theory, and landscape history. The theoretical argument is illustrated with case material from India, South Africa and Ghana.
Abstract: We describe a model that simulates use of chemical treatments, mechanical treatments (roller chopping and root plowing), and fire to manage woody vegetation in the Rio Grande Plains of southern Texas and northeastern Mexico. The model consists of two submodels representing dynamics of woody and herbaceous vegetation, respectively. Percent canopy cover of woody vegetation changes as the result of application of management schemes. Aboveground biomass of herbaceous vegetation changes as the result of differences in rates of net primary production, senescence, decomposition, and losses due to grazing and fire. The model is represented as a compartment model based on difference equations with a time step of 1 month. Model predictions of changes in canopy cover of woody vegetation, number of acres required to support a cow, and net production of herbaceous vegetation following application of each of the four treatments are similar to typical 25-year post-treatment response curves for the Rio Grande Plains. Simulation results suggest that the period of opportunity for effective use of fire to manage woody vegetation and sustain production of herbaceous vegetation is longest following root plowing, intermediate following use of chemicals, and shortest following roller chopping. In each case, the efficacy of fire in reducing canopy cover of woody vegetation diminishes rapidly as percent canopy cover increases from roughly 30-50%.
Abstract: Alternating bands of vegetation and bare soil, reported from many dryland regions, have been identified as indicators of rangeland deterioration triggered by overgrazing, cattle trampling or climatic change. Banded vegetation occurs at a range of scales and although it has been reported from a number of different environments, it is not characteristic of all degraded rangelands. It does appear particularly frequently on low angle, smooth slopes over soils of high erodibility but low permeability, where scant rainfall is sporadic or highly seasonal. It has been attributed both to wind and to water erosion, but few data on the processes active or their specific response to limiting environmental variables are available. Small-scale banded vegetation associated with small scour steps occurs on low angle alluvio-lacustrine flats surrounding Lake Baringo in semi-arid northern Kenya. In this area of strong moisture deficit, the dominant factor controlling the incidence of ground vegetation is variation in near-surface moisture storage. The regular spacing of the small-scale vegetation bands reflects preferential moisture storage in regularly-spaced sediment deposits. Field and laboratory runon and rainfall simulation experiments, previously reported, provided some data on the processes and conditions involved in formation of these deposits. This paper describes more closely-controlled laboratory rainfall simulation and runon experiments, carried out to identify the sequential scour and deposition processes involved, which are ultimately responsible for the regular variations in moisture storage capacity. These experiments, carried out in an 8.5 m long flume, show critical stream power ([Omega]) conditions in sheetwash and rain-impacted sheetflow required for sequential scour/deposition as 0.020-0.025 W m-2 and between 0.043 and 0.055 W m-2, respectively. Experimental results indicate that vegetation bands at the scale observed at Baringo are consistent with development by sequential scour and deposition, caused by some combination of sheetwash, rainsplash and rainflow. The vegetation bands are composed primarily of unpalatable low herbaceous plants, dominated by Trianthema triquetra. These plants colonize or survive better on deposition zones because of better soil moisture status. The vegetation bands can therefore indicate an initial stage in vegetation recovery rather than continuing rangeland deterioration, but at Baringo further development of vegetation appears to be restricted by high grazing intensities or by allelopathy.
Abstract: Within-site heterogeneity of soil N in arid and semi-arid grasslands is often less pronounced than in shrublands and, depending on the index used, can be difficult to detect. We compared biological and chemical indices of soil N from two perennial tussock grasslands of similar soil type in sub-tropical, northwestern Australia. We aimed to add to the minimal information on spatial heterogeneity of soil N in Australian arid environments and to identify indices suited to routine analysis in monitoring and rehabilitation programs in Australia's rangelands. Soils were collected from two sites per grassland type at the end of spring (dry season) from immediately adjacent to tussocks and open areas between tussocks and from 0-2 and 2-5 cm depth. Amounts of N mineralized in leached aerobic incubations (81 d, 40°C, 0-2 cm only) differed significantly between grasslands and between sampling positions (greater adjacent to tussocks) and ranged from 88 to 158 [mu]g g-1. Only NO3--N was produced during aerobic incubations and was about 20% of total N, irrespective of grassland and sampling position. In contrast, N produced during anaerobic incubations (7 d, 40°C) and by extraction in hot KCl was less than 1% of total N. Both of these indices were poorly correlated with others and were either highly variable or did not detect a pronounced depth effect. Oxidisable C and absorbance260 of 10 mM NaHCO3 extracts were better correlated with our aerobic index of N availability but relationships differed between grasslands. We recommend either absorbance260 of mild-salt extracts (soils leached and then aerobically incubated) or total N for relative estimates of N mineralization potential in hot, arid environments where soils are routinely [`]field-dry'. Strong correlations between variables in this study indicate that heterogeneity in relatively undisturbed, semi-arid soils of similar mineralogy and history is of sufficient magnitude for identifying appropriate indices of N availability.
Abstract: In this paper we discuss how low spatial resolution (1 km) ERS ATSR-2 and NOAA AVHRR satellite data were used to map and monitor changes in the grazing vegetation of the Badia region of Jordan. This area is typical of many arid zone grazing areas, comprising sparse vegetation and highly reflective soils. These two factors were found to severely limit the usefulness of satellite-derived vegetation indices that are frequently used to map and monitor vegetation in more temperate areas. Furthermore, the relationship between vegetation indices and percentage vegetation cover was found to be site-specific, thus reducing their application for large-scale vegetation monitoring. As an alternative, a hybrid geometric optical/empirically based model was developed for the area. This was based on the illumination geometry and reflectance values from the red and near-infrared scattergram of the satellite images. The output of the model was a series of maps indicating percentage vegetation cover for different dates and these were used to construct maps showing areas of vegetation change. Strong correlations (r2=0.837) were found between estimates of percentage vegetation cover derived from the model, and measurements made at a series of 16 field sites in the area. The use of geometric optical models based on satellite imagery improves the ability to map areas of grazing vegetation in arid areas such as the Badia and provides a good alternative to the use of vegetation indices.
Abstract: Emissions from vegetation fires in the tropics contribute significantly to atmospheric chemistry at continental and global scales. Africa is the continent where the largest number of vegetation fires annually occurs. The use of Global Area Coverage (GAC) data, from the Advanced Very High Resolution Radiometer (AVHRR) sensor onboard the NOAA satellites, allows a good description at continental level of the spatial distribution of intense active fire patterns and a unique temporal perspective over multi-annual periods of time. In this study, 5 years of active fire maps, from November 1984 to October 1989, derived from GAC data for the African continent were considered. In order to enhance the relationships between spatially distributed phenomena, such as regional patterns of active fires, and point data, such as experimental sites of atmospheric chemistry measurements, the rose diagram technique as derived from directional statistics was exploited. This methodological approach allowed the spatial characteristics of vegetation fires, which is considered the main source of atmospheric pollutants in Africa, to be described using measures of frequency and distance for each reference point. Comparison between rose diagrams of fires and nitrate (NO3-) content in precipitation as measured at Enyele (Congo), at the heart of the equatorial forest during both dry and wet seasons, confirmed the usefulness of satellite observations and the spatial analysis technique proposed.
Abstract: In southern Mali, cultivated area and herd size increase together with population growth. Consequently, periods of natural fallow shorten and traditional farming and animal husbandry techniques lead to a decrease of soil organic matter (SOM) content. Between 20 and 45% of the land is cultivated while less than 60% is arable area. To increase efficiency of natural fallow, a reduction in livestock herds is often proposed. By means of a linear programming model, the feasibility of maintaining actual SOM content in two villages in different agro-ecological zones was investigated. By adjusting animal numbers and cropping pattern, the model maximized: (1) SOM content under the condition of positive farm labour income; or (2) farm labour income under the condition of a positive SOM content. The model results suggested that maintaining SOM content requires the use of cereal crop residues for animal feed and for manure through bedding in kraals, but also higher animal densities. The last was feasible only through: (1) herding cattle of several farms together to overcome labour constraints; and (2) introducing P-fertilized leys, for grazing in the dry season. Grazing of the leys together with crop residues allowed animal densities up to 44 tropical livestock units (TLUs) km-2, while less than 16% of the produced rangeland fodder was grazed. In such conditions, a positive SOM balance and higher income was obtained with a minimum of 16.7% of ley in the crop rotation. Limiting the area cropped with cotton stabilized income and contributed to a positive SOM balance. Zero-grazing during the warm season allowed SOM surpluses to be achieved with 12.5% of ley. However, as income decreased, seasonal zero-grazing could only be adopted for high-producing animals and small herds.
Abstract: Recent political transformation in South Africa has laid the basis for significant socioeconomic change. One area in which the greatest socioeconomic disparities are discernable is the agricultural sector and rural development in general. Through the medium of a case study of the Eastern Cape province, the obstacles and opportunities facing the two predominant farming groups--emerging black small-scale farmers and white commercial farmers--are examined. The paper concludes with an examination of the economic potential of the former [`]white' areas to sustain the resettlement of people previously excluded from that land market on racial grounds.
Abstract: Microphytic crusts are important components of arid and semi-arid systems. They play important roles in ecosystem processes and are useful indicators of landscape health. Despite their importance, microphytic crusts and their component organisms are little understood, largely due to their small size and the difficulty in identifying them to species level. The influence of microphytic crust organisms on soils and landscapes, and their response to and recovery from perturbation is related largely by their morphology or external appearance. In this paper we examine the relationships between morphological groups of lichens and bryophytes associated with soil crusts, and their roles in ecosystem processes in rangelands. Using published and unpublished data we propose that the morphological group approach is a more efficient method of monitoring soil crust organisms than one based on the traditional species approach.
Abstract: Accelerated erosion by wind and water has taken place in arid western New South Wales, Australia, since the introduction of domestic and feral herbivores by Europeans in the nineteenth century. This action led to widespread soil loss by sheetwash, rilling, gullying, and aeolian deflation. Upland creek systems, formerly comprising shallow sinuous channels, are now entrenched into alluvial fills on the valley floor. Radiocarbon dating of charcoal from Aboriginal cooking pits, exposed by this erosion, indicates that the current phase of incision of the valley floor has occurred since grazing of domestic animals began about 140 years ago. Stratigraphic evidence is presented which suggests that this type of incision (gullying or arroyo cutting in the valley floor) may not have occurred before within the 20,000 year sedimentary history of the valley fills studied. Channel enlargement and knickpoint retreat, initiated by these changes, is ongoing, and the implications of this for land and heritage management in the region are discussed. A conceptual model is presented which summarises the hydrogeomorphic changes which have occurred in upland catchments in the region as a result of changes in landcover.
Abstract: The effect of both a non-prescribed summer fire and grazing at high stocking rate following fire on plant community composition, the frequency of occurrence of bare soil, grasses and shrubs, species diversity and biomass of herbaceous forage were evaluated for three growing seasons after fire. Changes in community composition occurred as a consequence of both fire and grazing. Communities were dominated by unpalatable shrubs and grasses in unburned sites as a result of a long history of overgrazing. Fire contributed to a conversion of those shrublands to communities with a more favourable balance between woody and herbaceous species. The frequency of palatable grasses and herbaceous forage biomass increased by a factor ofc. 3 at the expense of woody vegetation. Grazing after fire had significant positive (i.e. decrease in undesirable grasses) and negative (i.e. increase in bare soil) effects.
Abstract: Rangelands are complex systems with many interacting components. Modelling such systems presents two particular and interrelated problems. Firstly, the processes involved operate on greatly differing time scales: long-term changes in rangelands typically depend on much shorter-term processes such as rainfall, vegetation growth and livestock growth. Secondly, while complex mechanistic models of single animals or small herds have been developed (also involving differing time scales, from minutes to months), extending such models to an entire multi-species rangeland is generally an intractable problem. Recently, a new modelling paradigm has been introduced which facilitates the building of [`]economical' systems models by using the concept of a frame. Frames are chosen to represent distinct states of the system (e.g. grassland with scattered mature trees, as opposed to dense bush cover). Independent models are constructed for each frame; these models simulate the key processes identified within that frame (and may themselves be simplifications of more complex models). Rules are established for switching frames. In this paper we describe a frame-based model of a typical Southern African rangeland supporting cattle and goats. Simple quantitative models for each frame are developed from the output of a complex mechanistic model, depending on rainfall, stocking density and animal condition. Results from the overall frames model show how long-term responses of the system (in terms of production and vegetation state) to various management strategies (such as livestock sales) may be predicted, and in this way allows comparison of different management strategies.
Abstract: Costs and benefits derived from the introduction of cacti production into goat-production systems in the northeastern plain of Mendoza were examined by a simulation model. The model was run with 50, 100, 150, and 200 does and annual rainfall probabilities (f) from 0.1 to 0.9. Investments and costs were derived from data recorded by the present authors through the establishment and monitoring of experimental cacti plantations. Cactus production was based on a rain-use efficiency factor of 12.5 kg DM ha-1 year-1 mm-1 and the annual rainfall probabilities in the area. The cut-and-carry management method was considered for pen feeding during 110 days (last third of pregnancy and 60-day lactation) with 3.6 kg fresh material goat-1 day-1. A decrease in goat annual mortality from 10% to 2% and an additional annual amount of kids per goat were considered as direct benefits derived from supplementing goats with spineless cactus in the fall-winter period. As a consequence of this practice, an additional 0.2 kids appears to be obtainable in field conditions. A secondary benefit was the reduction of water consumption by goats. The internal rate of return (IRR) corresponding to 0.2 kids goat-1 and the additional kids required to reach an IRR equal to the opportunity cost of capital (12%) were determined. The establishment cost of cacti plantation ranged from US$ 525 ha-1 (50-head goat herd; f0.1) to US$ 242 ha-1 (200-head goat herd; f0.9), amounts that would be cost prohibitive for many stockmen. Cost of fence installation was the main item of establishment cost in most the analyzed scenarios. This cost may be reduced if a fence made of spiny cactus is established. If dependable rains (f0.8) are considered, the IRR would be lower than 12% for all goat-herd sizes, and the additional kids per goat required to reach 12% IRR would range from 0.21 to 0.29 for 200 and 50 does, respectively. Further efforts are needed to establish, under field conditions, the actual additional amount of kids that may be obtained as a consequence of supplementing goats with spineless cactus.
Abstract: This paper argues that, at present, ecotourism can contribute to safeguard biodiversity and ecosystem functions in developing countries, even though meeting the requirements for ecotourism is extremely difficult. A cost-benefit analysis of those ecosystems richest in species diversity, i.e. tropical rainforests, leads to the conclusion that non-use values often outweigh the values of conventional uses (clear-cutting, pasture, etc.), but are hardly considered in development decisions. Therefore, tourism and its high direct use value can play an important role as an incentive for protection. As tourism causes significant emissions, e.g. by flying, the concept of Environmental Damage Costs is introduced and integrated into the calculations. Further, international tourism development is analyzed and related to protection goals. Visitation rates of sensitive areas need to be limited; education, management, and control measures have to be integrated; and the proportion of money captured from tourists has to be increased. In the long run, tourism needs to undergo substantial changes.
Abstract: (Simulation of Production and Utilization of Rangelands) is a grassland ecosystem simulation model. integrates all previous versions of . The changes from 91 make the model more applicable to the southern Great Plains. The forage submodel from 2 predicts forage intake and diet selection by grazing herbivores, and the cow-calf submodel from 2 simulates all individuals in a herd for their full life cycle, based on defined genetic traits. The soil organic matter submodel from was added to improve soil carbon and nitrogen cycling. 2.4 output is compared with observed values from the Texas Experimental Ranch, Throckmorton, Texas. The changes made in creating 2.4 have considerably improved the utility and accuracy of the model for north Texas. Soil moisture predictions are improved (91 is 137% and 2.4 is 106% of observed, R=0.79-0.86), but run-off is still not adequate (R=0.65-0.76) and monthly evaporation is lower (91 is 94% and 2.4 is 95%) than observed. Soil carbon level predictions by the submodel are within range of the data, and output is stable over the simulation period. Predictions of individual plant species productivity compared with observed data are improved with 2.4 (R=0.79-0.98). Between-season plant growth and long-term persistence are simulated well. The addition of the soil organic matter submodel increased nitrogen level predictions resulting in more accurate predictions of animal weight gain. Steer weight gains are typical for north Texas. Simulation of cow-calf mass was good (R>0.98) as was production per hectare and per cow. The addition of the cow-calf model increases the utility of the model. The paper identifies portions of the model that need further validation and field research to improve model utility and credibility for use in natural resource management.
Abstract: A series of experiments on communally-owned grasslands in the barley–livestock zone of north Syria were conducted to test the hypothesis that introduction of Mediterranean annual legumes will increase productivity. The experiments were preceded by a survey to determine farmers' attitudes, describe the farming systems and to select appropriate collaborators. The first experiment examined the establishment of medics (Medicago spp.) and clovers (Trifolium spp.) distributed by hand, and monitored their effects on biomass and seedbank size. Later experiments extended these results to other villages. The principles of farmer participation in research were used to overcome the constraints imposed by the communal ownership of land. The survey revealed that the average size of the 20 villages was 36 families and that each village owned 887 sheep and 790 ha land. All villages had access to communally-owned grasslands, although their dependence on income from sheep varied greatly. These villages were subsequently divided into groups of high, intermediate and low potential.Of the 11 clovers sown in the first experiment, seed numbers of T. tomentosum, T. purpureum, T. haussknechtii, T. pilulare and T. resupinatum increased over three years. By 1996, there were more than 3000 legume seeds m−2 in the seeded treatment compared with less than 2000 in the unseeded treatment (mainly the naturally-occurring Trigonella monspeliaca). The number of medic and clover seedlings also increased significantly, while the number of Trigonella seedlings decreased significantly. Biomass production increased in the final two years and there was no response to added phosphorus.There were similar results in the later experiments. Seedbank size was greater in seeded treatments than in unseeded treatments, there were more seedlings in the seeded treatments, and the most successful species were T. campestre, T. tomentosum, T. speciosum and M. rigidula. The response in biomass was limited to the legume component, although total biomass increased in at least one of the two years. The highest biomass produced was 1112 kg ha−1 and there was no response to added phosphorus.The results suggested that the on-station research previously conducted at ICARDA headquarters was applicable to communally-owned land, although important modifications were needed. For example, at ICARDA phosphorus was necessary to stimulate the growth of legumes; in contrast, it was necessary to sow legumes at the four villages involved in these experiments. The results also suggested that the grasslands were common property, owned and controlled by defined groups of farmers.
Abstract: A paired site study was conducted of communally grazed eutrophic and dystrophic grasslands and adjacent ungrazed areas of varying periods of exclusion from communal grazing. This allowed determination of the rate and extent of change of a number of vegetation and soil variables following the removal of high and continuous grazing pressure characteristic of communal lands. Similarity indices for grass species composition between the grazed and adjacent ungrazed areas showed a significant exponential decrease with increasing time since protection from continuous grazing. Most change in grass species composition occurred within four to nine years of protection from communal grazing in eutrophic grasslands, and in six to nine years in dystrophic grasslands. In both grassland types palatability increased with time since protection. In eutrophic sites the abundance of perennials showed a significant increase with time since protection, while the abundance of annuals showed a concomitant decrease. This relationship was not evident in dystrophic grasslands. Grass species diversity, basal cover and density showed no relationship with time since protection in the eutrophic sites, but a general increase with time since protection was found in dystrophic sites. Soil bulk density, field capacity, pH and soil nutrients showed no evidence of a relationship with time since protection for either grassland type, while soil porosity increased significantly with time since protection at eutrophic sites, but not dystrophic sites. These relatively rapid changes following the removal of the high grazing pressure indicate that these systems are characterized by relatively high resilience. Copyright (C) 1999 John Wiley & Sons, Ltd.
Abstract: In order to determine evapotranspiration losses from the groundwater of an aquifer in Botswana during the dry season, the multi-step Surface Energy Balance Algorithm for Land (SEBAL) was applied using sequential Landsat TM and NOAA-AVHRR data. During satellite overpasses, continuous data on surface temperatures and soil moisture were available from a meteorological tower and field observations for calibration and partial validation of the results. The SEBAL method yielded high actual evapotranspiration (Ea) rates (1.5 - 3 mm/d), if relatively dense savannah vegetation was present, even when the water-table was over 30 m deep, as is the case in the upper part of the aquifer. No relationship between Ea and depth to water-table was found, except in the valleys, where riverine forests are fed by a system of discharging groundwater flow. The patterns on a vegetation map, based on a supervised classification using TM data, including thermal bands, showed similarity with the Ea patterns. The spatial distributions of vegetation types and of Ea have been interpreted as important uptake of water by deep roots; this is supported by increasing evidence from other parts of the world. Sap flow was measured in tall bushes near the tower site. The upper part (2 m) of the soil was dry. The results have implications for the groundwater recharge mechanism and the management of groundwater. Further validation studies have been initiated.
Abstract: Where species distribution data are inadequate reserve selection procedures have to rely on surrogate measures of biodiversity. The informativeness of land facets (the simplest units of a landscape with uniform slope, soils and hydrological conditions) as a local scale environmental surrogate was investigated in the Venetia-Limpopo Nature Reserve, South Africa. Multivariate analysis (MDS, ANOSIM) revealed that the land facets adequately represent distinct bird and dung beetle assemblages and are therefore useful surrogates. These land facets/assemblages were subsequently used as attributes in the following reserve selection procedures: (i) Percentage Area Representation (PAR--represent a nominated percentage area of each assemblage); (ii) Species-Assemblage Representation (SAR--represent each species within the smallest number of assemblages); (iii) Assemblage Diversity (AD--maximising diversity by first selecting areas containing most dissimilar assemblages). The influence of grid cell size, target representation percentages and an over-representation constraint on the efficiency of the algorithms were illustrated. The SAR procedure did not represent assemblages lacking distinguishing species and were thus more efficient in terms of total area selected. The AD procedure selected a slightly larger area than the PAR procedure, but was highly effective at rapidly increasing the diversity of the reserve network.
Abstract: Sediments from Sacred Lake and Lake Nkunga on the northeastern flank of Mount Kenya have a sequential palaeoclimatic and palæoenvironmental record covering most of the Late Quaternary period: from ca 115 to 0 ka. Most of the Late Quaternary period (110 to 14 ka - glacial period) was characterised by terrestrial C4 vegetation types (grassland) at higher altitudes and mixed C3-C4 (grassland with scattered trees and shrubs) vegetation types at lower altitudes, while low, productivity-related 13C discrimination occurred in the aquatic environment. The last interglacial and Holocene vegetation consisted of C3 forest-type elements, and high 13C discrimination occurred in the aquatic environment. The period 14 to 9 ka is transitional to Holocene climatic conditions, with progressive expansion of terrestrial C3 vegetation, and increased 13C discrimination in the aquatic environment. These changes occurred in step with, and were primarily driven by, palaeo-atmospheric CO2 changes. Thus, the estimates of temperature depression in the tropics during the last glaciation need to be revised as they are probably overestimated. Regionally, the changes on Mount Kenya are coherent with those observed at other high altitude sites across the tropics. Globally, they show a high coherency with Milankovitch periodicities, and are coupled to ocean circulation changes and ice sheet growth and disintegration cycles in the North Atlantic.
Abstract: We describe the changes in plant cover, species richness, and flowering after rainfall over an entire growing season (September 1989-January 1990) in a southern Atacama Desert site in Chile. One month after the rain, vegetation was dominated by annuals and geophytes which dried out after 19 weeks. Among all species, including shrubs, we found differences of 4-10 weeks in the length and peak of the flowering period. The flowering sequence of the species belonging to the families Brassicaceae, Liliaceae, Onagraceae, and Asteraceae matched closely the sequences described for temperate plant communities, suggesting that this phenological character is phylogenetically determined.
Abstract: Of the six species of wild geese which winter in Britain in large numbers, five are increasing in number and cause agricultural damage on a local scale. The management of grassland as feeding areas, to attract geese off agricultural land, is widely acknowledged as a potential solution to the problem. Similarly, grassland refuges are commonly established as a means of conserving rare or localised species of geese in Britain. Both require precise management guidelines if grassland areas are to be managed effectively. This paper summarises the information available concerning the management of grassland for wild geese wintering in Britain. We consider criteria for the location of feeding areas and the size of feeding areas required to support given populations of geese on local and national scales. Sward management is considered in terms of species composition and height, the value of fertiliser application and the relative merits of management through livestock grazing or mechanical cutting of grass pastures over the summer. The greatest potential for maximising goose numbers within an area appears to be through manipulation of sward height and fertiliser application. We discuss potential conflicts between managing grassland for geese and for other species and highlight possible directions for future research.
Abstract: A survey of mechanized rehabilitation methods attempted by rangeland managers was carried out. Two types of cultivation methods have commonly been used in parts of South Africa to combat further degradation and to improve the production potential. Depending on money and time it was found that certain cultivation methods were only suitable under certain conditions. Change of species richness, composition and total density of plants over time was determined. According to the results it appears that the dyker plough cultivation method gives better results in a clayish soil type and that ripper cultivation techniques are more suitable in standy soils, provided that the depth and distance of cultivation are optimal.
Abstract: Native snakeweeds, especially Gutierrezia sarothrae (Pursh) Britton and Rusby and Gutierrezia microcephala (DC.) A. Gray, are among the most widespread and damaging weeds of rangelands in the western United States and northern Mexico. The genus long ago spread to southern South America, where further speciation occurred. We have found several species of insects in Argentina that damage other species of snakeweeds there and are possible candidates for biological control in North America. The first of these, the root-boring weevil, Heilipodus ventralis (Hustache), was tested in Argentina and then sent to the USDA-ARS Insect Quarantine Facility at Temple, Texas, for host specificity testing on North American plants. We tested H. ventralis on 40 species of the family Asteraceae, in 19 tests of five types, using 686 adults and 365 larvae. Host specificity increased from adult feeding, to ovipositional selection, to larval development. At Temple, adults fed mostly on 6 species of the closely related genera Grindelia, Gutierrezia, and Gymnosperma, but with substantial feeding on four other genera of the two preferred subtribes Solidagininae and Machaerantherinae and on Baccharis in the tribe Baccharidinae, with lesser feeding on the subtribe Asterinae, all in the tribe Astereae, and on 1 species in the tribe Anthemideae. Females oviposited primarily on the same 6 species but very little on plants outside the 2 preferred subtribes. Larvae developed only on 9 of the 29 U.S. plant species tested, 6 within the two preferred subtribes and on Brickellia and Aster in other tribes. Only 5 species of three genera appear to be potential true hosts of H. ventralis in North America, on which all stages of the life cycle, adult feeding, oviposition, and larval development, can take place; these are Gymnosperma glutinosum (Spreng.) Less., Gutierrezia grandis Blake, Gut. microcephala, Gut. sarothrae, and Grindelia lanceolata Nutt. None of these genera contain species of economic or notable ecological value; the few rare species appear to be protected by habitat isolation from attack by H. ventralis. H. ventralis, therefore, appears sufficiently host specific for field release in North America. This is the first introduced biocontrol agent to be approved for release in a continental area to control a native weed.
Abstract: The recolonization by plants of overburden dumps created more than 20 years ago by opencast diamond-mining activities on the west coast of South Africa is very slow to non-existent. Only on dumps where the fossorial rodentParotomys brantsii has created burrow networks has some natural revegetation occurred. We tested the hypothesis that this plant colonization is facilitated by rodent burrowing activities which create soil patches containing organic matter and soil microbial propagules. Nearest-neighbour analysis of burrow-plant and random point-plant pairs showed that rodent burrows are associated with the occurrence of plants. There was a significantly higher pH, significantly lower electrical conductivity, and a five-fold increase in microbial activity between control and burrow mound soils on dumps. These fossorial rodents create small patches (c. 0·5×0·5 m) of increased [`]fertility' that encourage plant colonization in an otherwise edaphically hostile environment.
Abstract: Large-scale afforestation with pines is taking place in montane grasslands of South Africa. Many species dependent on the grass sward will be eliminated from the planted areas. Land should be maintained as conservation areas to ensure the long-term survival of the wildlife within the afforestable region. Ten land types, defined by combinations of classes of geology, altitude and rainfall, were sampled in the afforestable part of the Maclear district, Eastern Cape Province. Areas of five land types are required in a network of conservation areas to protect all the montane-endemic grasshopper, butterfly and bird species recorded. The addition of a sixth land type to this set of five would protect 93 183;8% of all the taxa considered. Regions within which conservation areas should be situated are indicated at the district scale.
Abstract: A comparison is made of national greenhouse gas inventories for the Climate Convention, (including US country study results) and an emissions database for global atmospheric research (EDGAR). The comparison pointed to some gaps in reporting and some large differences within sectors. In most cases the differences can be traced down to the use of different emission factors or the use of national statistics that differed from the internationally available ones. Comparison of inventories may stimulate the scientific exchange of data and increase the consensus on emissions. This comparison of semi-independent databases may therefore reduce uncertainties in emissions estimates. The exercise illustrated the usefulness of standard reporting formats and the availability of background information other than the official National Communications to the Climate Convention. The comparison may lead to major revisions of officially reported methane emissions in several countries.
Abstract: The selective use by cattle of range resources in the Sahel was assessed in terms of quantity and nutritional quality of the herbage grazed and diet selected. Peak standing crop was 1951 kg ha-1dry matter (DM) with 47 183;9 kg nitrogen (N) ha-1and 7 183;4 kg phosphorus (P) ha-1. Esophageally fistulated cattle diets were consistently (p 60;0 183;05) higher in N, P and organic matter digestibility (OMD) than the herbage grazed. Cattle consumed 48% of the mean annual herbage production. The results indicate grazing ruminants select a higher quality diet from Sahelian rangelands than can be predicted on the basis of pasture evaluation alone. Therefore, the foraging behaviour of the animals needs to be considered in the evaluation of Sahelian rangelands for animal production.
Abstract: Meeting the challenge of sustainable development requires substantial advances in understanding of the interaction of natural and human systems. The emerging ecosystem management paradigm of multiple stable states, non-linear systems behaviour, discontinuous change, self-organisation and multiple development pathways has major implications for when and how change in complex systems occurs and how it can be managed. It also poses considerable challenges for modelling the structure and function of natural and human management systems, including fundamental constraints relating to: scaling mismatches, synthesis of non-homogeneous information, multiscaled system interactions, complex management systems, uncertainty in causal relationships, assessment of trade-offs, and validation. This paper examines how a decision support system (DSS) for sustainable grazing management, called Landassess DSS, attempts to deal with some of these issues through an integrated systems approach to DSS development. This approach utilises object-oriented techniques, knowledge-based systems, geographical information systems (GIS), and a state-and-transition model framework to model the critical change processes. It provides for the identification of the major driving factors and constraints to change in complex resource management systems, as well as the assessment of the likely trade-offs between resource sustainability and economic production at a scale relevant to management decision-making (i.e., paddock or property).
Abstract: Spectral matching and linear mixture modeling techniques have been applied to synthetic imagery and AVIRIS SWIR imagery of a semiarid rangeland in order to determine their effectiveness as mapping tools, the synergism between the two methods, and their advantages, and limitations for rangeland resource exploitation and management. Spectral matching of pure library spectra was found to be an effective method of locating and identifying endmembers for mixture modeling although some problems were found with the false identification of gypsum. Mixture modeling could accurately estimate proportions for a large number of materials in synthetic imagery; however, it produced high variance estimates and high error estimates when presented with all nine AVIRIS endmembers because of high noise levels in the imagery. The problem of which endmembers to select was addressed by implementing a mixture model that allowed estimation of the errors on the proportions estimates, discarding the endmembers with the highest errors, recomputing the errors, and the proportions estimates, and iterating this process until the mixture maps were relatively free from noise. This methodology ensured that the lowest contrast materials were discarded. The inevitable confusion that followed was monitored the using the maps produced by spectral matching. Spectral matching was more effective than mixture modeling for geological mapping because it allowed identification and mapping of the relatively pure regions of all the surficial materials that exert an influence on the spectral response. The maps of the different clay minerals were of considerable value for mineral exploration purposes. Conversely, spectral matching was less useful than mixture modeling for rangeland vegetation studies because a classification of all pixels is needed and abundance estimates are required for many applications. Mixture modeling allowed identification of both nonphotosynthetic and green vegetation cover and thus total cover. Though the green vegetation mixture map appears to be very precise, the nonphotosynthetic vegetation estimates were poor.
Abstract: This study compares the inter-annual effects of patch-level defoliation with the broader effects of grazing history on Sahelian rangeland vegetation. Experimental plots were subjected to a range of clipping treatments over a 2-year period within four exclosures located along long-term gradients in seasonal livestock presence. In the third year of the study, the species composition and peak standing mass of vegetation were determined on all plots. Fractions of peak standing herbaceous mass contributed by the five dominant species were not affected by clipping treatment but were strongly associated with grazing history of the exclosure's site. These results raise questions about standard range evaluation approaches that uncritically link contemporary range condition with contemporary defoliation pressure. Alternative range evaluation and monitoring approaches that incorporate knowledge of local production systems and land-use history are supported.
Abstract: The powdery mildew fungus, Erysiphe cynoglossi (Wallr.) E. Braun, is a commonly occurring pathogen of houndstongue (Cynoglossum officinale L.) and may have a role in the biocontrol program being developed in North America for this introduced rangeland weed. To assess the effect of E. cynoglossi on the growth and reproduction of houndstongue, field observations were conducted to relate the level of infection to percentage seed set at three rangeland sites in British Columbia. Garden experiments also were conducted in Lethbridge, Alberta to assess the impact of E. cynoglossi on vegetative plant growth (1994) and on reproduction (1994 and 1995). Two of the three field sites examined showed a negative correlation between the percentage of the plant area infected by powdery mildew and the seed set. Diseased vegetative plants in the garden experiment were smaller in size by the season's end in 1994 compared to control plants. Powdery mildew reduced percentage seed set by about 20% in both 1994 and 1995. There also were significant reductions in nutlet number, nutlet size, and percentage germination of seed for infected versus control plants in 1995.
Abstract: The paper analyses factors influencing soil erodibility in a grassland area of the humid tropics subject to frequent wildfires. The interrelationships between aggregate stability, soil physicochemical properties and pore size characteristics are examined. At the multifire scale aggregate stability was significantly (P>0.01) correlated with cation exchange capacity (CEC) (R=0.76) and, in order of explained variance, exchangeable magnesium, aluminium, potassium, calcium and hydrogen concentration. At the individual fire scale only CEC and exchangeable magnesium had a significant ameliorating influence in the more recently burnt areas, whilst both exchangeable magnesium and calcium were significant in the area of longest post-fire recovery. At the multifire scale aggregate, stability was also significantly correlated with soil texture and organic matter partly through their influence on CEC. These interactions between aggregate stability and soil physicochemical properties influence soil drainage, and low but significant correlations were recorded between aggregate stability and total porosity (R=0.55 P>0.05) and the relative proportion of transmission pores to storage pores (R=0.44 P>=0.05). Water release curves showed that areas with the longest post-fire recovery times held higher amounts of water at most suctions and hence contained a greater volume of pores of different sizes, than more recently burnt areas. Soil erodibility in wildfire prone areas therefore reflects complex interactions and feedbacks between soil physicochemical properties, aggregate stability and pore size characteristics which vary spatially and with time as soil and vegetation recovery progresses.
Abstract: Focusing on the issue of veldt degradation and grazing pressure on rangelands, a simplified model was constructed for a sustainable stocking rate (SR) evaluation of the complex system of semi-arid and sub-humid regions in Southern Africa. The model considers the current activity in Southern Africa of multispecies herding, which allows a better utilization of vegetation and has a positive effect on plant and animal biodiversity. The model is intended as a practical and flexible tool supporting practical decision-making mainly at a local level, e.g. by extension services. It relies strongly on indigenous knowledge and flexibility. Users are therefore the main sources of information for the required inputs. The model combines the complexity of the range ecosystem with accuracy and precision of SR evaluation, while minimising input data requirements. The assessment of a grazing pressure compatible with the conservation of rangeland is based on a nutritional approach. Stocking rate (SR) is evaluated on the basis of the selected diet and total dry matter and energy intake. For a sustainable use of rangeland, forage availability is assumed to be the maximum consumption rate for each of the vegetation components (trees, shrub, grass) which does not endanger the long-term production of the vegetation. The whole model deals with a 12-month or a season period and it works on a regional scale, a portion of land surface delimited by its intrinsic physical, biological and socioeconomical characteristics, with a minimum dimension of 100 km2. The regional area under investigation is first divided into Grazing Unit Areas (GUA) homogenous in terms of their topography, soils, and vegetation cover. Results consist of three stocking rates (minimum, intermediate and maximum) calculated from a full consumption of the forage available on each of the vegetation components according to their respective levels of availability. After the discussion of the model, results of a case study are presented.
Abstract: The objective of this study was to examine the impact of provision of perennial water supply, as a management strategy to enhance game viewing, on herbaceous vegetation. Changes in herbaceous species composition and functional characteristics were investigated in relation to (1) distance from perennial and ephemeral surface water (spatial component), and (2) change over a 16-year period (1980-1996; temporal component). Herbaceous functional characteristics revealed a gradient of herbivore utilization in relation to proximity to perennial and ephemeral water. Herbaceous composition change since 1980 revealed significant deterioration in range condition. It has been hypothesized that the implications of an abundance of perennial water for game are made manifest by drought conditions and that a history of heavy utilization by herbivores prevents or inhibits recovery of the herbaceous vegetation to its pre-drought state.
Abstract: A set of global greenhouse gas emission inventories has been compiled per source category for the 1990 annual emissions of the direct greenhouse gases CO2, CH4 and N2O, as well as of the indirect greenhouse gases (ozone precursors) CO, NOx and NMVOC, and of SO2. The inventories are available by sector, both on a per country/region basis and on a 1°×1° grid. Developed by TNO and RIVM for constructing the Emission Database for Global Atmospheric Research (EDGAR) Version 2.0, in co-operation with the Global Emission Inventory Activity (GEIA) of IGAC/IGBP, the inventories meet the needs of both policy-makers and atmospheric modellers. The data sources for activity data, emission factors and grid maps are discussed with the focus on anthropogenic sources of primarily CO2, CH4 and N2O. The estimates of a standard group of anthropogenic sources are presented for each compound per world region.
Abstract: A global emission inventory of carbon monoxide (CO) emissions with 1° × 1° latitude-longitude resolution was compiled for 1990 on a sectoral basis. The sectoral sources considered include large-scale biomass burning (29%, of which savanna burning, 18%, and deforestation, 11%), fossil fuel combustion (27%, predominantly in road transport), biofuel combustion (19%, predominantly fuelwood combustion), agricultural waste burning (21%) and industrial process sources (4%). The inventory was compiled using mostly national statistics as activity data, emission factors at global or country level, and specific grid maps to convert, by sector, country total emissions to the 1° × 1° grid. A special effort was made to compile a global inventory of biofuel use, since this was considered to be a significant source on a global level, and a major source in some regions such as India and China. The global anthropogenic source of CO in 1990 is estimated at about 974 Tg CO yr-1. The inventory is available on a sectoral basis on a 1° × 1° grid for input to global atmospheric models and on a regional/country basis for policy analysis.
Abstract: Studies are discussed of the nutritional ecology of small ruminants under extensive conditions in northeastern Mexico. Spanish range goats selected greater amounts of foliage from shrubs (browse) than forbs and grasses throughout the year. Apparently high levels of the shrub Acacia rigidula (blackbrush) in the diets might have negatively influenced nutrient intake of goats. However, levels of crude protein and minerals in the annual diet were sufficient to meet adult goat requirements. Botanical composition of monthly diets of Pelibuey×Rambouillet range sheep grazing in a buffelgrass (Cenchrus ciliaris) pasture affected nutrient intake. In those months when level of browse increased in diets, the nutrient intakes increased. Native shrubs growing mixed with buffelgrass in pastures were important diet components for grazing sheep, especially during Fall and Winter. Browse during spring and summer provided adequate levels for sheep production of macro and trace elements, except for Cu which was deficient in most months. Browse also contributed a major percentage to the annual diets of white-tailed deer (Odocoileus virginianus, texanus) in northeastern Mexico. Even though browse provided food and cover for deer, high levels of shrubs negatively influenced the digestibility of their monthly simulated diets. In addition, P concentrations were very low, and high levels of digestion of forb plants in the digestive tract of deer may underestimate the composition of forbs in feces.
Abstract: Biologists are heavily reliant on the characterisation and description of disturbance phenomena and disturbance regimes. This dependency is well illustrated within research on fire recurrence and models of fire-frequency. It is well understood that the process of fire-return is subject to stochastic variation. However, a deterministic paradigm underlies many contemporary studies of fire-frequency to the possible detriment of robust ecological description. It is also commonplace for data on historical fire processes to contain some degree of either partial or missing data. Yet the parameter estimators of the prevailing two-parameter Weibull model of fire-recurrence are rarely seen to account for incomplete data structuring. The consequences of ignoring the structure of incomplete data will likely lead to misrepresentation of predicted fire frequencies and trends. In this paper, we introduce methods for incorporating parameter stochasticity into the two-parameter Weibull model under different degrees of data censoring. Both the explicit handling of censored fire observations and the intrusion of variability about the average predicted patterns in inter-fire interval recurrence are obligatory to any modelling that admits an effective ecological and evolutionary interpretation. These points are well illustrated through a worked example on modelling the fire-return interval regime within the Cape of Good Hope Nature Reserve, South Africa. Here, the observed process of fire recurrence is seen to include a substantial stochastic component about the trends predicted from the two-parameter Weibull model. The implications of a stochastic fire-regime interpretation to both management practises and to the evolutionary understanding of fynbos vegetation are discussed.
Abstract: Seasonal distribution of rainfall is thought to be important in structuring arid and semi-arid plant communities. Controlled studies of rainfall distribution have proven difficult, especially at the scale necessary to evaluate plant community changes. Simply comparing years with different rainfall distributions is problematic because rainfall amounts are seldom constant, and it is impossible to factor out other climatic variables (such as temperature). The authors describe an approach for studying rainfall distribution using large (12×30 m) fixed-location rain shelters. Rainfall was excluded and water was applied to three zones within each of five individual rain shelters. The treatments applied to the watering zones were: (1) average precipitation distribution from long-term records (50% from November to March, 30% April to June, and 20% divided among July, August, and October); (2) spring distribution (80% from April to July); and (3) winter distribution (80% from November to March). This approach allows for a comparison of treatments where only rainfall distribution is altered. Factors to consider in designing a study of this nature include: cost of structures and plot size necessary, quality of water to be applied to plots; differential animal use of treatments; and management of watering treatments.
Abstract: We present a remotely-sensed degradation assessment technique based on the measurement of landscape heterogeneity (a key determinant of degradation status). The moving standard deviation index (MSDI) is derived by passing a moving standard deviation filter across the Landsat TM band 3 (red band). Degraded/unstable landscapes exhibit higher MSDI values than their undisturbed/stable counterparts. Significant differences in MSDI were detected (p<0·001) across four fence-lines which separated rangeland of contrasting condition. The relationship of the index to normalized difference vegetation index (NDVI) was tested in five different ecosystems and significant correlations were obtained in all cases (p<0·001). We propose the MSDI as a powerful adjunct to vegetation indices.
Abstract: Phytolith investigations of surface soil samples and of soil profiles from rain forest soils of northeastern and eastern D.R. Congo (former Zaire, tropical humid Africa) and from a grass-covered Bas-Fond of the Central African Republic, produced a preliminary phytolith classification scheme. The classification scheme was used in soil phytolith counting procedures to produce typical opal phytolith spectra for comparisons. The spectra proved suitable to describe and characterize rain forest and grassland vegetation. Temporal variations in species composition of forests or grasslands were verifiable by phytoliths. Besides other characteristics, a high percentage of silt-sized spherical phytoliths were found to be typical for forests. Some specific, but not yet identified, opal phytoliths were shown to be widespread in central Africa. Phytolith content in tropical soils is presented in addition. The studies were carried out with the aim to improve the interpretation of fossil phytolith assemblages. Fossil opal phytoliths in soils or sediments can be used in the reconstruction of vegetation dynamics, palaeo-vegetation, and palaeo-climate.
Abstract: Over a 3 year period, selected sites in three categories of rangeland -- good, moderate and poor -- were subjected to varying levels of frequency and intensity of defoliation. Three watering regimes -- normal, below-normal and above-normal -- were applied. The effects of defoliation and levels of soil water were evaluated in terms of the production of above-ground phytomass and water-use efficiency (WUE) in relation to evapo-transpiration (Et). For all treatments, rangeland in good condition (RC1) produced significantly more phytomass (p<=0·01) and used water more efficiently (p<=0·01) than those in moderate and poor condition (RC2 and 3). High intensity/high frequency defoliation caused a significant (p<=0·01) increase in phytomass production and WUE, under conditions of high soil water availability. Generally, rangeland condition in interaction with the soil water content are the main determinants of optimal production and WUE. Statistically significant (p<=0·01) linear relationships between phytomass production and Et were determined for all rangeland conditions and defoliation treatments. In degraded rangeland, water is used inefficiently regardless of the quantity of water received.
Abstract: Invertebrate assemblages occurring on Paulshoek, a heavily grazed communal farm in Namaqualand, South Africa, were compared to those found on adjacent, moderately grazed farms. The study was conducted at three sites on the communal farm, each bordering a different commercially managed farm. Results of pitfall trapping and Berger-Parker dominance indices showed that invertebrate abundance was consistently higher in the heavily grazed areas. Species richness was greater on the moderately grazed areas at two of the three sites, while Shannon diversity was higher at all three moderately grazed localities. Cluster analysis, multidimensional scaling and ANOSIM (Analysis of Similarities) pointed to considerable differences in invertebrate assemblages where habitat degradation was severe. Invertebrate diversity decreased sharply with decreasing total and perennial plant cover. Dominance indices, on the other hand, tended to increase in response to decreasing vegetation cover. Greater invertebrate abundance in severely degraded areas may compound the effects of overgrazing, because further degradation of habitat may hinder recruitment by palatable perennials.
Abstract: The long-term Quaternary vegetation and climate history in South Africa's savanna biome since ca. 190,000 yr BP, is elucidated by the palynological record of lake sediments in the Tswaing Crater (the Pretoria Saltpan), and spring deposits from Wonderkrater, despite hiatuses in both sequences. Palaeotemperature trends from the two places are presented by means of Principal Components Analysis (PCA) of pollen data, allowing a new regional palaeoenvironmental reconstruction. Correlation in the older sections of the sequences, beyond radiocarbon dating, is tentative, suggesting that the Wonderkrater sequence is roughly 4 times younger than the Tswaing sequence. Combined, temperature indications from the two sites suggest cooling at ca. 14,000 yr BP and slight warming at ca. 15,000 yr BP. Although no data are available between ca. 15,000 and 21,000, and 25,000 and 31,000 yr BP, generally cool conditions are suggested between ca. 11,000 and 33,000 yr BP. Between ca. 33,000 and an extrapolated age of ca. 80,000 yr BP, at least three warmer pulses of varying intensity occurred. No data are available between ca. 80,000 and 150,000 yr, but between 150,000 and ca. 190,000 yr BP, two cool and two moderately warm phases are suggested.
Abstract: The aim of this study was to determine the water requirements for germination and early seedling establishment of four African savanna tree species, namelyAcacia karroo, A. nilotica, A. tortilisandMundulea sericea. The acacias are characteristic of nutrient-rich, andM. sericeaof nutrient-poor savannas. Imbibition times of scarified seeds ofA. karroo(4 h),M. sericea(6 h) andA. tortilis(8 h) were rapid relative toA. nilotica(28 h) and were inversely correlated with seed size. Imbibed water is lost in about 2 h after drying at 25°C for all species exceptA. nilotica(only 70% moisture loss). Seeds ofA. karrooandM. sericeakept at 40°C dried to below their original moisture contents within 2 h. Seeds ofA. niloticaandA. tortilisdried at 40°C lost viability relative to (undried) control seeds, while there was no significant loss of viability forA. karrooandM. sericea. For fully imbibed seeds to germinate in sandy savanna soils, all four species required at least the equivalent of 3 mm rainfall every 2 days under mild greenhouse conditions. However, most ungerminated seeds were still viable despite drying-out from a fully imbibed state. Maintenance of soil at 50% field capacity (FC), or watering to FC every 9th day is the maintenance requirements for 2-week-old seedlings ofA. niloticaandM. sericeato continue growth for a further 5 weeks under greenhouse conditions, althoughA. niloticamostly survived 25% FC with one seedling surviving 12·5% FC. Root penetration was rapid in sandy soils, withA. niloticaandM. sericeaattaining a depth of 40 cm within 15 days. Frequent, but not necessarily high, rainfall appears to be essential for germination and seedling survival over the first 7 weeks.
Abstract: An effective framework for drought assessment requires a definition of drought severity, a weather-soils database for the relevant region in a geographic information system (GIS), a reliable crop growth model, a method of forecasting daily weather data from the present date till the end of the growing season and a mapping procedure for the graphical representation of a drought situation. The development and main features of such a framework (system) which is already in use in the Free State Province of South Africa, is described. Based upon the phase of the southern oscillation index, it has been applied to quantify and map drought hazard in maize by running maize crop growth models in a GIS. Input and output data for the latter are grouped in 9800 homogeneous natural resource zones. For each, computed maize grain yield forecasts are compared against long-term cumulative probability distribution functions of yield to determine their probabilities of non-exceedence and used to delimit drought severity areas accordingly. The system enjoys wide acceptance and credibility in the province. To date, the results have been well received by a rapidly growing number of users, now totalling 360. Major users are grain merchants, importers and exporters, millers, the provincial government and maize producers. No tests of accuracy of the forecasting system have been possible at this stage because the computation procedures and software have only just been completed. A similar project has, however, yielded promising results.
Abstract: Pollen analysis of two cores from the Lake Sinnda, located in one of the driest areas of the southern Congo, reveals a history of vegetation and climate in this region during the past 5000 yr. A major change centered around 3000-2500 yr B.P. is indicated by an abrupt decrease in forest pollen and by a corresponding increase in grassland pollen. Concurrent drying up of the lake shows that climate, in particular aridity, was the major cause of this change. This paleoclimatic reconstruction conforms with evidence for drier conditions in other parts of western equatorial Africa, such as the development of isolated enclosed savannas and of heliophilous forested formations. The aridity is recorded more fully at Lake Sinnda than at the previous studied ones. It probably lasted longer, from 4200 to 1300 yr B.P., and was more progressive than previously inferred. The aridity predates agriculture marked by pollen of the oil palm at Lake Sinnda.
Abstract: The National Drought Policy of Australia was ratified by the Commonwealth, States and Territories in 1992. However, before it was fully implemented, one of the most severe droughts on record was already establishing itself across Australia. The Commonwealth government, therefore, devised measures to determine which areas had been exposed to exceptional drought so that financial assistance could be directed as effectively as possible. Six criteria were agreed to nationally, namely meteorological, agronomic, and environmental conditions, water supply, net farm income, and the spatial extent of the drought. Assessments during 1994-1995 had to account for the wide range of environments and farming systems. Useful data were often at a premium. In this paper we describe some of the ways in which these criteria have been estimated and assessed. Ways in which simulation models can be used to objectively estimate the extent and severity of drought are also demonstrated and discussed.
Abstract: From 1994-1996, 196 fallow sites in south-west Niger were surveyed using a plant sociological approach. Following a climatic gradient of 350 mm up to 650 mm precipitation, different geomorphologic units (dune, glacis, plateau, depression, dallol) were taken into account. Soils were sampled for each site and analysed for pHH2O, Corg, Ntotaland soil texture. The most important factors for the differentiation of the sites are soil texture and soil organic matter. Special sites like depressions, laterite sites or sites with compact soil surface layers due to heavy grazing can be easily distinguished with character species, but on sandy sites this becomes more difficult, and with different grazing intensities it is even more complicated. The fallow age has no importance for the differentiation of the plant communities which appear to vary according to a state and transition model which has yet to be described.
Abstract: A mosaic plant community pattern was studied in the northern Chihuahuan Desert grassland region of sourthern New Mexico. The principal plant species of the mosaic were tobosagrass (Hilaria mutica(Buckl.) Benth.) and burrograss (Scleropogon brevifoliusPhil.). Water runoff, sediment concentration, incremental sediment, and plant and soil properties of both species aggregations were measured. The study site was a large aggregation of burrograss plants in a tobosagrass matrix. Water runoff was three times greater from the burrograss aggregation than from the tobosagrass aggregation both before and after the growing season. Sediment concentration and cumulative sediment loss were also greater from the burrograss than the tobosagrass, except under wet conditions in the early autumn when sediment concentrations were similar. Differences are attributed to greater cover, phytomass, and surface roughness in the tobosagrass aggregation.
Abstract: Recent political changes in South Africa have required a new approach to project management, one that includes community involvement at all levels of project planning, decision-making and execution. This paper describes the challenges encountered and the lessons learned during the development and execution of a project addressing rangeland degradation and rehabilitation in the Mier Rural Area, South Africa. Discussed are difficulties encountered during the participatory execution of the project, many resulting from the conflict between community social requirements on one hand and ecological principles and financial constraints on the other. Another problem has been the community's apathy to threats of desertification. Because of higher priority problems such as medical care, education and the provision of water, sections of the community are questioning the applying of scarce financial resources to [`]lower priority' projects such as rangeland research and restoration. Furthermore, political and ideological differences within the community have resulted in various degrees of project acceptance and participation. A holistic approach to project management, with complete and open flow of information and joint decision-making, is vital to ensure full participation of all stakeholders affected by desertification.
Abstract: This paper examines the natural resource status of southern Africa and analyzes the critical linkages between the performance of southern African agriculture and natural resource use patterns. The implication of on-going natural resource use trends on poverty, food insecurity, and environmental degradation are also analyzed. The challenges that must be addressed including, how best to intensify agricultural production, the types of technologies to promote and the imperatives of production efficiency and intra-regional trade are examined. The paper concludes with some suggestions on how best to proceed in the future to be able to successfully address the challenges identified.
Abstract: Nomadic larks in the semi-arid Nama-Karoo, South Africa, depend on patches of temporally suitable habitat for breeding. These patches occur where rain has recently fallen, where there has been growth and seeding of grasses, and where invertebrates are locally abundant. They are also attractive to domestic livestock which may constitute a threat to successful breeding by the larks. Since rainfall in the Nama-Karoo is unpredictable in time and space on a regional scale, it is difficult a priori to select protected areas for such nomadic birds. As a first approach, we present a spatio-temporal model for estimating the survival of flocks in relation to different configurations of protected areas. The results show that neither one large protected area nor a high number of small protected areas provide the optimal solution. This is due to the impact of various spatial effects which affect the probability of a flock finding a suitable breeding area. These effects are identified and discussed. Furthermore, we are able to reproduce and explain the present spatial abundance of the larks on a regional scale with our model. The model is intended to complement and define the field studies needed to determine practical parameters more precisely.
Abstract: This paper examines the natural resource status of southern Africa and analyzes the critical linkages between the performance of southern African agriculture and natural resource use patterns. The implication of on-going natural resource use trends on poverty, food insecurity, and environmental degradation are also analyzed. The challenges that must be addressed including, how best to intensify agricultural production, the types of technologies to promote and the imperatives of production efficiency and intra-regional trade are examined. The paper concludes with some suggestions on how best to proceed in the future to be able to successfully address the challenges identified.
Abstract: There is much controversy surrounding the poverty-environmental degradation nexus. The predominant school of thought argues that poverty is a major cause of environmental degradation and if policy makers want to address environmental issues, then they must first address the poverty problem. Another school of thought argues that a direct link between poverty and environmental degradation is too simplistic and the nexus is governed by a complex web of factors. In this paper, a formal structure for analyzing the complex web of factors is formulated and used to review the existing literature on the links between poverty and the degradation of four natural resource sectors. The analysis highlights the important role institutional and market failure in encouraging agents from various income groups to exhibit unsustainable activities which in turn forces some of the agents to fall into poverty. Another important factor is the role of conflicts between different agents (income groups) in the povertyenvironmental degradation nexus. The analysis also highlights the presence of feedback loops between environmental degradation and poverty.
Abstract: Sporomorphs and dinoflagellate cysts from site GIK16867 in the northern Angola Basin record the vegetation history of the West African forest during the last 700 ka in relation to changes in salinity and productivity of the eastern Gulf of Guinea. During most cool and cold periods, the Afromontane forest, rather than the open grass-rich dry forest, expanded to lower altitudes partly replacing the lowland rain forest of the borderlands east of the Gulf of Guinea. Except in Stage 3, when oceanic productivity was high during a period of decreased atmospheric circulation, high oceanic productivity is correlated to strong winds. The response of marine productivity in the course of a climatic cycle, however, is earlier than that of wind vigour and makes wind-stress-induced oceanic upwelling in the area less likely. Monsoon variation is well illustrated by the pollen record of increased lowland rain forest that is paired to the dinoflagellate cyst record of decreased salinity forced by increased precipitation and run-off.
Abstract: The meteorological and agricultural assessment techniques that have been developed in South Africa are discussed, with reference to their strengths and weaknesses, application and suggested future developments. Future challenges in drought assessment as influenced by democratization are also considered. We conclude that meteorological methods have several inherent deficiencies which render them risky for the optimum allocation of drought relief. Agricultural drought assessment is suggested to be more preferable. Current agricultural drought models should nevertheless be improved to deal more successfully with the dynamic nature of rangeland. Evidence indicates that no absolute objective biophysical criteria for the quantification of the onset and the end of a drought have been identified and that all current criteria have an inherent subjectivity. Choosing appropriate interpolation techniques for mapping drought extent is a cause for concern, and there is scope for future research. Remote sensing techniques, integrated with crop modelling techniques, are options to pusue further. We finally suggest that in a democratic South Africa, more attention should be given to a multi-disciplinary approach where impacts, other than meteorological and agricultural, on previously disadvantaged black farmers are also assessed.
Abstract: Time-integrated normalized difference vegetation index (TI NDVI) derived from the multitemporal satellite imagery (1989-1993) was used as a surrogate for primary production to investigate climate impacts on grassland performance for central and northern Great Plains grasslands. Results suggest that spatial and temporal variability in growing season precipitation, potential evapotranspiration, and growing degree days are the most important controls on grassland performance and productivity. When TI NDVI and climate data of all grassland land cover classes were examined as a whole, a statistical model showed significant positive correlation between the TI NDVI and accumulated spring and summer precipitation, and a negative correlation between TI NDVI and spring potential evapotranspiration. The coefficient of determination (R2) of the general model was 0.45. When the TI NDVI-climate relationship was examined by individual land cover type, the relationship was generally better defined in terms of the variance accounted for by class-specific models . The photosynthetic pathway is an important determinant of grassland performance with northern mixed prairie (mixture of C3 and C4 grassland) TI NDVI affected by both thermal and moisture conditions during the growing season while southern plains grasslands (primarily C4 grassland) were predominantly influenced by spring and summer precipitation. Grassland land cover classes associated with sandy soils also demonstrated a strong relationship between TI NDVI and growing season rainfall. Significant impact of interannual climate variability on the TI NDVI-climate relationship was also observed. The study suggests an integrated approach involving numerical models, satellite remote sensing, and field observations to monitor grassland ecosystem dynamics on a regional scale.
Abstract: Ways of [`]tracking' environmental fluctuations could be of value in limiting drought-induced mortality and increasing output. We examined a range of tracking policies, designed to tackle climatic variation, using a simulation model of a semi-arid grazing system. These compared annual sales designed to limit stocking rate, pre-emptive sales triggered by insufficient rainfall, and variable sales and stocking rate regimes determined by the current season's rainfall. Although the flexible stocking strategies did reduce mortality losses, compared with fixed stocking, they did not increase average annual sales. The main reasons for this are that major losses of stock are associated less with 1-year than with 2-year droughts, which are difficult to track, and that destocking can be really effective only if the productive potential of the herd can be re-established more rapidly than is possible from depleted herd resources. Tracking policies did have a considerable advantage in terms of reduced inter-annual variability of sales, which would be of economic benefit to the commercial livestock sector. For subsistence pastoralists, the traditional policies of maintaining the maximum number of breeding stock, and of hoping that most of them will survive drought, may be as close as [`]opportunistic' management can get to dealing with drought.
Abstract: Based on pollen analysis of a sediment core from the Atlantic Ocean off Liberia the West African vegetation history for the last 400 ka is reconstructed. During the cold oxygen isotope stages 12, 10, 8, 6, 4, 3 and 2 an arid climate is indicated, resulting in a southward shifting of the southern border of the savanna. Late Pleistocene glacial stages were more arid than during the Middle Pleistocene. A persistence of the rain forest in the area, even during the glacial stages, is recorded. This suggests a glacial refuge of rain forest situated in the Guinean mountains. Afromontane forests with Podocarpus occurred in the Guinean mountains from the stages 12 to 2 and disappeared after. The tree expanded from higher to lower elevations twice in the warm oxygen isotope stage 11 (pollen subzones 11d, 11b) and at least twice during the warm stage 5 (pollen subzones 5d, 5a), indicating a relative cool but humid climate for these periods.
Abstract: Transitions from grassland to shrubland through woody plant encroachment result in potentially significant shifts in savanna ecosystem function. Given high resolution imagery, a textural index could prove useful for mapping woody plant densities and monitoring woody plant encroachment across savanna landscapes. Spatial heterogeneity introduced through mixtures of herbaceous and woody plants challenges quantitative assessments of changing woody plant density using remotely sensed imagery. Moreover, woody plant encroachment occurs across decadal time scales, restricting remote sensing analyses to historical aerial photograph records. Heterogeneity in vegetation structure has a significant influence on local pixel variance in high resolution images. We scanned black and white aerial photographs for 18 sites of varying woody plant density, producing images of 2-m grain size. Omnidirectional variograms derived from these images had ranges of approximately 10 m and sills highly sensitive to woody plant density, prompting us to use a textural index to indicate landscape variation in woody plant density. For validation purposes, we measured several woody overstory structural parameters in the field; a factor analysis revealed woody stem count as the best correlate with image texture. Significance of the regression of image texture on woody stem count declined as grain size of the 2-m images was coarsened to simulate that of SPOT and Landsat satellite sensors. At 10-m resolution, our textural index proved a significant indicator of woody plant density. We mosaicked sequential aerial photographs scanned at 10-m resolution and then applied our textural filter, producing maps of historical woody plant distribution that reflected patterns in soil and vegetation type. More accurate maps of canopy structure and structural change are needed to explore potential effects of woody plant encroachment on biophysical and biogeochemical processes at large scales.
Abstract: Changes in grazing areas and feed resources were described for a dry area of north-eastern Syria, from May 1994 to May 1995, to identify the characteristics of flock movement and the seasonal changes in feed resource utilization, and analyse the main factors which regulate the system of livestock management. The patterns of grazing areas were classified into three main categories in the study area, namely, (1) harvested barley fields in summer, (2) a combination of both harvested barley fields and rangeland from summer to autumn, and (3) rangeland from autumn to spring. Changes in grazing area were regulated mainly by the time of barley harvesting, the scantiness and/or richness of feed resources in harvested barley fields and on rangeland, water pounds and cold weather in the rainy season, and governmental policy. The main feed resources were barley straw and stubble in summer, a combination of barley stubble and native plants on the rangeland from summer to autumn, native plants on the rangeland or cotton residue in autumn, supplementary feeding of barley grain and straw in winter, and native plants on the rangeland in spring. The subsistence systems of rangeland grazing and cultivation activities competed with each other for land use, but compensated for each other in feed supply for small ruminants throughout the year. From the viewpoint of grazing management throughout the year, integrated land use between rangeland and cultivated fields is an inevitable system in the study area. The contents of feed resources in the study area are still very simple, mainly because of the possibility of only barley cultivation by rainwater and the vast unarable mountainous rangeland. Information about the characteristics and the system analysis of the flock management in the study area could offer important information for sustainable land use planning in dry mountainous areas of northern Africa and western Asia.
Abstract: Differences in reporting rates of birds on atlas checklists from major land-use categories (protected, unprotected, wildlife management area (WMA)) in Botswana were investigated to evaluate the conservation status of 12 ecological assemblages of birds. Large grassland birds and birds of prey were more frequently reported from protected than unprotected land or WMAs. Birds of canopy woodland, and the larger, resident insectivores were particularly frequently reported in WMAs and least frequent on unprotected land. Except for some intensely hunted species, waterbirds were indifferent to land use. The most dramatic difference between land use categories was for thornveld birds, which were much more frequent on unprotected land. Migrants also preferred unprotected land. Most differences between land uses can be ascribed to the widespread effects of intensive grazing by livestock, which results in a reduction of the herbaceous stratum and ultimately in bush encroachment. About half of the species typical of the Kalahari basin are thornveld species, and this group, which includes 18 regional endemics, benefits from this change. No regional endemic bird species typical for the Kalahari basin seems yet to have a critically poor conservation status in Botswana, but some species of open grasslands and the more intensely hunted species require monitoring. The shortclawed lark, a near-threatened restricted-range species, occurs only in unprotected areas. Only one of the globally threatened Cape vulture's breeding colonies in Botswana is within a (small) formally protected area.
Abstract: A three-year study was done to determine herbaceous biomass production and its utilization by herbivores in an arid zone inhabited by a largely nomadic population in northern Kenya. The indicator selected for study was aboveground live standing biomass of grasses, forbs, dwarf shrubs and the total sum biomass of these vegetation categories (total herbaceous layer). Sampling was done along grazing gradients in order to estimate the utilization levels in the arid zone 7 and the semi-arid zone 6. Mean peak standing biomass for grasses, forbs, dwarf shrubs and total herbaceous layer under non-grazed conditions was 184.4, 374.2, 1094.4 and 1504.0Â kg/ha in eco-zone 7, respectively. In the zone 6, mean peak standing biomass was 55.3, 98.8, 4259.1 and 4320.1Â kg/ha under non-grazed conditions, respectively. Results indicated graminoid removal to be respectively 57.1-99.8% and 24.2-87.2% of mean peak standing aboveground live biomass in the zone 7 and 6. Forb utilization in zone 7 was estimated to be 51.5-99.3%. Mean peak forb standing biomass however, showed a general increase on grazed sites compared to the non-grazed plot in zone 6. The corresponding utilization of the dwarf shrub layer was estimated to be in the range 40.5-80.0% and 76.6-92.3% in zone 7 and 6 respectively. Total herbaceous layer consumption of 39.3-85.3% and 74.0-90% was estimated for zone 7 and 6 respectively. These findings suggest that herbivores exert considerable control over biomass dynamics of the herbaceous layer in this zone and contribute to degradation in heavily utilised areas. Efforts to understand and tackle the desertification problem in this area must therefore take this fact into account.
Abstract: Rangeland models that simulate hydrology, soil erosion and nutrient balance can be used to select management systems which maximize profits for producers while they minimize adverse impacts on water quality. Values are needed for parameters that describe the growth of invading woody species in order to allow simulation of their competition with grasses. Three attributes useful for describing and quantifying plant growth are: the potential leaf area index (LAI) or ratio of leaf area divided by ground area; the light extinction coefficient (k) that is used to calculate the fraction of light intercepted by leaves, applying Beer's law; and the radiation-use efficiency (RUE) or amount of dry biomass produced per unit of intercepted light. Objectives in this study were to measure LAI, k, and RUE for eastern red cedar (Juniperus virginiana L.) and honey mesquite (Prosopis glandulosa Torr. var. glandulosa), without competing plants, as a first step toward simulating their growth. Seedlings were planted in the field at Temple, Texas, USA in early 1992 and kept free of competition from herbaceous plants. During 1993, 1994 and 1995 data were collected on biomass, leaf area and intercepted photosynthetically active radiation (PAR) for individual trees. Both tree species showed exponential biomass increases. At the end of the 1995 growing season, mean LAI values were 1.16 for cedar and 1.25 for mesquite. Mean k values were 0.34 for mesquite and 0.37 for cedar. Radiation use efficiency for aboveground biomass was 1.60±0.17 (mean±standard deviation) g per MJ of intercepted PAR for cedar and 1.61±0.26 for mesquite. The rapid growth in 1995 was accompanied by greater leaf area and thus greater summed intercepted PAR. These values are critical for quantifying growth of these two species.
Abstract: A recently published rangeland health assessment guide for arid shrublands of the Karoo, South Africa, addresses the problem of apathy toward rangeland. The guide is designed for land users with a minimal knowledge of plants and soil processes. More than 200 colour photographs, maps and diagrams introduce the rancher to the processes that maintain soil fertility and range productivity. Topics covered include soil formation, cryptogam crusts, water acquisition and storage by plants, plant population renewal and vegetation change. Then using subjective five-point scores, the guide assesses rangeland health by vegetation cover, forage value, utilization intensity, plant demography and soil health and protection. This hands-on, non-technical approach to range assessment is intended to avert rangeland damage by making the rancher more aware of the natural resources on which ranching depends. Ranchers who spend time in their rangelands and well understand the dynamics of plant populations in response to rainfall patterns and grazing are generally more successful than ranchers with little interest in their rangeland. A similar approach, combining subjective assessment of soil and vegetation, could be designed for ranchers in other arid and semi-arid regions subject to desertification through misunderstanding and inadvertent mismanagement.
Abstract: Herbaceous and woody alien plants visible from a moving vehicle were recorded along 1 km roadside transects at 5 km intervals over a distance of 5869 km in the semi-arid and arid Fynbos, Succulent Karoo, Nama Karoo and Arid Savanna (Kalahari) biomes in South Africa. Each 1 km transect was classified by biome and vegetation type, mean annual rainfall, rainfall seasonality, soil surface type and landuse adjoining the roadside. Although travelling speed affected the range and frequency of plant species observed, the method was repeatable at a speed of 100 km h-1. Alien plants occurred in 98% of 119 Fynbos, 81% of 204 Succulent Karoo, 72% of 661 Nama Karoo, 47% of 171 Arid Savanna and 100% of seventeen Grassland transects. Alien species richness per site was correlated with mean annual rainfall, but in all regions, sites adjacent to cultivation had significantly more alien species than sites adjoining rangeland. The alien plant assemblage of the arid winter-rainfall Succulent Karoo included species from mesic winter-rainfall lowland Fynbos and the arid Nama Karoo receives unseasonal rainfall. The frequencies of Prosopis spp., Atriplex spp. and Opuntia ficus-indica were not significantly greater near cultivation, and these perennial plants, all of which are dispersed by indigenous and domestic animals, can invade natural rangeland in arid and semi-arid southern Africa.
Abstract: This paper reviews how remote sensing is being used, and can be used, to assist in providing support for the decision-making process for the declaration of areas experiencing drought exceptional circumstances in Australia. To assess how remotely sensed data can be used, a review of current international uses of remotely sensed data was made and several topics requiring further research by remote sensing specialists identified. Consequently, the review focuses on current techniques used by Australian agencies, and also assesses current international methods, as well as proposing some possible new research directions that may use remote sensing for drought assessment and management. The primary scientific information that remote sensing can provide is the estimation of vegetation cover and condition, soil moisture, and the spatial limits to drought exceptional circumstances.
Abstract: Namibia is an extremely arid country with very low and erratic rainfall. It has a population of 1·7 million people; most Namibians are subsistence farmers living in communal areas that are underdeveloped and poorly managed. Most farmers raise livestock under harsh climatic conditions. The Sustainable Animal and Range Development Programme (SARDEP) helps communal subsistence farmers improve livestock production and range management. Work done by SARDEP concluded that communal farmers are poorly organized, unaware of participatory development and unfamiliar with the concept of self-help. SARDEP also suggests that sustainable livestock and range development in communal areas cannot be based on the conventional development approach. This top-down and input-oriented approach rarely meets farmer needs. In fact, the non-involvement of farmers in the development process leaves a wide gap of untouched development opportunities. To achieve sustainable development SARDEP decided to support a process that closes this gap between farmers and service institutions. SARDEP developed the [`]negotiation approach,' which supports the empowerment of grassroots-level organisations, considered the prime movers for development. At the same time SARDEP helps service institutions interact closely with target groups and reorient their services toward well-formulated farmer needs and demands. To allow such development to grow, SARDEP also contributes at the national level toward formulating a conductive policy framework for sustainable natural resource management.
Abstract: The grass Agrostis stolonifera L. is the most successful introduced vascular plant at sub-Antarctic Marion Island. Since its accidental introduction, probably in the 1950s, it has spread over the northern half of the island, and presumably will eventually reach all parts of the island. It invades undisturbed native vegetation and reaches dominance in a range of habitats. It is most abundant on wet slopes and on river banks, where it replaces the rosaceous dwarf shrub Acaena magellanica communities by dense grassland. These communities show a reduction of 50% in the mean number of native plant species per sample plot, although more macroinvertebrate and more mite species were found where A. stolonifera was dominant. The invasion by A. stolonifera does not seem to pose an immediate threat to the survival of any of the native species on the island, but the changes induced in the drainage line communities significantly reduce the value of the island both from a conservation viewpoint and as a natural laboratory for fundamental ecological research. Therefore, it is important to keep Marion Island free of any further introductions. This is even more important for neighbouring Prince Edward Island, which, because of the negligible impact of aliens on this island, is of exceptional conservation value.
Abstract: Environmental weeds are an escalating problem worldwide. Integrated control is unable to keep up with the demands for management strategies for existing and new, potentially invasive plant species. The primary goal of the ecosystem approach used here is sustainable conservation management of natural systems. Only ecologically and/or economically viable habitats are given priority for environmental weed management. We recommend that habitats be ranked according to criteria that encompass the habitat's status, protection and management. Highest priority areas are treated first according to available resources to balance urgent environmental needs with management budgets. Practical guidelines in drawing up control programmes and management plans are provided.
Abstract: Three experiments investigated the dose transfer of oil-based ultra-low volume (ULV) sprays of Metarhizium flavoviride to the desert locust: Schistocerca gregaria. Field tests against this locust are notoriously difficult in non-outbreak years so the applicability of [`]pre-field trials' is discussed. In an arena test, the effect of direct contact with spray droplets was quantified, and large semi-permanent cages were constructed to investigate the effects of droplet size and the importance of secondary pick-up of spray residues. A formulation containing approximately 1.0 × 1012 live conidia.l-1 was applied using a Micron [`]Micro-Ulva' to four groups of locusts in arenas positioned in four rows downwind of a single spray line. Their subsequent mortality (at days 8-12 after application) was correlated with the number of droplets per cm2 on artificial targets placed in each arena. Under these experimental conditions, at least 50 droplets.cm2 appear to be necessary to achieve > 90% mortality at 10 days by direct contact only, or approximately 30 droplets.cm2 to achieve a similar effect by day 12. In experiments carried out in large field cages, locusts were released onto millet plants sprayed using various versions of an air-assisted spinning disc sprayer: the [`]Ulvafan'. Droplet size spectra of these sprayers with an oil-based formulation are illustrated. In one test, there was no significant difference between mycoinsecticide applications with two different droplet sizes and 50% mortality was achieved by day 8. A second experiment indicated that although it took a shorter time to kill 50% of the insects directly exposed to spray droplets, there was no significant difference in the average survival time between locusts exposed directly and those picking up spores exclusively from the vegetation.
Abstract: As a result of deforestation, annual bush burning, overgrazing and intensive cultivation, most tropical forests have changed to derived savanna in many West African states. This change in vegetation has led to a decrease in rainfall and a change in many climatic conditions. Erosion problems have increased, soil fertility has declined in arable land and the soils have become compacted. Successive droughts and uncontrolled population growth have compounded the problem to the extent that traditional farming practices no longer ensure sustainability. Places where such deterioration of the environment has occurred in Nigeria and Ghana are highlighted. Results of experiments which demonstrate that nutrient deficiency in the Sahel savanna is a more serious problem than low rainfall and that nitrogen and phosphorus are the limiting nutrients in many savanna ecosystems are reviewed. The roles played by trees in the savanna such as provision of shade, preservation of water, reduction of susceptibility to erosion and nutrient pump are highlighted and species whose cultivation must be intensified so as to promote sustainability in savanna ecosystems are listed. The principles of agroecological restoration of savanna ecosystems whose focus is on the restoration of ecological balance and which has been successfully practiced in Ghana are highlighted.
Abstract: Processes, such as mountain building, changes in ocean gateways, natural changes in the carbon cycle and orbital changes, are [`]established' mechanisms for climatic changes. This paper focusses on human contributions in Africa to climatic changes. When man began to kill megaherbivores (body weight above 1000 kg), about 3.5 Ma BP, he interfered with the ecological balance of the African continent. With the progressing loss of large game through hunting and ecological feedbacks, litter and vegetation could accumulate, providing fuel for devastating [`]natural' fires: concomitant decomposition and, hence, fertilization declined. The intentional use of fire by man since about 1.5-1.9 Ma BP intensified the impact on the biosphere. The further eradication of game and use of fire led to an impoverishment of fauna and flora. Domesticated animals, imported during the Holocene, added to the ongoing environmental destruction. These animals emit significant amounts of methane (CH4), affecting the atmosphere, while wildlife releases hardly any CH4.
Abstract: An experiment designed to study the effects of habitat fragmentation on biological diversity in the montane grasslands of Southern Africa was launched in September 1994. The Groenvaly experiment is positioned on the western slopes of the Drakensberg escarpment in Mpumalanga, South Africa. The hypotheses being tested are: (1) that fragmentation reduces biological diversity; (2) that fragmentation alters community composition (invasion); (3) that the reduction in diversity is dependent on fragment size; (4) that species viability is differentially affected by distances between fragments; and (5) that afforestation causes irreversible community change. In addition, the experiment evaluates the relevance of mainland-island, metapopulation and source-sink models for describing the population characteristics of the grassland taxa. The experimental design comprises two fragment sizes (0.25 and 1.5 ha) replicated 12 times. Six replicates were retained as grassland fragments surrounded by newly established Pinus elliottii plantations. A further six replicates served as control fragments in an adjacent designated grassland conservation area. Sampling to monitor community composition (vegetation, Coleoptera, Orthoptera, arachnida, small mammals) and the population dynamics (mark-recapture) of selected taxa (small mammals to date) was conducted. Monitoring of the population dynamics of selected Coleoptera and Orthoptera taxa, identified as suitable models for further study, and the soil micro-fauna in fragments will commence in 1997. Two years following plantation establishment effective fragmentation has not yet been achieved. However, the analysis of pre-treatment data is used to evaluate the effectiveness of the experimental design. The analyses suggest that there is a sound basis for future interpretation of experimental results because no significant differences between the experimental and control plots were detected. The presence of some variation within experimental and control plots underscores the importance of adequate replication in ecological field experiments, a strength of the experimental design employed here.
Abstract: West Africa is poorly endowed when it comes to soil fertility. Unlike for example the Rift Valley area, west African soils never enjoyed volcanic rejuvenation. At low agricultural intensity, this does not matter as nutrients cycle through the soil and the natural vegetation and losses are few. However, the past decades have shown high population increases, the breakdown of traditional shifting cultivation systems, and a rapid decline of land productivity and soil fertility in particular. The present review paper shows how much is known about the severity of this process and the technologies at hand that can stop it. The information provided shows that on the technical side much is known now, but research output still is poorly integrated into development efforts.
Abstract: Studies of the auriferous Witwatersrand placers and associated rocks have revealed that certain palaeo-environments, especially braided fluvial, are particularly well represented in this part of the rock record. However, there is a paucity of lithofacies indicating certain other palaeo-environments. Possible reasons for their scarceness or absence are suggested in this paper. It is generally assumed that pre-vegetational fluvial systems would have been characteristically braided, because of the absence of land plants necessary to stabilise river banks. A question arising is what kind of downstream changes such pre-vegetational braided streams underwent. A recent study of a braided stream placer revealed that the depositing system retained its braided character right down to the palaeo-shoreline. However, gravel did not reach the palaeo-beach. As with many modern examples, beach conglomerates are rare in the Witwatersrand rocks. The paucity of conglomeratic beach placers is ascribed to the low probability of gravel being transported across coastal plains, because of the relatively low slopes or depths of rivers here. The Witwatersrand fluvial channels are generally considered to have had high width-to-depth ratios, because of the absence of land vegetation to stabilise channel banks. However, two examples of deep, relatively narrow scour features, with predominantly fine-grained fills, occur near the base of the Central Rand Group. The low width-to-depth ratios of these scour features, which probably represent palaeo-valleys, are ascribed to severe incision during a rapid sea-level fall. The auriferous fluvial systems of the Witwatersrand are generally considered to have been entirely braided, due to the lack of bank stability. However, the fluvial B placer of the Welkom goldfield is confined to discrete channels. Their banks are thought to have been stable, due to the cohesive nature of the lutite into which the gravelly streams incised. In addition, braiding sensu stricto was probably inhibited by initial incision and a low sediment supply. No deposits of specifically deltaic sub-environments have been found in the Central Rand Group. Their absence is attributed to the following factors: (a) the paucity (absence?) of well-defined palaeo-river mouths; (b) low concentrations of suspended sediment; (c) intermittent sediment supply to the palaeo-coastline; and (d) reworking by tidal and longshore currents. Alluvial-fan deposits are also apparently absent in the Witwatersrand rocks. The absence of fan deposits is attributed to the poor potential for development and preservation of fan deposits in the compressive tectonic setting proposed for the Witwatersrand Basin. Although ventifacts have been found in the Witwatersrand rocks, no aeolianites have been reported. Their apparent absence is probably due to (a) reworking in a predominantly humid climate, and (b) transport of sand by dominant winds to areas unfavourable for the preservation of aeolianites.
Abstract: Desertification has been recognized as a major environmental problem for more than 20 years. Control of desertification has been the subject of many international efforts; it has been a major focus of UNEP and there is a UN Convention to Combat Desertification. Despite this, control of desertification is considered by many observers to have been a failure. This paper reviews the history of formalized efforts to combat desertification, looks at the lessons that should be learned, and identifies opportunities for establishing closer links between desertification and other aspects of global change research. These include integrating biophysical and social science disciplines, the use of a hierarchical approach to research and monitoring, the development of functional classifications of landscapes and social systems, and the implementation of specific studies on key representative transects across the world. Progress towards repairing this form of land degradation will depend upon developing economic links between desertification and other global environmental problems.
Abstract: An ordination of floristic data from the grassy vegetation of the Darling Downs in southern Queensland describes four broad vegetation types, red gum (Eucalyptus camaldulensis/E. tereticornis) woodland associated with the flood-plain of the major streams, grassland on alluvial clay, poplar box (E. populnea) on clay loam terraces and hill woodland dominated by any of E. albens, E. crebra, E. melliodora, E. orgadophila. Ten per cent of species proved sensitive to grazing intensity categories (derived largely from land tenure) in hill woodland compared to 3% of species in grassland or poplar box woodland. There were no clear trends in the relative response of native and exotic species, although overall, species richness was greatest in either the moderate or heavily grazed treatment for all broad vegetation types. It is suggested that the interaction between Themeda dominance and the inter-tussock flora may contribute to the importance of grazing as a determinant of floristic composition in hill woodland broad vegetation type. Mechanical disturbance is implicated as a means of effecting the spread of exotic plants. However, there are relatively few exotic species that appear to have the capacity to displace native species without mechanical disturbance, although a notable exception is Phyla canescens in the flood-prone habitat. Moderate domestic stock grazing is compatible with nature conservation on the Darling Downs, although it is demonstrated that a proportion of the flora is sensitive to grazing. Remnants will need to be managed under a range of grazing regimes, including light total grazing pressure that excludes domestic stock to ensure the survival of the full range of species.
Abstract: Households in the West African semi-arid tropics (WASAT) face substantial risk--an inevitable consequence of engaging in rainfed agriculture in a drought-prone environment. It has long been hypothesized that these households keep livestock as a buffer stock to insulate their consumption from income fluctuations. This paper tests this hypothesis. Results indicate that livestock transactions play less of a consumption smoothing role than often assumed. Livestock sales compensate for at most thirty percent, and probably closer to fifteen percent of income shortfalls due to village-level shocks alone. We discuss possible explanations for these results and suggest directions for future work.
Abstract: Several global datasets on fire distribution are being generated from remotely sensed data to support research on the ecological impacts of biomass burning. This article examines the strengths and weaknesses of a number of approaches to the monitoring of biomass burning at a regional scale and suggests how to best combine the information content on fire distribution provided by different earth observation satellites. Remotely sensed data acquired over Central Africa from a variety of sensors (airborne video camera, SPOT XS, Landsat Thematic Mapper, NOAA Advanced Very High Resolution Radiometer, and ERS-1 Along Track Scanning Radiometer) were used to provide quantitative measurements of the spectral separability, and temporal and spatial sampling associated with the detection of burnt areas and active fires. Three main strategies to the monitoring of biomass burning were analyzed: detection of burnt areas at fine spatial resolution, detection of burnt areas at coarse spatial resolution and high temporal frequency, and detection of active fires at a coarse spatial resolution and high temporal frequency. In each case, we assess the detectability of the selected biomass burning indicator, the statistical representativity in time and space of the sample detected and whether the sample observations are an unbiased estimator of the total biomass burning events in the region. We conclude that while active fire detection remains important in defining the seasonality, timing, and interannual variations in biomass burning, the most reliable strategy for estimating biomass burning at a regional scale is a multisensor approach in which regional burnt area estimates from coarse spatial resolution data are calibrated on the basis of a sample of fine spatial resolution estimates of burnt areas, using a double sampling with regression estimator approach.
Abstract: This paper presents an overview of the current status, problems and prospects for achieving a better nutrient balance to support varying levels of productivity from the three major livestock systems in Africa. In free range grazing systems, livestock nutrient deficiencies are mainly overcome by moving the animals to better grazing areas. This makes monitoring and managing of nutrients within a system very difficult. Nutrient recovery, cycling and synchronization of manure with other recycled or purchased sources are greater in mixed crop-livestock systems. In these systems, inclusion of nitrogen-fixing leguminous forage/tree crops as companions or rotation crops with cereals further improves the nutrient use efficiency and balance. With more favourable market and policies, commercialized dairy systems are developing around the urban areas of Africa. Such systems heavily depend on purchased feeds and nutrients, and have serious implications for the nutrient balance and sustainability of land use systems in the rural areas which supply the feeds, and for the urban areas because of the risk of pollution from the accumulating animal wastes.
Abstract: An integrated survey along a continuum of two representative toposequences, crossing fluvial and interfluvial landscapes downstream of the confluence of two perennial rivers of the upper reaches of the River Ebonyi catchment resulted in a methodology for characterising toposequences and for identifying priorities for land evaluation. The so-called Integrated Toposequence Analysis (ITA) merges conventional biophysical surveying and participatory research techniques along toposequences and sets a framework for developing relational databases for land resource mapping at village and catchment scale. Relationships between physiographic position, soil characteristics, vegetation and land use demonstrate the physical and human influences affecting the current land status along the catenae. Indigenous appraisal of soil characteristics and productivity provides insight in current land use strategies at farm level, whereas, analysis from standard biophysical methods demonstrates the constraints to present land use trends. Results indicate the limited scope for further agricultural intensification on the upland interfluve areas with the present farming system practices, and show the increasing pressure to exploit the fluvial wetlands.
Abstract: Methane flux was measured from four tropical, Indian ecosystems: dryland, irrigated rice, seasonally dry forest and savanna. Flux from the irrigated rice paddies was in the range 2.14-8.23 mg CH4 m-2 h-1 during the crop period. In contrast, the dryland rice soil consumed 0.12-0.90 mg CH4 m-2 h-1. Application of wheat straw+fertilizer stimulated CH4 production in irrigated rice soil while it reduced CH4 consumption in dryland rice plots. CH4 flux measurements from nutrient-poor, well-drained dry deciduous forest and savanna soils indicated heavy methane consumption. Maximum CH4 consumption was observed during the winter season (0.46-0.95 mg CH4 m-2 h-1) at all the sites and was lowest during the rainy season (0.17-0.32 mg CH4 m-2 h-1). The results suggest that dryland rice soils and natural ecosystems are potential sinks of CH4. Conservative extrapolation of the results indicates that to compensate for CH4 production from 1 ha of irrigated rice about 2.4 ha of natural ecosystems are needed. Thus there is a need of further evaluation of the role of tropical dryland rice soils and naturally dry ecosystems in the global methane budget.
Abstract: This research addresses the potential contribution of strontium isotopes to the reconstruction of early hominid behavior at the Swartkrans site in the Sterkfontein Valley of Gauteng Provence (formally known as the Transvaal), South Africa. We report that, while there is considerable variability in the 87Sr/86Sr of whole soils within a 15 km radius of this site, available soil and grassland plant 87Sr/86Sr is much less variable and generally above 0.730. This value is higher (more radiogenic) than the 87Sr/86Sr of plants growing within the greenbelt surrounding the Blaaubank stream adjacent to Swartkrans and streamwater itself (0.721). The difference between grassland and riparian strontium isotope composition suggests a method for determining habitat utilization by early hominids. In this study, a geological explanation for a natural difference between Blaaubank stream and grassland Sr is suggested, based on relatively less radiogenic Sr (having lower 87Sr/86Sr values) in the carbonate component of the local dolomite when compared to other nearby geological formations. The explanation was tested initially using a top-down approach in which the 87Sr/86Sr ratios of water, soil, and plants from the entire Blaaubank catchment were measured. Next, a bottom-up approach was used to examine Swartkrans Member I faunal species known to have obtained their Sr from well-defined habitats. The results are that (1) pollution is not the explanation for the relatively low 87Sr/86Sr ratios of the Blaaubank stream, (2) Swartkrans Member I carbonate has a similar 87Sr/86Sr to that of modern Blaaubank water, indicating that relationships seen today existed in the Pleistocene, and (3) Pleistocene riparian fauna have relatively low 87Sr/86Sr ratios when compared to fauna adapted to drier habitats. Together these results make it possible to interpret the strontium isotope composition of Pleistocene early hominids from Swartkrans in terms of habitat utilization.
Abstract: The spatial characteristics of African protected areas classified as national parks (category II) by the World Conservation Union (IUCN) were quantified on a regional basis. Four groups of spatial statistics were used; park size, park abundance, park shape and park spacing. Eastern Africa has the greatest number of small national parks (< 100 km2 and 100-1000 km2), western Africa most within 1000-10,000 km2, and southern and south-central Africa most within 10,000-50,000 km2. Only two national parks are larger than 50,000 km2, one each in southern and northern Africa. Furthermore, southern Africa has the greatest, and western Africa the lowest, combined park area. Northern Africa has the greatest average, but lowest proportional, area covered by national parks, whereas western Africa has the lowest average area, and southern Africa the greatest percentage area accounted for by national parks. Parks in eastern Africa have the lowest perimeter: area ratio, whereas southern Africa have the highest. National parks are aggregated in all of the regions, but the mean nearest-neighbour distances and isolation index values reveal that, in reality, the parks are well separated across three spatial scales. Implications of the results for conservation, especially at the landscape level, are discussed. The large edge: interior ratios of national parks in all regions means that factors originating from surrounding land-uses will be expected to have a severe effect on park management. Large-scale movements between African national parks are important for species characteristic of African savannas. However, in general, the large distances between African national parks prevent such interaction between parks. This could only be addressed by regional conservation plans which consider the matrix surrounding the parks and aim to maintain processes.
Abstract: This paper reviews the application of the nutrient budget and balance approach from a range of settings and scales in Africa. The paper asks: can such analyses help in the design of effective policy which supports improved soil fertility management by Africa's small-holder farmers? Through the examination of existing studies, the paper highlights some of the difficulties with nutrient budget analyses, including potential problems with a snapshot approach when trying to understand longer term dynamic processes; the danger of extrapolation to wider scales from limited locale-specific data sets; the challenges of understanding diversity, complexity and uncertainty within small-holder farming systems; and the importance of insights into the many socio-economic and institutional factors which influence decision-making at farm level and so mediate the processes of environmental change. The paper concludes by recognising the potential contribution of nutrient budget analyses to the policy process, but suggests caution over uncritical use; particularly the employment of aggregate studies to diagnose generalised problems and suggest blanket solutions. The paper also highlights how nutrient budget analyses can be used as simple devices to encourage debate and dialogue among farmers, technical scientists and policy actors in a participatory process of negotiating interventions or policies for tackling issues of agricultural sustainability in Africa.
Abstract: This review examines the conservation, risk, productivity, viability and acceptability of range management technology as it relates to sustaining rangeland ecosystems specifically in arid and semi-arid climates. The efficiency, cost effectiveness and risk with which rainfall is converted into plant production, and eventually gross farming income, without deterioration of natural resources form the essence of sustainability of rangeland ecosystems in these areas. Range and soil degradation can dramatically influence soil water balance, nutrient cycling, soil loss, production and the economics of a farm unit. Management for long-term sustainability often requires sacrifice of short-term welfare. With respect to deterioration and loss of productivity of natural vegetation, a co-ordinated approach is needed towards establishing a comprehensive inventory of the condition of national vegetation resources on a geographically and scientifically sound basis.
Abstract: This paper examines the interest in the development and promotion of mixed farming in sub-Saharan Africa. For over 70 years mixed farming has been a dominant model for agricultural development despite the limited success of many of the programmes which have specifically promoted it. It is suggested that the establishment of mixed farming as a strong development theme is related to its promise to address a range of environmental and social concerns, and in so doing, help create order out of a [`]chaotic' African countryside. Mixed farming is again being highlighted with the more recent interest in sustainable, environmentally friendly agricultural systems. However, there is considerable evidence that African farmers have adopted a flexible principles-based approach to the use of component technologies commonly associated with the mixed farming model. This must be fully acknowledged, and the seduction of unitary models avoided, if agricultural research is to contribute efficiently to the development of more sustainable farming systems.
Abstract: The significance of encroacher woody plant browse (among other factors) in the composition of the diet of cattle was quantified for July 1996, March 1997 and September 1997. This is important because browse in general is typically ignored in carrying capacity estimates for cattle, while woody encroachers are considered a result of high cattle densities in communal rangelands and therefore undesirable for cattle as feed. There were significant differences in the activities of cattle and woody species utilized between the 3 months. Encroacher woody species (mainlyD. cinereaandG. flava) contributed 84.052% in March, 48.053% in July and 21.054% in September towards cattle's diet out of all the woody species browsed. The woody species recorded high crude protein levels as compared to the grasses. Both the grasses and browse, however, were found to be deficient in phosphorus and the major minerals, except calcium. A temporary protein deficiency for cattle was anticipated in September as the proportion of browse in the cattle's diet was very low due to the scarcity of browse during this period. There were, however, large quantities of low quality grass cover and cattle tended to graze more, hence no problems were expected with the overall energy supply. The importance of browse (especially woody encroachers) towards cattle's diet in a communal grazing system, even in a good rainfall year, is emphasized. There is, however, a need for more research to focus upon the dynamics and importance of this much neglected food supply.
Abstract: Nitrogen plays an important role in animal production because it is essential for the production of animal tissue, milk, eggs and wool. Grasses provide more than 70% of the global protein intake by animals. Two-thirds of the remaining protein is supplied by feedstuffs and one-third by products like kitchen wastes. The global efficiency of nitrogen in animal production is slightly over 10%, with the result that 102 Tg (1012 gram) nitrogen are excreted on a yearly basis by all domesticated animals. This article presents the nitrogen balance sheets for global animal production, global crop production and the global agricultural sector. It discusses the present nitrogen efficiency in animal production and possible improvements. For a sustainable world it is necessary to study and to establish the desired balance between human food and animal feed production.
Abstract: Vegetation community structure is a key indicator of long-term vegetation change in semi-arid ecosystems. This study uses ground-based spectral measurements and a canopy reflectance model to investigate the potential of Earth observation data to characterize variations in vegetation structure along a grazing gradient in the eastern Kalahari, Botswana. Despite differences in the bidirectional reflectances of soil, plant litter, bush and grass canopies towards the end of a dry season, it is unlikely that Earth observation data can be used to estimate vegetation structure at this time. This is due to an ambiguity in the relationship between spectral reflectance and vegetation structure caused primarily by the limited dimensionality of reflectance data. Variations in canopy architecture cause differences in the level of inter-canopy shadowing but the net effect--lower reflectance with an increase in bush cover--parallels the darkening effects of any vegetation cover on relatively bright sandy soils in semi-arid environments. These results highlight the continued need for long-term ground-based ecological monitoring in conjunction with satellite-based monitoring of changes in vegetation cover.
Abstract: Two pairs of a natural and an artificial watering point in each of the four largest land systems in the Kruger National Park, South Africa were randomly selected for study. The herbaceous community composition and basal cover were measured in transects starting at the water and radiating to 100Â m from the water. The community composition was converted to herbaceous forage and fine fuel production potential scores. A general linear model was used to test for differences between the impact of large herbivores on these parameters at natural and artificial watering points. There was no evidence of a difference in the impact of herbivores at artificial and natural semi-permanent watering points. Stabilization of natural semi-permanent watering points by artificially making than permanent is likely to have negligible impact on rangeland condition. Artificial watering points are likely to be foci of much greater degradation than seasonal sources and provision of artificial watering points in areas where only seasonal sources naturally exist is not recommended where the aim of management is the maintenance of biodiversity and natural ecological processes.
Abstract: Four Holocene pollen diagrams are presented from interdune depressions in the Manga Grasslands (northeastern Nigeria near 13°N). These sequences are interpreted using modern pollen spectra, statistical analyses and groupings based on phytogeographical affinity (Long Distance, Sahelian, Sudanian, Guinean). The roles of climate change and anthropogenic activity in the vegetational history of the central part of Sahel are evaluated. Particular attention is given to the separation of regional (Manga Grasslands) from local (individual depressions) vegetation trends. Humid conditions in the early and mid-Holocene (from 10,000 to ca. 3300 yr B.P.) enabled the establishment of, and sustained, swamp forest vegetation in the interdune depressions. The main taxa (Alchornea, Syzygium and Uapaca) have Guinean affinities. The surrounding dunefields consisted of open savanna with Sahelian and Sudanian (e.g., Combretaceae, Detarium) elements present. Drier conditions ca. 3300 yr B.P. produced abrupt changes in pollen stratigraphy and led to the establishment of the modern vegetation of the Manga Grasslands. Although occupied since at least 3700 yr B.P., there is little evidence of human activity in the pollen diagrams. The nomadic pastoralism practiced by the human occupants of the Manga Grasslands may be palynologically undetectable. Although the Holocene vegetational history of the Manga Grasslands appears to have been primarily controlled by climate, caution should be exercised before drawing climatic inferences from these pollen sequences. For the early and mid-Holocene differences of ca. 1000 years exist in the timing of vegetation changes between the individual depressions. While water levels in the depressions are likely to be coupled to climate, the vegetation response appears to be strongly influenced by local conditions (in particular variations in the depth of depressions and so the relative height of water table). In addition, the Guinean swamp forest vegetation of the early and mid-Holocene is unlikely to be representative of vegetation trends at this latitude, but rather developed extrazonally as a result of the particular topographic/hydrological conditions prevailing in the Manga Grasslands. The problems of lags between climate and vegetation change and the presence of extrazonal vegetation, experienced in the Manga Grasslands, are likely to be common to other Sahelian pollen sites. The palynological information presently available for this zone is deemed insufficient for detailed subcontinental scale reconstructions of vegetation and climate to be attempted.
Abstract: Using a simulation model of sheep and cattle grazing systems in different regions of the Australian rangelands, we tested the use of different measures and analyses for identifying an [`]exceptional circumstances' drought event, defined as occurring once in 20 years in the long term. Over the century-long simulations, all measures (rainfall, various soil moisture measures, pasture growth, liveweight gain and an economic productivity index) identified the major drought periods in each region. However, the measures differed considerably in the identification of marginal events, because economic and biological hardship are not always synchronised. Total soil moisture seems to be the best single measure, providing it is properly calculated, but there is a strong case for considering more than one measure. Periods perceived as exceptional are also greatly affected by the choice of averaging technique, moving window, and assumptions about baseline management strategies. Hence the choice of index has implications for sustainability. We also show that revocation criteria are as important as the criteria for declaring a drought, and discuss the difficult balance between objectivity and equity.
Abstract: Instead of maximizing the expected monetary return of land usage, Pacific islanders manage land so that it renders an optimal mix of cash income and non-monetary cultural goods. Evidence from cropping patterns in Fiji suggests that the production of these cultural goods is linked to traditional agriculture which produces less ecological deterioration than its commercial counterpart. The capacity for village land to support traditional activities is highest under a regime of communal land tenure where decision making is centralized. A regime of private land tenure lowers this capacity because decentralized decision making raises the coordination costs of preserving special areas of land for traditional purposes. This means that if development planners rush to replace traditional regimes of communal land tenure with [`]modern' systems of private land ownership, they might also observe a correlated increase in land degradation, even if new codes of private property are perfectly enforceable. A two-sector growth model can be used to show that the welfare-neutral [`]bribe' required from the government to increase the amount of village land preserved in the steady state is lower under a regime of communal land tenure. One counterintuitive result is that a high subjective discount rate does not always imply a high level of environmental degradation. Observations from the South Pacific have application for environmental policy in other developing countries.
Abstract: To account for the failure of state-driven development projects, policy makers and planners have tended to blame communal farmers for adhering to outmoded traditional values and practices. Ethnographic data from fieldwork in Matabeleland during 1990-1992 shows that far from being trapped within the straightjacket of tradition, villagers opposing the project were intimately enmeshed within modern discourses and practices. They were by no means trapped within a pristine traditional worldview, even though at times they drew on such discourse to challenge disruptive and unpopular state interventions. The findings challenge the ways in which an imaginary "great divide" between tradition and modernity has functioned in development discourses to account for local opposition to top-down, centralized bureaucratic state planning and development.
Abstract: Australia and South Africa are dominated by extensive agriculture, both countries being predominantly arid and exposed to a highly variable climate. Limiting land degradation, maintaining the financial viability of farms and improving the risk-management skills of farmers are common problems which government and industry in both countries are attempting to address. Both countries are currently refining their approaches to drought management, and have been making substantial use of science in improving the monitoring and assessment of drought, and the management of the land. Unlike the situation in Australia, however, South Africa's approach is being reviewed against the backdrop of a fundamental reorientation of broader agricultural policies in the context of that country's transition to a fully fledged democracy. The changing approach to drought policy in South Africa can therefore only be fully understood in the context of this broader process of change. This paper compares the climate and agriculture of Australia and South Africa, and how their different drought policies have evolved. Observations are made on the role of scientists in providing advice to political decision makers, and ways in which the process of decision making with respect to drought may be improved.
Abstract: Fifteen environmental variables, among them cattle density (hereafter [`]pressure index'), were measured along grazing gradients of eight boreholes at Olifants Drift in south-eastern Botswana. The aim was to investigate whether cattle density, among other variables, had any direct relationship with the occurrence of bush-encroaching woody plant species. This is important because high cattle densities in the communal rangelands of Botswana have been held responsible for the increasing dominance of woody encroachers. On the basis of thet-values and the variance inflation factors (VIF) obtained from CANOCO (canonical community ordination) programme, four environmental variables were retained as significantly influencing woody plant species composition along the grazing gradients: cattle density, soil nitrogen, distance from borehole and tree cover. The retained variables were forward-selected in a regression and cattle density explained most (33%) of the variance out of the total 60% explained by the four variables. Woody plant species associated with high cattle density were also found on high nitrogen sites, and these were thorny plant species that have been previously classified as encroachers. Therefore, high cattle density around boreholes is associated with bush-encroaching woody plant species. High cattle density is also likely to be found around natural water points (pans and wells), rivers and kraals, hence encroaching woody plant species are likely to dominate in such places. Shifting of the high cattle density foci (boreholes, wells, kraals, etc.) is likely to result in most of the grazing pasture being composed of the encroaching woody plant species at the expense of the non-encroaching woody plant species.
Abstract: Most systematic assessments of future conservation areas rely on selection units--parts of the landscape that are analysed as the potential building blocks of an expanded system of reserves. Selection units can be natural, administrative or arbitrary subdivisions of the landscape. They differ widely in size between studies and within regions. The paper begins with a review of the role of selection units in conservation planning and the implications of using them. The review is followed by quantitative analyses on a large regional data set. We show that the total extent of new reserves needed to represent all land types (land systems in this case) to different targeted levels depends strongly on the size of the selection units. Differences in required total areas are related to the extent to which some land types are represented above target levels. The results indicate that some degree of inefficiency is inevitable in any reserve selection exercise based on units that are large enough to function as viable reserves or to be amalgamated realistically into viable reserves. We also show that the actual representation of land types in selected reserves is related to their distributional parameters, so that the extent of above-target representation is predictable to some extent. Finally, we show that patterns of actual vs targeted representation from a reserve selection algorithm are very different from those arising from random selection of the same number of areas. Selection algorithms introduce a degree of above-target representation which is the price of guaranteeing that all features are represented at least to target levels.
Abstract: The Conservation Reserve Program (CRP) was initiated to reduce water and wind erosion on marginal, highly erodible croplands by removing them from production and planting permanent, soil-conserving vegetation such as grass. We conducted a field study at two sites in Wyoming, USA, in order to quantify changes in soil C and N of marginal croplands seeded to grass, and of native rangeland plowed and cropped to wheat-fallow. Field plots were established on a sandy loam site and a clay loam site on wheat-fallow cropland that had been in production for 60+ years and on adjacent native rangeland. In 1993, 6 years after the study was initiated, the surface soil was sampled in 2.5Â cm depth increments, while the subsurface soil was composited as one depth increment. All soil samples were analyzed for total organic C and N, and potential net mineralized C and N. After 60+ years of cultivation, surface soils at both study sites were 18-26% lower (by mass) in total organic C and N than in the A horizons of adjacent native range. Six years after plowing and converting native rangeland to cropland (three wheat-fallow cycles), both total and potential net mineralized C and N in the surface soil had decreased and NO3-N at all depths had increased to levels found after 60+ years of cultivation. We estimate that mixing of the surface and subsurface soil with tillage accounted for 40-60% of the decrease in surface soil C and N in long-term cultivated fields; in the short-term cultivated fields, mixing with tillage may have accounted for 60-75% of the decrease in C, and 30-60% of the decrease in N. These results emphasize the need to evaluate C and N in the entire soil solum, rather than in just the surface soil, if actual losses of C and N due to cultivation are to be distinguished from vertical redistribution. Five years after reestablishing grass on the sandy loam soil, both total and potential net mineralized C and N in the surface soil had increased to levels equal to or greater than those observed in the A horizon of the native range. On the clay loam soil, however, significant increases in total organic C were observed only in the surface 2.5Â cm of N-fertilized grass plots, while total organic N had not significantly increased from levels observed in the long-term cultivated fields.
Abstract: The role of herbivores in controlling plant species richness is a critical issue in the conservation and management of grassland biodiversity. Numerous field experiments in grassland plant communities show that herbivores often, but not always, increase plant diversity. Recent work suggests that the mechanisms of these effects involve alteration of local colonization of species from regional species pools or local extinction of species, and recent syntheses and models suggest that herbivore effects on plant diversity should vary across environmental gradients of soil fertility and precipitation.
Abstract: A herbivore faces challenges while foragingthat make selecting a nutritious diet a vital affair. Foraging behaviours arise from simple rules that operate across levels of resolution from cells and organs to individuals and their interactions with social and physical environments. At all these levels, behaviour is a function of its consequences: a behaviour operating on the environment to induce changes is itself changed by those events. Thus, behaviour emerges from its own functioningand its ability to discriminate familiar from novel foods—arise from the functional integration of sensory (smell, taste, texture) and postingestive (effects of nutrients and toxins on chemo-, osmo-, and mechano-receptors) effects. The ability to discriminate among foods is critical for survival: all problems with poisonous plants are due to an inability to discriminate or a lack of alternatives. Animals eat a variety of foods as a result of nearing or exceeding tolerance limits for sensory and postingestive effects unique to each food. After eating any food too frequently or excessively, the likelihood increases that animals will eat alternative foods owing to exceeding sensory-, nutrient-, and toxin-specific tolerance limits. Cyclic patterns of intake of a variety of foods reflect seemingly chaotic interactions among flavours, nutrients, and toxins interacting along continua.
Abstract: Surface temperature (Ts), air temperature (Ta), atmospheric precipitable water (U), and vapor pressure deficit (D) have been derived from algorithms that use satellite observations of visible, near infrared and thermal infrared radiation in order to obtain higher spatial resolution data than is possible from meteorological station observations. The inferences of these four variables are compared with field instrument observations for sites with contrasted climates and vegetation including boreal forest (BOREAS), tropical bush savanna (HAPEX-Sahel), tall-grass prairie (FIFE) and a region with mountain, prairie and intensive agriculture (Red- and Arkansas-river catchments). The results showed that Ts could be retrieved with RMS errors of 3.5°C for a range of 48°C; Ta with 3.9°C over a range of 36°C; U with 0.6 cm over a range of 3.6 cm; and D with 10.9 mb over a range of 58 mb. Although the results had low absolute accuracies, the field data themselves are not without error--not least because, although the inferences were for a >1 km2 area made instantaneously, they were compared with point field values generally not measured at exactly the same times in the day. Maps of retrieved variables had good relative accuracy and possibly better absolute accuracy than the comparisons with point measurements suggest.
Abstract: A 10-year sheep grazing experiment was conducted in southern Patagonia to test the hypothesis that high stocking rates would promote transitions from open grasslands to dwarf shrublands. Treatments included three stocking rates and an exclosure. Total aerial vegetation cover grew in all treatments, but especially under low stocking rates and exclosure. Short grasses and herbaceous dicots increased significantly in these last treatments. Bunchgrasses increased under low stocking rates, but decreased in the exclosure. Cover of dwarf shrubs did not change in any treatment. Diversity of the community, measured in Shannon-Wiener and species richness index, increased in the exclosure, and species richness was reduced under high stocking rates. Transitions were explored by means of PCA. While all treatments moved along the axes of the multivariate space, we detected no thresholds and found no indications of having induced transitions to alternate states with the grazing treatments imposed.
Abstract: The central Mendoza plains (56,000 km2), located in the eastern foothills of the Andes, belong to the vast phytogeographic province of [`]Monte' (c.500,000 km2) in Argentina. This area is a typical warm arid zone and vegetation is typically a shrubland. Perennial grasses are predominantly C4species. Land-use is for livestock grazing; the average stocking rate is 28 ha per large stock unit (LSU), year-long. Ecological and range research have been actively pursued in the region by IADIZA over the past 25 years. Two experiment stations were established 25 and 10 years ago, respectively: The Ñacuñán Biosphere Reserve and the El Divisadero Cattle and Range Station. Primary production and its relationship to climatic and edaphic parameters were analysed and compared in the two stations. Rain-use efficiency (RUE, kg DM ha-1year-1mm-1) and useful rains efficiency (URE, P -0·1 PETp) were similar in both cases (RUE = 1·7 and 2·0; URE = 3·0 and 2·9, respectively), when herbs are concerned. However, the variability of annual production was much higher on the silty soils of Ñacuñán than on the coarse sands of El Divisadero; PRVR (Production to Rain Variability Ratio) was 2·5 and 0·53, respectively. Utilization of such experimental figures allows for the prediction of primary production and carrying capacity for a given year, based on rainfall probabilities and, therefore, to determine stocking rates in a rational manner. Basing stocking rates on annual dependable rains (f 0·8) and on useful rains probability (P - 0·1 PETp) proved to be a sound and realistic assessment, validated by long-term experiments and experience. The results of the studies on brush control, cattle diet composition, animal productivity and feed value of forage species were analysed. Current and future research programmes in IADIZA for the Mendoza plains are mentioned. Although research on resource inventory and basic ecological processes in the Mendoza plains should carry on, the emphasis and therefore the resources should henceforth be devoted to the consequences of resource management alternatives on overall arid land productivity, i.e. research for development. A better integration of applied ecology for management and investigations on basic arid land ecological processes should appear in IADIZA programmes.
Abstract: Monthly botanical composition of cattle diet was determined for the period July 1994 to June 1995 in faecal samples by microhistological analysis. Principal components and cluster analyses were used to evaluate diet homogeneity among months. November through March diets were mainly composed of grasses and forbs (50 to 73%). During the April-September period, shrubs represented 36 to 57% of the overall diet. In October more than half the diet came from two species, one shrub (32%) and one grass (25%) making this month very different from the rest. The composition of cattle diets was significantly correlated with temperature and/or rainfall.
Abstract: The objective of the present study was to evaluate the digestibility of Albizia harveyi (AH), Delonix elata (DE) and Grewia similis (GS) dried leaves and the effect of feeding the leaf meals on the performance of goats fed low quality hay. The four treatments consisted of the three browse species combined with Cenchrus ciliaris (CC) hay and a control with concentrate + CC hay or pure CC hay. Data from twelve bucks in the digestibility experiment and twelve does with single kids in the production experiment were analyzed. All the browse species had high crude protein contents (17-20.4%) and low content of neutral detergent fibre (31.3-60.7%) and acid detergent fibre (17.9-34.7%). AH had the highest fibre content of the browses but lower than that of grass hay. Results indicate that irrespective of the higher concentration of phenolic compounds, DE leaves were better digested than leaves from AH and GS. Supplementation of low quality hay with GS leaves and concentrate increased total DM and nutrient intake but reduced DM intake of the basal diet. Does fed with GS leaves had significantly higher milk yield and kid weight gains. The poor performance of the DE supplemented goats could be associated with the presence of the relatively high levels of total soluble and soluble condensed tannins in the leaves, whereas in the case of AH, leaf dust and hair could have lowered leaf intake.
Abstract: Long-term ecological research under the International Biological Program and several other programs at research stations within the former USSR collected a large amount of data on phytomass, productivity and element cycling, together with climatic and soil regimes for various types of grassland ecosystems. This provides a unique opportunity to assess the performance of CENTURY across a wide environmental gradient from the luxuriant highly productive meadow-steppes of Central Russia to the ultracontinental steppes of Central Asia and the arid ephemeral grasslands in the Middle-Asian republics of the former USSR. The model simulations across this broad environmental gradient proved that the CENTURY ecosystem level model reproduced the seasonal, the mid-term, and in some cases the long-term dynamics of the live and dead aboveground phytomass of the grassland ecosystems in highly different natural-climatic zones of the former USSR. The r2 for the comparison of observed and simulated live phytomass varies from 0.41 to 0.98 and the ratio of the absolute mean error of live phytomass to the peak seasonal live phytomass varies from 10 to 20%. The means and variation limits of the model are close to that of field data. The results suggest that many of the model discrepancies are a result of the fact that the model does not consider year-to-year changes in plant species composition. The measured Russian phytomass data for all of the sites are available on the World Wide Web.
Abstract: Detection of vegetation change in arid Australian rangelands at different scales and with different ground-based techniques was investigated. Changes caused by grazing could not be detected without stratifying for spatial patterns at fine scales. Temporal variation in rainfall and grazing was such that species numbers fluctuated markedly; numbers were best assessed when favourable conditions produced the maximum response. More heavily grazed sites supported fewer species and composition was unstable over time; there was a threshold beyond which recovery did not occur. Several species were identified as useful indicators but it was not possible to reduce them to functional groups, to simplify interpretation.
Abstract: Portable computers presently allow documentation of real-time grazing behavior under field conditions. Researchers are still challenged, however, with the task of selecting proper and easily recorded variables to test their hypotheses. The objective of this research was to examine relationships among variables describing grazing behavior and forage utilization by goats to identify the most easily monitored activity capable of accurately ranking their relative preferences among forages. Relationships were investigated in grassy paddocks and on native shrub/steppe rangeland. Variables recorded for each forage included: total visits, total bites, bites per visit, total grazing time, time per visit, and bite rate in both environments, and number of plants grazed, number of plants regrazed, number of regrazing events, percent utilization, grazed plant utilization, and number of plants utilized in the grassy paddocks. In grassy paddocks, with eight different forages available, total visits, total bites, total time, number of plants grazed, number of plants regrazed, and number of regrazing events were highly correlated (r >= 0.94 and P < 0.01) during both the boot and dormant stages of phonology. Rank correlation coefficients (rs) among forages with these variables averaged 0.96. Any of these six variables would probably give satisfactory ranking of relative preferences if the animal in question was confined to or elected to forage from a single life form (grass, forb, shrub, or tree). Utilization data were significantly (P < 0.01) but poorly correlated (mean r = 0.74) with total bites, total visits and total time. Correlations among grazing behavior variables were all statistically significant (P < 0.01) but much weaker in shrub/steppe vegetation where a variety of life forms were available (mean r = 0.45), Only total time versus total bites and bites per visit versus time per visit exhibited correlations of 0.94 or greater (P < 0.01). The poorer correlations obtained on rangelands were attributed to a wide array of foraging techniques used by the goats to graze the various grasses, forbs, shrubs, and trees. Total time was the only variable consistently correlated with total bites in both the grassy paddock and shrub/steppe pastures (mean r = 0.94). Monitoring of grazing time devoted to each forage could be more easily accomplished than the more attention demanding process of tallying individual bites. We suggest that adequate rankings of relative forage preference of goats could be obtained by a single observer recording grazing time expended on each forage.
Abstract: Rangeland ecologists, particularly those in North America, have traditionally worked with a paradigm founded on the notion of Clementsian succession. This is increasingly being called into question. New ideas (notably from Australia, the U.S.A. and South Africa) have begun to emerge which see rangeland changes occurring as a result of grazing management, habitat type and episodic events. New methods for assessing vegetation dynamics have been put forward which approach the older techniques favoured by plant sociological geobotanists. This paper explores the basis for current and past thinking in rangeland ecology and the potential application of geobotany to rangeland inventory and monitoring. A case study from semi-arid northern Iran is used to illustrate the way in which site potential can be characterised by using soil-based and plant-based attributes.
Abstract: Tropical moist forest is being destroyed at the rate of 11 million hecares per year, much of which degrades into fire-maintained savanna or low-productivity pasture. Greater economic and ecological benefits can be realized from much of this land if it can be converted into more productive secondary forest ecosystems. This study was conducted to deterimine if anthropogenic savannas could be converted into production forest through relatively inexpensive protection of the forest edge by plowing the soil with an agricultural tractor in highly-degraded (Ancient) and less-degraded (Nascent) savannas on the coastal plain of Gabon, Central Africa. After three years of protection, vegetation surveys revealed rapid colonization of Nascent savannas by 45 species of tree seedlings. Ancient savannas also experienced colonization by tree seedlings, but at a much lower rate. Analysis of soils determined that Nascent savannas have 5 times more calcium and magnesium and higher organic matter than Ancient savannas; indications of their less-degraded nature. Protection of the forest-edge from fire can be an effective, low-cost method of converting anthropogenic savannas into production forest through natural regeneration. The rate of conversion can be maximized by focusing on less-degraded sites to capitalize on more abundant seedling recruitment and higher ecosystem nutrient stocks, but even highly-degraded sites may be reclaimed with additional management.
Abstract: The main conclusions of the research project on soil erosion and sedimentation in Swaziland are as follows. (1) Soil erosion has worsened over the last 20 years. The proportion of an 1800 km2 study area in the Middleveld classified as [`]high erosion class' has increased from 6.7 to 13.6% between 1972 and 1990. (2) Gully erosion is the main process and is concentrated within the Manzini, Jabuleni, Lobamba and Chibidze land systems, all characterised by soil-saprolite complexes. (3) Overgrazing and compaction along paths and tracks lower the infiltration rate of the clay-rich ferralitic soils, promoting surface runoff and the formation of rills. (4) Once the rill deepens and cuts through the soil on to the underlying saprolite, gullies develop rapidly because of the low shear strength of the material. (5) Soil erosion problems are compounded by the existing system of land tenure and increasing pressure of livestock and population on the land. (6) In some instances, population pressure can lead to improvements in land management and better soil protection. Recommendations for controlling soil erosion and for further research are presented.
Abstract: [delta]13C values in paleosols and fossil teeth have been used to document the expansion of C4 plants in South Asia, Africa, and North America during the late Miocene. However, the exact timing and rate of expansion of C4 vegetation is unclear outside the Old World because of a lack of high-resolution records. We present a high-resolution record from northwest Argentina in which the [delta]13C values of soil carbonate rise above a threshold of -8[per mille sign], suggesting the presence of C4 plants, starting at 7.3-6.7 Ma. [delta]13C values of fossil teeth from well dated sections in South and North America display a concomitant increase of C4 plants in the diets of large herbivores. These results show that the late Miocene expansion of C4 plants was global, but occurred at different rates in each region. While it is has been suggested that declining pCO2 levels during the late Neogene caused C4 plant expansion, climate change, such as an increase in summer-dominated rainfall regimes globally, is an alternative explanation. The [delta]18O soil carbonate records from South Asia, East Africa and now also northwest Argentina all show an increase of at least 3-4[per mille sign] in the late Neogene, either the result of climate change or of greater evaporation in average grassland soils.
Abstract: There is an increasing need for data on land-cover changes at broad spatial .scales. In this study, a remote sensing-based technique for land-cover-change analysis was applied to the African continent for the last decade. Ten years of daily, continental-.scale satellite remote sensing data (front the National Oceanic and Atmospheric Administration's advanced very-high resolution radiometer) were analyzed. Deviations in. the seasonal trajectory of the land surface--characterized by its brightness temperature and a vegetation index--were interpreted in terms of land-cover change on a yearly basis, from 1982 to 1991. Land-cover-change magnitudes were measured and mapped for every year. The major categories of seasonal patterns of changes were identified. Multiyear patterns of change also were categorized, and all areas affected by a continuous decrease and gain in vegetation cover over the decade were snapped. Results were related to published high-resolution remote sensing-based studies, rainfall data, and other evidence of land-cover changes. This study's results demonstrate that inte-rannual land-cover changes in Africa mostly involve erratic variations in land-corer conditions due to interannual climatic variability and temporary nwdifncations in seasonality. Continuous, unidirectional change processes (decrease or gain in vegetation cover) affected less than 4% of sub-Saharan Africa during the study period. Althongh such linear changes are just a fraction of the total land-cover changes detected, their effect on ecosystems and sustainability of livelihood might be significant. In the semiarid regions, temporary modification of the biophysical attributes of the surface driven by variations in rainfall is the dominant process. Future work will focus on finer-scale interpretation and validations of patterns of changes.
Abstract: Five techniques that are generally used in the western part of the grassland biome of southern Africa were evaluated. The techniques were tested on the mid-slopes (high species diversity) and pediments (low species diversity). The techniques were tested particularly with regard to their sensitivity for monitoring range condition changes. The Degradation Gradient Technique, as well as the Weighted Key Species Technique (to a lesser degree), appear to be the techniques best suited to this region at present.
Abstract: The arid central dune field of the Namib Desert is characterized by a pronounced rainfall gradient across its west-east, 160 km breadth, and a correlated increase in sand stability and grass community complexity. In addition to these macro-gradients, micro-gradients of sand stability and available moisture across each dune slope result in stratified grass communities on the dunes. The effects of abiotic factors and plant associations on the community structure of VA-mycorrhizal fungi in a naturally arid and unstable grassland could thus be investigated. Mycorrhizal fungal communities associated with five grass species were sampled at sites located across the gradients. Diversity and abundance of spores, as well as percent mycorrhizal colonization of plant roots were used to characterize the fungal communities and their plant specificity. FiveGlomusspecies (Glomales) were associated with grasses at all sites, but no plant specificity was observed. Rather, the fungal communities varied in diversity and abundance both within a dune site and across the dune field. Regression analyses showed that spore abundance and colonization levels were significantly affected by abiotic factors. Sand stability affected spore abundance and thus determined the limits of distribution of the fungal community in the dune grassland. In contrast, colonization levels were primarily affected by moisture availability, and fungal growth and spore production following an isolated rain event were closely associated with moisture availability. A rapid and opportunistic growth response to moisture, production of resilient spores in response to declining moisture, and lack of plant symbiont specificity are characteristics which allow mycorrhizal fungal communities to function under hyperarid conditions.
Abstract: Sinking boreholes to tap groundwater supplies facilitated expansion of all-year round livestock production into the semi-arid Kalahari. Increased grazing and trampling pres sure around the boreholes often caused vegetation changes and range degradation. The long-term influences of cattle grazing on vegetation pattern around watering points in the southern part of the semi-arid Kalahari are investigated using a grid-based simulation model. Shrub-grass dynamics are modelled for two regimes with high and low rainfall and under various stocking rates. Results indicate the formation of distinct vegetation zones ('piosphere' zones) at the high rainfall site. Under all tested stocking rates distinct zones of bare soil, woody shrubs and a mixed grass-shrub savanna develop. The piosphere zones expand outwards at a rate correlated with the grazing pressure. At the lower-rainfall site zone development is limited and influenced by rainfall. Under abnormally high stocking rates an increase in shrub cover occurs within 50 yr under the low rainfall regime, leading to less distinct zones than under the high rainfall scenario. Modelling results suggest that the recovery potential of shrub-encroached piosphere zones after withdrawal of cattle is negligible in a time span of 100 yr.
Notes: Times Cited: 61
38th Symposium of IAVS on the Importance of Spatial and Temporal Perspectives for Understanding Vegetation Pattern and Process
Jun 04-10, 1995
Rice univ, houston, tx
Abstract: Concentrations of nitrate, chloride, and bromide in groundwater were obtained for 57 wells in a rural, three-county area of north-central Texas. The counties straddle the outcrop of the Trinity Group, an important source of groundwater in the region. Predominant land uses in the area are cropland/pasture and rangeland. The highest nitrate concentrations were associated with cropland/pasture. In general, nitrate concentrations increased as well depth decreased. However, well depth did not influence chloride or bromide concentrations. Outliers were as high as 1.3 g/L for chloride and 8.40 mg/L for bromide. There are numerous oil and gas wells in the study area, which may account for elevated chloride and bromide concentrations. Neither chloride nor bromide was correlated with nitrate, but they were strongly correlated with each other. Dry farming and scant precipitation recharge may account for an absence of nitrate levels above the drinking water standard (45 mg/L). Collectively, the results suggest that agricultural fertilizer and oil field brine are likely sources of groundwater contamination in the study area.
Abstract: Montane grasslands in high rainfall areas of South Africa are subject to large-scale afforestation, making wildlife conservation evaluations necessary. A system which uses landscape features to predict conservation value would be beneficial. This is an initial assessment in the afforestable region of the north-eastern Cape. Sampling of grasshoppers, butterflies and birds was done along a gradient of land types. Differences in conservation value between land types and between landscape elements were demonstrated, but rankings differed according to the criterion used. High-altitude land types and low-altitude Protea savanna were most valuable for conserving endemic species. Low-altitude land types with a Molteno sandstone lithology and the high-altitude land type with a Clarens sandstone lithology had the highest conservation values for taxic richness.
Abstract: We present an operational two-source (soil+vegetation) model for evaluating the surface energy balance given measurements of the time rate of change in radiometric surface temperature (TRAD) during the morning hours. This model consists of a two-source surface component describing the relation. between TRAD and sensible heat flux, coupled with a time-integrated component connecting surface sensible heating with planetary boundary layer development. By tying together the time-dependent behavior of surface temperature and the temperature in the boundary layer with the flux of sensible heat from the surface to the atmosphere, the need for ancillary measurements of near-surface air temperature is eliminated. This is a significant benefit when TRAD is acquired remotely. Air temperature can be strongly coupled to local biophysical surface conditions and, if the surface air and brightness temperature measurements used by a model are not collocated, energy flux estimates can be significantly corrupted. Furthermore, because this model uses only temporal changes in radiometric temperatures rather than absolute temperatures, time-independent biases in TRAD, resulting from atmospheric effects or other sources, do not affect the estimated fluxes; only the time-varying component of corrections need be computed. The algorithm also decomposes the surface radiometric temperature into its soil and vegetation. contributions; thus the angular dependence of TRAD can be predicted from an observation of TRAD at a single view angle. This capability is critical to an accurate interpretation of off-nadir measurements from polar orbiting and geosynchronous satellites. The performance of this model has been evaluated in comparison with data collected during two large-scale field experiments: the first International Satellite Land Surface Climatology Project field experiment, conducted in and around the Konza Prairie in Kansas, and the Monsoon 039;90 experiment, conducted in the semiarid rangelands of the Walnut Gulch Watershed in southern Arizona. Both comparisons yielded uncertainties comparable to those achieved by models that do require air temperature as an input and to measurement errors typical of standard micrometeorological methods for flux estimation. A strategy for applying the two-source time-integrated model on a regional or continental scale is briefly outlined.
Abstract: The reconstruction of African tropical grassland history during the late Holocene can be carried out using phytolith analysis. Fossil phytolith assemblages from Lake Guiers, in the Sahelian region of Senegal, and from Lake Sinnda, in the Guineo-Congolian region of Congo were investigated. The results are interpreted on the basis of modern phytolith assemblages from the same regions and compared to pollen data previously obtained. Tall or short grass associations are discriminated by their phytolith index Iph(%) = saddle/(cross + dumbel + saddle), while the density of shrubs and trees is indicated by relative proportions of the dicotyledon phytoliths. The phytolith data emphasize that, in the Guineo-Congolian region around Lake Sinnda, the driest phase of the late Holocene occurred between 4000 and 1200 yr B.P., commencing with the opening of the dense forest and its replacement by a short grass savanna. From ca. 1000 yr B.P., wetter climatic conditions developed, as represented by the setting up of a tall grass savanna woodland. The modern shrub and tall grass savanna was developed ca. 700 yr B.P. In the Sahelian region around Lake Guiers, the driest phase occurred after about 2000 yr B.P. and has not been followed by moister conditions. A tall grass savanna woodland was gradually replaced by a shrub and short grass savanna which still occurs. A short period of development of swampy vegetation, which can be related to a lake level change, interrupted the semi-arid adaptation of the vegetation, between about 2000 yr B.P. and the present.
Abstract: A near real-time crop-specific drought monitoring system that combines crop modelling and a geographical information system (GIS) has been developed in South Africa. The system is intended to provide decision support for resource managers concerned with drought aid. Individual crop growth simulations are run for cells representing an area of 14 km2. Values of the weather elements used to drive the models are obtained from interpolation of ground observations and processing of weather satellite imagery. Monitoring is undertaken throughout a production season, with updates provided on a fortnightly basis. Predictions of expected yield at the end of the season are made by using observed data up to the current date and completing the season with surrogate historical weather data. Appropriate surrogate scenarios are chosen, based on the synoptic situation in the current season. Maps and tabulated information are produced showing the spatial distribution of drought-stricken areas and the intensity of the drought in these areas. Favourable comparisons were obtained for recorded average maize yields and simulated average maize yields per magisterial district. The root mean square error of these comparisons was 221 kg ha-1, whereas the mean absolute difference was 191 kg ha-1.
Abstract: The grasslands of Cape York Peninsula in monsoonal north Queensland, Australia represent extensive examples of this formation that have been relatively undisturbed by agricultural development. Fourteen grassland units are mapped on the basis of their relationship to soils and landforms. Nine grassland communities were derived from a floristic analysis of the site data, and are related to the mapping units. Half of the grassland map units have less than 10% of their area protected in conservation reserves. The annual forb sickle pod Senna obtusifolia is considered to be the most serious exotic weed at present, because it dominates large areas of unreserved Imperata cylindrica grassland, a community that does not occur extensively elsewhere in Australia. Wetland exotic grasses that are being actively promoted for agriculture pose a potential threat to the Oryza grasslands that occur over large areas of the seasonally flooded coastal plains. It is recommended that further exotic pasture species should not be grown on Cape York Peninsula unless their containment can be assured. Some grasslands appear to be maintained by fire. Data are provided that demonstrate the conversion of some grassland types to woodlands in the last 30 years, and it seems probable that the change is a result of altered fire regimes. Even if adequately reserved, appropriate fire management is required to maintain the grasslands of Cape York Peninsula.
Abstract: The components of the canopy radiation balance in photosynthetically active radiation (PAR), phytomass and leaf area index (LAI) were measured during a complete annual cycle in an annually burned African humid savanna. Directional reflectances measured by a hand-held radiometer were used to compute the canopy normalized difference vegetation index (NDVI). The fraction fAPAR of PAR absorbed by the canopy (APAR) and canopy reflectances were simulated by the scattering from arbitrarily inclined leaves (SAIL) and the radiation interception in row intercropping (RIRI) models. The daily PAR to solar radiation ratio was linearly related to the daily fraction of diffuse solar radiation with an annual value around 0.47. The observed fAPAR was non-linearly related to NDVI. The SAIL model simulated reasonably well directional reflectances but noticeably overestimated fAPAR during most of the growing season. Comparison of simulations performed with the 1D and 3D versions of the RIRI model highlighted the weak influence of the heterogeneous structure of the canopy after fire and of the vertical distribution of dead and green leaves on total fAPAR. Daily fAPAR values simulated by the 3D-RIRI model were linearly related to and 9.8% higher than observed values. For sufficient soil water availability, the net production efficiency [epsilon]n of the savanna grass canopy was 1.92 and 1.28 g DM MJ-1 APAR (where DM stands for dry matter) during early regrowth and mature stage, respectively. In conclusion, the linear relationship between NDVI and fAPAR used in most primary production models operating at large scales may slightly overestimate fAPAR by green leaves for the humid savanna biome. Moreover, the net production efficiency of humid savannas is close to or higher than values reported for the other major natural biomes.
Abstract: The pressing need to increase food production in the tropics to feed the burgeoning population of the Third World requires that crop yields ha-1 must be increased without prejudicing the resource base for future generations. Biological nitrogen fixation (BNF), especially that associated with legumes, has great potential to contribute to productive and sustainable agricultural systems for the tropics, but more research is required to investigate how biologically fixed N, and the increased BNF contributions resulting from research innovations, can be incorporated into viable agricultural systems to increase crop or pasture yields and to substitute N fertiliser inputs. A majority of the soils of the humid and semi-humid tropics have mineral fractions composed of 1:1 lattice clays or sesquioxides of relatively low capacity to retain nutrients (CEC) and water (WHC). It is the soil organic matter (SOM) which has high CEC (after liming) and WHC, and soils under undisturbed climax vegetation are usually high in organic matter which is responsible for their fertility. The key to the long term fertility of such soils is to maintain their soil organic matter by the preservation of crop residues and the selection of suitable crop rotations or fallows. In this review we examine several types of agricultural systems utilised in the tropics ranging from pastures, ley cropping, zero-till rotations as well as green manuring and discuss the management options that can be adopted to preserve their agricultural productivity through the strategic use of legumes in these systems, and their effects on pasture and crop yields. The introduction of forage legumes into tropical pastures can increase and sustain their productivity, with only modest inputs of lime and P and K fertilisers. Similarly, crop and pasture rotations (ley cropping) maintain SOM and soil fertility and crop yields can benefit greatly from the introduction of pasture legumes into the ley. Continuous cropping under minimum or zero tillage can maintain soil cover, and stimulate the retention of SOM, such that nutrient losses are often minimal, and legume derived N can be efficiently transferred to subsequent crops. The options for the resource-poor small-holder to efficiently utilise biologically fixed N as a N supply for cereal grains are more limited and need more attention from researchers as well as less neglect from government organisations. The addition of lime and P fertiliser in modest quantities in many under-developed regions could make large contributions to increased crop yields. If such modest fertiliser inputs were to be combined with suitable crop rotations including green manure or grain legume crops, larger increases in crops yields could be achieved on a sustainable basis, but in many regions agricultural extension services are non-existent and poor farmers have little access to even these basic chemical inputs.
Abstract: The present study was conducted in a rainfed area located in Western Sudan between latitudes 9.5 and 16.7 176;N and longitudes 27 and 32.5 176;E. Three types of legumes (pigeon pea, cow pea and clitoria) were cultivated during the rainy season to be fed as a supplement to dairy Nubian goats during the dry season. The goats were kept under natural range management conditions. The range pasture consists of various species of trees (Acacia seyal, Acacia potyacantha) shrubs (Leptadenia pyrotechnia, Maerua crassifora) and grasses (Cenchrus biflorus, Panicum tergidum). The chemical composition and in vitro digestibility of the grazed pasture and legume hays revealed the better quality of the hays supplement over the grazed pasture. Milk yield and plasma phosphorous levels were higher (P 60; 0.01) in the supplemented group. Although the increase in body weight was not significant, kids that belonged to the supplemented group showed higher (P 60; 0.05) increases in body weight. Goats are highly selective animals and so are able to maintain body weight during the dry season. Legume hays provide an excellent source of protein when quality pasture deteriorates, resulting in an increase in both milk yield and kid body weight.
Abstract: The present study was conducted in a rainfed area located in Western Sudan between latitudes 9.5 and 16.7 176;N and longitudes 27 and 32.5 176;E. Three types of legumes (pigeon pea, cow pea and clitoria) were cultivated during the rainy season to be fed as a supplement to dairy Nubian goats during the dry season. The goats were kept under natural range management conditions. The range pasture consists of various species of trees (Acacia seyal, Acacia potyacantha) shrubs (Leptadenia pyrotechnia, Maerua crassifora) and grasses (Cenchrus biflorus, Panicum tergidum). The chemical composition and in vitro digestibility of the grazed pasture and legume hays revealed the better quality of the hays supplement over the grazed pasture. Milk yield and plasma phosphorous levels were higher (P 60; 0.01) in the supplemented group. Although the increase in body weight was not significant, kids that belonged to the supplemented group showed higher (P 60; 0.05) increases in body weight. Goats are highly selective animals and so are able to maintain body weight during the dry season. Legume hays provide an excellent source of protein when quality pasture deteriorates, resulting in an increase in both milk yield and kid body weight.
Abstract: Intensification of agriculture in the tropics has resulted from a shortage of farmland and insufficient food production to satisfy the needs of an expanding population. Many tropical farmers are challenged by the prospect of intensifying their production while sustaining or improving the fertility and productivity of soils with only locally available natural resources. The waste products of plant and animal production represent some of the most abundant natural resources available for use by tropical farmers to achieve these goals. The efficient use and management of these resources depends on understanding the role that decomposer biota play in regulating the structure and function of agricultural ecosystems. Furthermore, the development of agricultural management practices which promote the beneficial attributes of these organisms will be essential to sustaining the productivity and environmental integrity of tropical agriculture. Finally, understanding the role of biodiversity among decomposer biota in maintaining the functional properties of tropical agricultural ecosystems is critical to achieving this goal. The objective of this review is to further that understanding by describing the taxonomic and functional diversity of decomposer biota in the tropics and evaluating known links between their diversity and the function of agricultural ecosystems. We further describe the effects of changing land-use and agricultural intensification on the structure and diversity of decomposer communities in the tropics and suggest some priorities for future research.
Abstract: New geochemical and palynological data and a sedimentological reinterpretation of two cores from Lake Albert allow a revision of the paleoclimatic and paleohydrologic history of northwest Uganda over the last 30,000 14C yr BP. Our findings document one and possibly three periods of significantly reduced inflow to the Nile River system from the White Nile. Based on sediment fabric and mineralogy, shifts in percentages of total organic carbon (TOC) and total organic nitrogen (TON), hydrogen index (HI), and [delta]13C and [delta]15N, as well as poor preservation of sporopollenin and siliceous microfossils, we recognize two mature paleosols that formed between 18,000 and 12,500 14C yr BP at the surface of exposed lacustrine muds. A thin fossiliferous zone between the two soils documents a brief period of flooding. Lake Albert was below the level of the coring site, and thus a closed basin, for several thousand years during the late Pleistocene. Around 12,500 14C yr BP the younger vertisol was flooded by a major rise in lake level. Relatively deep-water conditions were established soon after this transgression, but an apparent change in sedimentation rate sometime between 8,000 and 3,400 14C yr BP may reflect another, briefer period of low water, which resulted in interruption of sedimentation at the coring site. Palynological data document a rapid and abrupt shift to drier conditions around Lake Albert from 11,400 to 9,900 14C yr BP coincident with the cool Younger Dryas event of the Northern Hemisphere. Geochemical evidence suggests that throughout the terminal Pleistocene and early Holocene, and again in the late Holocene, the water column was relatively well-mixed with little tendency to persistent anoxia.
Abstract: The Caldenal or Southern Espinal is a temperate, semi-arid region covering about 40,000 km2in central Argentina. Cattle raising on natural vegetation is the major economic activity in this region. Mostly because of overgrazing after the introduction of domestic livestock in the early 1900s and fire prevention by ranchers, the physiognomy of the vegetation has changed from a grassland with isolated shrubs and trees to a shrubland, with visible signs of soil erosion in the system. This paper presents an up-to-date synthesis of major findings obtained in the Caldenal during the last 20 years, as well as ongoing research, towards a common objective: to develop management guidelines conducive to a greater, sustainable rangeland productivity while preserving the renewable natural resources in the region. Research has mainly been conducted to study the effects of the major stresses at the Caldenal (fire, drought, defoliation) on grass and/or shrub responses, as well as more basic studies on the ecophysiology of these species.
Abstract: This paper describes a participatory research process designed to gather and structure community knowledge (local and scientific) into a single accessible decision support system, based on case-based reasoning methodologies. Special reference is made to the continuous enhancement of the knowledge base through research (by scientists), and implementation and monitoring of management action outcomes (by land managers).
Abstract: Hypotheses about the relative productivities and impacts of current and officially recommended stocking rates were tested in a case study in southern Africa. They support the view that biased measurements of livestock productivity and inappropriate measurements of rangeland degradation can lead to under-estimates of the productivity of African communal rangelands, overestimates of the urgency of de-stocking, and misunderstanding of the strengths of measures required to effect it. By including the full range of livestock products in estimates of productivity and calculating output per unit of land area rather than per unit of livestock, more accurate estimates of productivity can be made. Estimates of degradation based on irreversible changes enable discrimination between trivial and important impacts of grazing. Modelling suggests de-stocking is not in general worthwhile at present in eastern Botswana. It may be necessary to regulate numbers of animals in the future. If livestock densities increase, grass cover could fall below the critical level and rates of degradation increase suddenly and rapidly. Adverse climatic change could reduce herbaceous productivity with the same effect. The approach used here should help decision making in those circumstaces. Choosing an appropriate stocking rate should be an ethical decision requiring negotiations among stakeholders. Practitioners should recognise that it is socially, not technically determined and that it is but one level among many possible densities.
Abstract: In natural ecosystems, termites are typical ecosystem engineers and, in semi-arid ecosystems, often keystone species. It is thus likely that termites play a major beneficial role through promotion of essential ecological processes in agroecosystems in conflict with their well-established role as pests. This paper reviews the impacts of land clearing and preparation, cropping systems and management practices on termite diversity and activity. Current knowledge of the role of termites in agroecosystem function is discussed with reference to soil processes, vegetation cover, atmospheric gas exchanges and agricultural intensification. Methods for assessing termite diversity and function are outlined and priority research areas are suggested.
Abstract: The effect of fires on land cover was investigated with coarse spatial resolution remote sensing data on West Africa. We tested whether fires lead to land-cover changes or maintain land cover in a state of equilibrium. This was measured independently for early- and late-.season fires, for different ecological ones, and for areas characterized by different levels of land-use intensity. Spatial associations between broad-scale land-cover-change maps and fire-distribution maps were calculated. The statistical results reveal that, for a few subregions, there is a statistically significant relation between fire occurrence and land-cover changes as measured by coarse-resolution remote sensing data, whereas, at a broad .scale, there is no such relation. The main conclusion is that the scale of the data analyzed in this study is inappropriate for reaching any definitive conclusion on the effect of fires on land cover. This is due, first, to an inadequate spatial resolution to detect all fires and their associated ecological effects and second, to the heterogeneity of the population, given the size of the study area.
Abstract: Indigofera spinosa (Forsk.) is a key forage resource in the arid rangelands of northern Kenya inhabited by nomadic pastoralists. Because it is highly relished by livestock, it is subjected to heavy periodic and in some areas permanent browsing impact wherever it occurs. This study evaluated the effects of simulated herbivory on yield and reproduction of this species. Different levels of impact (light, moderate, moderately-heavy and heavy) were inflicted on individual shrubs at fortnightly and monthly intervals respectively. Results indicate that I. spinosa is highly resilient to browsing. Maximum regrowth compensation was achieved at the moderate level of impact. Heavy clipping reduced residual mass to an extend whereby the ability to compensate for lost vegetative organs was severely curtailed. A longer clipping interval tended to enhance regrowth, especially at the moderate intensity. Reproduction was significantly reduced by clipping impact. At the heavy clipping impact, reproduction was completely halted. Irrigation mitigated the impact of clipping by increasing the amount of regrowth and reproductive activity. To optimise the production and utilisation of I. spinosa pastures during the growing (wet) seasons, it is recommended that grazing should be moderate to leave browse height of 10-15 cm. At this intensity, adequate reproduction will be stimulated while ensuring availability of residual mass critical for dry season feeding and long term sustainable production. Yield to browsers will also be optimised at this level of impact.
Abstract: From a review of published information on the nutritive value of indigenous browse in Africa, the intake of ruminant species of wild ungulates and the energy requirements for maintenance of these animals, an analysis has been carried out to assess the supply of energy and protein from browse in relation to meeting requirements. Although there are a large number of data giving chemical composition of browse, there is relatively little information on digestibility and energy value. Results on intake and energy requirements have been reported for a few species of wild ungulates and these have been used as such or formed the basis of derived values for other species. The analysis indicates that for four species of wild ungulates, differing in size from 20 to 500 kg, the intake of metabolisable energy may be 12-27% greater than or substantially less than the amount required for maintenance. The difference arises from the choice of values for fasting metabolism. The establishment of models of energy and protein systems, together with more measurements on the nutritive value of indigenous browse are advocated in order to obtain a better knowledge of the nutrient needs and productivity of wild ungulates that utilize indigenous browse.
Abstract: Recent work to establish and produce multipurpose trees is reviewed in terms of their production and role in animal feeding systems. A great deal of variability was found in fodder production, with Acacia angustissima, Leucaena leucocephala cv. Cunningham, Gliricidia sepium and to some extent Cajanus cajan producing the highest fodder yields at both Domboshawa and Makoholi sites. However, with C. cajan the yields at Makoholi were much lower than at Domboshawa. Among the alternative species to the psyllid-prone L. leucocephala, A. angustissima has shown superior fodder productivity. Within the Leucaena genus L. esculenta subsp. paniculata (OFI 52/87), L. diversifolia subsp. stenocarpa (OFI 53/88), L. pallida (G2137) and to some extent L. pulverulenta (OF 84/87) have shown the greatest potential at both Domboshawa and Makoholi. Due to differences in chemical composition, the different fodder trees were variable in the extent to which they can be relied upon as feed resources in Zimbabwe. Notable differences were found in fibre content, in vitro dry matter digestibility, acceptability and intake by livestock and therefore, their potential in affecting animal productivity.
Abstract: The gradual decline in the ecological condition of natural pastures as a result of over-utilization and the application of insufficient management decisions, coupled with the detrimental effects of long-term drought, has left extensive areas of high potential grazing land in southern Africa in urgent need of restoration. However, due to the limited number of grasses currently available for rehabilitating and restoring the vast number of different habitats encountered, an extensive research programme was initiated aimed at selecting indigenous grasses suitable for restoration of denuded areas in the arid and semi-arid grasslands of southern Africa. Forty-five specimens ofDigitaria erianthawere collected and included in an investigation using 23 morphological characters in a principal component analysis to assist in the delimitation of ecotypes. Results presented here indicate are representatives of this sample of the species.Digitaria erianthacan be delimited into five ecotypes, each associated with a particular rainfall region and/or habitat condition. The second part of the paper deals with the mode of reproduction employed by eachD. erianthaecotype identified, where the degree of sexuality and reproductive potency of each ecotype was determined. Ecotypes DEBTUF, DEBSENW and DEKTUF displayed the best seed germination and the worst vegetative reproductive potencies. Ecotypes DEBSTOL and DEKSTOL proved to be better adapted for vegetative reproduction by stolon scions. The presence of ecotype variation, different reproductive modes and a wide geographic distribution imply that an extensive and diverse genetic adaptability for survival under fierce environmental conditions exists withinD. eriantha. Acquisition of hardier, more viable ecotypes may prove invaluable for the restoration and reinforcement of degraded land, especially areas subjected to extreme environmental stresses.
Abstract: With increasing interest in airborne and satellite-based sensors for mapping regional and global energy balance, there is a need to determine the uncertainty involved in aggregating remotely-sensed variables [surface temperature (Tk) and reflectance ([pi])] and surface energy fluxes [sensible (H) and latent ([lambda]E) heat flux] over large areas. This uncertainty is directly related to two factors: (1) the nonlinearity of the relation between the sensor signal and Tk, [pi], H or[lambda]E; and (2) the heterogeneity of the site. In this study, we compiled several remotely-sensed data sets acquired at different locations within a semi-arid rangeland in Arizona, at a variety of spatial and temporal resolutions. These data sets provided the range of data heterogeneities necessary for an extensive analysis of data aggregation. The general technique to evaluate uncertainty was to compare remotely-sensed variables and energy balance components calculated in two ways: first, calculated at the pixel resolution and averaged to the coarser resolution; and second, calculated directly at the coarse resolution by aggregating the fine-resolution data to the coarse scale. Results showed that the error in the aggregation of Tk and [pi] was negligible for a wide range of conditions. However, the error in aggregation of H and [lambda]E was highly influenced by the heterogeneity of the site. Errors in H larger than 50% were possible under certain conditions. The conditions associated with the largest aggregation errors in H were: - sites which are composed of a mix of stable and unstable conditions;- sites which have considerable variations in aerodynamic roughness, especially for highly unstable conditions where the difference between surface and air temperature is large; and- sites which are characterized by patch vegetation, where the pixel resolution is less than or nearly-equal to the diameter of the vegetation [`]element' (in most cases, the diameter of the dominant vegetation type or vegetation patch). Thus, knowledge of the surface heterogeneity is essential for minimizing error in aggregation of H and [lambda]E. Two schemes are presented for quantifying surface heterogeneity as a first step in data aggregation. These results emphasized the need for caution in aggregation of energy balance components over heterogeneous landscapes with sparse or mixed vegetation types.
Abstract: Ecosystem models have an important integrative role in allowing available data to be used to predict the potential impacts of changing climate or disturbance patterns. No such model has previously existed for the rangelands of Central Australia. In this paper we develop an ecosystem model for arid chenopod shrublands south of Alice Springs which takes account of inherent landscape heterogeneity and temporal variability, but which uses simple empirical relationships because of the small amount of available data on which to base any such model. The model is focused on the dynamics of simple herbage and shrub biomass pools; further breakdown of species composition is not attempted. Herbage dynamics are most dependent on grazing effects, as measured by distance from permanent watering points and average paddock stocking rate, and on the erosional status of the soil. Shrub dynamics are most sensitive to erosional status. The model is tested against historical Landsat MSS imagery transformed by a plant cover index. Correspondence is good, except on highly erosional sites which appear more dynamic than predicted. Further work is needed to quantify rates of soil erosion and deposition at different grazing levels, and of shrub growth and dieback in arid climates. Accurate means of assessing plant biomass from satellite imagery also require further development.
Abstract: Detailed reconstructions of vegetation structure are critical to understanding morphological and behavioral adaptations of Plio-Pleistocene African hominids. Savanna grassland habitats are often postulated as being influential in the evolution of many hominid adaptations (e.g., bipedality, foraging behaviors), yet the existence of this habitat type throughout the African Plio-Pleistocene has not been clearly established. Broad-scale reconstructions of hominid habitats as "savanna-mosaic" do not account for the fact that African grasslands may be classified into at least two different types: edaphic grasslands, which include seasonally flooded valley grasslands; and secondary grasslands, which include vast, relatively dry savanna grasslands. Though edaphic grasslands have existed for millions of years, it is unknown when secondary grasslands became widespread. The presence of specific micro-habitats, including secondary grasslands, at a number of hominid sites was investigated in this study through reconstruction of diet and habitat preference in five extinct bovid taxa that were contemporaneous with early hominids. To reconstruct diet in extinct taxa, morphological correlates of dietary preferences were identified through a comparative study of cranial form in extant bovids. Metric data from cranial material of the five African Plio-Pleistocene bovid taxa were compared with extant bovid results, which yielded information of specific feeding behaviors of the extinct taxa. Reconstructed diets suggest that the earliest taxa to inhabit secondary grasslands in East Africa wereConnochaetes gentryiandParmularius altidensat around 2Â m.y.a. It may therefore be inferred that secondary grasslands became prevalent at this time. This inference of secondary grassland development suggests that adaptations to this habitat type were not related to the origin of the Hominidae or to the evolution of bipedality in hominids. However, evidence suggests that this habitat type was influential in the evolution ofHomo erectus sensu latojust after 2Â m.y.a. in East Africa.
Abstract: Lake Njupi, 1 km east of Lake Nyos, on the Cameroon Volcanic Line, was formed by the damming of a local crustal depression. Two cores from Lake Nyos were analysed which penetrated sediments at the margin of the lake. The older deposits give an age of 3400 years BP and this date is proposed as a minimum age for Lake Njupi. Sedimentological, palynological and geochemical studies of a 2 m section provide an opportunity to reconstruct the Late Holocene environmental history. It is an organic-rich deposit (organic carbon up to 30%) with an abundant Silicospongia spicules fraction. An obvious sedimentary homogeneity is interrupted by 5 fine to coarse layers with sandy quartz and lignitic remains. Such inputs were denoted by carbohydrate maxima or sometimes by phenolic compounds. This study confirms the evidence of an arid period culminating between 2500 and 2000 yrs BP. This crisis began around 3000 yrs BP in the rain forest area of West Cameroon and also further to the south in Congo. Lake Njupi, situated today in a mostly grassland savanna environment known as the "Grass Fields", provides evidence for environmental changes from a mosaic of forest and savanna before 2500 years BP to a savanna characterised by high grass pollen contents (75 to 85%), with small islands of forest. The mountain vegetation characterised by Podocarpus and Olea capensis retreated around 2300 years BP at the time Elaeis guineensis (the Oil Palm) began its extension as a pioneer tree, later providing opportunities for its domestication by man.
Abstract: Several studies have demonstrated the potential of brightness indices, especially red band reflectance, from Earth resources satellite sensors to estimate vegetation canopy cover and biomass in semiarid savannas as well as in boreal forests. These studies showed that the relation between woody canopy cover and red reflectance varies with geographical location, season, and other factors. This paper models the relation between woody canopy cover and red reflectance, using two simple geometric canopy models developed by Li-Strahler and Jasinski, respectively. Model simulations show that the relation between woody canopy cover and red band reflectance is sensitive to changes in background reflectance, canopy reflectance, solar zenith angle, and topography, which together determine the intercept, slope, and linearity of the relation. The nwdel results provide a theoretical framework that serves as a guide for the most effective conditions for the use of reflectance measurements to estimate canopy cover to be selected a priori. It is predicted that woody canopy cover is best estimated with the use of red band measurements acquired at a solar zenith angle less than 30° in a season when the contrast between background reflectance and canopy reflectance is the largest during the year.
Abstract: This paper investigates the predictability of the soil erodibility factor (K) in the revised universal soil loss equation from soil clay content (C), the Naperian logarithm of the geometric mean particle size (DG) and organic matter content (OM), using a global dataset compiled from published studies. A multiple regression equation accounted for only 41% of the observed variance. Because of the large unexplained variance, an alternative procedure was explored to describe theK data in terms of the lower and upper bounds of the range of variation and the most probable value in this range. However, this approach did not provide sufficient information about the distribution of the observedK values. A procedure based on fuzzy logic and fuzzy mathematical theories was then developed, using the program FUZKBAS, which describes the frequency distribution of observedK values for a given soil, characterised byDG,C and OM, in terms of membership functions.
Abstract: Although vertebrate herbivory has existed on land for about 300 million years, the grazingadaptation, principally developed in mammals, did not appear until the middle Cenozoic about 30 million years ago. Paleontological evidence indicates that grazing mammals diversified at the time of the spread of grasslands. Recently revised fossil calibrations reveal that the grazing mammal guild originated during the early Miocene in South America about 10-15 million years earlier than it did during the late Miocene in the northern hemisphere. Carbon isotopic analyses of extinct grazers' teeth reveal that this guild originated predominantly in C3 terrestrial ecosystems. The present-day distribution of C3 and C4 grasslands evolved on the global ecological landscape since the late Miocene, after about 7 million years ago.
Abstract: It has long been recognized that alternative vegetation states may occur in terrestrial grazing systems. This phenomenon may be of great importance as small environmental fluctuations may lead to relatively sudden and irreversible jumps between vegetation states. Early theoretical studies emphasized saturation of herbivore feeding to explain multiple stable states and catastrophic behaviour. Recent studies on semi-arid grasslands and arctic salt marshes, however, relate catastrophic events in these systems to plant-soil interactions.
Abstract: We use a dynamic stochastic simulation model of forage, herbivores, predators and domestic livestock in the Machakos District of Kenya to address policies related to the multiple use of rangeland resources. The particular policy examined is that of switching from a traditional system, where commercial ranchers do not harvest wildlife herbivores, to one where ranchers are provided economic incentives to adopt multiple-use management of the range resource. Simulations using an adaptive controller indicate that the effects of the policy change on wildlife populations depend on the conditions of the ecosystem and, importantly, on ranchers' attitudes to risk. When forage is abundant, and game and livestock do not compete for food, the policy change leads to reduced wildlife populations, especially of the relatively more valuable species. This indicates that game cropping may not be more compatible with nature conservation than standard pastoralist practices. However, in periods of drought when competition for forage occurs, the policy change may dampen the decline in game populations, as risk-averse ranchers may decide to sell more cattle and harvest wildlife instead. Game cropping reduces wildlife populations, but increases their stability.
Abstract: Optimal economic policies with respect to stocking rate and season of grazing for an arid chenopod pasture type were derived for various starting states under a stochastic optimal control framework. Optimal policies were determined using decision criteria which involved either no discounting of future returns or a discount rate of 6%, and were further evaluated by analysing their long-run economic and ecological consequences. All optimal policies involved either year-long set stocking or destocking. Policies involving seasonal grazing or variable stocking rates were not economically viable at the specified cost levels. Optimal stocking rates increase with the level of forage biomass and the density of adult plants, but decrease with the level of either young or old seedlings when these provide an opportunity for regeneration of degraded range. Without discounting, pastoral use of this vegetation type can be both economically and ecologically sustainable. Long-run vegetation dynamics under this criterion are similar to those expected in an ungrazed community. However, land which is severely degraded is, for all practical purposes, not recoverable either by privately optimal grazing management or by complete removal of grazing. Discounting of future returns results in a more exploitative set of grazing policies and reduces opportunities for regeneration of degraded land. Pastoralism under this criterion is not ecologically sustainable although it is economically viable. The role of such analyses in pastoral management decision-making, and the implications of the results for policy with respect to administration of public rangelands, are briefly discussed.
Abstract: Modern soil samples from Western Uganda, from a range of ten plant communities belonging to five African phytogeographical regions and distributed along an altitudinal gradient from 650 m (grass savannas) to 4400 m (Afroalpine moorland) were analyzed for pollen content to define modern pollen/vegetation relationships. Correspondence analysis applied to the pollen counts (100 sites and 167 taxa) indicates four distinctive vegetation types arranged along an altitudinal gradient and thus a temperature one with respect to axis 1(contrast between montane and lowland vegetations), and along a physiognomical gradient (from densely structured to open vegetations) defined by axis 3. These results confirm the empirical interpretation proposed on the initial pollen data set and are in agreement with those previously obtained on modern or fossil pollen spectra from other African regions.
Abstract: Alteration of land use will continue to be the dominant driver of environmental change in the tropics for the next several decades. It can take the form of fundamental vegetation cover transformation, or of intensification of existing land use without substantial change in cover type. Atmospheric composition changes and resultant climate changes could become ecologically significant within the next century. Changes in atmospheric composition in the tropics are essentially the same as those in higher latitudes, despite differences in the source and sink strengths for trace gases. Such changes can affect the functioning of tropical ecosystems through several processes, principally those related to carbon and nutrient assimilation and their interactions. Atmospheric composition may also have an indirect affect on tropical ecosystems via its effects on the climate. Predicted temperature increases in the tropics are less extreme than at high latitudes, but could still be biologically significant, especially at the tropical margins. The structure and productivity of ecosystems of the subhumid and dry tropics are very sensitive to changes in water balance, which could be caused by a combination of changes in precipitation and temperature. It is presently not possible to predict rainfall changes at ecologically meaningful scales with any confidence.
Abstract: Soil particle size distribution and infiltration of water into the soil were measured in transects radiating from drinking troughs in the Kruger National Park. Soil particle size distribution remained relatively constant along the transects, making it unlikely that any gradients in the infiltration rate were the result of variation in the soil particle size distribution. Concentration of large herbivores around the troughs was indeed causing a negative impact on the infiltration rate of the soils, with implications for the rate of soil loss and the soil moisture regime.
Abstract: A 5 × 5 latin square design experiment using five male sheep (60-70 kg live weight) was carried out to assess the effects of supplementing poor quality veld hay with groundnut hay on intake, digestibility, rumen environment and digesta kinetics. Five diets were formulated in which veld hay with 1% urea was fed alone (Control) or together with 100 g, 200 g or 300 g groundnut hay (100Gnut, 200Gnut or 300Gnut, respectively) and groundnut hay fed alone (Gnut). The forages were coarsely chopped prior to feeding. The groundnut hay supplements increased total feed intake and in vivo digestibility of the diets (P < 0.05). Intake of veld hay tended to decline with increasing levels of groundnut hay in the diet. This decline in veld hay intake was however less than anticipated if there had been simple substitution. Supplementation increased the concentration of ammonia and volatile fatty acids in the rumen fluid, but had no significant effect on in sacco degradation of veld hay. Measurements using chromium-mordanted hay and Co-EDTA, showed that rumen digesta volume/pool size were not affected by supplementation, while digesta outflow rate was increased. In the absence of positive associative effects on digestion of the poor quality forage, the increase in digesta outflow rate was probably the mechanism facilitating an increase in feed intake.
Abstract: The amount and quality of inputs into soil organic matter will be altered by both climate and landuse change. The increase in growth of plants caused by increasing CO2 concentration implies not only potential increases in yields but also increases in plant residues. Simulation models using doubled CO2 levels predict global net primary productivity (NPP) to increase by 16.3%, over half of which will occur in the tropics. For tropical ecosystems increases in NPP will be dominated by the effects of elevated CO2, with water and nitrogen availability and temperature playing a less significant role. Phosphorus limitation may determine whether the potential for increased plant growth will be realized. The distribution of C3 and C4 species in the tropics could be affected by landuse change and estimates of yield increases will be dependent on their proportions. The allocation of photosynthate to the root will increase under elevated CO2, resulting in increased fine root dry weight and root length. Root sink strength and the turnover of roots and associated symbionts are critical knowledge gaps. Carbon: nitrogen ratios in tissues will increase resulting in decreased decomposition rates. The concentration of secondary compounds will be affected more by nitrogen limitations than a direct CO2 effect. Changes in lignin, tannin and polyphenol levels are more important in the decomposability of tropical litters than changes in the C : N ratios. Decomposition models will have to be altered to take into account changes in plant composition. The role of models in predicting the effects of management practice on long-term fertility is addressed.
Abstract: The effect of grazing cattle on vegetation was studied on a natural pasture during the rainy and dry seasons of 1995 in the Ethiopian highlands. The study used 0.01 ha plots, established on 0-4% and 4-8% slopes located close to each other at Debre Zeit research station, 50 km South of Addis Ababa. The grazing regimes were: light grazing stocked at 0.6 animal-unit-month per hectare (AUM ha-1); moderate grazing stocked at 1.8 AUM ha-1; heavy grazing stocked at 3.0 AUM ha-1; very heavy grazing stocked at 4.2 AUM ha-1; very heavy grazing on ploughed pasture stocked at 4.2 AUM ha-1; and a control of [`]no grazing'. Heavy grazing significantly reduced vegetative cover and biomass yields, especially on steeper slopes. Light to heavy grazing did not affect the botanical composition of the vegetation at both sites, but very heavy grazing resulted in species normally less preferred by animals dominating the botanical composition. Grazing did not have significant effect on ground vegetative cover on the 0-4% slope except at very heavy grazing pressure, but on the 4-8% slope even moderate grazing significantly reduced vegetative cover. Light to moderate grazing at the beginning of the dry period enhanced plant biomass productivity, while any grazing reduced plant productivity during the periods of reduced growth. Species richness increased with increasing grazing pressure compared with no grazing, but decreased sharply at very heavy grazing pressure. We concluded that there is need for developing [`]slope and time specific' grazing management practices, and to assess short and long term effects of grazing and trampling on vegetation.
Abstract: In 2 consecutive years using fresh batches of lambs, poor-quality veld (natural pasture) hay dominated by Hyparrhenia grasses (23 g crude protein per kg dry matter) was fed ad libitum either alone or with one of three herbaceous tropical legumes at the rate of 0.25 of total feed consumed. The legumes Desmodium uncinatum (Silverleaf desmodium), Stylosanthes guianensis (Oxley fine-stem stylo) and Macroptilium atropurpureum (Siratro) contained 143, 114 and 159 g crude protein per kg dry matter, respectively, and, to varying degrees, increased feed intake, digestibility, energy intake and nitrogen retention and reduced live weight loss (P < 0.05). Legume supplementation also marginally increased the fractional outflow rate of particles from the rumen from 0.015 to 0.020 per hour (P > 0.05). Average daily consumption of total dry matter was 465 g in animals given veld hay alone compared with 636, 681 and 754 g in those supplemented with D. uncinatum, S. guianensis and M. atropurpureum, respectively. The daily intake of the basal veld hay was significantly increased (P < 0.05) by M. atropurpureum (574 g) but not by S. guianensis (514 g) and D. uncinatum (480 g). Average apparent digestibility coefficients of organic matter were 0.394, 0.440, 0.466 and 0.464 with veld hay alone, veld hay/D. uncinatum, veld hay/S. guianensis and veld hay/M. atropurpureum, respectively. Proportions of metabolisable energy intake relative to that required for maintenance were 0.61, 0.96, 1.11 and 1.20 in animals given veld hay alone and with D. uncinatum, S. guianensis and M. atropurpureum, respectively. Average calculated microbial nitrogen production was 3.46, 5.33, 6.07 and 6.58 g per day, respectively, in animals given veld hay alone and with D. uncinatum, S. guianensis and M. atropurpureum. Respective values for nitrogen retention and live weight gain were -1.44, 0.29, 0.70 and 1.06 g per day, and -98, -32, 0 and -8 g per day. Relative to nitrogen consumed per day, animals given D. uncinatum tended to excrete more nitrogen in their faeces (0.83) than those given S. guianensis and M. atropurpureum (0.71) probably due to a higher content of acid detergent insoluble nitrogen in D. uncinatum (608 g per kg total nitrogen) than in the other legumes (273 to 285 g per kg total nitrogen). Overall, M. atropurpureum appeared to be the best legume supplement for veld hay, followed by S. guianensis.
Abstract: The effect of grazing pressure on infiltration, runoff, and soil loss was studied on a natural pasture during the 1995 rainy season in the Ethiopian highlands. The study was conducted on 0.01 ha plots established on sites with 0-4% and 4-8% slopes at the International Livestock Research Institute (ILRI) Debre Zeit research station, 50 km south of Addis Ababa. The grazing regimes were: light grazing stocked at 0.6 animal-unit-months (AUM) ha-1; moderate grazing stocked at 1.8 AUM ha-1; heavy grazing stocked at 3.0 AUM ha-1; very heavy grazing stocked at 4.2 AUM ha-1; very heavy grazing on ploughed soil stocked at 4.2 AUM ha-1; and a control with no grazing. Heavy to very heavy grazing pressure significantly increased surface runoff and soil loss and reduced infiltrability of the soil. It was observed that fine textured soils were more susceptible to trampling effects than coarse textured soils, and that reduction in infiltration rates was greater on soils which had been tilled and exposed to very heavy trampling. The problems of high runoff and erosion rates on the upper slopes is likely to be exacerbated by the fact that during the rainy season higher grazing pressure is exerted on the upper than lower slopes. Sediments produced from the highlands, which form headwaters of major rivers in the region, are likely to pollute streams and lakes and pile up on bottom-lands, in stream channels, and in reservoirs. With some modifications, the plot design presented here can be used for assessing livestock impacts on natural resources on different landforms at large scales such as watersheds. How the same amount of livestock mass dispersed by different livestock species impacts on the grazing lands needs to be studied further.
Abstract: Rainfall simulation studies on rangeland in the Ntondozi area of Swaziland showed that soil loss decreased exponentially with increasing vegetation cover. Vegetation exerted an important hydrological control by increasing the infiltration capacity of the soil which, in turn, influenced the time to and duration of runoff. The expected effects of vegetation on soil protection and soil strength were not demonstrated. Instead, the amount of soil loss occurring in an individual storm appeared to depend on the supply of loose material on the surface which could be transported by the runoff.
Abstract: Although it is widely recognised that gully and sheet erosion threaten sustained agricultural production in much of Swaziland, very little information is available about the current status of erosion and whether the situation is worsening. Since the country is very active geomorphologically, it is not clear whether an inherently erodible environment or human impact is the major causal factor explaining the severity and spatial distribution of erosion. Soil erosion is associated particularly with deeply weathered saprolite but few studies have been made on applied issues related to the physical and chemical properties of this material.
Abstract: An overview is given of pasture evaluation and improvement of existing germplasm in South Africa. The literature is reviewed from the perspective of upgrading the natural vegetation, reclamation of eroded soils, defining constraints, supplementation on cultivated pasture and improvement of low quality forages. Intake studies have also been emphasized because of the profound influence of intake on grazing capacity and as a distinguishing factor when screening cultivars and new introductions. Although temperate species which can be cultivated in the higher rainfall areas or under irrigation are discussed, the review largely concentrates on subtropical grasses and legumes that are drought tolerant and adapted to relatively poor soils.
Abstract: The structural and functional attributes of the herbaceous sward were contrasted under three land uses (commercial cattle farms, communal cattle lands and private game farms) and two catenal positions in a region of relatively uniform soils and climate. Catenal position had no significant effects on the nature of the sward, whilst land use did. Plant density, basal area, proportion of annuals and proportion of palatable and unpalatable species was highest in the communal cattle lands relative to the other two land uses. They were also characterised by the smallest tufts for both annuals and perennials. The proportion of species with intermediate palatability was lowest in communal cattle lands. Commercial game farms had the lowest density of tufts, basal area and proportion of unpalatable species, as well as the highest proportion of perennial species, and species of intermediate palatability. Attributes of the herbaceous sward in commercial cattle farms were generally intermediate between the above two extremes.
Abstract: The loss of resilience in systems characterised by multiple equilibria is indicated by a discontinuous change in the state of the system, or the transition from one locally stable state corresponding to a particular mix of species to another state corresponding to a different mix of species. The resilience of the system (the state of the range in this example) may be influenced by the management regime through its impact on the response to disturbances. The paper shows that optimal management of an event-driven system should be sensitive to the opportunities created by such events.
Abstract: Within the scope of the HAPEX-Sahel experiment, the hydrological functioning of two small nested catchments was studied at two different scales: the plot scale (of the order of 100 m2) and the catchment scale (0.2 km2). At local scale, four runoff plots were set-up on the typical soil surface conditions observed on the catchments (plateau bare soil, two plots on fallow grassland) and an additional one was installed on a millet field. soil moisture investigations at the plot scale have shown that infiltration was limited between 0.6 to 2 m deep on three sites, but was deeper than 3.4 m on the most pervious site (millet). The maximum water storage on all the sites was found to be reached at the maximum activity of the rainy season (late August), and not at the end of the season. During the dry months, the soil was fully dried off by evapotranspiration, resulting in the absence of inter-annual soil water storage. No influence of vegetation cover on runoff was observed on the fallow sites, but runoff generation was found to be very sensitive to tillage on the millet field. The parameter Pu, calculated from a rainfall hyetograph and defined as the rainfall depth that can actually produce runoff, is shown to be relevant to compute runoff on untilled soils, as it explains more than 87% of the variance in runoff depth. On tilled soils, it is necessary to take into account additionally the temporal evolution of the soil surface, especially the days after weeding operations. Simple linear relationships were derived to compute runoff depth from Pu on the plots for the most typical soil moisture conditions observed, and modified SCS equations have been derived for the catchments. Using the linear equations derived at the plot scale in a simple, empirical, semi-distributed model lead to formulate the assumption that the partial source area concept applied on the catchments. Analysis of discharge data at the catchment scale highlights that seepage through the bottom of a gully between two gauging stations leads to the abstraction of non negligible volumes of water. Moreover, the water totally infiltrates in a spreading zone downstream from the outlet of the largest catchment showing that discontinuities occur in the surface water transmission within a catena. Such discontinuities constitute a major problem for the concern of aggregation of hydrologic processes.
Abstract: A field study was carried out in 1989 to quantify the effects of grazing on soil and plant properties in aLeymus chinensisgrassland on the Songnen plain of north-eastern China. Five intensities of grazing were examined using 15 sample plots in each. Soil bulk density and pH increased with grazing intensity, while soil moisture and organic matter decreased. As the canopy covers of more palatable plants, such asL. chinensisand legumes, diminished, those of less palatable plants, such asSuaeda corniculataandAeluropus littoralis, increased significantly. Changes in floristic composition were reflected primarily in decreases in the numbers of perennial mesophytes (such asL. chinensis, Calamagrostis epigeiosand legumes), and increases in annual grasses (especiallyChloris virgata) and halophytes (such asS. corniculataandPuccinellia tenuiflora), with halophytes becoming dominant under heavy grazing. Species diversity was greatest at the intermediate grazing intensities and least in the lightly grazed plots. Plant community biomass decreased significantly as grazing intensity increased--by as much as 47% (above-ground) and 53% (below-ground). Overgrazing appears to be the principal reason for deterioration of this grassland.
Abstract: The continued threat to the world's land resources is exacerbated by the protracted food crisis in sub-Saharan Africa. Per capita food production continues to decrease even though this region compares favorably with other tropical regions in terms of climate and soil resources. The main determinant of this situation is the widely recognized need for an enabling policy environment that favors smallholder rural development. However, there are two other key determinants to food security and environmental sustainability in Africa that have not received sufficient attention in the past and are the focus of this contribution: (1) the need to tackle soil fertility depletion as the fundamental biophysical constraint to food security and (2) the need for more intensive and diverse land use, based on the domestication of indigenous trees to produce high value products while increasing agroecosystem resilience. Approaches that include these three issues will transform smallholder farming in Africa into productive and sustainable enterprises and will contribute greatly to food security and environmental conservation, in a win-win situation.
Abstract: Three experiments, each of a 5 × 5 Latin square design, were carried out using sheep to assess the effect of supplementing poor quality natural pasture (veld) hay with graded levels of napier or groundnut hay on intake and digestibility. In Expt 1, napier hay was fed at 0, 100, 200, 300 g/day or ad libitum. In Expt 2 the same levels of feeding were used with groundnut hay, while in Expt 3 napier and groundnut hay were each fed at 0, 150 or 300 g/day to enable a direct comparison of the two supplemental forages. All the forages used were chopped to a particle size of about 1 cm prior to feeding. The veld hay was supplemented with 1 percent urea and was always offered ad libitum. The forage supplements were fed separately. In all the experiments, the forage supplements increased total feed intake (P < 0.05). In Expt 1, total feed intake was greatest with the daily supplement of 300 g napier. The forage supplements did not reduce intake of veld hay. After correcting for differences in the digestibility, intake of veld hay was always greater than anticipated if there had been simple substitution. Although the forage supplements increased digestibility, differences were only significant (P < 0.05) between the 0 and 300 g forage supplemented diets. In all the experiments, nitrogen retention was also increased by supplementation (P < 0.05). Response to supplementation was similar between groundnut and napier. These results demonstrated that small amounts of forage supplements can be effective in increasing nutrient intake when animals consume poor quality forages.
Abstract: We tested the potential of artificial neural networks (ANNs) as predictive tools in ecology. We compared the performance of ANNs and regression models (RM) in predicting ecosystems attributes, with special emphasis on temporal (interannual) predictions of functional attributes of the ecosystem at regional scales. We tested the predictive power of ANNs and RMs using simulated data for six functional traits derived from the seasonal course of the normalized difference vegetation index (NDVI): the annual integral of the NDVI curve (NDVI-I), the maximum (MAX) and minimum (MIN) NDVI, the date of the MAX NDVI (DM) and the date of start (SGS) and end (EGS) of the growing season. For one of these traits (NDVI-I), we also generated a set of data that incorporated the effects of the state of the system in previous years (inertial effects). Even simple non-linearities in the actual functional form of the relationship between environmental variables and ecosystem attributes preclude a precise prediction of these attributes when the rules are not explicit. That was evident for predictions based on both ANNs and RMs under absolutely deterministic conditions (error-free scenario). Non-linearities in the simulated traits of the NDVI curve derive from multiplicative terms in the models. Under the presence of these non-linear terms, a different aggregation of the driving variables (monthly vs. annual or quarterly climatic data) reduce substantially the ability of both RMs and ANNs to predict the independent variable. For the six traits analyzed, the ANNs were able to make better predictions than RMs. The correlation between observed and predicted values of each of the six traits considered was higher for the ANNs than for the RMs. ANNs showed clear advantages to capture inertial effects. The ANN used was able to use previous year information on climate to estimate current year NDVI-I much better than the RM that used the same input information.
Abstract: Selectivity by cattle for the more important species in their diet and the effect of stocking rates on species selectivity were determined in spring, summer, and fall-winter during a 3-year period. The selection index ((%diet - % available in field)/(% diet + % available in field)) × 10 was calculated. Grasses were classified as preferred:Chloris castilloniana,Digitaria californica,Sporobolus cryptandrus, andPappophorum philippianum, the latter only in spring and summer; proportional:Panicum urvilleanum; variable:Setaria leucopila; and rejected:Aristidasp. Most of the woody species were avoided in summer and had higher selectivity in spring and fall-winter. Several species tended to be more highly selected as stocking rates increased.
Abstract: Runoff and interrill erosion are significantly affected by amount and type of cover and growing season on semi-arid rangelands. However, little is known about hydrologic and erosion processes in semi-arid rangelands of northern Mexico. Runoff rates and interrill erosion were measured by using simulated rainfall within a shortgrass community in five grass cover classes during the growing and dormant seasons. Differences in runoff and interrill erosion were found between classes of grass cover during both seasons. Runoff and interrill erosion are affected mostly by basal cover of grasses, aerial cover of grasses, organic matter, soil water content, sand content and percentage of cover by rock and gravel.
Abstract: A formal survey was conducted in 1993 to identify small ruminant production systems and constraints in the Beka'a Valley of Lebanon. Cluster analysis revealed three basic production systems. Cluster 1 consisted of medium size (200 head) sedentary village flocks comprised of > 70% sheep with rangelands supplying less than 20% of their annual diet. Cluster 2 consisted of large migratory flocks (400 head) of sheep and goats in roughly equal numbers. The flocks owned by landless farmers made heavy use of rangelands (> 45% of annual diet). Cluster 3, with medium size (200 head) mixed flocks, made moderate use of rangelands, 30% of annual diet. The results indicated seasonality in production components and low productivity in all three clusters. Supplemental feeding and grazing reflected differences in feed sources used among clusters. Hand-feeding, however, accounted for 85% of diets between December and March. Small ruminant production contributed an average of 70% of farmers' income in all clusters, supplemented by off-farm activities (19%) and crop production (11%). Farmers' perception of the major constraints to sheep and goat productivity were similar among clusters. They include: (1) health problems, namely infective diseases and parasites, and lack of veterinary services, (2) feed availability, in particular expensive feed supplements, (3) poor marketing of animal products. Future research is needed in the following fields: (1) full-screening of all diseases to develop an adequate health program, (2) on-farm feeding trials to optimize feeding systems, (3) range and grazing research to determine proper stocking rates and season of use, (4) bioeconomic analysis and marketing research to asses the future viability of the small ruminant sector.
Abstract: Perennial grass responses to cattle grazing under a year-long continuous and four-pasture, one-herd grazing system, both with 20, 50 and 80% removal of grass annual production were evaluated from 1990-94. Live basal diameter, density and frequency of occurrence of each species were estimated on 1 m2quadrats placed along 30 m fixed line transects. Based on these data, total live basal cover, botanical composition by cattle selectivity category and diversity of grass species were derived. Data from the first 4 years of the study suggest that rotational grazing (80% removal) resulted in a significant decrease (p< 0·05) in total live basal cover, proportion and frequency of occurrence of the preferred grasses. Significant positive effects on those response variables were observed under rotation (50%) and continuous (20%) grazing.
Abstract: Polycultural agroecosystems, such as rangelands, are too complex and poorly understood to permit precise numerical simulation. Management decisions that depend on behavioral predictions of such ecosystems therefore require a variety of knowledge sources and reasoning techniques. Our approach to designing a computer system that provides advice concerning such ecosystems is to incorporate various reasoning paradigms and apply whatever paradigm is most appropriate to each task arising in the advice process. This approach is based on a particular process description of expert human problem solving that uses four different reasoning paradigms: model-based reasoning (MBR); case-based reasoning (CBR); rule-based reasoning (RBR); and statistical reasoning. The process description is implemented in CAse-based Range Management Adviser (CARMA), a computer system for advising ranchers about the best response to rangeland grasshopper infestations. CARMA attempts to emulate the human ability to integrate multiple knowledge sources and reasoning techniques in a flexible and opportunistic fashion. The goal of this approach is to enable computer systems to optimize the use of the diverse and incomplete knowledge sources and to produce patterns of reasoning that resemble those of human decision-makers.
Abstract: Smoke is now widely recognized as a germination cue for fire-dependent and non-fire-dependent plant species. Although the identity of the stimulant(s) and its mode of action remain unknown, it needs to be established whether burning or heating of all plant materials generate the active compound(s). In view of the variation in fire intensity in the wild it must also be established at what temperatures the active compound(s) is produced. Heating dry Themeda triandra leaves at a range of temperatures showed that the active component(s) is produced between 160 and 200°C. At higher temperatures activity is lost, apparently due to volatilization of the stimulatory compounds. Aqueous smoke extracts prepared from a range of plants, and extracts prepared by heating agar and cellulose, contained compounds that stimulated the germination of light-sensitive lettuce seeds. Chromatographic evidence obtained by thin-layer chromatography and high-performance liquid chromatography suggest that the same active compound(s) is produced from T. triandra leaves, agar and cellulose used in this study.
Abstract: Potential cattle production in the plain of Mendoza was estimated from the dependable rains (f 0·80/mean) and the rain-use efficiency (RUE) factor. Herbaceous and browse RUE factors were derived from data obtained from the African Sahel, which has ecological and range conditions similar to the study area. Grazing livestock population and total carrying capacity were equivalent. Through the incorporation of available production technology, cattle productivity could be 70% above the actual productivity. The use of RUE factor gave carrying capacities that vary from 16 to 100 ha per animal unit, figures in line with values empirically used in the study area.
Abstract: Alien plants invade many ecosystems worldwide, often having substantial negative effects on ecosystem structure and functioning. The apparent complexity of invasions has impaired the development of a predictive framework of alien plant spread. Such a framework requires both a conceptual understanding of the ecology of invasions and appropriate modelling tools. We demonstrate, using a simple conceptual model and illustrative examples from the literature, that a predictive understanding of invasions can be established. Potential modelling tools are reviewed by categorizing models of plant spread as either simple-demographic, spatial-phenomenological or spatial-mechanistic, based on the model's data inputs and outputs. The assumptions, predictive potential, knowledge and data requirements of these modelling tools are discussed in the context of selecting the most appropriate alien plant spread model for a given case.
Abstract: The discussion about rangeland degradation in African pastoral systems has so far largely been based on the conventional theory of [`]carrying capacity'. This paper argues that the carrying capacity concept and the related [`]destocking policy' as a management strategy to increase productivity and to protect rangelands from degradation are of little applicability in African pastoral systems. They ignore the spatial and temporal variability in primary biomass production, as well as the effect of spatial and temporal fluctuations in forage quality on animal production. A case study from Northern Kenya shows that the rapid decrease in forage quality in the dry season is the crucial factor determining livestock production and pastoral land use patterns. The results of a principal component analysis indicate that rangeland degradation does not occur in most of the range units considered because grazing is limited to a short time span in a year. In contrast, the few range units with a good potential are susceptible to degradation when formerly mobile pastoral households become sedentary and overuse these key resources. An example from Marsabit District, Northern Kenya, shows that carrying capacity figures overestimate the potential livestock-supporting capacities. Destocking rangelands would result in a serious decline in the productivity of pastoral production systems and is not likely to halt rangeland degradation. It is concluded that land use policy interventions in Northern Kenya should not focus on the manipulation of absolute livestock numbers, but rather on the optimal distribution of animal abundance in space and time.
Abstract: Primary production on terra rossa and brown rendzina soils on the hills of the Galilee in Israel is severely restricted by nutrient, mainly phosphorus, deficiency. The purpose of this study was to investigate the residual effects of a single application of P fertilizer and the long-term role of P in the production and botanical composition of herbaceous vegetation. A fertilizer trial on brown rendzina soil (Lithic Haploxeroll) with P and N treatments was established and monitored for 6 years. Phosphate fertilization consisted of a single surface application of 45 or 90 kg P ha-1 as enriched superphosphate (25% P2O5). In the first year, yield of herbaceous vegetation in P fertilized plots increased fourfold compared with the control, and about two-fold during the following 5 years. In the sixth year, production in the fertilized plots diminished, but was still significantly higher than in the control plots. In addition, there was a large increase in the legume cover that improved the nutritional quality of the range vegetation. Concentration of P and N in the plants as well as total P and N uptake, increased significantly. Available P concentration in the soil increased two- to five-fold in the year after fertilizer application and a strong residual effect persisted for up to 5 years. A single application of P (45-90 kg ha-1) on brown rendzina soil in the Galilee raised the total 5-year primary production from 780 g m-2 dry matter in the control plots to 1840-2100 g m-2 dry matter in the fertilized plots. Forage quality was also improved for an extended period of over 5 years. Phosphate nutrition was shown to be the key to raising productivity of these soils. The long duration of the effect increases the chance that infrequent P fertilization on these rangelands will be economically feasible in certain conditions.
Abstract: This paper considers the nature of riparian vegetation in south west Western Australia and issues relevant to its management. Riparian forests and vegetation in Western Australia are generally less species rich than adjacent upland communities. This correlates with the few studies in other parts of Australia and South Africa, but is in contrast with the situation in Europe. Structurally, the vegetation is usually more complex than that of upland areas. Riparian vegetation has been severely degraded in many parts of Western Australia and plant species biodiversity is threatened by a number of environmental problems. Foremost among these are clearing, grazing, salinization, weed invasion, urbanisation and frequent burning. The relative importance of these problems is related to the geographical area in question. Management practices to maintain biodiversity need to be tailored to the conditions of each particular area. In relatively undegraded areas an integrated management approach, especially in relation to weeds, is likely to provide the best outcome. In more degraded areas, biodiversity is greatly decreased from that of natural systems. The priority in these areas should be to enhance the value of the system through revegetation and moderation of degrading influences. A primary need in this area is a data-bank of recruitment requirements of suitable riparian plant species to enable their re-establishment on riverbanks.
Abstract: Data on fuelwood harvesting, construction timber requirements and the number of people in two settlements in the Eastern Transvaal Lowveld (Athol and Welverdiend) is combined with woody biomass information in the form of a numerical model. This allows the investigation of the relationship between woodland supply and local wood demand. The effects of uncertainty in primary data collection, and of possible changes to the harvesting pressure on the woodland are illustrated. Given the assumptions of the model, current harvest rates around Athol are shown to be sustainable, although the increase in wood demand resulting from an estimated population growth rate of 3% will cause woodland stocks to decline after 20 years. The Welverdiend model shows a marked imbalance between available supply and demand. Continuation of current harvesting practice would lead to severe deforestation within 15 years. The investigative scenarios presented emphasize the advantages to be gained from rapid reduction in woody biomass harvesting, resulting in better long term sustainable harvests. The significant changes in per capita fuelwood harvest would however seriously impact on households, and it is thus important that the models be utilized within a much broader holistic framework in the development of solutions appropriate to local areas.
Abstract: Fast growing Eucalyptus trees are grown in Congo for industrial purposes, on a very poor sandy savanna soil. The sustainability of such land use is questionable, particularly regarding nutrient availability. Among the lacking nutrients, nitrogen (N) deserves special attention as N status is supposed to be improved by N-fixing trees. To assess N changes in tree plantations, N cycling was studied in Eucalyptus and Acacia stands and compared to the native savanna. Nitrogen accumulation in vegetation and soil, together with N flows in the ecosystem, were estimated. It was assumed that the difference between N amounts in Acacia stands and in Eucalyptus stands was an estimate of the amount of N fixed symbiotically in the former. The results showed that 800-1000 kg N ha-1 were accumulated during 7 years in Acacia stands. Nitrogen fixation was higher in Acacia auriculiformis than in Acacia mangium. Nitrogen cycling through litter fall was high in Acacia stands, up to 170 kg ha- I per year, and low in Eucalyptus and Pinus stands. However, in Eucalyptus stands, slow litter decay and reduced N release from decaying litter resulted in a relative accumulation of organic N in the forest floor. Decrease in N content was observed in organomineral fractions under the trees. In top-soil (0-10 cm) N mineralization was higher in tree stands than in savanna and total N decreased significantly under 7-year-old Eucalyptus. Under older Eucalyptus, decreasing N content of organic matter was shown by the increase in C/N ratio. Under Acacia, soil N increase was significant in the older stands studied but not in the younger ones, and fixed N accumulated in trees and in the forest floor first. The implications of these observations are discussed.
Abstract: Higher ocean productivity has often been proposed to explain lower atmospheric carbon dioxide during the last glacial episodes. But recent consideration of marine cores from different areas show that higher local productivity can be postulated for interglacials as well as for glacial periods. Based on the detailed study of two piston cores from the northwest Africa upwelling system, the results presented here, including [delta]18O stratigraphy, organic carbon contents and fluxes, Ti/Al ratios and grain size measurements, clearly indicate that the two cases of sedimentary records can even co-exist within a single upwelling system. This regional heterogeneity is presumably attributed to combined wind stress and sea-level changes that would induce different sedimentary records in the northern and in the southern part of the system. These results emphasize the importance to understand and to model the response of the main kinds of highly productive oceanographic regional systems which are spatially heterogeneous due to complex continent-ocean interactions, or to the presence of mobile hydrodynamic heterogeneities. For such an understanding it is not necessary to acquire a huge amount of core data throughout the world ocean, but to increase the density of cores as well as the regional-scale modelling efforts in systems such as coastal and equatorial upwelling areas, and the migration areas of the southern polar front.
Abstract: The [`]facts' about environmental problems are usually left to the scientists to discern. There is increasing recognition, however, that scientific reality is not generated from objective study but rather, it is socially constructed. Such a view gives greater credibility to alternative, competing perspectives. This paper presents various discourses on land degradation in the Uluguru Mountains, Tanzania. It considers the foundations of, and influences upon, perceptions and assessments of degradation made by colonial administrators, scientists and local people. It also examines the way power is used to legitimise different knowledge claims.
Abstract: The overriding question that this article addresses is: What are the immediate and future costs of land degradation for a nation? The objectives of the analysis are to find appropriate measures to express the national level costs of land degradation, and suitable methods to estimate such measures. Furthermore, the aim is to document and interpret the results of existing studies. To meet these objectives, a set of 12 studies from Sub-Saharan Africa (SSA) is reviewed, using a consistent, cross-study analytical framework derived from the objectives above. With regard to measures of the cost of land degradation, this article identifies ten different dimensions, which illustrate the importance of qualifying statements about "the costs of land degradation" by rigorous clarification of what type of measure has been used. Furthermore, with regard to methods of deriving costs of land degradation, this article illustrates a spectrum of approaches. One sub-group has used a replacement cost approach, while a productivity loss approach has been used in the majority of the studies reviewed. The latter approach is further sub-divided into five different categories ranging from the most informal to the most rigorous. It is evident that very few original estimates exist of soil loss yield decline functions in Sub-Saharan Africa. Hence, some of the basic work in this area is "recycled" for use in areas that may exhibit quite different conditions. Finally, with regard to study results, there is considerable variance of cost estimates pertaining even to the same country. These differences can be explained, however, and a rational assessment allows a choice of the most appropriate results. Results across countries are reasonably well clustered in terms of their productivity impact per soil loss unit. With local knowledge of soil conditions, but in the absence of local yield loss data, this provides a useful interval of reasonable assumptions. As one would expect, the national costs of land degradation vary considerably across countries. This sometimes leaves room for considerable investment in soil and water conservation, but should not invoke images of a rapidly approaching doomsday.
Abstract: In the Sahel of West Africa, the productivities of rangelands, croplands and livestock are inextricably linked. Cattle, sheep and goats graze rangelands and crop residues, and their manure/urine is used to fertilize crops. Rangelands provide important feeds during the manuring period, resulting in a net nutrient transfer from rangelands to croplands. This paper examines the sustainability of nutrient transfers in integrated rangeland/cropland systems of the Sahel by examining the impact of grazing on rangeland vegetation structure and floristic composition, the impact of livestock on nutrient balances of rangelands and croplands, and the role of livestock in offsetting nutrient deficits through manuring. Rangeland nutrient balances are in equilibrium (inputs = offtakes) whereas croplands lack the internal capacity to replenish nutrient offtakes in grain (as food) and crop residues (as feed). Although soil nutrient mining is of general concern for the Sahel, local management practices of some farmers (e.g. corralling animals overnight on fields between cropping seasons, use of fertilizers) offset cropland nutrient xD;deficits. The number of additional livestock, and their feed requirements needed to supply sufficient manure to offset cropland nutrient deficits, depend on rangeland and cropland productivity, livestock production goals, and management strategies of farmers. Livestock must be managed so they do not deplete the nutrient supply of rangelands in order to increase the manure supply for improving cropland productivity. Sustained rangeland productivity in the Sahel will depend largely on producing alternative feeds derived mostly from croplands. Land use and tenure policies that inhibit livestock mobility and, therefore, farmers 039; access to the manure of pastoralists herds, will greatly undermine the resilience of Sahelian rangelands, and increase the need for other external nutrient inputs such as fertilizers to prevent declines in soil fertility and crop yields.
Abstract: The dynamics of soil water was evaluated in different landscapes during four growing seasons in a semi-arid grassland of Patagonia. At intervals of 60-90 days, the (gravimetric) soil moisture content was determined at four depths in uplands and north-eastern slopes of grazed and ungrazed areas. Climatic data (precipitation and maximum and minimum temperature) were recorded daily. Maximum and minimum soil temperature per sampling interval was also registered. Soil moisture was strongly influenced by the recharge through precipitation. Most precipitation occurred during autumn and winter and the highest soil moisture values were measured at the end of the winter (September) after snowmelt. The occurrence of wet and dry years was observed during the study period and, as occurs in other semi-arid ecosystems, it may be attributed to the amount of rain delivered in events exceeding 10 mm. Soil moisture varied spatially with the topographic site while maintaining a similar seasonal pattern. North-eastern slopes were drier than uplands. These differences may be traced back to the protection of these slopes from the strong westerly winds prevailing in the area that results in a more favourable thermic balance as compared with uplands. No grazing related effects on soil moisture were observed in this study. This fact may probably be explained by a variety of factors involved in the partition of soil water between transpiration and evaporation. These results show north-eastern slopes to be sensitive places for land degradation which eventually may have a restricted restoration potential imposed not only by physical changes in the upper soil but also by limited soil water availability.
Abstract: SPUR (Simulation of Production and Utilization of Rangelands) is a physically-based model designed to simulate the complexity of rangeland ecosystems (Wight and Skiles, 1987). Results of extensive validation testing in Texas indicated a need to modify the model to improve submodel integration and procedural guidelines. A description of the modified model (SPUR-91) is provided. A sensitivity analysis was conducted, examining the influence of changes in model output corresponding to perturbations made to individual input parameters. The model was then extensively validated using a Texas data set composed of simultaneous measurements of hydrology, plant, livestock, and meteorological parameters. Results of validation testing of SPUR-91 confirmed that the model: (1) predicted initial soil water content within 3% of observed; (2) predicted evapotranspiration, even under very low cover conditions, within 1% of observed; (3) provided a good correlation of temporal fluctuation (R = 0.72) of observed herbaceous production, the observed 4-year mean live standing crop for the major individual species was predicted within 1-13%; (4) could produce a determinant-type growth curve to approximate the long-term response of shrubs and trees; and (5) responded to management (grazing, vegetation manipulation) in a manner consistent with observations. A discussion of why modifications to SPUR improved the performance of SPUR-91 is presented.
Abstract: Chromolaena odorata (L.) King & Robinson, a perennial, semi-woody, herbaceous scrambling shrub of neotropical origin, is an invasive weed of agriculture, forestry and conservation in many parts of the world. Although considered beneficial in parts of central Africa, in southern Africa it rapidly degrades indigenous forests and savannas and is a weed problem in commercial plantations. Research has shown that C. odorata is easily killed by herbicides applied to the foliage, stumps or to the soil at the base of the plant, or by mechanical or cultural means. A cost-effective integrated control and management strategy has been developed in South Africa which incorporates rehabilitation by oversowing or natural succession and makes provision for judicious follow-up control. Notwithstanding these efforts, the spread of the weed has not been curbed. Successful biological control remains the only viable solution for reducing the current and potential impact of C. odorata in southern Africa.
Abstract: Sediment composition, grain size and clay mineral record of a high-resolution sediment core from the continental slope off Namibia was investigated to gain information on the deposition of terrigenous matter in this part of the Southwest African continental margin during the last 18 k.y. The depositional processes involved are fluvial input by the Kunene River and eolian input from the Namib and Kalahari deserts, each supplying characteristic mineral suites. During low sea level, erosion of the exposed shelf yields additional material. The amount of eolian or fluvial matter depends on the strength of the transport process, which is a function of aridity or humidity of the source area, thus allowing paleoclimatic interpretations. Arid conditions prevailed during a low sea level from 18 to 15 ka and unconsolidated shelf sediment was mobilized and supplied to the slope by short-distance transport by southerly winds. A dramatic increase in the accumulation of terrigenous sediment is recorded from 15 to 10 ka without major changes in sediment composition, which is attributed to increased runoff of the Kunene River and fluvial erosion of shelf sediments. This period coincides with a strengthening of the monsoonal system during a precessional minimum, which is observed in numerous sites in Central Africa and indicates an intensified influence of the monsoon at the Kunene headwaters. A distinct shift in clay mineralogy towards river-derived material marks a second period of increased river runoff--during high sea level--from 9 to 5 ka, indicating maximum humidity in the source area from 6 to 5 ka. This corresponds to the Holocene climatic optimum observed in the arid belts of Northern Africa. The present balance between fluvial and eolian input was reached approximately at 4 ka.
Abstract: Mature Angora goats were pastured in plots supporting eight selections of grasses used for rangeland reclamation in the northern Great Basin. The objectives were to establish the relative preferences of goats for these forages at two stages of phenology (late-boot and dormant) and relate selective preferences to forage production and quality attributes. Numbers of each selection visited, total bites harvested, and percent plant weight utilized characterized diets of goats. Forage attributes included herbage production, CP, and IVOMD. Crested wheatgrass selections (cultivars [`]Nordan' and [`]Hycrest II') were consistently ranked as preferred forages at both stages of phenology, with the two receiving 80 + % of the grazing activity. Cultivars [`]Magnar' and [`]Trailhead' basin wildrye, [`]Goldar' bluebunch wheatgrass, and [`]Bozoisky' Russian wildrye were ranked as indifferently foraged upon, and a numbered selection (No. 9021076) of thick-spiked wheatgrass and the closely related cultivar [`]Secar' Snake River wheatgrass ranked as avoided. Variation in herbage production among selections was significantly and positively correlated with visits to selections and total bites but not well enough to be an accurate predictor of selectivity. Indices of forage quality (CP and IVOMD) were not significantly correlated with selectivity. Adequate livestock performance can probably be attained on the preferred and indifferently ranked forages through mid-summer without supplementation. The two thick-spiked wheat-grasses, No. 9021076 and [`]Secar' Snake River wheatgrass, are not recommended as forages for Angora goats.
Abstract: The botanical composition of the diet of eight Spanish goats was studied on the Northern Great Basin Experimental Range during two stages of plant phenology (active growth in early July and cured forage in mid-August) to assess their potential for control of sagebrush (Artemisia tridentata subspp. wyomingensis Nutt.) and western juniper (Juniperus occidentalis Hook.) and the nutritional value of their diets on sagebrush steppe rangelands. Diets were quantified by documenting the number of visits to each species, the number of bites harvested and time expended grazing each forage over four consecutive days in each period. Forage chemical characteristics evaluated included: CP, NDF, ADF, ADL and IVDMD. Diet composition and forage quality indices varied significantly (P < 0.05) with changes in plant phenology. Vegetation cover averaged 52% in the pasture and consisted of 36% grasses, 8% forbs, 7% shrubs and 0.6% trees. Available herbage (excluding woody plants) was 534 kg ha-1 during active growth trials and 572 kg ha-1 when forages had cured. When forages were green goats acquired 28% of their total bites from grasses, 71% from forbs, 0.3% from shrubs and 0.9% from juniper trees. After forages had cured values were 35% from grasses, 56% from forbs, 0.1% from shrubs and 8.8% from juniper. The browsing of juniper (both foliage and bark), after herbaceous forages had cured, was the only substantive use of woody plants. Sagebrush was only lightly used (0.2% of total bites) when herbaceous forages were actively growing. Available herbage was of relatively high quality during both trials. When forages were actively growing, CP of grasses ranged between 8.9-5.6%, forbs from 17.7-8.5%, sagebrush scored at 8.5%, juniper foliage at 8.1% and juniper bark at 3.2%. After herbaceous forages had cured, grass CPs ranged between 6.2 and 3.1%; forbs from 10.4 to 4.4%; shrubs were not sampled; and juniper foliage averaged 7.6%. Given the low levels of browsing exhibited by goats on sagebrush and juniper we see little opportunity for control of these woody plants when pastures provide a diverse (n = 25 species) array of readily available (534-572 kg ha-1) and nutritious forages and pastures are lightly stocked (0.63 goats ha-1 month-1). We do need, however, to explore further their potential for control of these species under several other regimes. These include: extended trials on more deteriorated rangelands; trials during seasons or conditions where forage is limited and the animal' s selective opportunity is restricted; and trials in high quality environments on newly established sagebrush and juniper seedlings.
Abstract: Botanical composition of cattle seasonal diets (faecal sampling with microhistological analysis) was determined in a four-pasture, one-herd grazing system during a 3-year period. Diets were classified using cluster analysis. Three diet groups were identified: beginning of rainy season (spring), peak of rainy season (summer) and dry season (fall and winter). Contribution of grasses and woody species to these diet groups was significantly different (p< 0·001). Grasses were the most important component of cattle diets throughout the rainy season, while shrubs and trees were important in the dry season. The major shifts in diets occurred in response to changes in grass phenology.
Abstract: In West Africa, crop-livestock mixed farming is emerging from the currently predominant nomadic pastoralism and agropastoralism. It is hypothesized that competitiveness between crop and livestock enterprises may be an important determinant of the pace of this evolution. A field study in the derived savanna of southwest Nigeria shows that at the current stage of evolution, as a crop farmer adds livestock to his business, there is a small gain in the beginning, then an increasing rate of substitution between crop and livestock follow. As a livestock rearer engages in crop production, there is a decreasing rate of substitution between livestock and crop. This situation derives from the fact that crop production is more intensive than livestock production, which depends principally on grazing natural pastures. Results indicate that if increased population pressure and cropping intensity severely limit access to grazing land, farm and herd sizes will become smaller, then the degree of integration between crop and livestock will increase significantly.
Abstract: This paper presents a structured research design to achieve an economically viable and ecologically sustainable land use. It includes the major elements required to achieve a predictive capability at ranch, watershed and regional scales. A management protocol is proposed, incorporating client feedback to aid in producing relevant technology and information in a useable format. Sustainable land use depends on: (1) accounting for environmental effects, (2) decreasing reliance on depletable and polluting non-renewable resources, and (3) maintaining ecosystem resilience.
Abstract: The general characteristics of global vegetation during the middle Pliocene warm period can be reconstructed from fossil pollen and plant megafossil data. The largest differences between Pliocene vegetation and that of today occurred at high latitudes in both hemispheres, where warming was pronounced relative to today. In the Northern Hemisphere coniferous forests lived in the modern tundra and polar desert regions, whereas in the Southern Hemisphere southern beech apparently grew in coastal areas of Antarctica. Pliocene middle latitude vegetation differed less, although moister-than-modern conditions supported forest and woodland growth in some regions now covered by steppe or grassland. Pliocene tropical vegetation reflects essentially modem conditions in some regions and slightly cooler-than-or warmer-than- modern climates in other areas. Changes in topography induced by tectonics may be responsible for many of the climatic changes since the Pliocene in both middle and lower latitudes. However, the overall latitudinal progression of climatic conditions on land parallels that seen in the reconstruction of middle Pliocene sea-surface temperatures. Pliocene paleovegetational data was employed to construct a 2 ° × 2 ° global grid of estimated mid-Pliocene vegetational cover for use as boundary conditions for numerical General Circulation Model simulations of middle Pliocene climates. Continental outlines and topography were first modified to represent the Pliocene landscape on the 2 ° × 2 ° grid. A modern 1 ° × 1 ° vegetation grid was simplified and mapped on this Pliocene grid, and then modified following general geographic trends evident in the Pliocene paleovegetation data set.
Abstract: This article contributes to the development of a general applicable method to characterise landscapes by presenting a technique to obtain data on actual land use by means of transect surveys and farmer interviews. This technique is developed as an alternative to existing ones which generate data on land use mainly as a by-product. As part of a multiscale agro-ecological characterisation methodology, the Integrated Transect Method (ITM) generates data at the semi-detailed level, and bridges gaps between disciplines, scales, and agro-ecological zones. The method is illustrated using bio-physical results from inland valley agro-ecosystems in two agro-ecological zones in Côte d'Ivoire, West Africa. So-called [`]agro-ecosystem diagrams' offered scope for easy presentation of collected information. Additionally, various quantified land and land use characteristics were used to scale up data from the level of the transect, via inland valleys and valley systems to the level of the agro-ecological subunit. Application of ITM showed that this technique can be used effectively as a tool to analyse bio-physical differences in land use within landscapes and compare differences between them under different agro-ecological conditions. The required integration of bio-physical and socio-economic parameters, however, is the subject of further study.
Abstract: In transect surveys during summer 1988-1993 at 86 tallgrass prairies in Illinois, Iowa, Minnesota, Missouri, and Wisconsin USA, 80,906 butterflies of 90 species were counted. Individuals were recorded with respect to habitat, type of management (burning or haying), and number of growing seasons since last management. The effects of recent management were analyzed separately for 34 species while controlling for other factors affecting variability in abundance (geography, flight period, weather, yearly fluctuation, vegetation quality and type, patch size, site diversity). While each butterfly species had its own individual response to fire, the prairie specialists (Oarisma poweshiek, Hesperia ottoe, H. dacotae, H. leonardus, Atrytone arogos, Speyeria idalia) showed the most negative effect from fire, which may persist for 3-5+ years. The broader the habitat adaptation, the more over-represented the species tended to be in more recently burned areas and the more under-represented in longer unburned areas. Fire also appeared to affect butterfly abundance based on the species' number of generations per year, vagility, location during fire, and response of their key plants to fire. Specialist numbers were much higher in hayed than burned prairies, while invaders and generalists did not decline markedly with haying. Habitat maintenance with haying is much more favorable for prairie-specialist butterflies than burning.
Abstract: This paper describes a step-wise method to quantify the effect of biomass removal by grazing on infiltration, runoff and primary production and is used to explore the long-term consequences of grazing on the stability of the Sahelian rangeland ecosystem in average and dry years. A concept of Rawls et al. (1989) was used to estimate the effect of canopy cover on a single composite infiltration parameter, i.e. the sorptivity, S, for Sahelian rangelands. Dependence of this sorptivity (mm min-1/2) on canopy cover, CAN (%), for a common soil type (loamy sand) can be described by: S = 0.48 + 0.016 * CAN - 0.000055 * CAN2. From 30-year rainfall records in the north and south Sahel, four normal years (probability 50%) and four dry years (probability 90%) were analyzed in detail. Daily rainfall was distributed over three classes, i.e. < 10, 10-20 and > 20 mm. Average rainfall in each of these classes was 4.4, 14.6 and 32.9 mm. Combination of these classes with intensity classes (from a separate rainfall intensity analysis) resulted in 12 standard showers. For each of these standard showers, infiltration was calculated using the equation I = S * [radical sign]t. Using the number of showers in each class, an annual runoff can be computed that results in the relation: R (% of rainfall) = 66.02 * exp(-0.549 * S). The potential length of the growing season is derived from a statistical analysis of 30-year rainfall records. Actual length of the growing season, L, depends on soil evaporation and runoff. Nutrient-limited growth can be calculated as: Y(Nut) = L * 35 (kg ha-1 yr-1). Crop available water, AW, in the actual growing season is calculated and water-limited production calculated as: Y(Wat) = AW * 10 000/TC (kg ha-1 yr-1), TC being the transpiration coefficient of Sahelian pastures. Actual primary production is the minimum value of Y(Wat) and Y(Nut). Primary production functions that were derived are: Y(normal year) = 3604 + 15.06 * R - 0.89 * R2 and Y(dry year) = 3104 - 17.77 * R - 0.80 * R2 (kg ha-1 l yr-1). The obtained equations are used to explore the consequences of grazing on the stability of the Sahelian rangeland ecosystem. For a sequence of normal years, different grazing intensities lead to different equilibrium values for the annual runoff. For a sequence of 1, 2 or 3 consecutive dry years, the initial runoff value determines the maximum grazing intensity.
Abstract: Invasive plants and plantations may be detrimental to native, ground-living, invertebrate fauna. Using pitfall traps at 20 sites in Pietermaritzburg, South Africa, an assessment was made of the distribution of epigaeic fauna under stands of the exotic invader plants: Acacia longifolia (long-leaved wattle), Acacia mearnsii (black wattle), Lantana camara (lantana) and Solanum mauritianum (bugweed), and also under a canopy of two major plantation trees: Eucalyptus grandis and Pinus patula. Control plots were minimally disturbed grassland and woodland in the same area. The effects of the invasive and cultured plants suggest that the impact is a complex interaction of factors. In general, there was a lower (but not significantly so) species richness, and also diversity, of invertebrates in exotic compared with indigenous vegetation. Certain individual species rather than whole families were affected most by these types of vegetation. There was a different assemblage of species associated with exotic compared with indigenous vegetation, with some species being good indicators for exotic or for indigenous vegetation. Although the weeds and vegetation caused a few species to increase in abundance, many other species decreased or even disappeared locally. Whereas different species assembled according to whether vegetation was exotic or indigenous, families and orders assembled along a gradient of closed to open canopy vegetation irrespective of origin. Although a few species were restricted to exotic vegetation (presumably having invaded at some time in the past from somewhere apart from the control sites), many others were restricted to indigenous vegetation. Vegetation management should be sensitive to the needs of certain invertebrate species so as to conserve them when native vegetation is replaced by exotics. Some management recommendations for conserving local invertebrate diversity are made.
Abstract: In the savanna biome of southern Africa, introduced mesquite species have transformed at least 200,000 ha in the northern Cape Province of South Africa and could have a significant effect on insect diversity in this biome. The effect of a dense Prosopis glandulosa stand on a savanna dung beetle assemblage was investigated over a 16-month period using pitfall traps baited with cattle dung. A total of 41 species was recorded in the undisturbed savanna compared to 34 in the thicket. In addition, the two habitats differed in the biomass, numbers, dominance, diversity, equitability and size distribution of the species. Larger dung beetles (> 20 mg dry weight), particularly telecoprids, showed a marked aversion to the Prosopis thicket, while they comprised 60% of the assemblage in the open savanna. Rare species in the assemblage from undisturbed savanna all showed a marked decline in the Prosopis thicket. It is argued that greater attention should be given to land management practices in arid savanna regions where bush encroachment is likely.
Abstract: The emergence and spatial distribution of grass seedlings were studied in a degraded savanna in south-eastern Botswana. When the rainy season started early, several separate establishment opportunities occurred, but with late rains only one germination wave was observed. Small rainfall events of 10-12 mm were unable to trigger germination. The phenology of emergence confirms the presence of a drought avoidance syndrome in this semi-arid climate. Seedling densities varied from a few in perennialEragrostis rigidiorgrassland to 3000 m-2in annualTragus berteronianusgrassland influenced by runoff processes. Seedlings emerged mainly from the top 1 cm of the soil. Vertical distribution of seeds showed a concentration in the top 1 cm of soil and the litter layer. Grass seedling survival was positively correlated with seed size. The importance of seedlings for the regeneration of grasslands is discussed.
Abstract: Simultaneous measurements of atmospheric CO2 flux, Fc, and latent heat flux, E, from a shrub savanna in Niger, West Africa, were made by eddy correlation. The vegetation at the study site consisted of scattered shrubs with an understorey of grasses and herbs. The measurements made available some of the first data on CO2 and H2O exchange for an semi-natural, mixed plant community, growing in the semi-arid tropics. Such data are necessary for the development of improved soil-vegetation-atmosphere models, able to describe the complex interplay between atmospheric CO2, vegetation conductance and the surface energy balance of the Sahel in global climate models. In this framework, the effect of the extreme and highly variable environment, represented by the saturation deficit, D, and integrated water content of the upper soil layers, [Phi], was discussed. Fc and E were measured throughout the transition from the wet to the dry season (September-October) during the HAPEX-Sahel Intensive Observation period, in 1992. At the same time, leaf stomatal conductances, g1, of the shrubs and two understorey herb species was measured. Daily totals of Fc decreased by 50% (peak values declined from -10 to -5 [mu]mol m-2s-1) over 3 weeks following the last rainfall of the wet season. During the same period, g1 decreased roughly four-fold for all sampled species. D appeared to be the main controlling parameter in the exchange of CO2 and H2O. g1 and [`]water use efficiency', Fc/E, were well correlated with D, which also considerably influenced the response of Fc to photosynthetically active radiation, Qp. Simultaneously, a decreasing [Phi] caused lower values of g1 and Fc. However, soil moisture had little effect on the empirical relationships found between atmospheric variables (D or Qp) and g1 or Fc.
Abstract: A photochemical study including measurements of ozone, peroxides, and formaldehyde together with nitrogen oxides and the photolysis rate of nitrogen dioxide was conducted in the Venezuelan savannah during the wet season, September 1993. Pronounced diurnal variations were observed with midday maximum and early morning minimum concentrations for peroxides, formaldehyde, and ozone of 2/0.1, 1.5/0.2, and 15/2 ppbv, respectively. The NOx concentrations ranged from less than 0.4 ppbv during midday conditions to I ppbv in the evening. Evaluation of the photostationary state deviations indicated high production rates of ozone. These evaluations were however not in agreement with the observed concentrations. Possible explanations for this contradiction can be interferences in the NOx measurements or perturbations due to soil NO emissions.
Abstract: Abstract 10.1002/qj.49712253008.abs An atmospheric general-circulation model with realistic land-surface properties is used to investigate the climatic effect of doubling the extent of the earth's deserts. Control and anomaly integrations are performed for 10 years. In the anomaly case, deserts are expanded over northern and southern Africa, Australia, south-central Asia, south-western North America, and parts of South America. In the anomaly case, the troposphere is cooler across most of the tropics and subtropics, including all areas where desertification occurs. Remote effects in the winter circulation include a pronounced trough over northern Europe, and increased geopotential heights over the southern oceans. The response of climate in deforested areas is not uniform between the regions. The magnitude and seasonality of the changes, particularly in precipitation, seem to be functions of the monsoon regime. Northern Africa suffers a strong year-round drought, suggesting this area is most sensitive to desertification, and southern Africa has a somewhat weaker year-round drought. Rainfall over desertified parts of Asia, Australia and western South America decreases only during the summer, and not during the winter. North America and the Nordeste region of Brazil show the least sensitivity to desertification. Most regions show a notable correlation between decreases in evapotranspiration and resulting precipitation. However, regional land–sea distributions in the vicinity of each desertified area appear to determine the sensitivity and response of the local climate via induced changes in moisture flux convergence. Thus, different regions exhibit different responses of climate to desertification. Surface temperature decreases over most desertified areas, owing to reduced absorption of short-wave radiation by the brighter surface. Some regions, particularly the Sahel, show an increase in surface temperature caused by decreased soil moisture and latent-heat flux.
Abstract: The diets of euros or hill kangaroos (Macropus robustus), domestic sheep (Ovis aries) and feral goats (Capra hircus) in hilly, shrub rangeland in southern Australia were examined in a 12-year study. Levels of dietary overlap between these herbivores, their foraging in relation to resource availability, and the potential for competition in different conditions were also examined. The diet of euros was based around grasses. In dry seasons some shrubs were also eaten but in severe drought grass formed more than 80% of their diet. While grass was important to sheep in wetter conditions, they ate much shrub in dry conditions. Feral goats had broad diets but their preference for browse was high. In drought, euros had only a modest dietary overlap with sheep and goats. Data for dietary niche breadths and electivities pointed to only limited competition between the herbivores.
Abstract: Spatio-temporal variation in dung beetle distribution and cattle dung dispersal was quantified across a spectrum of summer rainfall habitat types in South Africa, i.e. grassland, open woodland and thickets on both sand and clay. This study facilitates the selection of further Afrotropical dung beetle species to optimize dung and fly control in similar Australian habitats. Substantial dung beetle activity and dung removal were recorded during the warm rainy season. However, there was considerable spatial variance for which soil type was primarily responsible. Differences between harder (clay) and softer soil types (sand) include, lower biomass of dung-burying and lower abundance of predatory dung beetles, lower rates and amounts of dung removal, and greater shredding of pad remnants on clay. Positive correlations between dung beetle biomass and dung removal were most frequent for large, fast-burying tunnellers on sand and for ball rollers on clay. The implications of spatio-temporal differences in dung beetle functional group structure and dung dispersal are discussed with regards to the necessity of further introductions of both dung-burying and predatory dung beetles from African into Australia.
Abstract: The northern Guinea savanna in Africa (NGS) with a season length of 151-180 days and an altitude below 800 m has long been recognized as highly suitable for crop production and animal husbandry. At present, land use intensity and farming as well as livestock systems vary widely across the zone. Subsistence farming and traditional pastoralism are present as well as intensive, market-oriented production of cash crops and highly integrated crop-livestock systems. This article presents an approach for addressing the challenge of technology development and transfer in the NGS. It is based on an analysis of the evolutionary change of agricultural systems. Exogenous and endogenous determinants have been identified for the formation of, at present, four agricultural systems, five major resource domains and at least ten major farming domains in the NGS. The domains cluster areas of similar resource endowments and development potential which are at a similar point along generalized evolutionary pathways. The additional differentiation of farmer domains integrates changes in equity and externalities into the concept. Resource degradation, biotic constraints and issues of equality are briefly analyzed according to the framework.
Abstract: SummarySouth Africa contains an extensive, well-managed protected area network which generates considerable economic benefits from tourism, but the extensive land and financial resources required by the parks and reserves are difficult to reconcile with the acute social and economic development needs of poor rural people with very limited access to any kind of resources. Local communities have incurred substantial costs from the establishment of these parks while receiving few benefits in return. National and provincial governments, as well as the conservation authorities, have now recognized that the long-term future of parks and reserves depends on taking effective steps to redress the local imbalance of benefits and costs. Integrated conservation-development projects (ICDPs) are beginning to test a range of specific measures to increase local community participation in the benefits from protected areas. Parks have considerable resources and expertise which they can use to support local development through ICDPs, although it would be unrealistic to expect parks to solve widespread rural poverty amongst their neighbours. Instead, park authorities should take the lead in forming partnerships to mobilize the combined resources and expertise of other national and provincial government agencies, NGOs and the private sector, as well as the local communities themselves. Community participation in wildlife tourism may best be achievable through joint ventures with the private sector or park management authorities.
Abstract: Soil moisture measurements by the neutron probe method were analysed to provide the parameters required for a daily model of actual evaporation from three land uses--grassland, indigenous bamboo and plantation softwood--in the Aberdare range of hills, Kenya. These daily estimates of evaporation were summed to provide annual totals and used, on a percentage land cover basis, in water balance calculations for three experimental mixed land use catchments, two of which were undergoing land use change. The annual water use, given by the difference between rainfall inputs and streamflow outputs, of the undisturbed catchment could normally be predicted to within 10%, whereas differences in the predicted and measured water use of the other two catchments were related to the changes in vegetation.
Abstract: The characteristics and dynamics of dry savanna vegetation cover are receiving considerable attention from the perspectives of both global change and range degradation studies. Problems include the establishment of major savanna determinants and the floristic response of vegetation cover to given stimuli. Basic work on determinants is required to assess the nature and causes of natural resource depletion, particularly in the Kalahari region. Use of image processing techniques involving the association of pixel values and field data have resulted in the development of a vegetation map indicating floristic content and structure. Results indicate that a clear distinction can be made between classes containing high proportions of taller woodland species and those that contain mainly woody weeds. Degraded areas with sparse vegetation cover and large areas of bare soil were also identified. The GIS technique of buffer analysis was applied to determine the extent to which herbivory (livestock) and the gathering of bush products by the local population were directly involved in the spatial distribution of savanna types. Results indicate that most of the degraded areas are within 2 km of villages and boreholes. Most of the woody weed areas fall within a 2-4-km zone around boreholes. Spatial association indicates that uncontrolled bush product harvesting and goat grazing are primarily responsible for village-centred degradation, while cattle grazing around numerous boreholes is a primary cause of woody weed development. These kinds of savanna adaptive responses are difficult to reverse in rural Botswana because of increasing population pressure and concomitant poverty.
Abstract: The renewable natural resources sector in Africa is of particular importance because of the relatively high proportion of livelihoods that it supports in comparison to other developing regions. Threats to these livelihoods arise from the relative fragility of the sector in the context of continuing, rapid, population growth. Key concerns include the need for agricultural intensification in the context of systems that are often located in marginal areas; the demands made by rapid urbanization which contribute to the difficulties in developing sustainable systems; and access rights to key resources such as water. The policy and institutional environment can exacerbate difficulties since trends towards greater democracy often prove destabilizing or deflect the political agenda towards short-term expediency rather than longer term strategies that are essential to the RNR sector. Structural adjustment has not yielded the expected benefits and it has become increasingly apparent that the private sector alone will not be able to meet growth and distributional objectives. It appears that a broader-based strategy is needed including not only government institutions at national and local levels, but also NGOs and community organizations, and even regional and international bodies (e.g. for research). Sub-Saharan Africa has probably suffered more than most regions from an overdose of dogma; what is really required is a flexible, pragmatic approach that recognizes the legitimacy and complementary roles between both public and private sector.
Abstract: Chromolaena odorata (L.) King & Robinson continues to spread through southeast Asia into the south Pacific, and into central and eastern Africa from the infestations in western and southern Africa. It is regarded as a very serious threat to agriculture and the environment in most of these countries. The climate-matching program CLIMEX was used with data from the known distribution of the weed in Asia and the Neotropics to predict areas suitable for its growth in Africa, Australia and Oceania. Results indicate that much of tropical Africa, the eastern coast of Australia and most Pacific islands are susceptible to invasion.
Abstract: Three experiments were carried out using lambs to assess the effect of level of napier hay and urea supplements on the utilization of poor quality natural pasture (veld) hay. In all the experiments the lambs were given graded levels of napier hay as supplements to the basal diet of veld hay. In Experiment 1, the veld hay was not supplemented with urea; in Experiment 2, the veld hay was supplemented with 1% urea while in Experiment 3, the veld hay was supplemented with 1% or 2% urea. In all the experiments napier hay supplements increased total feed intake and in vivo digestibility of the diet (P < 0.05). High levels of napier supplementation tended to reduce the intake of veld hay below the level achieved on the unsupplemented control diet. However this decrease in veld hay intake was not as much as anticipated had the napier hay (corrected for its digestibility) simply replaced veld hay. Increasing the level of urea from 1 to 2% did not increase feed intake or digestibility or alter the pattern of substitution of veld hay by the napier. Across treatments, there was some evidence that the gain in the intake of veld hay resulting from napier supplementation was greater when urea was not added to the veld hay. In all the experiments, the increase in food intake was associated with an increase in faecal dry matter excretion suggesting that the increase in feed intake was facilitated by an increase in digesta passage rate. These results confirm that forage supplements are effective in increasing the utilization of poor quality forages and the response to the napier supplements was not entirely due to increasing nitrogen intake.
Abstract: Land degradation in the southern central part of the South Island, New Zealand is a pressing environmental issue. There is a requirement for a method encompassing integrated monitoring and modelling. This paper describes an approach that combines ecological modelling using regression methods and neural networks with spatial information including remotely sensed information. Regression techniques are used initially for modelling with result of r2 = 0.68. Prompted by some residual concerns about disaggregation, a series of neural networks were designed. The result of these latter tests produced r2 = 0.86. A study was undertaken to analyse these results and to use the models for extrapolation. The models were useful for the prediction and simulation of ground based land monitoring data, and successfully predicted the condition of a large area of land when applied to a spatial dataset.
Abstract: During the Washita '92 field experiment, the local surface energy balance was evaluated at four locations in the USDA-ARS Little Washita River Watershed near Chickasha, OK, using the Bowen ratio-energy balance (BREB) approach. For any given day, differences in the partitioning of the available energy appeared to be mostly a function of the type of vegetation at the site, while the actual magnitude of the fluxes was mostly affected by cloud cover. The soil surface was initially wet, and gradually dried during the field experiment. However, there was not a corresponding decrease in the evaporative fraction, which would have indicated a decreasing contribution of soil evaporation to the total latent heat flux. Ground weather data indicated a large shift in the direction and magnitude of the surface winds, and a significant increase in air temperature and vapor pressure deficit. During this period, the evaporative fraction actually increased at two of the four sites. The response of the different sites to the changing near-surface atmospheric conditions was studied in more detail by evaluating the canopy resistance (rc) to evaporation using the Penman-Monteith equation and the Priestley-Taylor parameter ([alpha]). Midday averages of (rc) and ([alpha]) tended to decrease (increase) with increasing vapor pressure deficit for two of the sites while such a trend was not evident for the other two sites. Estimates of stomatal resistances indicated that significant plant physiological differences existed between the sites containing weedy vegetation versus the grasses at the pasture/rangeland sites. Even though soil moisture conditions were relatively wet, a was less than 1 at all sites and there was no trend in [alpha] as a function of surface soil moisture conditions. These findings suggest that vegetation types C in mixed agricultural /rangeland ecosystems can have significantly different responses to similar atmospheric forcing conditions.
Abstract: In the process of dredge mining, employed since 1977 on the Zululand coast, heavy minerals are extracted from the dunes after the complete removal of the existing vegetation. The tailings are then reshaped to approximate their original contours, covered with topsoil and revegetated with a cereal cover crop, together with indigenous seeds of long-lived (woody) species. The existence of stands of different ages over a recorded period provided an opportunity to study changes in species composition and vegetation dynamics. Five random 10 × 10m quadrats were sampled in stands of age 4, 5, 7, 8, 9, 10, 11 and 12 years respectively, and cover data were used for multivariate analysis using TWINSPAN and DECORANA. Importance values of each species, and total and mean species richness were also calculated. Pre-mined and mined soil samples were analysed for trace elements, organic matter and pH. Recently rehabilitated areas of 4 to 5 years were dominated by Acacia karroo, but species richness showed a progressive increase with age of rehabilitated stands, with more woody species in the older stands and a slight decline in dominance of A. karroo. TWINSPAN classified older and younger stands into distinct groups which were related to a chronological succession gradient, also shown by the DECORANA ordination. Some soil nutrients of rehabilitated areas compared favourably with the pre-mined topsoil and subsoil, but percentage organic matter content was still higher in natural dune forests. Increases in soil nutrients suggest that nutrient retention and the establishment of substantial soil flora and fauna are occurring, providing evidence for the sustainability of the soils. From this study it appears that successional changes follow the facilitation pathway, and rehabilitation will eventually lead to the restoration of the dune forest.
Abstract: Evidence on late Quaternary palaeoenvironments of the western and southwestern Cape of South Africa has facilitated detailed reconstructions mainly for the mountains, where organic sediment accumulation has been favoured by relatively humid climates. On the lowlands, particularly those of the west coast region, the search for sites traditionally regarded as suitable for the accumulation of sediments containing preserved fossil pollen has commenced only more recently. This area of the Western Cape Province has, however, provided Quaternary scientists with a rich archaeological record that has yet to be tested against independent lines of palaeoecological evidence. A sequence of sediments which have accumulated in what is today a large freshwater coastal lake, Verlorenvlei, has been sampled at Grootdrift, 15 km inland of the coast. A series of seven sediment cores was extracted during 1991 and three of these have now been sub-sampled, radiocarbon dated and subjected to a range of palaeoenvironmental techniques, in particular pollen analysis, sedimentology and geochemistry. Three pollen diagrams are presented which reveal the vegetation history of both the immediate Grootdrift environment and the wider catchment during several periods over the last 5500 years. A mid-Holocene higher sea-level is evident in two of the cores which were examined for pollen throughout their length. The surrounding area appears at this time to have been somewhat more arid than today. Following a hiatus in sedimentation some time after 4300 BP, the marine conditions at the site disappear and are replaced by fresh water as the dominant hydrological and ecological influence. Around the time of colonial occupation of the region, some 300 years ago, lacustrine conditions prevailed at Grootdrift and greater moisture availability is indicated in the catchment. During the last 300 years, the picture revealed by high resolution palynology of the third core is one of progressive levels of human disturbance both in and around the Verlorenvlei. Evidence from a textural and geochemical analysis of the sediments is consistent with the interpretation based on fossil pollen. The implications of this information are examined against the archaeology and palaeoecology of several cave sites in the vicinity of the vlei. The consistency apparent in the range of types of evidence suggests that some reliance can be placed on the mid-late Holocene palaeoenvironmental reconstruction at Verlorenvlei. The paper thus provides insight into the nature of the complex interactions between late Holocene climate change, sea-level fluctuation, vegetation change, vlei hydrology and human activity in the Western Cape coastal region.
Abstract: Dead shrubs lying on the soil surface in an arid shrubland in the southern Karoo have half-lives of 9 to 18 years depending on wood density which varies among species. Dung pellets of sheep and springbok can remain intact on the soil surface in Karoo shrubland and desert grassland for five years or more. Burial hastens the breakdown of dung, but decay may be slower in fine-textured soils than sandy soils. This preliminary study highlights the dearth of information on ecosystem processes and their response to landuse and climate in arid southern Africa.
Abstract:
The Brazilian cerrado vegetation comprises a natural gradient of physiognomies, from open grassy fields to savannas and woodlands, according to soil conditions and local water availability. However, disturbances mainly caused by man tend to modify the natural distribution of cerrado physiognomies, taking them towards more primitive successional stages or even to other vegetation types. To understand the functioning and the dynamics of cerrados submitted to disturbances and to support management decisions for conservation, an extensive amount of documented material (obtained from the literature) and non-documented information (obtained through an interview survey of 48 experts) was pulled together and analyzed, and a qualitative successional model was built, considering the following disturbances in cerrados: fire, grazing, wood cutting, weed invasion, drought and frost occurrences. This predictive model follows the [`]state-and-transition' type. In the model, different communities are suggested according to the intensity, frequency and seasonality of the disturbances, as well as the combination of two or more disturbances, in a non-linear successional gradient, and the idea is to make use of them as management tools in cerrados, under proper regimes. The model is not conclusive and it is presented as a research prototype. Although every step in the model is based on literature evidence and/or expert opinion, a great amount of experimental research is necessary to validate it.
Abstract: In 1989, the opportunity was identified to create a botanical map series which could be used by authorities to make informed decisions and which would highlight the potential impact significance of proposed coastal developments on affected plant community types. In the past, vegetation impact assessments were conducted on a site specific basis and usually included community descriptions and species lists, which contributed little towards objective decision making. Impact significance at a broader, more meaningful spatial scale, for example biogeographical regions, was rarely established. Based on the needs and the recognised problems, the CSIR developed a protocol for coastal vegetation mapping which included the following: 1. Simplification of the phytosociological complexity by recognising community types rather than communities as the phytosociological units; 2. Development of simple algorithm to determine a relative conservation importance hierarchy for the community types. Variables which are considered to be important for determining conservation importance are used in the algorithm; 3. Creation of a standard colour code to represent relative botanical importance for easy interpretation by non-experts; 4. Division of an approximately 1 km wide strip of the South African coastline into biogeographical regions so that botanical importance could be established initially at an ecologically meaningful spatial scale; 5. The use of recent, 1:10000 colour aerial photography as a baseline for all mapping and the standardisation of the mapping scale at 1:10000, based on the orthophoto map series, which is a recognised planning scale and which is adequate to identify and map community types; 6. The use of a Geographic Information System to capture and store the vegetation data and to produce high quality maps. The benefits of the vegetation maps are that better decisions can be made with respect to the assessment of the significance of potential development impacts on coastal vegetation. Also, where vegetation importance is a key issue, this is recognised early in the decision making process. The strategy used to express relative botanical conservation importance has greatly facilitated the capability to perform objective first level assessments of potential development impact significance on coastal vegetation.
Abstract: This paper examines the advantages of the traditional cattlepost system against the recent drive towards the fencing of Botswana's rangelands and the establishment of privatised, commercial beef ranches. Consideration of operational and environmental factors emphasise the benefits of the cattlepost system, while socio-economic and political factors explain why the current drive towards fenced ranches will continue for the foreseeable future. It is concluded that while the degradation issue on Botswana's rangelands has been overstated, alleged concern for the conservation of the grazing resource is explicitly driving Botswana's current New Agricultural Policy. By accentuating the existing marked socio-economic inequalities within the livestock sector, such misplaced policies will fuel much graver environmental problems, as the underlying equity issue remains unaddressed.
Abstract: SUMMARYThe effects of species composition and sward structure on the ingestive behaviour of cattle and sheep grazing a mesic, low quality grassland in South Africa were investigated over the 199005) effect on sheep bite size and on cattle and sheep bite rates but had no effect on dry matter intake rate (IR). Species composition could, however, affect IR over longer grazing periods than those used in the experiment.Sward structure had a major effect on ingestive behaviour. Cattle and sheep bite rates and cattle grazing time, were negatively correlated (P < 005) with sward greenness. Bite size and hence IR in cattle and sheep were strongly correlated (P < 025 cm. Sheep IR, expressed per unit of body mass, increased from 013 g/min/kg at plant heights of 10–15 cm. For sheep there was evidence of a non-asymptotic functional response at some sites with IR being maximized at certain sward heights but declining thereafter. This suggests the possible existence of a third, quality dimension to the functional response on these low-quality grasslands.
Abstract: Previous archaeological and palaeoenvironmental work relating to the late Quaternary of the Lesotho highlands, southern AFrica, is reviewed. Emphasis is placed upon the region's importance for the investigation of late Pleistocene hunter-gatherer settlement-subsistence systems and of the transition from Middle (MSA) to Later Stone Age (LSA) technologies. The paper then reports on the re-excavation of Sehonghong rock-shelter in 1992 and provides an improved radiocarbon chronology for the site and initial results of the analysis of the late Pleistocene and Holocene assemblages recovered. Of particular importance is the identification of assemblages transitional between MSA and LSA stoneworking techniques, but a re-assessment of the existing industrial subdivisions of the Later Stone Age of southern Africa may also be supported by the Sehonghong sequence. The palaeoenvironmental potential of the extensive faunal and botanical assemblages recovered is stressed, especially given the limited extent of previous palaeoenvironmental work in Lesotho. The importance of the Lesotho highlands for investigating differences in site use and subsistence strategies through the late Pleistocene and the Holocene is emphasized, within an overall aim of testing previously proposed models of resource exploitation under glacial and interglacial conditions.
Abstract: The Penman-Monteith equation is useful for computing evaporation rates of uniform surfaces, such as dense vegetation or bare soil. This equation becomes less useful for evaluation of evaporation rates at the regional scale, where surfaces are generally characterized by a patchy combination of vegetation and soil. This is particularly true in the arid and semi-arid regions of the world. The approach proposed here is an attempt to use remotely-sensed measurements of surface reflectance and temperature to allow application of the Penman-Monteith theory to partially-vegetated fields without a-priori knowledge of the percent vegetation cover and canopy resistance. Basically, the Penman-Monteith equation was combined with the energy balance equation to estimate the surface temperature (Ts) associated with four states: surfaces characterized by full-cover vegetation and bare soil with evaporation rates at potential and zero. Then, linear interpolations between Ts values computed for full-cover and bare soil conditions were used to provide information at intermediate states based on measurements of actual surface reflectance and temperature. The approach was first tested using ground-based measurements of surface reflectance and temperature at a rangeland site; the results compared well with on-site measurements of surface evaporation rate (RMSE = 29 W M-2). Then, the approach was tested based on a set of four Landsat Thematic Mapper (TM) images acquired in southeast Arizona during 1992. Maps of surface air temperature and wind speed were combined with maps of surface temperature and spectral vegetation index to produce regional estimates of evaporation rates for the grassland biome.
Abstract: Cheatgrass (Bromus tectorum L), an exotic annual, is a common, and often dominant, species in both the shadscale and sagebrush-steppe communities of the Great Basin Desert. Approximately 20% of the sagebrush-steppe vegetation zone is dominated by cheatgrass to the point where the establishment of native perennial species is nearly Impossible. This paper discusses the historical factors that led to the establishment and dissemination of cheatgrass in the Great Basin, examines the processes that further cheatgrass dominance, provides examples of subsequent influences of the grass to human activities, and links the ecological history with range condition models. Evidence suggests that cheatgrass was introduced accidentally to the Great Basin as a grain contaminant at the end of the 19th century at the same time that largescale domestic grazing was occurring. Imported from Mediterranean Europe and central and south-western Asia, seeds of cheatgrass exploited an ecological niche, as no native annual was dominant in the Great Basin. Cattle, sheep, and feral horses facilitated establishment, for they spread the seeds in the same areas that they disturbed. Once established, cheatgrass promoted the likelihood of fire to the detriment of the native species. in addition, other factors, such as the effects of the lack of vesicular arbuscular mycorrhizae and selective lagomorph grazing have worked in concert to further establish cheatgrass dominance. The ecological consequences of cheatgrass establishment have been an increase in fire frequency and intensity, a decrease in species diversity, and a landscape susceptible to severe erosion. Bunchgrasses interspersed with longlived perennial shrubs now are replaced with either nearly pure patches of cheatgrass or swaths of cheatgrass and shortlived perennial shrubs. Some consequences to human activities involve the numerous ramifications of rangeland fires with costs of approximately US$20 million annually, the undependability of cheatgrass as a source of forage for cattle and sheep, and the value of biotic diversity as numerous plant and animals species undergo high amplitude population fluctuations. Management of these Great Basin vegetation communities should be approached using the state and threshold range condition model.
Abstract: This review reveals that crop residues of common cultivated crops are an important resource not only as a source of significant quantities of nutrients for crop production but also affecting soil physical, chemical, and biological functions and properties and water and soil quality. When crop residues are returned to the soils, their decomposition can have both positive and negative effects on crop production and the environment. Our aim as agricultural scientists is to increase the positive effects. This can only be achieved with the better understanding of residue, soil, and management factors and their interactions, which affect the decomposition and nutrient release processes. Data on nitrogen benefits and nitrogen recoveries from residues show that a considerable potential exists from residues, especially leguminous residues, not only in meeting the N demands of the succeeding crops, but also in increasing the long-term fertility of the soils. In addition, crop residues and their proper management affects the soil quality either directly or indirectly. Intensive cropping systems are very diverse and complex, so no one residue management system is superior under all situations. Ideally, crop residue management practices should be selected to enhance crop yields with a minimum adverse effect on the environment. It is suggested that in each cropping system, the constraints to production and sustainability should be identified and conceptualized to guide toward the best option. Multidisciplinary and integrated efforts by soil scientists, agronomists, ecologists, environmentalists, and economists are needed to design a system approach for the best choice of crop residue management system to enhance both agricultural productivity and sustainability.
Abstract: Summary Plants with the C4 photosynthetic pathway occur in a broad array of biomes as both minor and major components of plant communities (Ehleringer and Monson, 1993). However, in a few community types, notably some temperate grasslands and tropical or subtropical savannas, C4 plants dominate in terms of biomass, productivity, and cover. It is in these communities that studies of C4 photosynthesis and its relationship to environmental stress can help identify the abiotic and biotic factors that ultimately control the ecological success of C4 plants. Similarly, a comparative assessment of functional traits in the dominant C4 and subdominant C3 species can provide insight into a variety of adaptive characteristics associated with the C4 photosynthetic pathway.
Abstract: Summary The significant advances made in agricultural technology during the past 40 years have made it possible for U.S. farmers to produce surplus food for millions of people worldwide, despite only 2% of the American population being engaged in agriculture (Peeples, 1994). Weeds represent one of the most costly and limiting factors in crop production. Weeds can cause substantial losses in the form of yield reductions through competition with crop plants for light, water, nutrients, heat energy, carbon dioxide, and space. Reductions may also be caused by the production of growth-inhibiting compounds, a phenomenon referred to as allelopathy. Weeds can also cause losses by reducing food, feed, and fiber quality as well as increasing the cost of land preparation or harvesting. Over the past four decades, chemical herbicides have dominated weed management strategies in developing countries ([Abernathy and Bridges, 1994] and [Wyse, 1992]). In the United States, chemical herbicides have accounted for nearly 60% of the total amount of all agricultural pesticides applied (Aspelin, 1994). Although herbicides have proven to be an extremely effective means of vegetation control, their use has come with a number of direct and indirect costs that may now be considered as outweighing the benefits in many cases. Public concern has increased over the contamination of water sources as well as agronomic problems caused by the overapplication and soil persistence of many herbicides. Herbicide resistance, which has been noted in more than 100 weed species, continues to be of increasing concern (Holt, 1992). These factors, coupled with the banning of many chemical pesticides, more stringent and costly registration and regulation, and the necessity for nonchemical alternatives in environmentally sensitive areas, have further opened avenues for the use of plant pathogens as biological control agents for weeds.
Abstract: Conventional production agricultural practices are partly responsible for intensifying the degradation of productive lands throughout the world. In monitoring the impacts of these practices, a variety of biological, physical, chemical, landscape, and economic measures are being used as indicators of environmental change. This chapter is largely a review of both common and uncommonly used environmental indicators of agricultural systems. Soil organic matter content is discussed in detail as a candidate environmental indicator. A ranking scheme is proposed for the use of multiple indicators in decision-making applications.
Abstract: Summary C4 plants are different from C3 plants in anatomy (Hatch and Slack, 1970) and in their [delta]13C values (Bender, 1968) and (Smith and Epstein, 1971). These differences can be used in the geological record to determine the presence of C4 plants. C4 plants have Kranz anatomy that has both mesophyll cells, in which CO2 is fixed by C4 acids, and bundle-sheath cells, where RuBP carboxylase fixes CO2 derived from the C4 acids of the mesophyll cells. The different photosynthetic pathways have different [delta]13C values, which result from their different biochemical pathways of CO2 fixation, averaging about -26%. to -27%. for C3 plants and about -12%. for C4 plants. Verification of Kranz anatomy or unequivocal stable isotope evidence can therefore be used to identify C4 plants or C4 ecosystems in the geological record.
Abstract: Summary In the United States, 500 major species of weeds cause estimated annual losses of about $8 billion (Chandler, 1980). These weeds infest cropland, rangeland, recreational, and aquatic areas and vary in their economic importance and need for control. Cultural and chemical controls for weeds are effective, but relief is temporary at best and often uneconomical. In fact, the more effective the chemical control, the sooner other more herbicide-resistant or herbicide-tolerant weeds may fill the vacant niches. Thus, improved weed control is no longer a matter of improved plant kill. Planning and ingenuity are required to minimize immediate losses without inviting incursions by replacement weed species. As Aldrich (1984) noted, weeds are part of dynamic ecosystems continually evolving in response to natural and cultural control pressures. Biological control is a proven method of weed control. An increasing volume of literature is devoted to this approach, including a quadrennial international symposium and proceedings which update and highlight current activities and thought. Biological control continues to offer promise and expanded application in reducing weed losses.
Abstract: Summary C4 photosynthesis is a CO2-concentrating mechanism that increases the carboxylation rate of Rubisco while simultaneously minimizing oxygenase activity and the inhibitory effects of photorespiration(Chollet and Ogren, 1975). From a photosynthetic standpoint, the greatest advantage of C4 photosynthesis is in situations that promote photorespiration in C3 plants, most notably high temperature and low intercellular CO2 concentrations that result from restricted stomatal aperture, and low atmospheric CO2. Simple predictions based on relative performance of C3 and C4 photosynthesis are that C4 species should outperform C3 species in warm habitats and conditions promoting stomatal closure (drought, high salinity, and low humidity). Thus, the textbook generalization has become that C4 photosynthesis is an adaptation for warm, high-light habitats with limited moisture availability (Barbour, et al, 1987), (Taiz and Zeiger, 1991) and (Raven, et al, 1992).
Abstract: Summary Nitrogen loss from cropping systems has interested agronomists since the early recognition by Liebig and others that most crops are nitrogen limited. The widespread early adoption of crop rotations that include legumes (Oakley, 1925) and (Francis and Clegg, 1990) provides historical acknowledgment of the importance of nitrogen gains and losses to cropping system success. It is now recognized that even in semiarid regions (Breman and deWit, 1983) nitrogen is usually the principal resource limiting crop production (Fig. 1).
Abstract: Summary The abundance and density of C3 trees and shrubs on predominantly, C4 gransslands in many parts of the world (Africa, Australia, North America, South America) have increased dramitically during approximately the last 125 years (Mayeux, et al, 1991) and (Archer, 1994). This rapid change in vegetation is evident from historical accounts and photographic records (Hastings and Turner, 1965) and repeated aerial photography (Archer, et al, 1988) and (Knight, et al, 1994) and censuses of permanent plots or similar areas (Glendening, 1952), (Buffington and Herbel, 1965) and (Hennessy, et al, 1983) analyses of the stable carbon isotope composition of soil organic matter (Tieszen and Archer, 1990), (Steuter, et al, 1990) and (McPherson, et al, 1993), and palynological evidence (Davis and Turner, 1986). Some woody species (e.g., Prosopis glandulosa, mesquite) apparently expanded within their historical ranges from refugia, like drainages or rocky outcrops that had been occupied for centuries, or increased in stature and visibility from suppressed populations (Bogusch, 1952) and (Johnston, 1963). For other species (e.g., Larrea tridentata, creosotebush), recent changes are an acceleration of an increase in density and range extension initiated centuries before (Hunziker, et al, 1977) and (Johnson and Mayeux, 1992). Production of grasses and other herbaceous species in many of these systems declines following woody ingress (Glendening, 1952), (Heitschmidt and Dowhower, 1991) and (Hobbs and Mooney, 1986), thus reducing the value of grasslands and savannas for livestock grazing and other uses. The shift in growth or life form composition also alters ecosystem-level processes, including surface-atmosphere transfers of matter and energy, that potentially influence rates and patterns of carbon sequestration (McPherson et al., 1993; H. B. Johnson, unpublished data) and local, regional, or even global climates (Schlesinger et al., 1990). By reducing grass production, for example, woody plants may lessen the frequency and intensity of fires and the accompanying return of carbon and nitrogen to the atmosphere (Medina, 1982) and (Hobbs, et al, 1991). By increasing spatial heterogeneity of soil water and nitrogen (Schlesinger et al., 1990) or in other ways altering the hydrology of grasslands (Joffre and Rambal, 1993), woody ingress can change surface albedo, evapo-transpiration, runoff, and fluxes of trace gases to the atmosphere.
Abstract: Summary Carbon dioxide (CO2) levels in our atmosphere have increased by 30% over the past 200 years, with much of that increase coming during the past 100 years (Boden et al., 1990). Expectations are that by the middle of the 21st century atmospheric CO2 will be double current levels. Much conjecture has occurred as to the impact of that increase in atmospheric CO2, primarily centering around climate change, but with a recent concerted effort on the effects of elevated CO2 on terrestrial ecosystem processes. Although there have been several research reports concerning the effects of elevated CO2 on insect diet effects (Butler, et al, 1986), (Lincoln, et al, 1986), (Fajer, 1989) and (Fajer, et al, 1989), there has been relatively little work on ruminant responses. Worldwide, natural ecosystems provide the majority of food resources for ruminants (Semple, 1970), with rangelands supplying 95% of the food needs for wild ruminants (Holochek et al., 1989). Therefore, the potential impact of CO2 enrichment on forage quality and dietary conversion efficiencies is of paramount importance. Because nutrient resources in natural systems are fixed to a great degree, the impact of increased carbon fixation with elevated CO2 may lead to dietary deficiencies of essential nutrients for herbivores (Owensby, et al, 1993a) and (Owensby, et al, 1993b). Although C:N ratios of different plant species have been variable with CO2 enrichment, the prevalent response, when productivity has been increased by CO2 enrichment, has been an increase in the C:N ratio (Newton, 1991). Lower nitrogen concentration in forages results in reduced digestibility and conversion efficiency of ingested forage to ruminant growth or reproduction (Huston and Pinchak, 1991). Because ruminant digestion is microbial (Hume and Warner, 1980), reduced forage quality would lower both the amount of forage digested and the rate of digestion (Huston and Pinchak, 1991). Ruminants retain forages in the rumen for extended periods which allows efficient nutrient extraction (Bell, 1971).
Notes: 00028916 xD;edited by G. Lemaire ... [et al.]. xD;ill., maps ; 24 cm. xD;Edited and revised versions of papers presented at an international conference held in Curitiba, Parana, Brazil, Aug. 24-26, 1999. xD;Includes bibliographical references and index.
Abstract: The paper presents the simulator SEPATOU that can reproduce the day-to-day dynamics of two interactive systems: the decision system representing the dairy farmer 039;s management behavior and the biophysical system that encompasses the herbage production, consumption and transformation into milk. The activities to be managed concern the type and amount of conserved feed, where to fertilize and how much, the choice of fields to cut and, most importantly, what field to graze next. Typically, SEPATOU is designed to be used by extension services and farming system scientists. It provides a flexible environment through which learning about a satisfying management strategy of a given dairy production system can take place by iterating simulation and evaluation of tentative ones.
Abstract: The management and monitoring of agricultural and environmental resources and the origin of foods are of increasing importance today. GIS have proved to be important tools in solving problems encountered. Advances in the capabilities of the Web language have enabled information providers to include animation and interactive elements in their web sites. These developments have expanded the potential of the GIS world. The Internet Map Server provides a framework for requests and for delivering information to Web browsers from a GIS application on their WWW server. The result is ready access to maps and information anywhere on the Internet.
Abstract: The Mceula Commonage Land in the Hewu district lies due northwest of Whittle sea and west of Queenstown in the Eastern Cape. This thesis has two main objectives. Firstly, to survey and analyse the condition of the natural resource. base in the Hewu district with particular reference to water, soil, vegetation and land use. Secondly, to investigate the relationship between scientific approaches to assessing land use degradation and to compare these to the results obtained using a participatory approach of the rural environment of the Hewu district of the Eastern Cape. Random quadrats (4m2) were sampled and corresponding line transects were done with increasing distances from the villages. The Braun-Blanquet method was used to find the cover and abundance of the various species of plants. Data obtained from point sampling along 100 metre line transects was used to assess the condition of the veld using Trollope's technique. Six communities were defined using TWINSP AN, and grazing capacities and veld condition scores of the respective sites were calculated. It was concluded that the six communities were distributed along a gradient of palatable to non palatable grass and grasslike species. Rangelands close to the villages had low veld condition scores and percentage plant cover as opposed to those farther away from the villages. The null hypothesis of no significant difference between the percentage plant cover and condition of the veld close to the villages and farther away from the villages was rejected. Whilst it is urgent to resolve political disputes around land through land distribution, a key issue for the future is sustainability of the natural resource base of South Africa. To attain this, the old traditional methods of research must be supplemented with the participatory method, where the local community becomes fully involved. The central theme of the participatory approach was to investigate the possibility of promoting local management of the natural resources. Workshops were conducted to involve the local community in the project. The community formed six discussion groups that met regularly to discuss environmental issues. The six groups that were formed were: Firewood or woodlot collectors, shepherds / livestock raisers, crop fanners / agriculturists, water collectors, building material / soil collectors and medicinal plant users. The results obtained from the meeting of the discussion groups were used to compare the scientific results obtained from Braun-Blanquet method. Perceptions about their environment, which came out of the results of the discussion groups showed that the local knowledge of the rural community of Mceula was sufficient to train them to manage their environment sustainably.
Abstract: A comparison of soil degradation between communal grazing and controlled grazing was undertaken in the Victoria-East district of the Eastern Cape. The study was undertaken in the communal rangeland of Dyamala village and the University of Fort Hare Research Farm to represent communal grazing and commercial farming management system respectively. The study used variables such as soil properties, soil loss, and vegetation cover to investigate soil degradation between the two rangelands which are under different management systems. Statistical tests (ANOVA) were used to determine the significance of differences between the two rangelands. A number of soil physical properties were used to quantify the state of degradation of each of the rangelands. This included particle size distribution of the soil, soil moisture, bulk density and porosity, aggregate stability, surface compaction and infiltration rates. The bulk density, porosity, aggregate stability and infiltration rates did not show any significant differences between the sites. These soil properties indicated a similar state of the soil between the two rangelands. However a significant difference in soil moisture and surface compaction was found between sites. The Research Farm had higher soil moisture and was less compacted than the communal rangeland. The two sites were more or less equally losing the finer soil particles through erosion. The erosion process selected the finer particles. In terms of two chemical soil properties, pH and soil organic matter, the two rangelands were similar as there were no significant differences between them. However the two rangelands were losing twice as much soil organic matter in the eroded sediment compared to the in situ soil. This was due to the loss of the finer soil particles through the erosion process. The two rangelands were thus degrading at a similar rate in terms of losing soil fertility. Sediment movement on the slope was monitored for eighteen storms using Gerlach troughs. In the short term the two rangelands seemed to be degrading at the same rate as there were insignificant differences during storm events. Cumulative sediment losses, however, were significantly different between sites as well as slope position. The Research Farm had lower soil movement (loss) than the communal sites. The erosion response of the Research Farm was 60 per cent of that of the communal rangeland indicating higher erosion in the communal area. Contrary to these results the soil depth of the A horizon did not reveal any significant differences between the sites but only between the different topographical positions of the slope. Moles and earthworms were found to be significant contributors of sediment in the erosion process in the communal system and the Research Farm respectively. Significant differences in vegetative cover were found between the sites, with the Research Farm having higher vegetation cover than the communal sites. The vegetation cover was however good in all three sites, being well above 80 per cent. The higher biomass of the Research Farm did not translate into effective vegetative cover. The vegetation in all sites was effective in arresting soil movement as witnessed by the amounts of sediment collected. Both rangelands were found to be in good condition, though the Research Farm was less degraded compared to the communal rangeland.
Abstract:
Abstract
The Addo Elephant National Park (AENP) is the only existing national park situated in succulent thicket. This unique veld type is endemic to the Eastern Cape, and forms an important centre of endemism for small succulents and geophytes which comprise the subdominant component of the vegetation. It is regarded as the most threatened vegetation type in the Eastern Cape, as much of it has been severely degraded by farming activities and its rate of regeneration is very low. Thus the AENP represents an important sanctuary for certain species. However, large herbivores, particularly elephants, pose a further threat to the vegetation, and areas from which elephants have been excluded in the park (botanical reserves) have been shown to be more speciesrich than the surrounding vegetation. Most elephant-impact studies have focussed on the large shrub component of the vegetation, and only preliminary studies have been done in AENP to date. As the elephant population continues to grow, there is pressure to utilise the botanical reserves to increase the amount of available grazing. It is thus important that the botanical reserve system be highly effective and efficient in terms of area. Existing botanical reserves were established ad hoc and are therefore not necessarily optimal in this regard. An iterative reserve-selection algorithm was used to maximise plant species conservation in the most efficient area.
Abstract: A history ofland degradation is reconstructed in a part of the dividing ridge between the Great Fish and Keiskamma rivers, in Peddie District, former Ciskei. The study entails a comparative investigation of the progressive changes in land use, vegetation and soil erosion in three tenure units, namely: former commercial farms, traditional and betterment villages. Analysis of the sequential aerial photography of the area for 1938,1954, 1965, 1975 and 1988 is employed. This is backed by groundtruthing exercises. Data thus obtained are quantified, and linkages between degradation, anthropogenic and physical factors are derived using PC ARC/INFO GIS. Differences in land tenure systems emerge as the main controlling factor to variations in land degradation. Confinement of vegetation diminution and erosion to traditional and betterment villages is observed at all dates. Scantily vegetated surfaces and riparian vegetation removal are a characteristic feature of both areas throughout the study period. 'Betterment,' introduced in the early 1960s to curb land degradation is, instead observed to exacerbate it, particularly soil erosion. Trends in land use change are characterised by the abandonment of cultivated land, which is noted to coincide with a sharp rise in population. Erosion intensification into severe forms particularly between 1965 and 1975, coincident with a period of extreme rainfall events, emerges as the most significant degradation trend. A close spatial correlation between abandoned cultivated land and intricate gullies is identified. So is the case between grazing land and severe sheet erosion. Within the grazing lands, an examination of erosion and categories of vegetated surfaces reveals that erosion occurs predominantly on the scanty vegetation category. Such erosion-vegetation interaction largely explains the non-recovery of the scanty vegetation category, even during periods of intense rainfall. Extensive channel degradation is evident along stream courses with scanty riparian vegetation. Physical factors are noted to have a significant bearing on erosion. The high prevalence of erosion on the Ecca group of rocks confinns its erosion-prone nature. Pockets of colluvium and alluvium accumulation in the steep bottomlands are identified as the sites of the most severe gully erosion. Field surveys at some of the sites indicate that a dolerite sill through the area fonns a boundary of colluvium accumulation and the upslope limit to gully incision. That these sites are recognised as fonnedy cultivated land, portrays the interaction between physical and anthropogenic variables with regard to inducing degradation in the area.
