GSSA-Publications-2004

Abstract: This paper outlines a general approach for analyzing siliceous microfossils from plants (phytoliths) in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central Great Plains during the late Tertiary. Phytolith assemblage analysis is widely employed for reconstructing vegetation types in Pleistocene-Holocene paleoecology and archaeology, but no standardized methodology is currently available. Published phytolith studies are often system-specific and tailored after specific modern analogues. As a result, they vary in extraction technique, classification scheme, and method of inference. For ancient phytolith assemblages whose modern analogues are not well understood, a more general analytic approach is necessary. This analytic approach includes studying all size fractions (2-250 mm), using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection, and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure. This general method was applied to late Eocene to early Miocene sediment samples from northwestern Nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique [Strömberg, Paleogeogr. Paleoclimatol. Paleoecol. 177 (2002) 59]. In both studies, phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units: (1) the late Eocene Chadron Formation and the early Oligocene Brule Formation (White River Group); (2) the late Oligocene-early Miocene Monroe Creek Formation, the early Miocene Harrison Formation and Anderson Ranch Formation (Arikaree Group); and (3) the early Miocene Runningwater Formation and Box Butte Formation (Ogallala Group). The two techniques, general vs. specific, produced results that differ markedly. Data from the general approach indicate the presence of relatively closed habitats in late Eocene to early Oligocene, typified by the presence of phytoliths from bambusoid grasses, woody and herbaceous dicotyledons, and palms. The introduction and spread of modern, open-habitat grasses, such as pooids, arundinoids, and panicoids, occurred between the late Oligocene and early Miocene. This resulted in a savanna or woodland type habitat by the early Miocene. In contrast, analysis using the specific method suggested the presence of open habitats in northwestern Nebraska from the late Eocene onward. The difference in interpretation based on the two approaches is principally due to inclusion of phytoliths >50 mm and the use of an expanded reference collection in the current study (general analytic approach). These results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record.

Abstract: In this study, we present grain-size distributions of the terrigenous fraction of two deep-sea sediment cores from the SE Atlantic (offshore Namibia) and from the SE Pacific (offshore northern Chile), which we [`]unmix' into subpopulations and which are interpreted as coarse eolian dust, fine eolian dust, and fluvial mud. The downcore ratios of the proportions of eolian dust and fluvial mud subsequently represent paleocontinental aridity records of southwestern Africa and northern Chile for the last 120,000 yr. The two records show a relatively wet Last Glacial Maximum (LGM) compared to a relatively dry Holocene, but different orbital variability on longer time scales. Generally, the northern Chilean aridity record shows higher-frequency changes, which are closely related to precessional variation in solar insolation, compared to the southwestern African aridity record, which shows a remarkable resemblance to the global ice-volume record. We relate the changes in continental aridity in southwestern Africa and northern Chile to changes in the latitudinal position of the moisture-bearing Southern Westerlies, potentially driven by the sea-ice extent around Antarctica and overprinted by tropical forcing in the equatorial Pacific Ocean.

Abstract: The influence of burning (head and back fire) on seedling recruitment and survival of different grass species in a semi-arid grassland were quantified over the 2000/01 to 2001/02 growing seasons. The behaviour of the head and back fires was also monitored. Soil temperature and soil-water content were recorded once a week at 10mm and 50mm depth intervals respectively. At ground level, the back fire exceeded 100degreesC, while the head fire recorded temperatures of less than 100degreesC. Due to the lower basal cover (28% lower than for unburnt grassland over the first year after the fire) of the burnt grassland, the soil temperature, daily and seasonal to a depth of 50mm, increased (P < 0.05) while the soil-water content decreased (P < 0.05). The seedling survival was significantly lower due to the fire, which can possibly be ascribed to the lower basal cover and resultant change in micro-climate. The average seedling density of the surviving seedlings in burnt (average of head and back fires) and unburnt grassland at the end of the first season after burning, were 0.48 and 0.86 seedlings m(-2) respectively. Fire influenced the species richness negatively. Pioneer grass species (Aristida congesta and Tragus koelerioide) intruded in the burnt grassland, which were not present in the unburnt grassland. The seedling establishment of Eragrostis chloromelas, Themeda triandra and Elionurus muticus were heavily decreased by fire. Eragrostis chloromelas was the species forming most seed culms per tuft over the growing season regardless of burning, with Elionurus muticus most stimulated for seed formation due to the fire, and Themeda triandra not much influenced by fire. The burning of semi-arid grassland did have an important impact on the seasonal survival of seedlings over the short-term, and therefore the resultant functioning of the grassland ecosystem.

Abstract: The short-term (2 years) influence of fire burning with the wind (head fire) and against the wind (back fire) on the productivity (above-ground phytomass and litter) and fire behaviour were determined over seven growing seasons (1995/96-2001/02) in a semi-arid rangeland. The results showed that head fires had significantly greater flame height and rate of spread than back fires. Fire caused a decrease of 40.5% and 22.5% in basal cover for the first and second seasons after burning respectively. The seasonal above-ground phytomass production and litter were significantly decreased by fire over all growing seasons. Seasonal production losses due to fire varied between 225 and 430 kg ha-1. The relation between above-ground phytomass production loss due to fire, and two independent variables namely seasonal rainfall and fuel load (above-ground phytomass plus litter) before burning, were investigated. The multiple linear regression equations obtained for one (r=0.89) and 2 years (r=0.86) after a fire, can be used with great success in estimating seasonal production losses due to fire in semi-arid rangeland.

Abstract: The carbon isotope signature of fossil phytoliths (silica bodies produced in abundance in the tissue of grasses) presents a promising tool for reconstructing the biogeography of C3 and C4 grasses during the Neogene. Previously applied isotopic techniques, such as the carbon isotope signatures of soil carbonate, herbivore tooth enamel, and leaf-waxes, are limited in that they cannot distinguish between C3 grasses and C3 shrubs/trees. As a result, these records do not provide any information on the relative dominance of C3 vs. C4 grasses. Phytolith carbon isotope ratios, on the other hand, have the potential to provide a direct record of the photosynthetic pathway (C3 or C4) of grasses specifically. Because this technique is still in its infancy, several modern calibration issues remain and are examined here through the presentation of some new data and the synthesis of existing published data on the [delta]13C values of phytoliths from modern grasses and soils. First, fresh phytoliths extracted directly from grasses exhibit depleted isotopic values relative to the source plant and phytoliths from C4 grasses are more depleted than phytoliths from C3 grasses. This difference in depletion is most likely the result of lipids present within phytoliths, which are also generally more depleted in C4 plants than C3 plants relative to whole plant values. Second, phytolith assemblages from modern soils do not share the same degree of isotopic depletion or compression as fresh phytoliths. This suggests that soil phytolith assemblage [delta]13C is affected by pedogenic or taphonomic processes. The weight of current evidence suggests that pedogenic alteration is less of a concern, while selective preservation (taphonomic bias) may play an important role. Even so, comparison of the [delta]13C values of phytolith assemblages with [delta]13C values of soil organic matter (SOM) from modern soils indicates that phytoliths can record the C3/C4 contribution to the soil. It appears that phytoliths retain a longer-term, smoothed record in contrast to the more rapid turnover of SOM pools that can be influenced by even recent land-use changes. Third, the interpretation of fossil phytolith [delta]13C in terms of proportion of C3 and C4 grasses requires isotopic end-member values. End-members from fresh phytoliths cannot be used because they fail to capture the range of soil phytolith assemblage data. Comparison of soil phytolith [delta]13C values with SOM [delta]13C yields empirically derived end-member values that take into account any taphonomic effects. These end-members (C3=-26.8[per mille sign], C4=-15.3[per mille sign]) capture the range of observed values for soil and paleosol phytolith [delta]13C values spanning the last 650,000 years. The modern calibration work presented here provides the necessary groundwork for applying this technique to paleoecological reconstructions of Neogene grasslands.

Abstract: During the dormant winter period the semi-arid rangeland areas of South Africa are characterized by unplanned fires, either by lightning or negligence by man. The quantification of the impact of burning in terms of the above- and below-ground phytomass production, rain-use efficiency (RUE), crude protein, root/shoot ratios and plant density of the grass sward was conducted in a semi-arid rangeland over 2 years (2000/2001-2001/2002 growing seasons) following an accidental fire. Fire (head fire) had a significant (p<0.01) influence on plant density. Grass species with larger tufts (Cymbopogon plurinodis and Themeda triandra) suffered the most dieback due to the fire. The initial advantage in quality (crude protein) accompanying the fire does not neutralize the reduction in half of above-ground phytomass production and poor (p<0.01) RUE occurring in the first season following the fire. Burnt rangeland takes at least two full growing seasons to recover in terms of above- and below-ground phytomass production, litter and RUE. Fire lowered (p<0.01) RUE for both growing seasons especially during the first four months. The average RUE was 3.72 and 2.86 kg ha-1 mm-1, respectively, for unburnt and burnt rangeland for the 2 years. Root mass decreased (p<0.01) by 59% over the first 100 mm depth due to fire. More than 80% of the root mass was found in the top 0-300 mm soil layer. The below-ground growth is more sensitive to burning than above-ground growth. Fire reduced the root/shoot ratio from 1.44 to 1.30. These results can serve as scientific guidelines in claims for damages and short-term risk management of semi-arid rangeland after an accidental runaway fire driven by August winds.

Abstract: Land deterioration does not occur uniformly over time or over a landscape. The differential use of preferred areas in the landscape results in uneven distribution of animal impact, and periods of below average precipitation compound the effects of herbivory, providing periods of accelerated deterioration. This study investigates whether rotational grazing during a drought cycle allows reduction of deterioration caused by patch-selective grazing in large (1800-2100 ha) paddocks by providing adequate rest between grazing events. From 1995 through 2000, herbaceous and bare ground changes were measured on adjacent heavily grazed and lightly grazed patches in rotationally and continuously grazed paddocks. The weather interacted with grazing treatment (p<0.0001), species (p<0.0001) and the combined effects of the other factors (p<0.0014), indicating the dominant effect of weather, particularly precipitation, on changes in herbaceous basal area. When summer growing conditions were favorable, the rotational grazing treatment resulted in greater increases of perennial herbaceous basal areas (p<0.05) and lower proportions of bare ground (p<0.10) than the continuously grazed treatment. Although rotational grazing did not prevent deterioration in basal area and bare ground with the series of four drought years, it did decrease the rate of deterioration. The changes in basal area were primarily due to changes in summer growing perennial C4 midgrasses and C4 shortgrasses. Grazing treatment did not influence species aerial biomass composition (p>0.1). When monitoring to effect sustainable use, the commonly used parameter of species composition appears to be a much less sensitive indicator of change than bare ground and basal area. This study provides evidence that, in large paddocks in this environment, rotational grazing can reduce the deterioration and allow improvement of both shortgrass and midgrass patches.

Abstract: Abstract. Shrub encroachment, i.e. the increase in woody plant cover, is a major concern for livestock farming in southern Kalahari savannas. We developed a grid-based computer model simulating the population dynamics of Grewia flava, a common, fleshy-fruited encroaching shrub. In the absence of large herbivores, seeds of Grewia are largely deposited in the sub-canopy of Acacia erioloba. Cattle negate this dispersal limitation by browsing on the foliage of Grewia and dispersing seeds into the grassland matrix. In this study we first show that model predictions of Grewia cover dynamics are realistic by comparing model output with shrub cover estimates obtained from a time series of aerial photographs. Subsequently, we apply a realistic range of intensity of cattle-induced seed dispersal combined with potential precipitation and fire scenarios. Based on the simulation results we suggest that cattle may facilitate shrub encroachment of Grewia. The results show that the severity of shrub encroachment is governed by the intensity of seed dispersal. For a high seed dispersal intensity without fire (equivalent to a high stocking rate) the model predicts 56% shrub cover and 85% cell cover after 100 yr. With fire both recruitment and shrub cover are reduced, which may, under moderate intensities, prevent shrub encroachment. Climate change scenarios with two-fold higher frequencies of drought and wet years intensified shrub encroachment rates, although long-term mean of precipitation remained constant. As a management recommendation we suggest that shrub encroachment on rangelands may be counteracted by frequent fires and controlling cattle movements to areas with a high proportion of fruiting Grewia shrubs.

Abstract: Conflicts associated with natural resource use are common in rural areas of Africa. Political ecology's analytical and methodological foci on these conflicts is shared by other quite different schools of thought that strongly influence policies on environment and development. The influential "environmental security" and "common property management" perspectives generally conceptualize resource-related conflicts as scarcity-driven while political ecologists have made major contributions toward more multidimensional, complex views about the genesis of resource-related conflict. This paper explores two moral dimensions of resource conflict. First, it continues the tradition within political ecology of questioning popular notions of resource conflict. It does so by analyzing farmer-herder conflict in the Sahel--a type of resource-related conflict that seemingly fits the view that conflict is generated from increased competition over a dwindling pool of resources. By seriously engaging with the materiality of agropastoral production, this paper illuminates the complex relationships between political interests, moralities, and resource access that underlie these conflicts. Second, this paper considers the ethics of how we portray resource conflict. In the present policy context in Africa, overly-simplistic treatments of resource conflict by political ecologists or others may unintentionally support programs that are likely to negatively impact the human subjects of research, conservation or development.

Abstract: This paper investigates the ways in which national and regional policies relate to farming activities and concerns amongst the rural population in an area of southern Africa. The struggle to make a living through farming was a common theme to emerge from research about changing livelihoods in response to both variability in the environment and changes in policy. This local discourse echoed regional debates about land and agrarian reform in post-apartheid South Africa and the uncertain future of mixed farming in Botswana. It also raised broader questions about the viability of the future of small-medium-scale farming systems in rural areas in Africa, especially those within dynamic dryland environments such as the Kalahari. This paper looks specifically at the links between poverty and asset holding and aims to identify the ways in which people are or are not able to utilise or mobilise these assets in times of need. We argue that this can vary significantly between seemingly similar settlements, and similar households and that understanding this complexity is the key to recognising how future interventions many impact upon people's lives. Too often, in the quest to produce understandings of poverty and livelihoods, the complexity, incongruity and reality of day-to-day practices are overlooked. Thus we seek to draw out the interactions between policy and natural resource use, and the capital asset changes involved in these interactions, which influence the sustainability of livelihoods and the differing levels of poverty and vulnerability.

Abstract: Carbon sequestration in soil organic matter is increasingly advocated as a possible win-win strategy in the rehabilitation of degrading dryland agro-ecosystems because it simultaneously contributes to the reduction of global atmospheric greenhouse gas concentrations while enhancing local land productivity. A study was conducted in Senegal's Old Peanut Basin to assess current carbon stocks and to examine management options for their increase. Average soil and woody biomass carbon contents were 11.3 and 6.3 t carbon (C) ha-1, respectively. CENTURY, a biogeochemical model, was used to simulate soil and biomass carbon over a period of 25 and 50 years under a series of land use and management options. These simulated practices resulted in C dynamics ranging from -0.13 t C ha-1 yr-1 from a worst-case millet-sorghum rotation to +0.43 t C ha-1 yr-1 on intensively managed agricultural fields. Agroforestry simulations involving Faidherbia albida (Del.) Chev. and Leucaena leucocephala (Lam.) deWit. also resulted in promising carbon gain (+0.22 and +0.12 t C ha-1 yr-1, respectively), suggesting that improving agricultural practices is key to enhancing food production and mitigating climate change. Results from a sensitivity analysis suggest that woody biomass carbon is more sensitive to long-term changes in precipitation and temperature than soil carbon. Other management strategies likely to result in lower rates of soil carbon sequestration, including short-term improved fallows, should also be considered viable opportunities because promoting too narrow a set of [`]best management practices' risks weakening local adaptability and opportunistic management regimes, both of which are crucial elements in small-scale farming systems in drylands.

Abstract: Implementation of the United Nations Convention on Combating Desertification (CCD) requires an identification of areas where vegetative production is consistently declining. Time series of remote sensing data are well suited to this task, and methods have been developed for assessing long-term trends in savannah net primary production (NPP) or biomass and crop yields, using time series of NOAA AVHRR normalized difference vegetation index (NDVI) data. In this study, trend analysis is used to identify areas within the Peanut Basin in Senegal with apparent positive or negative trends in agricultural productivity. Having identified such areas, in-depth analysis is undertaken to determine whether long-term changes in agricultural productivity are mainly a function of rainfall patterns or are due to anthropogenic influences. The trends observed cannot be solely explained by rainfall data, and there seems to be a significant correlation with changes in land cover and land use. It is concluded that NDVI trend analysis may be used to investigate long-term and wide-scale environmental changes, and that by pinpointing areas of major change it can serve as a starting point for local-level analysis or action.

Abstract: Preliminary phytolith analysis of ephemeral lake fill sediment at Long Pocket, near Toomba, northeast Queensland, Australia, indicates that a C4-dominated grassland with a minor woody component has been present in the region since ca. 8000 cal yr B.P. Based on the modern distribution of C4 and C3 native grasses in Australia, this suggests that mean summer temperatures of at least 14°C (ca. 10°C cooler than present) were maintained since the early Holocene. This interpretation is comparable with previous studies, which together imply that the establishment of C4-dominated grasses in central and northeast Australia occurred between the last glacial maximum (most likely after ca. 16,000 14C yr B.P.) and ca. 7200 14C yr B.P. (ca. 8000 cal yr B.P.). Taxonomic composition of the grassland appears relatively consistent since the early Holocene at Long Pocket and includes phytoliths comparable with those from modern Arundinoideae, Panicoideae, and Chloridoideae. Rare non-grass phytoliths are also present. A gradual decrease in abundance of saddle phytolith forms (attributed to Chloridoideae grasses) from the base of the record at ca. 6500-7000 cal yr B.P. suggests decreasing aridity throughout the Holocene. This trend could reflect a locally drawn out effect of the end of the postglacial arid period due to the well-drained basalt flow catchment maintaining a local arid habitat for the Chloridoideae grasses.

Abstract: The New South Wales Government recently introduced the Native Vegetation Conservation Act to protect the native grassland and woodland of the state. The Act protects biodiversity by preventing farmers from clearing such vegetation on their properties but, as a consequence, reduces farm incomes and land values. An economic model of the relationship between land value and percentage of farm in native vegetation is integrated with an ecological model of the relationship between species lost and percentage of the farms in native vegetation. The integrated framework is applied to estimate the opportunity costs of the Act for one important agricultural area of the state, the northern part of the Brigalow Belt South Bio-Region. If all the vegetation were protected, the reduction in land value would be at least 14.3%, which is an opportunity cost of at least $148.5 m for the area. Both the benefits and costs of biodiversity protection must be accounted for, so risk simulations are then combined with benefit-cost analysis to compare the benefits of biodiversity protection to these costs.

Abstract: The organic matter of lake sediments contains information that allows for the reconstruction of past environmental and climatic changes. The elemental composition and isotopic characteristics of sedimentary organic matter enable discrimination between allochthonous (vegetal matter from within the catchment) and autochthonous (phytoplanktonic and fixed algae) components. This approach makes it possible to distinguish between the inputs of organic matter from C3- vs. C4-type land plants. Sedimentary records from South America and Africa provide examples of applications of organic bulk composition in palaeoenvironmental reconstructions. The records from two African lakes show that, during the Last Glacial Maximum (LGM), the distribution of Corg/Norg-[delta]13C pairs indicates the dominance of organic material having a C4 terrestrial origin. These inferences are supported by pollen analysis, which indicates opening up of the forest at both sites, consistent with drier climatic conditions than present. The record from Siberia Lake (Bolivia), ca. 3000 m altitude, shows that, during the LGM, the sedimentary organic matter is dominated by the phytoplanktonic fraction, as indicated by the Corg/Norg-[delta]13C pairs. The petrographic analyses show that this material is not well preserved, suggestive of drier conditions, consistent with interpretations from the pollen record. The beginning of the Holocene is marked by a shift from a scattered C4 signal to one with a greater terrestrial C3 and aquatic phytoplanktonic influence. These results indicate climatic amelioration towards more humid and warmer climatic conditions, leading to forest development in the lake catchment, together with increasing lake levels conducive to greater phytoplankton production. These conditions persisted during the Holocene, as shown by the Corg/Norg-[delta]13C pairs in all lakes, with a terrestrial C3 signal predominating at the Carajas and Siberia lakes. Only Dom Helvécio Lake shows a different pattern during the beginning of the Holocene in the distribution of Corg/Norg-[delta]13C pairs. This pattern indicates that the sedimentary organic material is dominated by C4 terrestrial material coming from savanna expansion in the lake catchment during a period of relative aridity in central Brazil.

Abstract: Concern for the potential global change consequences of increasing atmospheric CO2 has prompted interest in the development of mechanisms to reduce or stabilize atmospheric CO2. During the next several decades, a program focused on terrestrial sequestration processes could make a significant contribution to abating CO2 increases. The reclamation of degraded lands, such as mine-spoil sites, highway rights-of-way, and poorly managed lands, represents an opportunity to couple C sequestration with the use of fossil-fuel and energy by-products and other waste material, such as biosolids and organic wastes from human and animal sewage treatment facilities, to improve soil quality. Degraded lands are often characterized by acidic pH, low levels of key nutrients, poor soil structure, and limited moisture-retention capacity. Much is known about the methods to improve these soils, but the cost of implementation is often a limiting factor. However, the additional financial and environmental benefits of C sequestration may change the economics of land reclamation activities. The addition of energy-related by-products can address the adverse conditions of these degraded lands through a variety of mechanisms, such as enhancing plant growth and capturing of organic C in long-lived soil C pools. This review examines the use of fossil-fuel combustion by-products and organic amendments to enhance C sequestration and identifies the key gaps in information that still must be addressed before these methods can be implemented on an environmentally meaningful scale.

Abstract: This paper reviews hypotheses and evidence about the development pathways (common patterns of change in livelihood strategies) occurring in hillside and highland areas and their implications for sustainable land management and poverty reduction, based upon community level survey results from Honduras, Uganda and Ethiopia. Several common development pathways were found in these three countries, all of which include cereal production as the primary or secondary activity. These include expanding or intensifying cereal crop production, mixed cereals/livestock, cereals/perennials, cereals/perishable annuals, cereals/non-farm employment, and in Honduras, cereals/forestry activities. These pathways were largely determined by four types of factors affecting local comparative advantages: agricultural potential, access to markets and roads, population density, and presence of programs and organizations. Adoption of improved land management was higher and productivity, resource and welfare outcomes were better in the pathways associated with higher value crop production or non-farm employment. In less-favored environments where such pathways have less potential, other development pathways should be facilitated and improved. Opportunities for socially profitable investments have been shown to exist even in less-favored environments, but these need to be tailored to the different comparative advantages of these areas.

Abstract: Woody shrubs, including honey mesquite (Prosopis glandulosa Torr. var glandulosa) and juniper (Juniperus ashei Buckholtz and Juniperus pinchotii Sudh), have invaded the native prairies and savannas of much of central Texas. As a consequence of this "brush" encroachment, many of these grasslands may have lost some ability to provide water yield and habitat for some native wildlife species, particularly grassland birds. In some areas, brush management followed by rangeland manipulation treatments may enhance water yields and improve habitat for some grassland-associated wildlife. The relative effectiveness of brush control treatments varies according to the treatment objective and location within a watershed. There are often multiple objectives when public monies are committed for cost-sharing brush management treatments on private lands. When considering multiple objectives (e.g., water yield and grassland bird habitat), the priority ranking process for determining the most cost-effective treatment locations can be confounded. The goal of this study was to reduce this confounding by creating a methodology for prioritizing areas within two watersheds for brush management cost-share programs. We developed a sub-basin scale prioritization method using total society cost of implementing a brush treatment program, hydrologic impacts and grassland bird responses to brush treatments. Results show which sub-basins within the Edwards Aquifer recharge zone and Twin Buttes reservoir watersheds may be the most attractive candidates for brush treatment cost-share programs with the goal of optimizing water yield and grassland bird habitat. By adjusting weights for water and grassland bird efficiency criteria, this approach can be adapted to prioritize different levels of ecosystem responses to brush treatments.

Abstract: Holocene climatic changes in West Africa are usually explained by increased/decreased activity of the monsoon from the Guinean Gulf toward the continent. According to a diatom record from Lake Ossa (3°50'N, 9°36'E), we suggest that, in the near coastal areas of Cameroon, phases of intensification of the monsoon were marked by reduced precipitation and reduced evaporation, conditions nowadays prevailing South of the equator (4-5°S) during the austral winter. Lake Ossa is a shallow lake located in one of the rainiest area of the African rain forest belt. During the wet season (March-November) it is fed by acid meteoric waters entailing low pH in the lacustrine waters. During the dry season (December-February) groundwater discharges allow the persistence of acid waters near the borders of the lake, but, in the inner parts, the waters tend to be alkaline, alkaliphilous diatoms are abundant in the surface sediment samples and are used as indicators of low precipitation. At that time, atmospheric dust containing reworked diatoms from Saharan Quaternary deposits is transported by the northern trade winds and reaches the Ossa area. Wind blown diatoms are considered as a signature of the northern trade winds. A diatom record from the western deep part of Lake Ossa has provided climatic data for the mid-late Holocene at a resolution of 50-60 years. A major climatic change at 2700 cal yr BP was marked by the appearance of wind blown diatoms. A millennial-scale alternation between low and high precipitation episodes is recorded during the last 5500 years. The low precipitation episodes before 2700 cal yr BP are interpreted as a consequence of a northward extension of the climatic conditions that nowadays characterize the Southern Congo during the austral winter, when the monsoon extends into West Africa and reaches the northern sub-tropical latitudes. The effects of low precipitation on the water balance and on the rain forest were obliterated by an extremely low evaporation. Between 2700 and 1300 cal yr BP, precipitation was high and the rain forest intensively disturbed in response to convective storms. A low precipitation episode between 1300 and 600 cal yr BP is explained, contrarily to the previous similar episodes, by tropical rainfalls located farther South than today during a larger part of the year. The modern climate settles at about 600 cal yr BP. The climatic oscillations on a millennial time scale were apparently coincident with temperature changes in the Northern and Southern Atlantic suggesting that the monsoon over West Africa was essentially driven by interactions between both hemispheres. This interpretation is in agreement with available data from other equatorial and sub-tropical regions of West Africa.

Abstract: The effects of livestock grazing on composition and structure of ant communities were examined in the eastern Mojave Desert, USA for the purpose of evaluating ant communities as potential indicators of rangeland condition. Metrics for ant communities, vegetation, and other ground-cover elements were evaluated as a function of distance from livestock water tanks, which represents a gradient in level of livestock activity in desert settings. Data were collected at six isolated water tanks used by cattle during early summer, with seven plots (90 m � 90 m; 100 pitfall traps) per tank. Thirty-eight species of ants were recorded, with an average of 14 ant species per plot. Ant species richness did not differ as a function of distance from the water tank. Also, overall species composition, as measured by a similarity index for species presence/absence for paired-comparisons of plots, did not show differences attributable to the gradient in grazing impact. In contrast, the relative abundance of several taxa and functional groups was significantly related to distance from the water tank. The predominant pattern was for the greatest abundance to occur at the water tank, with little difference in ant abundance among plots away from the water tank. This pattern was shown by the abundant ants species, Conomyrma bicolor and Pheidole tucsonica, and the groups Conomyrma spp., Pheidole spp., homopteran tenders, and plant foragers. However, two species, Aphaenogaster megommata and Monomorium wheelerorum showed the greatest relative abundance at a distance away from the water tank. A number of ant metrics were significantly related to ground-cover metrics (R2 > 0.5). Organic debris was the variable most frequently related significantly to ant abundance metrics, always in a positive direction, followed by cover for perennial grasses, annual forbs, and shrubs, and bare patch size. Ant community metrics in the study region appear to have little potential to serve as indicators of rangeland condition because differences were evident primarily in severely degraded localized conditions rather than in intermediate widespread conditions.

Abstract: Abstract:The ability to predict which areas of conservation importance are most vulnerable to transformation and to rank the relative damage that transforming land uses could cause to biodiversity are important components of an effective and realistic conservation planning process. We used the South African grassland biome as a case study to illustrate the assessment of vulnerability to land-use transformation through the construction of a �threat map.� We identified the dominant transforming land uses and created suitability models based on area appropriateness for each. Land uses were scored according to their expected relative impacts on biodiversity, with a framework that included compositional, structural, and functional components. This information, once combined, resulted in a map that highlighted the areas most vulnerable to transformation in terms of the likelihood of their transformation and the impact on their biodiversity. We propose that such an analysis of the threat of transformation, in combination with species-representation approaches, will aid the integration of conservation planning theory and decision making. This approach can be applied at any scale and in any region with a robustness and accuracy dependent on data quality, resultant suitability models, and comprehension of how land uses affect an area's biodiversity. Resumen:La habilidad para predecir las áreas de conservación que son más vulnerables a la transformación y para clasificar el daño relativo que pudieran causar las transformaciones del uso de suelo a la biodiversidad son componentes importantes de un proceso efectivo y realista de planeación de la conservación. Utilizamos el bioma de pastizal sudafricano como estudio de caso para ejemplificar la evaluación de la vulnerabilidad a la transformación del uso de suelo por medio de la construcción de un �mapa de amenazas.� Identificamos las transformaciones de usos de suelo dominantes y creamos modelos de aplicabilidad basados en la aptitud de área para cada una. Los usos de suelo fueron calificados según los impactos relativos esperados sobre la biodiversidad en un marco que consideraba componentes estructurales y funcionales. Esta información, una vez combinada, resultó en un mapa que realzaba las áreas más vulnerables a la transformación en función de la probabilidad de su transformación y el impacto sobre su biodiversidad. Proponemos que tal análisis de la amenaza de transformación, combinada con enfoques de representación de especies, contribuirá a la integración de la teoría de planeación de la conservación con la toma de decisiones. Este enfoque puede ser aplicado a cualquier escala y región con una robustez y una precisión dependiente de la calidad de los datos, de los modelos de aplicabilidad resultantes y la comprensión de los efectos de la transformación del uso del suelo sobre la biodiversidad de un área.

Abstract: In previous papers we have considered the optimal mix of biodiversity in semi-arid rangelands, focusing on the steady state. This paper addresses the question of conservation in the optimal use of rangelands, where conservation is understood to mean maintenance of the system in a [`]natural' state. We consider a rangeland that may exist in one of two states. In the [`]natural' state, its dynamics are regulated by fire. In the [`]managed' state, its dynamics are regulated by grazing pressure by livestock. We show that the optimal use of rangelands may include its maintenance in both states at different points in time, depending on initial conditions and the set of relative prices.

Abstract: Abstract Aim This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid-Holocene and at the last glacial maximum (LGM). Methods Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 1000 14C yr bp. Results 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad-scale patterns of vegetation distribution. The north�south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed-canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad-scale pattern emerges. 2. Differences between the modern and mid-Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south-eastern Australia some sites show a shift towards more moisture-stressed vegetation in the mid-Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm-temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture-demanding vegetation in the mid-Holocene than today. South-western Australia was slightly drier than today. The single site in north-western Australia also shows conditions drier than today in the mid-Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid-Holocene, in sites occupied today by cool-temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9 °C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity. Main conclusions This study provides the first continental-scale reconstruction of mid-Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project.

Abstract: ABSTRACT Most national or regional initiatives aimed at managing biological invasions lack objective protocols for prioritizing invasive species and areas based on likely future dimensions of spread. South Africa has one of the most ambitious national programmes for managing plant invasions in the world. There is, however, no protocol for assessing the likely future spread patterns needed to inform medium- to long-term planning. This paper presents an assessment of the climatic correlates of distribution of 71 important invasive alien plants, and an analysis of the implications of these findings for future invasions in different vegetation types in South Africa, Lesotho and Swaziland over the next few decades. We used a variant of climatic envelope models (CEMs) based on the Mahalanobis distance to derive climatic suitability surfaces for each species. CEMs were developed using the first three principal components derived from an analysis of seven climatic variables. Most species are currently confined to 10% or less of the region, but could potentially invade up to 40%. Depending on the species, between 2% and 79% of the region is climatically suitable for species to invade, and some areas were suitable for up to 45 plant invaders. Over one third of the modelled species have limited potential to substantially expand their distribution. About 20% of the vegetation types have low invasion potential where fewer than five species can invade, and about 10% have high invasion potential, being potentially suitable for more than 25 of the plant invaders. Our results suggest that management of the invasive plant species that are currently most widespread should focus on reducing densities, for example through biological control programmes, rather than controlling range expansions. We also identify areas of the region that may require additional management focus in the future.

Abstract: Abstract 10.1002/ldr.609.abs What is overgrazing? Does it cause soil erosion? The recent debate from the ecological literature is reviewed as background to the debate on overgrazing and soil erosion. This debate stresses the need to view dryland grazing systems as dynamic ecosystems driven more by rainfall events than by livestock numbers. The case for soil erosion is then examined. Two case studies from communal rangelands in the Eastern Cape, South Africa, have cast doubts on the conventional wisdom that overgrazing leads to soil erosion. The first, a study of historical land-use change and erosion in a communal area, showed that the most intense erosion, taking the form of steeply dissected badlands, was associated with cultivated land that had been abandoned and reverted to grazing from the 1960s onwards. Such severe erosion was generally absent from land that had been under grazing since the 1930s. The second study demonstrated that erosion rates from communal grazing lands (�overgrazed�) were only slightly higher than those from land under �optimal� grazing, that is grazing at a level considered not to exceed the carrying capacity of the land. These results support the ecologist's contention that communal grazing systems do not necessarily degrade the range condition relative to management systems based on a notional carrying capacity. Copyright © 2004 John Wiley & Sons, Ltd.

Abstract: Recent attempts to streamline the identification of areas requiring immediate conservation attention have resulted in the development of prioritisation procedures that identify areas of biodiversity importance facing large threats in the near future. This study incorporated biodiversity data on bird and vegetation distribution with an assessment of land use suitability for cultivation and afforestation for the Limpopo Province of South Africa. The low altitude savanna regions in the northeast contain high species diversity, but are unsuitable to alternative forms of land use and are well conserved (by e.g., the Kruger National Park). The central and eastern mountain ranges, sites of high biodiversity, are suitable to dryland cultivation and afforestation and are thus potential conservation priorities. Areas with high biodiversity values, e.g., irreplaceable areas that contain biodiversity features essential for meeting conservation targets, were then investigated for their potential land-use threats in order to prioritise those needing immediate conservation actions. We suggest how losses of biodiversity could be minimised by reaching such decisions more quickly.

Abstract: Fossil soils, burrows and mammals of the upper John Day Formation in central Oregon are evidence of bunch grasses and open, semiarid vegetation as old as late Oligocene (earliest Arikareean, 30 Ma). Root traces in these paleosols include both stout, tapering tubes, like roots of trees, as well as sinuous filamentous tubes, similar to roots of grasses. Paleosol structure is fine subangular blocky, with patchy distribution of grass-like roots, as in wooded grassland and sagebrush steppe with bunch grasses. Cursoriality in horses (Mesohippus, Miohippus) and hypsodonty in rhinos (Diceratherium) is also evidence for open grassy vegetation. Trace fossils of Pallichnus (dung beetle boli) and Edaphichnium (earthworm chimneys) are characteristic of wooded grassland paleosols, whereas Taenidium (cicada burrows) dominates desert shrubland paleosols, as has also been found in Quaternary paleosols and soils of eastern Washington. In both Oligocene and Quaternary paleosol sequences, arid shrubland and semiarid grassland paleosols alternate on Milankovitch frequencies (23, 41, 100 ka). The oldest known paleosols in Oregon with crumb structure and abundant fine fossil root traces characteristic of sod grasslands are dated by mammalian biostratigraphy as Hemingfordian (early Miocene, ca. 19 Ma). Wooded grassland habitats are indicated by scattered chalcedony-calcite rhizoconcretions from large woody plants, and by fossil chalicotheres (Moropus), camels (Gentilicamelus, "Paratylopus") and horses (Parahippus). Silty texture and silcrete horizons are evidence of semiarid to arid paleoclimate, and are in striking contrast to highly calcareous, and clayey underlying paleosols of the John Day Formation. These silcrete paleosols may represent the Miocene onset of summer-dry (Mediterranean) seasonality, as opposed to a summer-wet (monsoonal) pattern of seasonality found in this region during the Oligocene. Oregon's early rangelands can be compared with those in the North American Great Plains. Granular-structured calcareous paleosols of the Brule Formation of South Dakota are evidence of dry, bunch grasslands as old as 33 Ma (early Orellan, early Oligocene), and crumb-structured paleosols of the Anderson Ranch Formation of Nebraska are evidence of sod grasslands as old as 19 Ma (late Arikareean, early Miocene). Although grasses were a conspicuous part of dry rangelands well back into the Oligocene, early and middle Miocene sod grasslands in North America were restricted to regions estimated to have had less than 400 mm mean annual precipitation.

Abstract: Scientists assert that integrated research is a foundation of Sustainable Development. However, they often presume that differences between the bio-physical and social sciences are hurdles in the way of integration. We show that need not be the case. The problem lies in the way environmental research is organised. The essay goes on to discuss how the problem is being resolved, and the implications for [`]environmental science'.

Abstract: South African grasslands support a rich flora that is attracting growing conservation interest. Fire has long been used to manage grasslands for livestock production. However, there is very little information on the effects of fire on forb diversity to help guide conservation management. We studied plant diversity at scales of 1 and 100 m2 in three long-term burning experiments in mesic, montane and semi-arid grasslands, respectively, to explore forb responses to different fire regimes. Though the dominant grasses were strongly influenced by season and frequency of fire, forb diversity showed no consistent trends. Ordination results showed that forb composition varied less with fire treatment than with local site conditions. Forbs in all three grasslands seem remarkably resilient to fire. However, all three sites showed large compositional changes if fires were excluded for about 10 or more years, with the replacement of many species by a suite of, mostly, woody species. Patterns of beta-diversity sampled in the montane grassland, showed somewhat different patterns, with species turnover increasing with inter-fire interval. Our results indicate that most forb species tolerate a wider range of season and frequency of fires than the dominant grasses. However, to accommodate those species with low tolerance of frequent fires, parts of the landscape will require less frequent fires.

Abstract: Abstract Ant communities have been widely used as indicators of minesite rehabilitation in Australia and are beginning to play a similar role in other parts of the world. Here we examine ant communities on rehabilitated ash dams associated with a coal-fired power station on the highveld of South Africa, to improve our understanding of ecosystem development on these substrates. Ants were sampled using pitfall traps at 11 ash-dam sites, ranging from unrehabilitated to 9-year-old rehabilitated sites, as well as two adjacent natural grassland sites. Sampling was conducted on 12 occasions from March 1997 to January 1999. Forty-nine ant species from 19 genera were recorded during the study. Site species richness was positively correlated with rehabilitation age, ranging from 10 to 25 at ash-dam sites, compared with 28 and 34 at the two natural grassland sites. There was a humped relationship between total ant abundance and rehabilitation age, with abundance peaking after 5�7 years at levels far higher than those at natural sites. Ordination analysis showed clear separation between ash-dam and natural sites along the first axis. The unrehabilitated ash-dam site was also separated from rehabilitated sites along the first axis. Sites of different rehabilitation age were separated along the second axis. Individual ant species showed clear successional patterns across the rehabilitation gradient. Although there was a clear successional trend for the development of ant communities on rehabilitated ash dams, this trend was not toward natural grassland. The lack of convergence toward ant communities of natural grasslands reflects the markedly different substrate and plant composition on ash dams and supports the widely held view that restoration of natural grassland communities is not a realistic goal of ash-dam rehabilitation. However, the development of species-rich ant communities, containing at least some late-successional species, indicates the potential for rehabilitated ash dams to support diverse and complex ecosystems.

Abstract: Mechanical shrub control with roller choppers can be an inexpensive and non contaminant system for increasing grassland production in rangelands dry regions. A field experiment was carried out between October 1997 and October 2001 in the 34;Caldenal-Jarillal 34; botanic district of Argentina, a natural rangeland ecosystem with a high water deficit throughout much of the year. The trial was conducted on a Typic Ustortent and consisted of the following treatments: a control, the undisturbed natural condition (N), and rolled with (I) and without (R) interseeding of Panicum coloratum. Results showed that I and R improved soil water content within the upper 100 160;cm, dry matter production of grasses, amount of litter and water use efficiency as compared to N. The positive effect of rolling on soil water content was detected only in autumn months when water balance was positive. In summer months, when a negative water balance occurred, soil water content of rolled treatments was not different from that of the unrolled one. Consumptive water use was similar in rolled and unrolled treatments, and equivalent to the rainfall, reflecting the low soil water-holding capacity. The higher efficiency of water use in rolled treatments indicated that grasses were more efficient in using the consumed water. The I and R treatments had similar values of soil water content within the upper 100 160;cm, grass dry matter production, amount of litter and water use efficiency. However, a higher grass dry matter production in R than in I was noticed in part of the last year of this study. Grass dry matter production increased at the same rate in all treatments after 4 years, but litter remained constant in the unrolled treatment and decreased in the rolled ones. Mechanical shrub control with a roller chopper decreased shrub competition, thereby increasing the productivity of the ecosystem.

Abstract: Burning of the vegetation in the African savannahs in the dry season is widespread and may have significant effects on soil chemical and biological properties. A field experiment in a full factorial randomised block design with fire, ash and extra grass biomass as main factors was carried out in savannah woodland of the Gambella region in Ethiopia. The microbial biomass C (Cmic) was 52% (fumigation-extraction) and 20% (substrate-induced respiration) higher in burned than unburned plots 12 160;d after burning. Both basal respiration and potential denitrification enzyme activity (PDA) immediately responded to burning and increased after treatment. However, in burned plots addition of extra biomass (fuel load) led to a reduction of Cmic and PDA due to enhanced fire temperature. Five days after burning, there was a short-lived burst in the in situ soil respiration following rainfall, with twice as high soil respiration in burned than unburned plots. In contrast, 12 160;d after burning soil respiration was 21% lower in the burned plots, coinciding with lower soil water content in the same plots. The fire treatment resulted in higher concentrations of dissolved organic C (24-85%) and nitrate (47-76%) in the soil until 90 160;d after burning, while soil NH4+-N was not affected to the same extent. The increase in soil NO3�N but not NH4+-N in the burned plots together with the well-aerated soil conditions indicated that nitrifying bacteria were stimulated by fire and immediately oxidised NH4+-N to NO3�N. In the subsequent rainy season, NO3�N and, consequently, PDA were reduced by ash deposition. Further, Cmic was lower in burned plots at that time. However, the fire-induced changes in microbial biomass and activity were relatively small compared to the substantial seasonal variation, suggesting transient effects of the low severity experimental fire on soil microbial functioning.

Abstract: To investigate land-sea interactions during deglaciation, we compared proxies for continental (pollen percentages and accumulation rates) and marine conditions (dinoflagellate cyst percentages and alkenone-derived sea surface temperatures). The proxies were from published data from an AMS-radiocarbon-dated sedimentary record of core GeoB 1023-5 encompassing the past 21,000 years. The site is located at ca. 2000 m water depth just north of the Walvis Ridge and in the vicinity of the Cunene River mouth. We infer that the parallelism between increasing sea surface temperatures and a southward shift of the savanna occurred only during the earliest part of the deglaciation. After the Antarctic Cold Reversal, southeast Atlantic sea surface temperatures no longer influenced the vegetation development in the Kalahari. Stronger trade winds during the Antarctic Cold Reversal and the Younger Dryas period probably caused increased upwelling off the coast of Angola. A southward shift of the Atlantic anti-cyclone could have resulted in both stronger trade winds and reduced impact of the Westerlies on the climate of southwestern Africa.

Abstract: The number of tsessebes in Kruger National Park, South Africa, increased during 1977-1985, but declined after 1986. We used tsessebe number and age structure to determine year-to-year variation in adult survival. Adult survival rate was positively correlated with dry-season rainfall (a measure of grass productivity during the dry season) and with the cumulative rainfall surplus. Juvenile survival rate (as indexed by the juvenile:female ratio) was also correlated with the cumulative rainfall surplus. Tsessebe feed in broad, grass-covered drainage lines within Colophospermum mopane shrubland on basaltic soils. Here drainage is slow and the cumulative rainfall surplus or deficit, relative to the mean annual rainfall, is an index of dry-season soil moisture, which, in turn, determines dry-season grass productivity and hence the food supply for tsessebe. Adult survival rate was density-dependent, indicating that there was intraspecific competition for food. When the relationships between survival rates and rainfall were used in a model of tsessebe population dynamics to predict juvenile and adult survival rates from the recorded annual and dry-season rainfalls, the modelled population changes were similar to those observed. We conclude that changes in tsessebe numbers probably resulted from rainfall-induced changes in food availability during the dry season, which caused adult survival to decline after 1986. The principal management implication is that the tsessebe decline can be reversed only by several successive years of above-average annual rainfall. The importance of green grass during the dry season as a key resource is emphasised, not only for tsessebe, but also for other African antelopes that graze selectively.

Abstract: Soil macrofauna are sensitive to land use changes and this may have implications to soil functioning. The impact of the conversion of native ecosystems into extensive or intensive pastures on soil macrofauna were assessed with a standardised methodology in two neotropical phytogeographical regions, i.e. a tropical savanna area (Eastern Plains of Colombia) and a tropical rain forest area (Brazilian Amazon). In the savanna area, extensive cattle ranching only led to a slight enhancement of earthworm populations and to short-term fire-induced decreases of macrofaunal density. In intensive pastures, the initial taxonomic richness and composition of soil macrofauna were maintained, while native earthworm biomass was strongly increased. This may be explained by the similar mesologic conditions between these systems (similar vegetation structure) and by the higher quality of the organic inputs in the pastures (roots, litter and cattle faeces). Increased macrofaunal activity with a high taxonomic diversity is expected to have positive impacts on the sustainability of pastures in Colombian savannas. In the Amazon basin, slashing and burning of the forest for intensive pasture establishment resulted in more dramatic effects on native macrofauna. Taxonomic diversity was particularly strongly affected. Native earthworm species were largely depleted at the expanse of exotic peregrine species like, e.g. Pontoscolex corethrurus. These results are probably bound to the deep environmental changes that follow the conversion of forest into grassland ecosystems. Such modifications of macrofaunal communities are known to have potential negative effects on soil functioning and on the sustainability of agropastoral systems in this area.

Abstract: Ozotoceros bezoarticus celer is the most endangered subspecies of pampas deer. Although common in the Argentine Pampas 100 years ago, it persists in only two small populations. The largest population has survived due to the rarity of roads, internal farm subdivisions, and the low cattle density. However, habitat condition for this population has changed dramatically in the last 16 years. Five Landsat images (1985, 1992, 1997, 1999, 2001), covering 4608 km2, were used to quantify pampas deer habitat loss due to the replacement of natural grassland by exotic pastures and crops. Image classification showed that natural grassland cover was reduced from 84.5 to 37.8% between 1985 and 2001. The annual transformation rate increased significantly from 1.4 to 10.9%. Average paddock size was significantly reduced from 1470 to 873 ha, and the number of paddocks increased from 129 to 227. The land within this area proposed for a national park has not escaped these habitat changes. In the last 6 years the amount of replaced area within the proposed park has increased from 9.1 to 51.1% due to actions by ranchers to avoid inclusion within park boundaries. Three patches of natural grassland still remain within the pampas deer distribution, one of which is the proposed national park. The implementation of a national park is a decisive challenge for the survival of pampas deer and its habitat in Argentina.

Abstract: Two experiments were performed to determine the effects of inoculation with N2 fixing bacterium Azospirillum brasilense on forage production and root growth in seedlings of Wilman lovegrass, weeping lovegrass, and sideoats grama. Two sources of inorganic nitrogen (N) were tested: Urea, CO(NH2)2 (45%) and ammonium nitrate NH4NO3 (33.3%). Crude protein (CP), calcium (Ca) and phosphorous (P) concentrations were determined. In both experiments top dry matter (DM) production was significantly affected for grasses and inoculation but no differences were found for inorganic nitrogen applications. Maximum amount of top DM was obtained with the Wilman lovegrass with 5.70 160;g, weeping lovegrass reached 2.70 160;g, and sideoats grama only reached 1.58 160;g. Inoculated treatments reached 3.37 160;g while the no-inoculated treatments obtained 2.74 160;g. A similar trend was also noted for root phytomass. CP, Ca and P concentrations for the first experiment did not show any trend; therefore, they were not determined for the second experiment. Inoculation of grasses with A. brasilense may be a feasible practice for seeding some rangeland where N deficiency is a problem.

Abstract: A central goal of ecosystem ecology is to understand how the cycling of nutrients and the growth of organisms are linked. Ecologists have repeatedly observed that nutrient mineralization and plant production are closely coupled in time in many terrestrial ecosystems. Typically, mineralization rates of limiting nutrients, particularly of nitrogen, during the growing season determine nutrient availability while pools of mineral nutrients remain low and relatively constant. Although several previous reports suggest nitrogen mineralization has the potential to vary seasonally and out of phase with plant production, such a phenomenon has been poorly documented. Here we report results from a semiarid savanna ecosystem characterized by distinct temporal asynchrony in rates of soil nitrogen cycling and plant production. Periods of positive plant growth following the onset of rains coincide with periods of low N turnover rates, whereas higher rates occur late in the wet season following plant senescence and throughout dry seasons. Plant uptake from the substantial mineral N pool present early in the growing season is sufficient to explain most of the N allocation to aboveground plant biomass during the growing season, even in the absence of any wet-season mineralization. The mineral N pool is subsequently recharged by late wet- and dry-season mineralization, plus urine inputs at sites with high levels of ungulate activity. These findings suggest fundamental changes in the quality of substrates available to decomposers over a seasonal cycle, with significant implications for the partitioning of limiting nutrients by plant species, the seasonal pattern of nutrient limitations of aboveground production, and the effective use of N fertilizers in semiarid ecosystems.

Abstract: Three major problems are faced when mapping natural vegetation with mid-resolution satellite images using conventional supervised classification techniques: defining the adequate hierarchical level for mapping; defining discrete land cover units discernible by the satellite; and selecting representative training sites. In order to solve these problems, we developed an approach based on the: (1) definition of ecologically meaningful units as mosaics or repetitive combinations of structural types, (2) utilization of spectral information (indirectly) to define the units, (3) exploration of two alternative methods to classify the units once they are defined: the traditional, Maximum Likelihood method, which was enhanced by analyzing objective ways of selecting the best training sites, and an alternative method using Discriminant Functions directly obtained from the statistical analysis of signatures. The study was carried out in a heterogeneous mountain rangeland in central Argentina using Landsat data and 251 field sampling sites. On the basis of our analysis combining terrain information (a matrix of 251 stands 215;14 land cover attributes) and satellite data (a matrix of 251 stands 215;8 bands), we defined 8 land cover units (mosaics of structural types) for mapping, emphasizing the structural types which had stronger effects on reflectance. The comparison through field validation of both methods for mapping units showed that classification based on Discriminant Functions produced better results than the traditional Maximum Likelihood method (accuracy of 86% vs. 78%).

Abstract: A common problem when classifying remotely sensed images in order to map land use/cover is spectral confusion: different land use/cover classes present similar spectral signatures and are misclassified. This paper presents a procedure for mapping land use/ cover combining the spectral information from a recent image and data about spatial distribution of land use/cover types obtained from outdated cartography and ancillary data. Two fuzzy maps, which indicate the membership of each land use/cover class, were generated from the ancillary and spectral data, respectively, using an artificial neural networks approach. The combination of both maps was obtained using fuzzy rules. In comparison with spectral classification, this procedure allowed a statistically significant increase of accuracy of land use/cover classification (from 67% to 79%). The advantages of this procedure for combining spectral and ancillary data, with regard to others previously published in the literature, are that it allows one to take into account previous mapping efforts and to establish relationships between land use/cover and environmental variables specific to the mapped area.

Abstract: Urban nature conservation issues in South Africa are overshadowed by the goal to improve human well-being, which focuses on aspects such as poverty, equity, redistribution of wealth and wealth creation. The growing need for urban employment is closely associated with the increase of squatting and informal settlements along the urban fringe, which contributes to habitat fragmentation and sprawling of cities. This increasing urbanisation is one of the main threats to biodiversity in the Grassland biome as the natural vegetation in and around cities in the North-West Province of South Africa is destroyed at an alarming rate. The lack of detailed ecological data is a major problem in the implementation of conservation-orientated policies in urban planning and management. This paper gives a brief overview of urban nature conservation in the world, the obstacles to implementation in South Africa and the importance of socio-economics and environmental legislation. We focus specifically on projects involving phytosociological studies and biotope mapping in cities in the western Grassland Biome of the North West Province. The visible presence of native vegetation is essential and integral to urban nature conservation. There is a vital need to present urban environmental data in a format that is convincing and useful to decision makers. We propose an integrated approach towards urban ecological studies culminating in effective urban nature conservation.

Abstract: Monthly composites NOAA-advanced very high resolution radiometer (AVHRR) normalized difference vegetation index (NDVI) images (June 1992-October 1993) were used to analyze the phenology of savanna ecosystems in the Llanos del Orinoco region. The objective was to elaborate an ecosystems map of the area based on the temporal pattern analysis. Expert knowledge of savannas allowed the selection of representative ecosystems to monitor changes in NDVI. From 54 satellite images, model curves were created for each selected ecosystem. They were analyzed with the objective to characterize and identify each ecosystem. From these temporal patterns and statistical analyses, six satellite images were chosen to carry out a supervised classification using Mahalanobis distance methodological approach. Validation of the map was implemented using ground control points. Differences in phenology between ecosystems are strongly related to the environmental climatic conditions, especially to seasonal rainfall. Therefore, the phenology for each ecosystem can be explained based on water availability. A methodological approach, which reveals the phenology of the most important savanna ecosystems in Venezuela, was applied in this work. This study represents an improvement in mapping of ecological processes.

Abstract: This study assessed the nutritive value of the most important forage species of the Calden forest (central semi-arid La Pampa, Argentina), for samples collected in fall, winter and spring, under grazing conditions and during two successive years, for ranges of good and fair conditions. The crude protein concentration (CP) of short-winter grasses (Piptochaetium napostaense, Poa ligularis, Stipa clarazii and Hordeum stenostachys) was about 10%. Mid-winter grasses (S. tenuissima and S. gynerioides) never reached 6% CP. Summer grasses (Digitaria californica and Trichloris crinita) ranged from 7% to 9% CP. In vitro dry matter digestibility (IVDMD) was similar among short-winter and summer grasses (40-50%). Mid-winter grasses had the lowest IVDMD for all seasons ( 60;40%). Effects of sampling year and range condition on CP were consistently significant only for short-winter grasses. Good condition ranges provide a more acceptable forage supply than fair condition ranges.

Abstract: Abstract Aim Although sharing many similarities in their vegetation types, South America and Africa harbour very dissimilar recent mammal faunas, not only taxonomically but also in terms of several faunistic patterns. However late Pleistocene and mid-Holocene faunas, albeit taxonomically distinct, presented many convergent attributes. Here we propose that the effects of the Holocene climatic change on vegetation physiognomy has played a crucial role in shaping the extant mammalian faunistic patterns. Location South America and Africa from the late Pleistocene to the present. Methods Data presented here have been compiled from many distinct sources, including palaeontological and neontological mammalian studies, palaeoclimatology, palynology, and publications on vegetation ecology. Data on Pleistocene, Holocene and extant mammal faunas of South America and Africa allowed us to establish a number of similar and dissimilar faunistic patterns between the two continents across time. We then considered what changes in vegetation physiognomy would have occurred under the late Pleistocene last glacial maximum (LGM) and the Holocene climatic optimum (HCO) climatic regimes. We have ordained these proposed vegetation changes along rough physiognomic seral stages according to assumptions based on current botanical research. Finally, we have associated our hypothesized vegetation changes in South America and Africa with mammalian faunistic patterns, establishing a putative causal relationship between them. Results The extant mammal faunas of South America and Africa differ widely in taxonomical composition; the number of medium and large species they possess; behavioural and ecological characteristics related to herbivore herding, migration and predation; and biogeographical patterns. All such distinctions are mostly related to the open formation faunas, and have been completely established around the mid-Holocene. Considering that the mid-Holocene was a time of greater humidity than the late Pleistocene, vegetation cover in South America and Africa would have been dominated by forest or closed vegetation landscapes, at least for most of their lower altitude tropical regions. We attribute the loss of larger-sized mammal lineages in South America to the decrease of open vegetation area, and their survival in Africa to the existence of vast savannas in formerly steppic or desertic areas in subtropical Africa, north and south of the equator. Alternative explanations, mostly dealing with the disappearance of South American megamammals, are then reviewed and criticized. Main conclusions The reduction of open formation areas during the HCO in South America and Africa explains most of the present distinct faunistic patterns between the two continents. While South America would have lost most of its open formations within the 30° latitudinal belt, Africa would have kept large areas suitable to the open formation mammalian fauna in areas presently occupied by desert and semi-arid vegetation. Thus, the same general climatic events that affected South America in the late Pleistocene and Holocene also affected Africa, leading to our present day faunistic dissimilarities by maintaining the African mammalian communities almost unchanged while dramatically altering those of South America.

Abstract: Als prinzip des Ackerbaues muss angesehen werden, dass der Boden in vollem Massen wieder erhalten muss was ihm genommen wird. It should be borne in mind that as a principle of arable farming, what is taken from the soil should be returned to it in full measure. Von Liebig, 1841 Analysis of agricultural production systems in West Africa at the end of the 1980s revealed that arable farming without external inputs would lead to expansion of arable land at the expense of grazing land. With increasing population and demand for cereals, fallow systems would change to permanent cultivation, with the risk of decline in soil fertility of both grazing and arable land. This development finally would lead to decreasing land productivity jeopardising food security. Despite this alarming picture, food security has improved in the last decades. This paper reviews literature in order to revisit the analysis by testing the following hypotheses: - Decline of soil fertility over time is hard to estimate and to measure.- Expected decline in soil fertility is counteracted by farmers through reallocation and intensified use of organic material produced within the system.- As farming systems develop soil fertility is first managed through reallocation and intensified use of organic material and mineral fertilisers are only used when such options are exhausted. To test the first hypothesis nutrient budgets and the direct monitoring and measuring of soil fertility to detect changes in soil fertility are discussed. To evaluate the second and third hypotheses a possible pathway of development of farming systems is presented substantiated with supportive evidence. Nutrient budgets show negative trends in stocks, which are probably overestimated because lateral in- and outflows are scale-dependent, difficult to estimate and often ignored. Under farming conditions, decline in soil fertility can hardly be measured. Factors involved are inherent low soil fertility, heterogeneity of soils and highly variable soil fertility management in space and in time. However, at coarser scales, gradients in soil fertility are detected being a result of centripetal transport of organic material. In the schematic development pathway, soil fertility management practises follow the path from fallow, via intensifying recycling of nutrients combined with increased integration of livestock and arable farming to using external inputs. Spatial analysis shows that the different stages in development co-exist. It is concluded that the first analysis in the 1980s has overestimated the negative trends in soil fertility decline through increased use of organic material by increased labour use. However, current systems at many places will face a shift towards use of external inputs, i.e., fertilisers. This development is apparently only possible if market attractiveness permits.

Abstract: Time-series of normalized difference vegetation index (NDVI) are shown to capture essential features of seasonal and inter-annual vegetation variability at six nearby yet distinct vegetation communities in semi-arid New Mexico, USA NDVI values tend to follow a uniform order across communities, related directly to local vegetation. All communities exhibit a bimodal growing season on average, with peaks in springtime and summer. NDVI fluctuations are more spatially uniform in spring than in summer. NDVI variability corresponds to precipitation variability from the North American monsoon and El Niño-Southern Oscillation, and shows agreement with regional ground measurements.

Abstract: There is a pressing need for an objective, repeatable, systematic and spatially explicit measure of land degradation. In northeastern South Africa (SA), there are large areas of the former homelands that are widely regarded as degraded. A time-series of seasonally integrated 1 km, Advanced Very High Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) data was used to compare degraded rangelands [mapped by the National Land Cover (NLC) using Landsat Thematic Mapper (TM) imagery] to nondegraded rangelands within the same land capability units (LCUs). Nondegraded and degraded areas in the same LCU (paired areas) were compared by: (i) testing for differences in spatial mean [summation operator]NDVI values, (ii) calculating the relative degradation impact (RDI) as the difference between the spatial mean [summation operator]NDVI values of paired areas expressed as a percentage of nondegraded mean value, (iii) investigating the relationship between RDI and rainfall and (iv) comparing the resilience and stability of paired areas in response to natural variations in rainfall. The [summation operator]NDVI of degraded areas was significantly lower for most of the LCUs. Relative degradation impacts (RDI) across all LCUs ranged from 1% to 20% with an average of 9%. Although [summation operator]NDVI was related to rainfall, RDI was not. Degraded areas were no less stable or resilient than nondegraded. However, the productivity of degraded areas, i.e., the forage production per unit rainfall, was consistently lower than nondegraded areas, even within years of above normal rainfall. The results indicate that there has not been a catastrophic reduction in ecosystem function within degraded areas. Instead, degradation impacts were reflected as reductions in productivity that varied along a continuum from slight to severe, depending on the specific LCU.

Abstract: Soil moisture is important information in semiarid rangelands where vegetation growth is heavily dependent on the water availability. Although many studies have been conducted to estimate moisture in bare soil fields with Synthetic Aperture Radar (SAR) imagery, little success has been achieved in vegetated areas. The purpose of this study is to extract soil moisture in sparsely to moderately vegetated rangeland surfaces with ERS-2/TM synergy. We developed an approach to first reduce the surface roughness effect by using the temporal differential backscatter coefficient ([Delta][sigma]wet-dry0). Then an optical/microwave synergistic model was built to simulate the relationship among soil moisture, Normalized Difference Vegetation Index (NDVI) and [Delta][sigma]wet-dry0. With NDVI calculated from TM imagery in wet seasons and [Delta][sigma]wet-dry0 from ERS-2 imagery in wet and dry seasons, we derived the soil moisture maps over desert grass and shrub areas in wet seasons. The results showed that in the semiarid rangeland, radar backscatter was positively correlated to NDVI when soil was dry (mv<10%), and negatively correlated to NDVI when soil moisture was higher (mv>10%). The approach developed in this study is valid for sparse to moderate vegetated areas. When the vegetation density is higher (NDVI>0.45), the SAR backscatter is mainly from vegetation layer and therefore the soil moisture estimation is not possible in this study.

Abstract: Bare patches are found throughout the Nama Karoo. The development of bare patches is a degradation process that can be attributed to poor grazing practices such as overgrazing and patch selection, usually in combination with drought conditions. The restoration of vegetation in such degraded rangeland is seldom achieved through the withdrawal of livestock alone. Some form of intervention is usually necessary to promote a favourable environment for the establishment of plants. In this study various methods of re-establishing vegetation in bare patches were identified and tested, either alone or in combination. The treatments were: seeded, seeded+branches, tilled, tilled+seeded, tilled+seeded+branches and a control. The tilled+seeded+branches treatment was the most successful in providing a suitable environment for the establishment of desirable plant species, but the tilled treatment the most cost-effective.

Abstract: Many external effects of land use change are based on modifications of lateral flows of soil, water, air, fire or organisms. Lateral flows can be intercepted by filters and thus the severity and spatial range of external effects of land use change is under the influence of filter effects. Wherever lateral flows are involved, research results cannot be simply scaled on an area basis, and overall impact does not follow simple linear causal relationships. This complexity has consequences for relationships amongst the primary agents who initiate or exacerbate external effects, other stakeholders who are affected by them and policymakers who attempt to mitigate problems that reach sufficient visibility in society. In this paper we review how the relative importance of lateral flows and filter effects differs among a number of externalities, and the implications this has for research methods. If flows and filters are incompletely understood, policies may be based on fallacies. Whereas [`]fire-breaks' act as filters in the lateral flow of the high temperature pulse of a fire, smoke from land-based fires can be intercepted only by rainfall acting as a filter and the external impact of smoke is determined by the atmospheric conditions governing lateral flow and chemical transformations along the pathway. Causal relations in smoke and haze problems are relatively simple and may form a basis for designing policy interventions to reduce downwind damage. For biodiversity issues, landscape connectivity, the absence of filters restricting dispersal and movement of organisms, is increasingly recognised as an influence on the dynamics of species richness and its scaling relations. Biodiversity research methods can extend beyond the current descriptive stage into clarifying causal relations with a lateral flow perspective. The question whether connectivity is in fact desired, however, depends on stakeholder interests and situation. Forest functions in watershed protection, presumably leading to a continuous flow of clean water in the dry season through the subsoil instead of a rapid surface transfer, have been generally attributed to the trees rather than the forest, with its rough surface structure, swamps and infiltration sites. A new synthesis of site-specific hydrological knowledge and tree water balance studies may be needed to separate myth from reality, and avoid wasting public funds on tree planting under the heading of reforestation, without restoring the hydrological regime of a real forest. Soil movement can be intercepted at a range of scales and in as far as soil transport entails movement of soil fertility, filter zones can be very productive elements of a landscape. To achieve [`]integrated natural resource management' all external effects of land use will somehow have to be taken into account in farmer decision making about the use of natural resources on and off farm. Farmers' ecological knowledge may include concepts of lateral flows and should be further explored as an integral part of a new landscape ecological approach.

Abstract: Abstract Aim To determine whether patterns of avian species turnover reflect either biome or climate transitions at a regional scale, and whether anthropogenic landscape transformation affects those patterns. Location South Africa and Lesotho. Methods Biome and land transformation data were used to identify sets of transition areas, and avian species occurrence data were used to measure species turnover rates (β-diversity). Spatial congruence between areas of biome transition, areas of high vegetation heterogeneity, high climatic heterogeneity, and high β-diversity was assessed using random draw techniques. Spatial overlap in anthropogenically transformed areas, areas of high climatic heterogeneity and high β-diversity areas was also assessed. Results Biome transition areas had greater vegetation heterogeneity, climatic heterogeneity, and β-diversity than expected by chance. For the land transformation transition areas, this was only true for land transformation heterogeneity values and for one of the β-diversity measures. Avian presence/absence data clearly separated the biome types but not the land transformation types. Main conclusions Biome edges have elevated climatic and vegetation heterogeneity. More importantly, elevated β-diversity in the avifauna is clearly reflected in the heterogeneous biome transition areas. Thus, there is spatial congruence in biome transition areas (identified on vegetation and climatic grounds) and avian turnover patterns. However, there is no congruence between avian turnover and land transformation transition areas. This suggests that biogeographical patterns can be recovered using modern data despite landscape transformation.

Abstract: We analyzed data sets on phytomass production, basal cover, and monthly precipitation of a semiarid grassland in South Africa for good, medium, and poor rangeland condition (a) to investigate whether phytomass production per unit of basal cover differed among rangeland conditions, (b) to quantify the time scales of a carryover effect from production in previous months, and (c) to construct predictive models for monthly phytomass. Finally, we applied the best models to a 73-year data set of monthly precipitation data to study the long-term variability of grassland production. Our results showed that mean phytomass production per unit of basal cover did not vary significantly among the rangeland conditions-that is, vegetated patches in degraded grassland have approximately the same production as vegetated patches in grassland in good condition. Consequently, the stark decline in production with increasing degradation is a first-order effect of reduced basal area. Current-year precipitation accounted for 64%, 62%, and 36% of the interannual variation in phytomass production for good, medium, and poor condition, respectively. We found that 61%, 68%, and 33%, respectively, of the unexplained variation is related to a memory index that combines mean monthly temperature and a memory of past precipitations. We found a carryover effect in production from the previous 4 years for grassland in good condition and from the previous I or 3S month for grassland in medium and poor condition. The memory effect amplified the response of production to changes in precipitation due to alternation of prolonged periods of dry or wet years/months at the time scale of the memory. The interannual variability in phytomass production per unit basal cover (coefficient of variation [CV] = 0.42-0.50 for our 73-year prediction, CV = 0.57-0.71 for the 19-ycar data) was greater than the corresponding temporal variability in seasonal rainfall (CV = 0.29).

Abstract: This paper examines the melding of two discourses in southeastern Zimbabwe: land reform and wildlife management. The former seeks to redistribute large, [`]under-utilized' landholdings to smallholders whilst the latter needs extensive land holdings to be viable. These two discourses are rooted in very different models of development. The land reform exercise emphasizes direct redistribution, equity and land for crops; whilst the wildlife management discourse tends to stress maximizing foreign exchange earnings, encouraging public-private partnerships and trickle down. Yet there has been a recent flurry of interest in the development of [`]wildlife models' for land reform which would combine the two. This paper investigates whether the competing discourses about land for smallholders and wildlife-based land reform are compatible or can be successfully reconciled. It traces the ways they have come together in Zimbabwe's southeast lowveld and examines the [`]science' and politics underlying their melding. Finally it explores the potential implications for rural people's livelihoods of this development. It concludes that land reform and wildlife management can be reconciled, but probably not in a particularly equitable way: it is more likely to provide an opening for an equitable land reform agenda to be usurped by local and non-local elites with wildlife interests.

Abstract: Measurements of surface ozone in the southern African region are limited to a few active and passive monitoring sites. Over the region, the mean surface ozone concentrations exhibit strong seasonal and diurnal variations. The seasonal maximum generally occurs in the spring months from August to November and the minimum occurs in December and January. With the exception of Cape Point, a strong diurnal variation is observed at all sites. Ozone concentrations increase from a minimum near sunrise to a maximum in the afternoon, then decrease again to the early morning minimum. The highest ozone concentrations occur over Botswana and the Mpumalanga highveld. In both regions the springtime maximum is between 40 and 60 ppb, but reached more than 90 ppb as a mean in October 2000. In these two regions the monthly minimum is between 20 and 30 ppb. The mean daytime ozone concentrations in Botswana and on the highveld reach 40 ppb as early as 10:00 and remain above this level for up to 10 h. At the background stations at Cape Point, in Namibia and areas adjacent to the highveld the maximum concentrations are between 20 and 30 ppb with minimums between 10 and 20 ppb. In the Cross border Air Pollution Impact Assessment project, CAPIA, a threshold value of 40 ppb is used to assess the potential risk of damage to maize by ozone. Measured data show that this threshold is exceeded over Botswana and on the South African highveld.

Abstract: Distribution patterns were examined at both regional and local scales for an entire species assemblage of dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) from the margins of the semi-arid Nama Karoo and the more mesic Kalahari sands in South Africa. At regional scale, we examined geographical species ranges of the entire assemblage recorded on the farm, Brulpan (28°56'S 21°48'E), near Groblershoop, Northern Cape. At local scale on Brulpan, we examined differences in species abundance, geographical and functional group composition between the assemblages occurring in three habitats (shrub karoo, isolated Kalahari dune, tree karoo) characteristic of the two major regional ecotypes. The dung beetle assemblage of 37 species and 12,505 individuals was mostly endemic to the south-west of southern Africa. The dune sand assemblage was numerically dominated by two groups of sand specialist species with geographical distributions centred in the south-west Kalahari although some species also occurred in sand outliers elsewhere in southern Africa. The assemblage comprised equal proportions of ball rollers, tunnelers and kleptocoprids (use dung buried by other dung beetles). The Karoo assemblages on stony sand were numerically dominated by a group of primarily soil generalist species centred in the south-westerly arid late summer rainfall region of southern Africa. Ball rollers dominated both karoo assemblages with the balance comprising primarily kleptocoprids. The distribution patterns indicate how differences in climate and habitat characteristics between the Karoo and Kalahari systems have strongly influenced both local occurrence of dung beetles and their regional ranges and range edges in southern Africa.

Abstract: A total of 191 soil samples, taken in 1964 from grassland of southeastern Ireland, and 220 samples, taken in 1996 from the same area, were examined for soil organic carbon (SOC). Temporal and spatial changes in SOC concentration after the ca. 30-year interval were evaluated using conventional statistics, geostatistics and geographic information system (GIS) analyses. A lognormal distribution feature was observed for both data sets, and the results of a t-test showed that the difference between them was not significant. Spatial outliers were detected with the index of local Moran's I in order to obtain a robust variogram. Kriging was used for spatial prediction for both data sets using the same grid system. The difference between the two maps was determined using map algebraic functions and showed considerable spatial change. The analysis has enabled the delineation of two discrete sectors in the study area, which have clearly behaved differently: mean increase of SOC concentration in the eastern coastal sector was 30.2% compared to a mean decrease of 16.0% in the inland sector. Changes in land use or cultivation did not adequately account for the spatial difference. The division between the sectors appeared to coincide approximately with and to reflect both hill land and geological patterns. A satisfactory explanation for the difference has not been identified. Thus, a combination of geostatistics and GIS map algebra provides a useful tool for the examination of spatio-temporal changes in the environmental sciences and may detect features that are not discernible when only conventional statistics are used.

Abstract: Managing carbon stocks within landscapes is a key mid-term mitigation of atmospheric and climate change. Carbon (C) stocks residing in the vegetation and soils of five sites along a 120 km north-south transect within Senegal's Sahel were determined in degraded grasslands, grasslands with isolated and scattered shrubs, shrubby grasslands, and brushland with isolated trees. Total system carbon to 40 cm soil depth ranged between 12.0 and 31.2 t C ha-1 with an overall mean of 20.6 t C ha-1 (SEM=1.8). The canopy cover of woody vegetation was significantly related to total system C to 40 cm (kg ha-1). Total soil organic C (SOC) contents were not significantly different between plant communities despite ranging between 11.6 and 25.3 t C ha-1, an observation that is likely due to under-replication. The overall mean of SOC to 40 cm was 17.2 t C ha-1 (SEM=2.7) with 60 percent of that carbon residing in the top 20 cm. Woody bio-volume (m3 ha-1) was calculated from canopy coverage and average canopy height, and was significantly correlated with woody biomass (p=0.02), total biomass (p=0.03), SOC (p=0.05) and total system C (p=0.02) and warrants consideration as an indicator of land quality and carbon status in the Sahel. Assuming that degraded grasslands may be restored to woody grasslands over 20 years, then C sequestration rates of 0.77 t C ha-1 yr-1 may be achieved.

Abstract: Environmental degradation resulting from long-term drought and land use change has affected terrestrial carbon (C) stocks within Africa's Sahel. We estimated Senegal's terrestrial carbon stocks in 1965, 1985, and 2000 using an inventory procedure involving satellite images revealing historical land use change, and recent field measurements of standing carbon stocks occurring in soil and plants. Senegal was divided into eight ecological zones containing 11 land uses. In 2000, savannas, cultivated lands, forests, and steppes were the four largest land uses in Senegal, occupying 70, 22, 2.7, and 2.3 percent of Senegal's 199,823 km2. System C stocks ranged from 9 t C ha-1 in degraded savannas in the north, to 113 t C ha-1 in the remnant forests of the Senegal River Valley. This approach resulted in estimated total C stocks of 1019 and 727 MT C between 1965 and 2000, respectively, indicating a loss of 292 MT C over 35 years. The proportion of C residing in biomass decreased with time, from 55 percent in 1965 to 38 percent in 2000. Calculated terrestrial C flux for 1993 was -7.5 MT C year-1 and had declined by 17 percent over the previous 18 years. Most of the terrestrial C flux in 1993 was attributed to biomass C reduction. Human disturbance accounted for only 22 percent of biomass C loss in 1993, suggesting that the effects of long-term Sahelian drought continue to play an overriding role in ecosystem change. Some carbon mitigation strategies for Senegal were investigated, including potential C sequestration levels. Opportunities for C mitigation exist but are constrained by available knowledge and access to resources.

Abstract: Studying land degradation through a soil quality approach, which reveals soil functioning within the ecosystem, is necessary for sustainable management of land resources. This investigation was conducted to understand the changes of soil functions, resulting from exploitive management, using some soil quality indicators and their statistical and geostatistical measures. Undisturbed and disturbed sites were identified in each of two study areas, including an oak forest and a semiarid rangeland in central Iran. Soil organic carbon (OC), total nitrogen (TN), microbial respiration (MR), aggregate stability (AS), and hydraulic properties of the sites were determined. Statistical comparisons of frequency distribution functions of OC and MR revealed that these functions are normal in protected forest, while in the disturbed forest distributions deviate from normality. In the rangeland sites, the results were exactly the opposite. Spatial variability of the two variables in forest sites demonstrated pure nugget and spherical pattern in protected and disturbed sites, respectively. As for the rangeland ecosystem, pure nugget pattern was observed for both sites. According to our findings, protection of rangeland has resulted in higher OC and MR with no effect on the amount of TN and infiltration rate. The negative effect of this management system was a decrease in aggregate stability due to the formation of crust as a result of complete grazing exclusion. By contrast, improvement in all soil quality indicators in protected forest indicated the success of conservative management in this region.

Abstract: The remote sensing of pasture quality as determined by nitrogen, phosphorous, potassium, calcium and magnesium concentration is critical for a better understanding of wildlife and livestock feeding patterns. Although remote sensing techniques have proved useful for assessing the concentration of foliar biochemicals under controlled laboratory conditions, more investigation is required to assess their capabilities in the field, where inconsistent results have been obtained so far. We investigated the possibility of determining the concentration of in situ biochemicals in a savanna rangeland, using the spectral reflectance of five grass species. Canopy spectral measurements were taken in the field using a GER 3700 spectroradiometer. We tested the utility of using four variables derived from continuum-removed absorption features for predicting canopy nitrogen, phosphorus, potassium, calcium and magnesium concentration: (i) continuum-removed derivative reflectance (CRDR), (ii) band depth (BD), (iii) band depth ratio (BDR) and (iv) normalised band depth index (NBDI). Stepwise linear regression was used to select wavelengths from the absorption-feature-based variables. Univariate correlation analysis was also done between the first derivative reflectance and biochemicals. Using a training data set, the variables derived from continuum-removed absorption features could predict biochemicals with R2 values ranging from 0.43 to 0.80. Results were highest using CRDR data, which yielded R2 values of 0.70, 0.80, 0.64, 0.50 and 0.68 with root mean square errors (RMSE) of 0.01, 0.004, 0.03, 0.01 and 0.004 for nitrogen, phosphorous, potassium, calcium and magnesium, respectively. Predicting biochemicals on a test data set, using regression models developed from a training data set, resulted in R2 values ranging from 0.15 to 0.70. The error of prediction (RSE) in the test data set was 0.08 (±10.25% of mean), 0.05 (±5.2% of mean), 0.02 (±11.11% of mean), 0.05 (±11.6% of mean) and 0.03 (±15% of mean) for nitrogen, potassium, phosphorous, calcium and magnesium, respectively, using CRDR. When data was partitioned into species groups, the R2 increased significantly to >0.80. With high-quality radiometric and geometric calibration of hyperspectral imagery, the techniques applied in this study (i.e. continuum removal on absorption features) may also be applied on data acquired by airborne and spaceborne imaging spectrometers to predict and ultimately to map the concentration of macronutrients in tropical rangelands.

Abstract: Non-equilibrium processes in savannas are poorly understood because little data is available on how tree abundance has changed over long periods of time. Here I analyse fossil pollen and charcoal from Kanderi Swamp in Tsavo National Park, Kenya in order to investigate patterns of vegetation change over the past 1400 years. I compare the results with the predictions of cyclical, phase and transition and stochastic non-equilibrium models. Fourier analysis of the pollen data provides evidence of cyclical changes in tree abundance with a periodicity of 250-500 years, but the pollen data also suggests that the vegetation surrounding Kanderi swamp remained in a prolonged woodland phase, as predicted by phase and transition models, from approximately 770-1520 A.D. In addition, the results provided evidence of much shorter term changes in tree/grass abundance, perhaps reflecting stochastic variations in rainfall. The charcoal data suggests a link between vegetation change and fire history, possibly mediated through the effects of rainfall variation on the accumulation of combustible biomass in the herb layer. There was also evidence of extreme fires occurring twice in the past 1400 years. The results suggest that at the local scale, the vegetation near Kanderi Swamp has been mainly influenced by localised disturbance, rather than climatic shifts or the Rinderpest epidemic, and that elements of cyclical, phase and transition and stochastic models are needed in order to fully understand the observed pattern of vegetation change.

Abstract: Sagebrush-steppe ecosystems cover more than 36 million ha in North America and represent an important economic and ecological resource. These ecosystems have a climate with an extended cold period that can last more than five months. The CO2 fluxes during this protracted cold period likely play an important role in determining annual fluxes in these ecosystems; however, few studies have measured continuous CO2 fluxes in sagebrush-steppe ecosystems during the winter. The objective of our study was to obtain continuous measurements of CO2 fluxes during winter at representative sagebrush-steppe sites in the western USA and to study their relationships to environmental factors. Measurements of CO2 fluxes were obtained using Bowen ratio/energy balance (BREB) techniques during the winter at two locations in Idaho and one location in Oregon. Average daily ecosystem respiration during the winter period (November 1-March 15) was 1.31 ± 0.80 g CO2 m-2 day-1 and 1.23 ± 1.19 g CO2 m-2 day-1 at the two Idaho sites and 0.68 ± 0.56 g CO2 m-2 day-1 at the Oregon site. These values are well within the range of previously published results for similar ecosystems. Multivariate analyses showed that soil temperature, wind speed, and snow depth were the environmental factors most closely related to winter CO2 effluxes. Based on testing of empirical flux models, additional research will be required to develop mathematical models that reliably predict winter CO2 effluxes across a wide range of sagebrush-steppe sites.

Abstract: We use satellite data from different sensor systems to analyze and explain the causes, processes, and impacts of desertification in a Steppe grazing area in Syria, with the aim of supporting the formulation of a strategy for rehabilitating desertified areas. Through the mapping of parameters such as barley fields, eolian sand distribution, and drainage patterns from Thematic Mapper (TM) data, we identified barley cultivation as one major reason for increased sand erosion or its downhill deposition. With regard to the degradation of natural vegetation covers, we discriminate between climate-triggered and human-induced vegetation degradation by analyzing the natural response pattern of vegetation to rainfall. For the monitoring of vegetation covers, we used composited 10-day interval 8-km Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) data from 1981 to 1996. A consistently changing response of vegetation to rainfall over this time period, expressed in the residuals of the NDVImax/Rainfall linear regression calculations, is interpreted as nonclimate or human driven, where correlations between residuals and the time of their occurrence produce correlation coefficients >0.6. Pixels showing a negative temporal trend in residuals coincide with areas that are most heavily used by humans. Heavily used areas were located through detecting nomadic campsites from Indian Remote Sensing Satellite (IRS)-1C data. By combining campsite distribution with census data, such as flock size, average annual offtake, and grazing habits, we assess grazing pressures and put them in relation to the natural resources. This information provided the basis for the definition of protected areas or rehabilitation plots, and for elaborating measures to support the Steppe dwellers.

Abstract: Alpha or esparto grass (Stipa tenacissima) is a perennial tussock grass that coexists with Aleppo pines (Pinus halepensis) in semi-arid areas of southeast Spain and northern Africa where the pine is the tree most widely used in reforestation projects. Several authors have proposed that the improvement of soil characteristics by S. tenacissima in semi-arid slopes might be brought about in restoration programs by the introduction of shrubs and trees in these areas. In this paper we analyse the role of S. tenacissima as a nurse plant of P. halepensis and the consequences of pine canopy development on the performance of S. tenacissima. We hypothesised that an interaction between both species exists in alfa steppes, so that S. tenacissima facilitates the establishment of P. halepensis, which then negatively affects S. tenacissima. Our results show that in steep slopes the presence of P. halepensis individuals was heavily associated with the terracettes formed by the accumulation of sediments upslope of the tussocks of S. tenacissima. Even though the surface occupied by the terracettes was a third of the total, 72.9% of P. halepensis individuals occurred in this environment. Significant differences were also found in seedling emergence (P=0.001) and establishment (P=0.002) of P. halepensis. Both were higher in terracettes than on the bare ground among the tussocks, although no seedlings survived after the drought season. P. halepensis interferes negatively on the performance of S. tenacissima in some but not all of its life stages. The number of spikes per tussock was higher in steppes without pines and was also dependent on the tussock size (P<0.0001). Significant differences between both environments were also found in emergence (P=0.037) and survival (P<0.001) of seedlings of S. tenacissima. Seedlings that emerged in the sun also developed a higher number of leaves and root biomass (P=0.041 and 0.015, respectively). Pollination rates did not differ between the sites with pine cover and those without pine cover. These relationships may have important consequences for the dynamics and management of these plant communities.

Abstract: Abstract. Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long-term (> 50 yr) grassland burning and mowing experiment in KwaZulu-Natal, South Africa. Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27�42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances.

Abstract: Eighty-six Alpine kids, 18.765 (±0.510) kg BW, plus four cannulated adult goats were allocated to two treatments in a production trial lasting 150 days. They also were evaluated for in situ DM disappearance, VDMI, OMI, rumen degradation rate of passage, NH3 and VFA concentrations, apparent digestibility, pH, total fermentable carbohydrates, and weight gains. The first diet (n=43 kids, 19.120 (±0.700) kg BW plus two cannulated adult goats) were pastured daily on rangeland (RM) plus 200 g per day of a slow-intake urea supplement (SIUS) of previously established composition. A second group (n=43 kids, 18.410 (±0.600) kg BW plus two cannulated adult goats) were equally pastured and supplemented with 300 g per day of a balanced concentrate (BC) with also previously established composition. Both groups were managed on pasture divided by an electrical fence. Kid growth averaged 101 (±18) g per day for RM/SIUS and 83 (±26) g per day for RM/BC (P<0.05). Total DMI was 1010±293 g per day for RM/SIUS and 747±107 for RM/BC (P<0.05). Ammonia concentration and degradation of potentially digestible and indigestible fractions were augmented by RM/SIUS (P<0.05). Rumen pH rose slightly post-feeding for RM/SIUS goats and remained higher compared to RM/BC or RM 12 h after feed offer. Nitrogen intake was similar from RM/SIUS and RM/BC (118.60 g per day versus 122.53). In vivo N-digestibility was higher (P<0.05) in the RM/SIUS diet (79.12%) than for RM/BC (56.14%); fiber digestibility was also higher (P<0.05) for RM/SIUS. In situ DM disappearance did not show differences between diets at 9, 12, 24, 48, 72 and 92 h of incubation but was lower for RM. Digestion rate of NDF constant (kd, h-1) favored the RM/SIUS diet (P<0.05). Digestion rate for cellulose and hemicellulose was similar between diets. Passage rate (kp, h-1) for NDF differed between diets, 0.059 h-1 for RM/BC versus 0.080 h-1 for RM/SIUS (P<0.05). True digestibility was higher in RM/SIUS, 48.33% compared to RM/BC 34.11% (P<0.05). In situ degradation of potentially digestible fiber for cellulose was higher in RM/SIUS 67.14% compared to RM/BC 53.14% (P<0.05). Indigestible fiber was similar for RM/BC (51.42%) and RM/SIUS (66.27%). Time of disappearance of cellulose in RM/BC (17.54 h) was less (P<0.05) than in RM/SIUS (30.34 h). Hemicellulose in situ digestion was similar between diets. Passage rate was different (P<0.05) between RM/SIUS (0.080 h-1) and RM/BC (0.059 h-1). The half-time (t1/2) disappearance for hemicellulose was higher for RM/SIUS (31.14 h) as compared to RM/BC (22.14 h) (P<0.05). Propionic acid increased with time of sampling in the RM/BC diet (P<0.05). Butyric acid production did not differ between diets (P<0.05). Total amounts of VFA differed between BC and SIUS diets, allowing higher energy to RM/SIUS (P<0.05). Supplementation of high fiber diets with NPN did improve fermentation with better ammonia and VFA production. SIUS intake was consumed in 8-10 h after offer but the BC in 30 min. It was concluded that SIUS supplementation offered critical nutrients to the rumen, improved DM intake, rate of passage, increased ruminal pH and resulted in better weight gains than BC. Present results showed that high fiber forages could be used efficiently by ruminants (up to 70-80% DMI) when ruminal fermentation is improved with a continuous N supplementation.

Abstract: Computer-based methods of integrated modelling and assessment provide an important means for reviewing policy choices in natural resource management (NRM). Research in support of NRM needs to address a wide range of issues involved, from point-scale biophysical, to business-scale human, to regional-scale planning issues. Research covering the full scope of such issues is by default multi-disciplinary and integrative and therefore analytically, methodologically and operationally challenging. The recently initiated Ord-Bonaparte Program is an example of a research and development program attempting to achieve both levels of integration in an applied NRM context. One key requirement for the success of the program lies in developing a systems framework that: (i) enables the integration of the various disciplinary research activities; and (ii) facilitates the implementation of research outputs by making integrated science relevant to decision-makers and translating new knowledge into outcomes for sustainable regional development. This paper proposes an approaches for such a systems framework.

Abstract: Plant establishment in semi-arid rangelands is difficult because of low, unpredictable soil water and extreme soil temperatures. In these rangelands, biosolids disposal is limited to topical application; resulting soil coverage ameliorates microenvironmental conditions and may affect plant establishment. We investigated biosolids effects on soil water, soil temperature, and seedling emergence and growth of blue grama (Bouteloua gracilis) and green sprangletop (Leptochloa dubia) in a Chihuahuan desert grassland. Greenhouse and field experiments were conducted for 2 years. Biosolids did not affect mean soil temperature (at seed depth) but usually increased minimum and reduced maximum temperatures. Biosolids generally reduced soil water loss. These benefits may be insufficient under harsh conditions to promote seedling establishment, and unnecessary under favorable conditions. Under intermediate conditions, seedling establishment may be enhanced by biosolids application.

Abstract: The role of the hydrological cycle in contributing to the livelihoods of rural communities is often said to be important, but clear evidence of this is rarely offered. Furthermore, where such aspects are considered, they are largely focussed on the use of water from rivers, boreholes or some form of storage (blue water). In this study, the hydrological cycle is considered in its entirety. Links between rural livelihoods, land use and the goods and services provided by the evaporation and transpiration components of the hydrological cycle (green water) are assessed through analyses of rural livelihoods in the Luvuvhu catchment, Limpopo Province, South Africa. Results highlight the importance of green water, and thus the importance of access to land and use of the natural resource base, in disaggregated rural community livelihood strategies. Finally, we describe a methodology for linking common outputs from hydrological models to rural livelihood impacts. In this way, the potential role of land use change in disaggregated rural livelihoods can be assessed for various development scenarios, such as increases in commercial forestry and dryland agriculture.

Abstract: Climate, topography, vegetation and land use interact to influence fire regimes. Variable fire regimes may promote landscape heterogeneity, diversification in vegetation pattern and biotic diversity. The objective was to compare effects of alternative land use practices on landscape heterogeneity. Patch characteristics of fire scars were measured from 21 annual burn maps produced from 1972 to 2001 Landsat imagery. Trends in fire patterns under alternative land use practices were compared across a 250,000 ha savanna in southern Africa partitioned into three land use zones. Zone 1, Madikwe Game Reserve (MGR), has had mostly prescribed fires since 1993. Zone 2, cattle farms near MGR in South Africa (SAF), has experienced occasional fires. Zone 3, communal grazing lands in neighboring Botswana (BOT), has had the fewest fires. Cattle ranching was the predominant land use throughout the study area until 1992, when land use switched to conservation and eco-tourism in MGR. Sixteen landscape metrics were applied to this data set to uncover trends in the patch characteristics of the fire scars. A principal components analysis (PCA) reduced the dimensionality of the results so trends in the 10 most important size, shape, and proximity metrics could be better interpreted. The PCA results showed that more burning over time in MGR, and to a lesser extent in SAF, increased patch size, size variability, shape complexity and proximity, while fire exclusion in BOT produced no change or decreasing trends. We tested for significant differences in these metrics between the three land use zones and between two periods, 1972-1992 and 1993-2001. Most patch characteristics in MGR and SAF differed significantly from those in BOT, especially during the latter period, while between MGR and SAF they did not. Patch area, shape complexity and core area increased significantly between periods in MGR, while patch size, size variability and core area increased significantly between periods in SAF. In BOT, no patch characteristics changed significantly between periods. Within the time span analyzed for the study area, we conclude that increased fire occurrence promoted landscape heterogeneity while fire exclusion did not.

Abstract: Environmental policies in African rangelands affect development and welfare as well as environmental measures. Biodiversity is widely perceived as declining, and environments as undergoing degradation, through rural population growth and resource use. These assumptions are often underpinned by environmental discourses contesting control of natural resources, rather than by objectively measured trends and causalities. Orthodox biodiversity conservation policy advocates fortress conservation. Savanna species do better where they can disperse across wider landscapes with conservation-compatible rural land uses, rather than isolated in protected areas, but community-based conservation initiatives have been disappointing. Policies addressing land degradation, and their underlying assumptions, are subject to similar challenges. The paper outlines a natural experiment investigating biodiversity and land cover changes 1975-1995 for 100,000 km2 cross-border rangeland including the Serengeti-Mara conservation areas and their buffer zones. Ecological, ethnic and micro-economic continuities make it possible to control for confounding factors and identify main drivers of change. Privatisation of formerly communal rangeland, and its conversion to commercial monoculture, have driven drastic land cover and wildlife declines in Kenya. Population growth and agropastoral land use were not significant factors. The gap between natural and social science, and western versus local understandings, needs bridging to achieve more effective environmental policy.

Abstract: Abstract. Various attempts have been made to describe and map the vegetation of southern Africa with recent efforts having an increasingly ecologi cal context. Vegetation classification is usually based on vegetation physiognomy and floristic composition, but phenology is useful source of information which is rarely used, although it can contribute functional information on ecosystems. The objectives of this study were to identify a suite of variables derived from time-series NDVI data that best describe the phenological phenomena of vegetation in southern Africa and, secondly, to assess a classification of pixels of the study area based on NDVI variables using a preexisting map of the biomes that was delimited on the basis of life forms and climate. A number of variables were derived from the satellite data for describing phenological phenomena, which were analysed by multivariate techniques to determine which variables best explained the variation in the satellite data. This set of variables was used to produce a phenological classification of the vegetation of southern Africa, the results of which are discussed in relation to their concordance with the existing biome boundaries.

Abstract: Biological productivity of grazing livestock under semi-arid conditions in northern Kenya is limited by marked seasonal fluctuations in the availability and quality of rangeland resources. With the increasing trend towards sedentarization of pastoral herds and households, the search for an alternative to herd mobility as the most effective adaptive management strategy to attenuate the effects of seasonality in production resources is an issue of growing concern. Using data collected during an experimental study conducted in pastoral goats in northern Kenya, this paper is concerned with the assessment of the effects of controlled seasonal breeding on biological herd productivity. The experiment was conducted over a period of 4 years (1984-1988) in Isiolo District, northern Kenya. The experimental treatment consisted of six different mating seasons per year, which were replicated three times over the course of the experiment. Assessment of biological productivity was done with a previously developed procedure for steady-state productivity assessments in livestock herds. The criterion used to evaluate biological herd productivity was an energetic efficiency ratio, defined as the total gross energy output of the herd divided by its total metabolizable feed energy requirements at the stationary state. The first hypothesis for testing was that there is an optimal period in a year to which breeding can be restricted to improve overall biological productivity of pastoral goat flocks. Second, a simulated, aseasonally reproducing herd was used as a reference in testing whether controlled breeding is superior to uncontrolled breeding. The general conclusion that emerged from this study is that restricted breeding can effectively be used as a management control to manipulate overall biological herd productivity primarily because of its positive effect on youngstock mortality rates. For achieving maximum energetic efficiency in pastoral goat flocks, breeding should be constrained to the long dry season (June to October). However, when compared to this breeding regime simulated aseasonal breeding performed remarkably well, and more field research is required to ascertain the superiority of controlled over aseasonal breeding.

Abstract: A major contributor to degradation on rangelands in the western United States is the expansion of undesirable annual weeds following wildfire or other disturbance. The Simultaneous Heat and Water (SHAW) model was applied to three soil types (loamy sand, sandy loam, and silt loam) to simulate near-surface soil temperature and water for predicting potential seed germination in post-wildfire revegetation. Three parameterization methods including initial parameter estimates, calibrated parameters, and measured moisture-release curve parameters were compared to assess the effect of parameter uncertainty on germination prediction. Initial parameters for the sandy loam soil resulted in an underprediction of germination times by 4.7 days for cheatgrass to 12.8 days for bluebunch wheatgrass compared to germination estimated from measured soil temperature and water conditions. Initial parameters resulted in predicted germination within 2 days of estimates for the other two soils. Model calibration to optimize the surface 20-cm water-content did not necessarily improve predicted germination. Model simulations using measured moisture-release curves resulted in germination prediction within a few days relative to estimates for all sites. Results suggest that the model can be used for long-term simulations of seedbed microclimate necessary to evaluate potential germination response of revegetation species and their weedy competitors.

Abstract: It is estimated that approximately 40% of the Cerrado, the second largest biome in South America, have been already converted. In this study, situated within the scope of the Large Scale Biosphere-Atmosphere Experiment in Amazonia project (LBA), we conducted a wet season ground and airborne campaign over the Brasilia National Park (BNP), the largest LBA core site in the Cerrado biome, to measure the optical and biophysical properties of the major Cerrado land cover types. We investigated land cover discrimination through the analyses of fine resolution spectra, convolved spectra (MODIS bandpasses), and vegetation indices--the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI). At these three data levels, three major physiognomic domains (herbaceous, woody, and forested) could be readily identified, and the amount of data correctly classified into the five major land cover types found at BNP were 91% (full spectra), 78% (red and NIR), 75% (NDVI), and 71% (EVI). A synergism between the NDVI and EVI was also evident, and together, these two indices were capable of correctly classifying 82% of the total data set. Our results indicate the possibility of utilizing the MODIS NDVI and EVI images for operational land cover assessments in the Cerrado region.

Abstract: ABSTRACT Aim� To determine the geographical variation in serotiny in a common New Zealand shrub as a contemporary indicator of past fire regimes. The distribution of serotiny could then be used to explore factors limiting the spread of fire-dependent vegetation. Location� South Island, New Zealand. Methods� Serotiny was assessed as the proportion of closed capsules on a shoot of standard stem diameter for 5�35 plants in 45 widely scattered populations of Leptospermum scoparium. Site characteristics, including locality, altitude, rainfall, habitat type and minimum burnable area were recorded at sampling sites. Results� Serotiny was distributed bimodally within and among populations with capsules either mostly closed or mostly open. There was considerable geographical variation in capsule behaviour, most of which we attribute to variation in fire history. In wetlands and other sites unsuitable for forest growth, populations were all serotinous above a minimum area of 30 km2 and nonserotinous below this threshold. In grassy habitats in the drier eastern areas, most populations were serotinous. The nonserotinous exceptions occurred in areas thought to have been cleared of forests by Polynesian settlers before the arrival of Europeans or in areas with numerous barriers to fire in the form of large rivers, floodplains, glaciers and barren mountain tops. Conclusions� We suggest that serotiny in L. scoparium is a reflection of a long history of fire in the South Island. As such, it provides a contemporary signature of a past fire regime. Landscape barriers to the spread of fire were major obstacles limiting the spread of serotiny and associated fire-dependent vegetation. Rivers, lakes, glaciers, and sparsely vegetated floodplains prevented the spread of fire in high rainfall regions more than the lack of dry weather. People, by igniting fires in small open areas seldom struck by lightning, could radically increase the importance of fire on islands.

Abstract: The researchers calculated seasonal integrated normalized difference vegetation index (NDVI) for each of 7 years using a time-series of 1-km data from the Advanced Very High Resolution Radiometer (AVHRR) (1992-93, 1995) and SPOT Vegetation (1998-2001) sensors. We used a local variance technique to identify each pixel as normal or either positively or negatively anomalous when compared to its surroundings. We then summarized the number of years that a given pixel was identified as an anomaly. The resulting anomaly maps were analysed using Landsat TM imagery and extensive ground knowledge to assess the results. This technique identified anomalies that can be linked to numerous anthropogenic impacts including agricultural and urban expansion, maintenance of protected areas and increased fallow. Local variance analysis is a reliable method for assessing vegetation degradation resulting from human pressures or increased land productivity from natural resource management practices.

Abstract: Carbon monoxide (CO) measurements are obtained in an aircraft experiment during 1-7 September 2000, conducted over Central Brazil in a special region of anticyclonic circulation. This is a typical transport regime during the dry season (July-September), when intense biomass burning occurs, and which gives origin to the transport of burning poluents from the source to distant regions. This aircraft experiment included in situ measurements of CO concentrations in three different scenarios: (1) areas of fresh biomass burning air masses, or source areas; (2) areas of aged biomass burning air masses; and (3) areas of clean air or pristine air masses. The largest CO concentrations were of the order of 450 ppbv in the source region near Conceicao do Araguaia (PA), and the smallest value near 100 ppbv, was found in pristine air masses, for example, near the northeast coastline (clean air, or background region). The observed concentrations were compared to the number of fire pixels seen by the AVHRR satellite instrument. Backward isentropic trajectories were used to determine the origin of the air masses at each sampling point. From the association of the observed CO mixing ratios, fire pixels and air mass trajectories, the previous scenarios may be subdivided as follows: (1a) source regions of biomass burning with large CO concentrations; (1b) regions with few local fire pixels and absence of contributions by transport. Areas with these characteristics include the northeast region of Brazil; (1c) regions close to the source region and strongly affected by transport (region of Para and Amazonas); (2) regions that have a consistent convergence of air masses, that have traveled over biomass burning areas during a few days (western part of the Cerrado region); (3a) Pristine air masses with origin from the ocean; (3b) regions with convergent transport that has passed over areas of no biomass burning, such as frontal weather systems in the southern regions.

Abstract: The role of animal trampling in a hyper-arid environment is evaluated. Field observations on fluvial terraces of the Uniab fan in Namibia suggest that animal impact on level surfaces with gravel armouring is minimal. However, animal trampling along tracks across scarp slopes results in scarp recess and initiate cutback development. With continued growth ephemeral fluvial processes become more dominant and obscure the animal impact. Animal trampling effects are pronounced in hyper-arid environments due to the low rates of other slope processes. However, it is argued that large herd migration may have contributed significantly to cutback development in other environments, especially in Africa, but may be very difficult to substantiate by landform analysis.

Abstract: The relationship between climatic change and human evolution can be framed in terms of three major hypotheses. A modern version of the long-held savanna hypothesis posits that the expansion of grassland ecosystems in Africa was driven by global climatic change and led to the divergence of hominins from the apes and to the origin of the Homo clade. A related idea suggests that hominins originated in the late Miocene, and Homo in the late Pliocene, as constituents of broader pulses of faunal turnover synchronized by episodes of global climatic change. A more recent concept, the variability selection hypothesis, emphasizes the importance of fluctuating climates and environments, rather than any single trend, in shaping human adaptation and evolution. Here we evaluate these ideas for the Plio-Pleistocene in light of new analyses of fossil mammals from the Turkana Basin of Kenya and Ethiopia. Our results show that between 4 and 1 Ma (million years ago), there were profound faunal changes in the Turkana Basin. The most important of these changes include significant shifts in the abundance of the common families of mammals, episodes of high faunal turnover, and an increase in the number and abundance of species that show adaptations to grassland ecosystems. Episodes of relatively high faunal turnover occurred in the intervals 3.4-3.2, 2.8-2.6, 2.4-2.2, and 2.0-1.8 Ma. Paranthropus and Homo appear in the Turkana Basin during successive intervals of high turnover at 2.8-2.6 and at 2.4-2.2 Ma, while the appearance of Homo erectus is coupled to a major episode of turnover and grassland expansion after 2 Ma. Thus, there was not a single turnover pulse of relevance to late Pliocene hominins, but multiple events that successively led to the appearance of Paranthropus, early Homo, and H. erectus. Our results also show evidence of large-scale, 100 ky-periodicity shifts in the fauna beginning at 2.5 Ma, during the time that Homo and lithic artifacts first appear in the Turkana Basin, lending support to the variability selection hypothesis [Science 273 (1996) 922; Potts R., 1996b. Humanity's Descent: The Consequences of Ecological Instability. Avon Books, New York.] during the latest Pliocene. The savanna hypothesis may not explain the divergence of hominins from other apes, but it could be correct in stressing the importance of grasslands to the early evolution of Homo. The fundamental importance of grasslands may lie in the complexity and heterogeneity they added to the range of habitats available to the early species of the genus Homo. The turnover pulse hypothesis [Vrba, E.S., 1988. Late Pliocene climatic events and hominid evolution. In: Grine, F.E (Ed.). Evolutionary History of the "Robust" Australopithecines. Aldine, New York, pp. 405-426; Vrba, E.S., 1995. The fossil record of African antelopes (Mammalia, Bovidae) in relation to human evolution and paleoclimate. In: Vrba, E.S., Denton, G.H., Partridge, T.C., Burckle, L.H. (Eds.). Paleoclimate and Evolution, with Emphasis on Human Origins. Yale Univ. Press, New Haven, pp. 385-424.] may be correct in linking critical events in human evolution to broader pulses of faunal change ultimately driven by climate, but our results show that any such link is complex, with at least four rather than one pulse of change during the Pliocene and early Pleistocene of the Turkana Basin.

Abstract: In the tropical regions of Brazil there are at least 80 million ha (Mha) of pastures planted to grasses introduced from Africa, principally Brachiaria spp. It is estimated at least half of these pastures are degraded, that is, support very low stocking rates, show low plant cover, are invaded by non-palatable native species and often densely populated with termite mounds. The main causes of the process of pasture decline are lack of maintenance fertilisation and excessively high animal stocking rates. In this study the effect of increasing stocking rate on the fluxes of nitrogen (N) though the animal (forage consumption, production of faeces and urine) and through the plant (growth, senescence) pathways were studied on Brachiaria humidicola pastures grazed by Zebu beef cattle in the Atlantic forest region of the south of Bahia (Brazil). As stocking rate increased from 2 to 4 animals ha-1, live weight gain per animal decreased from 153 to 120 kg per animal per year but overall weight gain per hectare increased from 305 to 360 kg per year. Nitrogen exported in the animal weight gain only increased from 7.3 to 8.6 kg N ha-1, but the pathways of N cycling were radically changed. Increasing the stocking rate from 2 to 4 animals ha-1, increased total N consumed by the animal from 94 to 158 kg ha-1 per year, and that deposited in plant litter decreased from 170 to 105 kg ha-1. This resulted in increases in N deposited as urine and dung in the paddocks from 50 to 90 and 37 to 59 kg ha-1, respectively. A large proportion of these excretions were deposited in rest areas and around drinking troughs where the grass was so trampled that it could not take advantage of this N, and other nutrients. Data from complementary studies showed that N losses from urine could be between 35 and 80%, being much higher in areas without vegetation. We conclude that pasture decline is hastened by increasing stocking rates because of these losses of N and the decrease in N and other nutrients available for grass growth.

Abstract: This paper set out to analyse time-series and spatial livestock data in the arid west of Namibia over a period of 11 years. These were interpreted in the context of rainfall conditions and access to water points and encompass communally and commercially managed rangelands. The study showed that stock densities maintained by both, communal and commercial farmers, were remarkably lower than estimated national-level carrying capacities for these rangelands. In the arid communal areas (50-100 mm annual rain), these hovered on average around 1 kg ha-1, increasing to 4 kg ha-1 at 100-200 mm rain and to 8 kg ha-1 in the 200-300 mm annual rain bracket in commercial areas. Stock densities showed no statistical correlation to annual rainfall, but grazer-browser ratio did in communal areas. Although the spatial analysis showed shortcomings, some general trends--to be considered hypotheses for further testing--were evident in these arid rangelands: - Available grazing rather than access to water appeared to limit stock densities, particularly in the drier areas, since the number of water points was not statistically correlated with stock density.- Overall, stock densities in commercial areas were less affected by annual rainfall over the observed period than in the communal areas.- A shorter-term response to annual rainfall was indicated in the communal areas, compared to the commercial farming areas. This indicates that communal farmers adopted an opportunistic management strategy and effectively rested rangelands after a below-average rain year by reducing stock densities.- The shorter-term response strategy was also reflected in greater changes in grazer-browser ratio over time in the communal areas.- Equally, shorter-term responses followed a good season in communal areas by an increase in livestock numbers.- This shorter-term response strategy in communal areas could result in high stock densities coinciding with a poor rainy season, if a good season and the parallel increase in stock densities, is immediately followed by a poor season.

Abstract: Savannas and open grasslands often co-exist in semi-arid regions. Questions that remain unanswered and are of interest to biometeorologists include: how do these contrasting landscapes affect the exchanges of energy on seasonal and annual time scales; and, do biophysical constraints imposed by water supply and water demand affect whether the land is occupied by open grasslands or savanna? To address these questions, and others, we examine how a number of abiotic, biotic and edaphic factors modulate water and energy flux densities over an oak-grass savanna and an annual grassland that coexist in the same climate but on soils with different hydraulic properties. The net radiation balance was greater over the oak woodland than the grassland, despite the fact that both canopies received similar sums of incoming short and long wave radiation. The lower albedo and lower radiative surface temperature of the transpiring woodland caused it to intercept and retain more long and shortwave energy over the course of the year, and particularly during the summer dry period. The partitioning of available energy into sensible and latent heat exchanged over the two canopies differed markedly. The annual sum of sensible heat exchange over the woodland was 40% greater than that over the grassland (2.05 GJ m-2 per year versus 1.46 GJ m-2 per year). With regards to evaporation, the oak woodland evaporated about 380 mm of water per year and the grassland evaporated about 300 mm per year. Differences in available energy, canopy roughness, the timing of physiological functioning, water holding capacity of the soil and rooting depth of the vegetation explained the observed differences in sensible and latent heat exchange of the contrasting vegetation surfaces. The response of canopy evaporation to diminishing soil moisture was quantified by comparing normalized evaporation rates (in terms of equilibrium evaporation) with soil water potential and volumetric water content measurements. When soil moisture was ample normalized values of latent heat flux density were greater for the grassland (1.1-1.2) than for the oak savanna (0.7-0.8) and independent of moisture content. Normalized rates of evaporation over the grassland declined as volumetric water content dropped below 0.15 m3 m-3, which corresponded with a soil water potential of -1.5 MPa. The grassland senesced and quit transpiring when the volumetric water content of the soil dropped below -2.0 MPa. The oak trees, on the other hand, were able to transpire, albeit at low rates, under very dry soil conditions (soil water potentials below -4.0 MPa). The trees were able to endure such low water potentials and maintain basal levels of metabolism because ecological forcings kept the tree density and leaf area index of the woodland low, physiological factors forced the stomata to close progressively and the trees were able to tap deeper water sources (below 0.6 m) than the grasses.

Abstract: Summary Fire is a common phenomenon in grasslands but there is little experimental evidence of the mechanism involved in the rapid recovery of the plant growth. We tested under controlled conditions the hypothesis that after fire Spartina argentinensis leaves that restart growing have high photosynthetic rates. Photosynthetic rates and emergence of leaves and culms were registered. Initial photosynthetic rates were higher among plants which restarted growth after fire or clipping than in control ones, without effect of different water availability. High photosynthetic rate values remained during two months after fire or clipping treatments though then affected by water availability, and thereafter started declining towards the end of season. From January onwards no differences among treatments were detected except that control plants under water stress conditions had lower photosynthetic rates than all others. Leaf and culm emergence were promoted by both fire and clipping treatments. Though affect-ed by water availability, burned and clipped plants had the highest percentages of living tissues at the end of the experiment. Considering photosynthetic and growth responses after fire it can be concluded that burning is a regular component of the subtropical-temperate S. argentinensis habitat, among the South American grasslands.

Abstract: The paper reviews an important but little researched area of ethnopharmacology, namely, the effect of cultivation and post-harvest storage practices on levels of biological activity in traditionally used medicinal plants. Changes in COX-1 inhibition and antibacterial activity, for example, occur at the onset of senescence and, in some species, are influenced by plant age. Plants in cultivation were also shown to have reduced anthelmintic and antibacterial activity while hypoxoside production was affected by nitrogen and phosphorous. Irrigation treatments, however, increased anthelmintic activity and, therefore, could be applied to medicinal plants cultivated in low rainfall areas. Pesticides have also been implicated in the regulation of plant growth and secondary metabolite production in cultivated medicinal plants, but residue levels have, so far, not been monitored. Post harvest storage of medicinal plants has been poorly researched in southern Africa. Available data indicates that antibacterial and anti-inflammatory activity changes following storage and is both species and temperature dependent. Similar trends were noted for materials that had been rapidly aged. Fatty acids with antibacterial activity are stable in dry specimens and, as such, may account for the fact that activity is unaffected by storage in certain instances.

Abstract: Forests and savannas are the major ecotypes in humid tropical regions. Under present climatic conditions, forest is in a phase of natural expansion over savanna, but traditional human activities, especially fires, have strongly influenced the succession. We here present a new model, FORSAT, dedicated to the forest-savanna mosaic on a landscape scale and based on stochastic modelling of key processes (fire and succession cycle) and consistent with common field data. The model is validated by comparison between the qualitative emergent behaviour of the model and results of biogeographical field studies. Three types of forest succession are shown: progression of the forest edge, formation and coalescence of clumps in savanna and global afforestation of savanna. The parameters (frequency of savanna fires, climate and soil fertility) appear to have comparable effects and there is a sharp threshold between a forest edge progression scenario and the cluster formation one. Moreover, pioneer seed dispersal pattern and recruitment are determinant: peaked curves near a seed source and far dispersal combine to increase the fitness of the pioneers.

Abstract: Biodiversity conservation is a challenge within developing regions of the world. Landscape heterogeneity is largely directed by interconnected economic and social systems, which are largely driven by political, communal, and private control of the land estate. There is increasing evidence that areas of high species richness may coincide with dense human settlement. Influences of landscape pattern, human impact, and divergent past political land management on functional groups of bird species richness were examined in KwaZulu-Natal, South Africa. The functional groups included species of breeding, non-breeding, generalist, and specialist birds. A database of land-use/land-cover (LULCC) and human impact indicators was used to develop relationships and infer historic changes in bird richness derived from two censusing periods (1975-1979 and 1988-1992). The objective was to examine richness and compare relationships based on analyses using land management regions, avifaunal zones and socio-economic regions. Paired and two-sample t-tests documented differences in richness among land management regions and between regions over time. Landscape metrics, LULCC proportion, and other human impact variables were examined using Monte Carlo permuted multiple regressions to develop relationships for bird richness groups. Significant increases in bird group richness were shown between survey periods, as well as differences between land management regions. The statistical models explained 22-79% of variation in bird richness among avifaunal zones by functional group, and 32-99% of variation in bird richness among the socio-economic regions. The majority of the relationships were explained by LULCC proportion rather than landscape metrics denoting spatial arrangement. The analysis concludes that there have been significant increases in bird richness apparently related to land-use development during the study period. The apparent increase in richness may be due to maintenance of original vegetation-specific species in untransformed fragments in highly transformed areas combined with species that exploit transformed habitats well in the transformed areas. It is concluded that research on the interface between biogeography and human development should be seen as a perquisite for conservation assessments in developing regions of the world.

Abstract: Recently, Batabyal and Godfrey (J. Range-Manage. 55 (2002) 12) have used a discrete-time Markov chain model to analyse the problem of rangeland management under uncertainty. In the present note, I continue this line of inquiry. In particular, I first show how the technique of first step analysis can be used to derive a time-based objective function for a range manager. Next, I discuss aspects of the decision problem faced by a range manager who wishes to optimize the above objective function and thereby minimize the cost to society from range desertification.

Abstract: We examined the effects of an alien species, Lehmann lovegrass (Eragrostis lehmanniana), on the semi-arid grassland ecosystems of the south-western United States. In order to evaluate these effects, we examined soil disturbance by animals in areas dominated by Lehmann lovegrass in comparison with areas dominated by native grasses. We measured amounts and types of faunalpedoturbation at paired plots in two different study areas, the Jornada basin in New Mexico and the Santa Rita Experimental Range in south-eastern Arizona. Area of soil disturbed and volume of soil turnover was significantly decreased on plots dominated by Lehmann lovegrass, at the Santa Rita Experimental Range but not on plots in the Jornada basin. At the Santa Rita, ground squirrels and attine ant activity was reduced the most of any other species in Lehmann lovegrass dominated pastures. Differences in the diversity of disturbances were inconsistent at both study areas indicating variable responses by taxa to dominance by an alien grass species. Variations among, within, and between study areas were attributed to site history as well as geographic and topographic position. The degree to which Lehmann lovegrass affects faunalpedoturbation appears to be related to the history of the site, specifically the time since the establishment of Lehmann lovegrass.

Abstract: This study determined the influence differing soil surface textures and vegetative covers have on the magnitude of wind erosion in a semi-arid environment. The study was conducted from March 2000 through late April 2000 on the Jornada Experimental Range approximately 37 km north of Las Cruces, New Mexico. Big Spring Number Eight (BSNE) samplers placed at nine locations, collected particulates in suspension and saltation at heights of 5, 10, 20, 50, and 100 cm from the following surfaces: loose sand, thick silty physical crust, flaky physical crust, weak desert pavement, and a forb/grass ground cover. BSNE samplers collected the largest amounts of sediment were collected in areas of loose sand and at sites directly downwind from loose sand than sites containing heavy crusting, gravel, or a forb/grass cover. Differences between sites with gravel surfaces and those with forb/grass cover were insignificant. These results quantify the importance of surface cover as an agent towards reducing the extent of wind erosion on semi-arid landscapes.

Abstract: Prescribed burning has been suggested as a method to prevent shrub encroachment on desert grasslands. A concern for range managers is the prevalence of introduced African lovegrasses (Eragrostis spp.). These exotic grasses may compromise the effectiveness of fire as a range management tool in these areas due to their fire tolerance. In this study we examined the response of an established patch of Lehmann lovegrass to a prescribed burn. While Lehmann lovegrass was not adversely affected by the prescribed burn, all of the native grasses were compromised to some degree.

Abstract: A thorough understanding of the role of microbes in C cycling in relation to fire is important for estimation of C emissions and for development of guidelines for sustainable management of dry ecosystems. We investigated the seasonal changes and spatial distribution of soil total, dissolved organic C (DOC) and microbial biomass C during 18 months, quantified the soil CO2 emission in the beginning of the rainy season, and related these variables to the fire frequency in important dry vegetation types grassland, woodland and dry forest in Ethiopia. The soil C isotope ratios ([delta]13C) reflected the 15-fold decrease in the grass biomass along the vegetation gradient and the 12-fold increase in woody biomass in the opposite direction. Changes in [delta]13C down the soil profiles also suggested that in two of the grass-dominated sites woody plants were more frequent in the past. The soil C stock ranged from being 2.5 (dry forest) to 48 times (grassland) higher than the C stock in the aboveground plant biomass. The influence of fire in frequently burnt wooded grassland was evident as an unchanged or increasing total C content down the soil profile. DOC and microbial biomass measured with the fumigation-extraction method (Cmic) reflected the vertical distribution of soil organic matter (SOM). However, although SOM was stable throughout the year, seasonal fluctuations in Cmic and substrate-induced respiration (SIR) were large. In woodland and woodland-wooded grassland Cmic and SIR increased in the dry season, and gradually decreased during the following rainy season, confirming previous suggestions that microbes may play an important role in nutrient retention in the dry season. However, in dry forest and two wooded grasslands Cmic and SIR was stable throughout the rainy season, or even increased in this period, which could lead to enhanced competition with plants for nutrients. Both the range and the seasonal changes in soil microbial biomass C in dry tropical ecosystems may be wider than previously assumed. Neither SIR nor Cmic were good predictors of in situ soil respiration. The soil respiration was relatively high in infrequently burnt forest and woodland, while frequently burnt grasslands had lower rates, presumably because most C is released through dry season burning and not through decomposition in fire-prone systems. Shifts in the relative importance of the two pathways for C release from organic matter may have strong implications for C and nutrient cycling in seasonally dry tropical ecosystems.

Abstract: This paper presents a detailed description of the applied methodology used to study collective action in natural resource management. Data were collected in 48 villages in northeastern Burkina Faso, at the community, institutional, household and market levels. The paper first discusses the analytical framework underlying the study of collective action, and then describes in detail the methods used to measure collective action and community-level cooperative capacity, and the determinants of cooperative capacity. We also describe data collection methods as well as potential problems in eliciting unbiased information. The impact of cooperative capacity on a variety of outcomes observed at both the community and household level is then presented in order to highlight practical applications.

Abstract: The lack of information on the vegetation status before the use of fire as a management tool in protected areas leads to drastic destruction of the natural vegetation and biodiversity. This paper describes the use of spectral indices and simulation of savanna burning to assess risk of intensive fire propagation in a National Park (Niokolo Koba, Senegal, West Africa). Spectral parameters corresponding to thematic information (wetness, brightness, and greenness) were retrieved using an orthogonal transformation, the Tasseled Cap approach on LANDSAT-ETM images. Wetness and brightness indices were normalized ([sigma]=1 and MEAN=0) and then combined in a simple semi-empirical algorithm of fire risk levels discrimination. These two indices are proven to reflect qualitatively both fuel moisture and its distribution, which constitute the most foreseen determinants of fire propagation in savanna areas. The fire risk assessment algorithm (FIRA algorithm) was used to produce a fire risk map at the beginning of the management fire implement period. In parallel, a fire area simulator (FARSITE) developed by USDA was used with randomly spaced fire sources to determine areas which can be potentially burned in the study site. These simulated burned areas and the FIRA algorithm results were cross-compared to a real fire scars dated at the end of the same burning period and to land cover map. A great consistency was found between the different sources of information. More than 85% of fire prone areas identified by the FIRA algorithm or simulated by FARSITE were located in trees-shrub, woodland, and shrub savannas. These cover types included also 95% of real fire scars. Almost 88% and 84% of real fire scars were found in the risk zones determined by the FIRA algorithm and the simulated burned areas by FARSITE, respectively. The method used is simple and suited for an operational use for management fire implementation in savanna ecosystems.

Abstract: Palaeoecological data recording a pronounced environmental shift centred about 4000 years BP are presented from tropical Africa and South America. The environmental shift is particularly manifested as a change in the hydrological budget and vegetation within numerous swamp and lake catchments. The majority of sites in tropical Africa record a shift to drier environmental conditions that is in opposition to South America, where a shift to a wetter environment is generally recorded. The strength of between site signals varies from being relatively complacent to dramatic, in some cases reflective of whole-scale vegetation change. The magnitude of change is mainly dependent of the location of the site and the proxy under investigation. These ecosystem changes are likely to reflect changed precipitation regimes, increased evaporation, and or an extension/contraction of the dry season. This pronounced Holocene environmental shift is particularly interesting, as the marked changes within the tropics are either weakly recorded, or non-existent, at more extensively studied temperate latitudes and polar regions. The climate mechanisms responsible for this shift are reviewed and a model developed to explain such a strong signal from the tropical areas without associated changes at high latitudes, such as changes in polar ice-sheet extent. We propose changes in Pacific Ocean sea-surface temperature regime, and the establishment of El Niño conditions have imparted a direct influence on tropical Atlantic SST that could explain the rapid changes in terrestrial palaeoecological records. Other components of the terrestrial-ocean-atmosphere system are also likely to be important contributory factors in the environmental shift, in particular the large changes in land surface conditions could contribute to the climate shift. Given the scenario for tropical environmental change, to a degree independent from high latitudes, targeted areas of future research are indicated that incorporate development of climate and ecosystem modelling and palaeoenvironmental investigation with a tropical focus.

Abstract: Abstract Aim In the framework of the Global Land Cover 2000 (GLC 2000), a land-cover map of Africa has been produced at a spatial resolution of 1 km using data from four sensors on-board four different Earth observing satellites. Location The map documents the location and distribution of major vegetation types and non-vegetated land surface formations for the entire African continent plus Madagascar and the other surrounding islands. Methods The bulk of these data were acquired on a daily basis throughout the year 2000 by the VEGETATION sensor on-board the SPOT-4 satellite. The map of vegetation cover has been produced based upon the spectral response and the temporal profile of the vegetation cover. Digital image processing and geographical information systems techniques were employed, together with local knowledge, high resolution imagery and expert consultation, to compile a cartographic map product. Radar data and thermal sensors were also used for specific land-cover classes. Results A total of 27 land cover categories are documented, which has more thematic classes than previously published land cover maps of Africa contain. Systematic comparison with existing land cover data and 30-m resolution imagery from Landsat are presented, and the map is also compared with other pan-continental land cover maps. The map and digital data base are freely available for non-commercial uses from http://www.gvm.jrc.it/tem/africa/products.htm Main conclusions The map improves our state of knowledge of the land-cover of Africa and presents the most spatially detailed view yet published at this scale. This first version of the map should provide an important input for regional stratification and planning purposes for natural resources, biodiversity and climate studies. Résumé Objet Dans le cadre du projet Global Land Cover 2000 (GLC 2000), une carte d'Afrique d'occupation du sol a été produite à la résolution spatiale de 1 km à partir de données satellitales de 4 capteurs différents. Localisation La carte représente la distribution des principaux types de végétation et des surfaces non-végétales du continent africain plus Madagascar et les autres îles voisines du continent. Méthodes La plupart des données fut acquise durant l'année 2000 par le capteur VEGETATION, embarquéà bord du satellite SPOT-4. La réponse spectrale et le profil temporel des formations végétales ont permis la production de la carte d'occupation du sol. Des techniques de traitement d'image et de systèmes d'information géographique ont été combinées à la consultation d'experts locaux et à l'utilisation de cartes nationales et de données à haute résolution spatiale. Des images radar et thermiques ont servi à cartographier des classes spécifiques. Résultats Un total de 27 classes est cartographié, ce qui est plus que les précédentes cartes basées sur l'imagerie satellitale. Une comparaison systématique avec les cartes publiées et des images Landsat à 30 m est présentée. Les données sont libres d'accès pour un usage non-commercial à l'adresse http://www.gvm.jrc.it/tem/africa/products.htm Conclusion Cette carte accroît notre connaissance de l'occupation du sol de l'Afrique et présente la vue la plus détaillée jamais publiée à cette échelle. La première version de la carte devrait fournir une base importante pour une stratification régionale et pour la planification d�études sur les ressources naturelles, la biodiversité et le climat.

Abstract: Abstract. Tendency to crust is a potentially useful index for assessing soil degradation and for assisting land use planning in South Africa. In this study, the influence of land use, geology and vegetation cover on the tendency of soil to form a surface crust was investigated in six vegetation types. Crusting at all sites was greater in exposed soils than soils under vegetation, as determined by infiltration rate, water dispersible clay and modulus of rupture. In Renosterveld, crusting was markedly greater in exposed soil than vegetation covered soil (mean infiltration 16 vs 44 mm h�1; dispersible clay 2.6 vs 2.2%; modulus of rupture 121 vs 64 kPa). Greater crusting in exposed soil was attributed to lower soluble salt and labile carbon (C) contents and an asso ciated increase in the dispersion of clay. In Karoo, crusting of exposed, shale-derived soils was greater than that of exposed, dolerite-derived soils (infiltration 40 vs 83 mm h�1; dispersible clay 2 vs 1.2%), and a similar pattern was evident in Tall Grassveld (infiltration 18 vs 36 mm h�1; dispersible clay 1.2 vs 0.9%; modulus of rupture 31 vs 21 kPa). In Upland Grassland, cultivation of maize and rye enhanced crusting. In Thicket, crusting was greater in soils from open, degraded vegetation than intact, densely wooded sites (infiltration 19 vs 51 mm h�1; modulus of rupture 16 vs 34 kPa), probably due to lower content of soil C. In Bushveld, crusting was greater in annually burnt plots than unburnt plots (infiltration 109 vs 163 mm h�1; dispersible clay 0.9 vs 0.6% on granite-derived soils; and infiltration 56 vs 72 mm h�1; dispersible clay 1.5 vs 1.3% on basalt-derived soils). Greater crusting of soil from burnt plots was ascribed to a reduction in soil C and soluble salts as well as a greater exchangeable sodium percentage.

Abstract: Savannas and grasslands in South Africa are adapted to fire, yet long-term effects of fire on soil, water and nutrients remain largely unknown. To determine whether frequent burning increases the tendency of soils to crust and alters soil chemistry, topsoils from 19 sites were examined in Mpumalanga, KwaZulu-Natal and the Eastern Cape where annual burning and fire exclusion experiments had been conducted for at least 28 years. A comparison of soils from burnt and unburnt plots revealed that composite samples taken to a depth of 10 cm from burnt plots had lower laboratory infiltration, electrical conductivity (EC) of 1:5 extracts, water-soluble K, water-soluble NH4, total C, total N and labile C. Burnt plots had higher pH in KCl, water dispersible clay and modulus of rupture. Rate of soil respiration from composite samples (0-2 cm) from burnt plots was lower than from unburnt plots (means of 21 vs. 36 ng C g-1 s-1). Rainfall simulation on the same samples demonstrated that burnt plots crusted more rapidly than unburnt plots (19 vs. 35 mm h-1), while results from sampling at 1-cm intervals revealed that the greatest differences between burnt and unburnt plots were in the 0-1 cm layer. The top few centimetres of soil are likely to have a disproportionate effect on ecosystem functioning by influencing the rate of infiltration and mineralisation of soil organic matter. This thin surface layer has been named the pedoderm in this paper. Soil from 0-1 cm in burnt plots had lower total C (means of 0.8% vs. 2.7% for burnt and unburnt plots, respectively), total N (0.07% vs. 0.23%), (NH4)OAc-extractable Ca (7 vs. 17 mmolc kg-1), Mg (2 vs. 7 mmolc kg-1), K (0.8 vs. 1.5 mmolc kg-1) and a greater exchangeable Na percentage (17% vs. 8%). The results indicate that burning increases soil crusting. This was ascribed to a decrease in humus content (and associated disaggregating effect) and an increase in the dispersion of clay. Nutrients are lost from burnt plots over time, probably by the removal of ash in surface runoff. Calcium, Mg, and K were lost more readily than Na probably because plants take up these nutrients in greater concentration than Na. The net effect was an increase in the exchangeable sodium percentage (ESP). Crusting on burnt plots may be self-perpetuating, because increased runoff is likely to increase the loss of soluble salts.

Abstract: A new integrated approach, involving continuum-removed absorption features, the red edge position and neural networks, is developed and applied to map grass nitrogen concentration in an African savanna rangeland. Nitrogen, which largely determines the nutritional quality of grasslands, is commonly the most limiting nutrient for grazers. Therefore, the remote sensing of foliar nitrogen concentration in savanna rangelands is important for an improved understanding of the distribution and feeding patterns of wildlife. Continuum removal was applied on two absorption features located in the visible (R550-757) and the SWIR (R2015-2199) from an atmospherically corrected HYMAP MKI image. A feature selection algorithm was used to select wavelength variables from the absorption features. Selected band depths from the absorption features as well as the red edge position (REP) were input into a backpropagation neural network. The best-trained neural network was used to map nitrogen concentration over the whole study area. Results indicate that the new integrated approach could explain 60% of the variation in savanna grass nitrogen concentration on an independent test data set, with a root mean square error (rmse) of 0.13 (±8.30% of the mean observed nitrogen concentration). This result is better compared to the result obtained using multiple linear regression, which yielded an R2 of 38%, with a RMSE of 0.16 (±10.30% of the mean observed nitrogen concentration) on an independent test data set. The study demonstrates the potential of airborne hyperspectral data and neural networks to estimate and ultimately to map nitrogen concentration in the mixed species environments of Southern Africa.

Abstract: Remote sensing of grass quantity is important for providing information about the productivity and functioning of rangelands. Existing indices used to estimate grass quantity, such as normalized difference vegetation index (NDVI) are of limited value due to the saturation problem, especially in dense vegetation with 100% leaf area cover. Therefore, there is need to explore new techniques to resolve the saturation problem. In this study we tested the utility of band depth analysis to estimate grass quantity in dense vegetation. Band depth indices calculated from continuum-removed spectra of Cenchrus ciliaris grass, measured at canopy level in the visible spectral domain (550-750 nm) were used to estimate biomass. Band depth analysis results were compared to two narrow band NDVIs calculated using near-infrared and red bands. Results indicate that, the band depth analysis methodology could estimate quantity with a high coefficient of determination of 0.81, 0.83, 0.86 and 0.85 for band depth (BD), band depth ratio (BDR), normalized band depth index (NBDI) and band depth normalized to area (BNA), respectively. Narrow band NDVIs yielded lower correlations (0.31 and 0.32 for NDVI 1 and NDVI 2, respectively). Thus, band depth can estimate quantity in densely vegetated areas where NDVI values reach an asymptote.

Abstract: The abundance and distribution patterns of four threatened species of bustards (Eupodotis caerulescens, E. barrowii, E. melanogaster and Neotis denhami) in 3200 km2 of montane grasslands in the Wakkerstroom district, South Africa were characterised and related to altitude, topography and land use. During 2001 and 2002, 61 car-driven transects (544 km in total) were carried out to count bustards at the onset of the breeding season. The spatial patterns of land use and bustard occurrence along transects were characterised using geostatistics. The influence of explanatory variables on each species occurrence was assessed using logistic regression. There were inter-specific differences in distribution, with E. caerulescens occurring at higher altitudes than the other species. These differences were partly explained by different habitat preferences. Population estimates for the study area were [approximate]1400 E. caerulescens, 150 E. barrowii and 30 male E. melanogaster. The main threats for the bustard populations in the region are commercial afforestations (mainly for N. denhami) and agricultural intensification (mainly for E. barrowii and E. melanogaster). The results of this study can be used as a baseline situation against which future monitoring could be compared. The used method proved to be effective for characterising occurrence patterns and censusing bustard populations in relatively large areas, as well as describing large-scale habitat patterns.

Abstract: Much effort in systematic conservation planning has gone into devising measures and algorithms which are efficient at capturing the biological importance of different candidate areas. While cost is at the theoretical heart of complementarity based analyses, little empirical attention has been paid to explicitly incorporating cost into conservation planning. Here we begin to address this gap by utilising the first estimate of management costs for ecoregion conservation across the entire African continent to examine the consequences of incorporating estimates of management costs into conservation planning. We apply a recently developed equation linking empirical costs data to economic indicators and the size distribution of reserves to estimate the annual funding required to effectively manage reserve networks covering 10% of each of Africa's 118 ecoregions. Our estimates suggest that US$630 M/year (0.1% of African Gross National Income) would achieve this goal. However, within this the costs per ecoregion vary widely. Analysis of this variation in cost emphasises that high costs are likely to be correlated with high endemism or threat and that focussing exclusively on cheap areas is unlikely to achieve conservation goals. We also used the cost estimates to examine the potential for improving cost-effectiveness in conservation planning by comparing cumulative representation of vertebrate species and the associated management cost of reserves under different prioritisation schemes where cost was included or excluded. We found that factoring the cost of conservation management into the planning process results in a marked increase in the cost effectiveness of a given prioritisation scheme. This suggests that further improvements in systematic conservation planning are more likely to come more from measuring and integrating cost and other socio-economic considerations than from focusing exclusively on refinement of biological criteria.

Abstract: This study investigated the potential of Dichrostachys cinerea fruits as a protein supplement in semi-arid areas of Zimbabwe. The tanniniferous fruits were treated with aqueous solutions of polyethylene glycol (PEG) or sodium hydroxide (NaOH). Both treatments increased the soluble fraction, rate of degradation and effective degradability (ED) of nitrogen (N) in sacco. The PEG effects were higher than the NaOH effects (e.g. a 25% vs. 6% increase in effective N degradabilities, respectively). Five treatments were evaluated in a N-balance trial using Matebele goats: ground, PEG- or NaOH-treated D. cinerea fruits, a commercial protein supplement (CPS) and no supplement. Animals offered ground fruits or CPS retained most N (3.7 or 4.1 g N/day, respectively), while those offered NaOH- or PEG-treated fruits retained significantly less N (2.7 or 1.0 g/day, respectively). Unsupplemented animals were in negative N balance (-2.4 g/day). PEG treatment deactivated the tannins more than the NaOH treatment. PEG treatment resulted in excessive protein degradation in the rumen leading to high urine N loss. It is concluded that the D. cinerea fruits were beneficial for goat N-nutrition and that the tannins did not require inactivation. D. cinerea fruits can, therefore, replace the expensive commercial protein supplement. It is also suggested that the collection and grinding of fruits could be used as a management tool to control bush encroachment.

Abstract: Palaeoecological data recording a pronounced environmental shift centred about 4000 years BP are presented from tropical Africa and South America. The environmental shift is particularly manifested as a change in the hydrological budget and vegetation within numerous swamp and lake catchments. The majority of sites in tropical Africa record a shift to drier environmental conditions that is in opposition to South America, where a shift to a wetter environment is generally recorded. The strength of between site signals varies from being relatively complacent to dramatic, in some cases reflective of whole-scale vegetation change. The magnitude of change is mainly dependent of the location of the site and the proxy under investigation. These ecosystem changes are likely to reflect changed precipitation regimes, increased evaporation, and or an extension/contraction of the dry season. This pronounced Holocene environmental shift is particularly interesting, as the marked changes within the tropics are either weakly recorded, or non-existent, at more extensively studied temperate latitudes and polar regions. The climate mechanisms responsible for this shift are reviewed and a model developed to explain such a strong signal from the tropical areas without associated changes at high latitudes, such as changes in polar ice-sheet extent. We propose changes in Pacific Ocean sea-surface temperature regime, and the establishment of El Niño conditions have imparted a direct influence on tropical Atlantic SST that could explain the rapid changes in terrestrial palaeoecological records. Other components of the terrestrial-ocean-atmosphere system are also likely to be important contributory factors in the environmental shift, in particular the large changes in land surface conditions could contribute to the climate shift. Given the scenario for tropical environmental change, to a degree independent from high latitudes, targeted areas of future research are indicated that incorporate development of climate and ecosystem modelling and palaeoenvironmental investigation with a tropical focus.

Abstract: The viability of mixed farming systems in West African savannas relies largely on the management of endogenous organic resources. Assessment of the organic balance at both plot and village territory scales is needed as an indicator of this viability. Distribution of carbon (C), nitrogen and phosphorus in soil and plant biomass was thus quantified for a village in southern Senegal across the different land use systems (LUS) and farm holdings. The village exhibited ring-like organisation, including a compound ring, a bush ring, and lowland paddy fields, with positive gradients of intensification and food production from the savanna to the dwellings. Marked contrasts were found between holdings, especially in livestock availability. Clear relationships were evidenced between the spatial distribution of C and nutrients and the agricultural functions of LUS and holdings, while multi-scale diversity appeared to be the main factor that ensured the functioning of the system. Intensification schemes at the village level aimed at increasing organic resources and their cycling efficiency must thus take into account their impact on this diversity.

Abstract: Savanna rangelands are characterized by dynamic interactions between grass, shrubs, fire and livestock driven by highly variable rainfall. When the livestock are grazers (only or preferentially eating grass) the desirable state of the system is dominated by grass, with scattered trees and shrubs. However, the system can have multiple stable attractors and a perturbation such as a drought can cause it to move from such a desired configuration into one that is dominated by shrubs with very little grass. In this paper, using the rangelands of New South Wales in Australia as an example, we provide a methodology to find robust management strategies in the context of this complex ecological system driven by stochastic rainfall events. The control variables are sheep density and the degree of fire suppression. By comparing the optimal solution where it is assumed the manager has perfect knowledge and foresight of rainfall conditions with one where the rainfall variability is ignored, we found that rainfall variability and the related uncertainty lead to a reduction of the possible expected returns from grazing activity by 33%. Using a genetic algorithm, we develop robust management strategies for highly variable rainfall that more than doubles expected returns compared to those obtained under variable rainfall using an optimal solution based on average rainfall (i.e., where the manager ignores rainfall variability). Our analysis suggests some key features of a robust strategy. The robust strategy is precautionary and is forced by rainfall variability. It is less reactive with respect to grazing pressure changes and more reactive with respect to fire suppression than is an optimum strategy based on a deterministic system (no rainfall variability). Finally, the costs associated with implementing a robust strategy are far less than the expected economic losses when uncertainty is not taken into account.

Abstract: In arid and semi-arid areas, total evaporation is a major component of the hydrological cycle and seasonal water shortages and drought are common. In these areas, the role of land use and land use change is particularly important and it is imperative that land and water resources are well managed. To aid efficient water management, it is useful to demonstrate how changing land use affects water resources. A convenient framework to consider this is through the use of the [`]blue-water' and [`]green-water' classification of Falkenmark, where green-water represents water use by land and blue-water represents runoff. In this study the hydrological response of nine land-use scenarios were simulated for the upper reaches of the Mutale River, an important tributary of the Luvuvhu River in S. Africa. The ACRU and HYLUC land use sensitive hydrological models, were used to investigate the change in blue and green water under the various land-use scenarios. The GIS software ArcGIS(8.3) was used to analyse available spatial data to generate inputs required by the hydrological models. The scenarios investigated included the current land use in the catchment, an increase or decrease in forest cover, and an increase or decrease in the area irrigated. Both models predict that increasing either forestry or irrigation significantly reduces the proportion of blue water in the catchment. The predictions from the models were combined with maps of catchment land use, to illustrate the changes in distribution of green and blue water in a user-friendly manner. The use of GIS in this way is designed to enable policy-makers and managers to quickly assimilate the water resource implication of the land use change.

Abstract: We have documented elsewhere, and briefly reviewed here, the anomalously high species richness of browsing ungulates (hoofed mammals) in the mid Miocene (~18-12 Ma) woodland savanna habitats of North America. In the mid Miocene these habitats supported substantially more brachydont (browsing) species than do any present-day savanna habitats. We present some preliminary data to show that such species-rich browser communities are not observed after the mid Miocene. The data also suggest that these mid Miocene browser communities and their subsequent disappearance may have been a global phenomenon. We then focus on possible explanations for these observations. We discuss the possibility that the high species numbers are a preservational artifact, and conclude that taphonomic factors are unlikely to be responsible for the level of species richness observed. We then consider various possible explanations for high species richness, including the unique aspects of climatic change (cooling, drying, increased seasonality), unique biotic interactions (the effects of competition, keystone herbivores, changes in predator pressure), and consider that none of these are fully consistent with the available data. The most likely explanation for the observed species-rich browser palaeocommunities is an elevated level of primary productivity, relative to the present day, within (at least some) mid Miocene grassland habitats. Such an increase in productivity could possibly have been the result of higher-than-present levels of atmospheric carbon dioxide in the mid Miocene, but this conflicts with current interpretations of geochemical evidence, and a satisfactory mechanism for the inferred increased primary productivity is an unresolved issue.

Abstract: The objective of this research was to study the relationships between environmental factors and vegetation in order to find the most effective factors in the separation of the vegetation types in Poshtkou rangelands of Yazd province. Sampling of soil and vegetation were performed with randomized-systematic method. Vegetation data including density and cover percentage were estimated quantitatively within each quadrat, and using the two-way indicator species analysis (TWINSPAN), and vegetation was classified into different groups. The topographic conditions were recorded in quadrat locations. Soil samples were taken in 0-30 and 30-60 cm depths in each quadrat. The measured soil variables included texture, lime, saturation moisture, gypsum, acidity (pH), electrical conductivity, sodium absorption ratio, and soluble ions (Na+, K+, Mg2+, Cl-, CO32-, HCO3- and SO42-). Multivariate techniques including principal component analysis (PCA) and canonical correspondence analysis (CCA) were used to analyse the collected data. The results showed that the vegetation distribution pattern was mainly related to soil characteristics such as salinity, texture, soluble potassium, gypsum, and lime. Totally, considering the habitat conditions, ecological needs and tolerance range each plant species has a significant relation with soil properties.

Abstract: Eocene vegetation and climate data from tropical latitudes are sparse despite special interest in the Eocene as the warmest epoch of the Cenozoic and an often-cited analogue for greenhouse Earth conditions. Tropical Africa is noteworthy for its shortage of Eocene fossils, which could serve as proxies for climate and reveal community structural evolution during the continent's geographic isolation. In this paper, we report paleobotanical remains from a middle Eocene crater lake at 12°S paleolatitude in north central Tanzania, which provide a plant community reconstruction indicating wooded, rather than forest, vegetation and precipitation estimates near modern (660 mm/year). The plant community was dominated by caesalpinioid legumes and was physiognomically comparable to modern miombo woodland. Paleoprecipitation estimates, the first for the Paleogene of Africa, are calculated from fossil leaf morphology using regression equations derived from modern low-latitude leaves and climate. Mean annual precipitation estimates are 643±32 and 776±39 mm/year, and wet months precipitation estimates (all months averaging>=50 mm) are 630±38 and 661±38 mm. A slightly larger proportion of annual precipitation occurred in the dry months compared with today, which may indicate greater equability of precipitation in the Eocene.

Abstract: Attention has been directed towards both the impacts of future climate change on environmental systems and dunefield activity in the past, but there has been relatively little consideration of potential dune mobility in a future and possibly warmer world. This paper considers the use and limitations of four Global Circulation Models (GCMs) (Hadcm3, Hadcm2, CSIRO-mk2b and CGCM1), in combination with simple dune mobility indices to predict the activity of the Kalahari dunefield. It is clear that uncertainties surround GCM resolution and accuracy, mobility index robustness for the calculation of intra-annual dune mobility and data collection for mobility index calibration. Macro-scale studies that look at large areas of the world over long time scales are well suited to GCM and mobility index use, but dune mobility can be variable within a dunefield, and it is the extreme sand transporting events, occurring at high temporal resolutions, that are the most important for short term studies. To investigate intra-annual changes in dune mobility over a specific dunefield techniques such as downscaling, weather generators and probability curve fitting can help provide climate predictions for smaller areas over shorter time frames. However, these methods introduce uncertainty of their own, and they often rely on the accuracy of original GCM predictions or the climate parameter relationships observed at present. Analysis of intra-annual changes also requires mobility indices that can model monthly mobility patterns well, although existing indices have only been used for calculating annual dune mobility potential. When they are used for intra-annual predictions, the lack of lag response between precipitation decreases and the assumed vegetation dieback leads to an exaggerated amplitude pattern of dune mobility throughout the year. Calibration of dune mobility indices to dune mobility observed on the ground is therefore important but is hampered by a lack of observed measurements for individual months. Solutions are available to overcome some of the outlined problems, but they can provide their own set of uncertainties, which combine to further reduce the confidence given to future dune mobility predictions.

Abstract: This paper uses three recently generated southern African satellite burned area products for the month of September 2000 in a sensitivity study of regional biomass burning emissions for a number of trace gases and particulates. Differences in the extent and location of areas burned among products generated from Moderate Resolution Imaging Spectroradiometer (MODIS), Systeme Pour l'Observation de la Terre (SPOT-VEGETATION), and Along Track Scanning Radiometer (ATSR-2) data are significant and result in different emissions estimates for woodland and grassland land cover types. Due to the different emission profiles in woodlands and grasslands, favoring relatively more products of incomplete combustion in woodlands compared with products of complete combustion in grasslands in the late dry season, these changes are not proportional to the differences in the burned area amounts. The importance of accurate burned area information not just in terms of the total area but also in terms of its spatial distribution becomes apparent from our modeling results. This paper highlights the urgent need for satellite data producers to provide accuracy assessments associated with satellite-derived products. Preferably, these accuracy data will be spatially explicit, or defined in a way that can be applied in a spatially explicit modeling context, to enable emissions uncertainties to be defined with respect to different landscape units in support of greenhouse gas emissions reporting.

Abstract: This paper analyses the claim of Sumberg [Sumberg, J., 2002. The logic of fodder legumes in Africa. Food Policy 27, 285-300] that there is a [`]logic of fodder legumes' in Africa based on an idea from Europe applied inappropriately and unsuccessfully to livestock development in Africa by those who Sumberg calls [`]colonial masters'. We suggest that Sumberg was incorrect on many technical points and policy conclusions. We find that: fodder legume use in Africa was based on local experience and traditional practices; the development of fodder grasses has been a more important research theme in Africa in the past 100 years than the development of fodder legumes; there is no strong evidence that the agricultural revolution in Europe was a major contributing factor to a [`]logic of fodder legumes' in Africa; using appropriate methodology, national and international fodder researchers have developed some successful fodder grasses and legumes in Africa, especially for [`]crop' and [`]niche' roles; and there are at least three well-documented examples of successful promotion of fodder legumes in African crop-livestock systems. Our historical path to recognizing [`]development narratives' has therefore not found any evidence that there is a [`]logic of fodder legumes' in Africa. We also query Sumberg's recommendations for a more realistic systems-based approach to fodder legume research. This need was highlighted 15 years ago and, for the past 10 years, such improved approaches are having increasing impact on productivity in and policy for African crop-livestock systems.

Abstract: A 4.5 Ma record of fluvial and lacustrine deposits is well exposed at Gona, in the Afar Depression of Ethiopia. We use isotopic values of pedogenic carbonate and fossil teeth to reconstruct Plio-Pleistocene environmental change at Gona. An increase in [delta]13C values of pedogenic carbonates since 4.5 Ma points to a shift from woodlands to grassy woodlands in the early Pliocene, -10.4 to -3.9[per mille sign] (VPDB), to more open but still mixed environments in the late Pleistocene, -3.0 to -1.4[per mille sign] (VPDB). This pattern is also seen in isotopic records elsewhere in East Africa. However, at 1.5 Ma the higher proportion of C4 grasses at Gona is largely a result of a local facies shift to more water-limited environments. The wide range of [delta]13C values of pedogenic carbonate within single stratigraphic levels indicates a mosaic of vegetation for all time intervals at Gona that depends on depositional environment. Elements of this mosaic are reflected in [delta]13C values of both modern plants and soil organic matter and Plio-Pleistocene soil carbonate, indicating higher amounts of C4 grasses with greater distance from a river channel in both the modern and ancient Awash River systems. [delta]18O values of pedogenic carbonates increase up-section from -11.9[per mille sign] in the early Pliocene to -6.4[per mille sign] (VPDB) in the late Pleistocene. The wide range of [delta]18O values in paleovertisol carbonates from all stratigraphic levels probably reflects short-term climate changes and periods of strong evaporation throughout the record. Based on the comparison between [delta]18O values of Plio-Pleistocene pedogenic carbonates and modern waters, we estimate that there has been a 6.5[per mille sign] increase in mean annual [delta]18O values of meteoric water since 4.5 Ma. [delta]18O values of pedogenic carbonate from other East African records indicate a similar shift. Increasing aridity and fluctuations in the timing and source of rainfall are likely responsible for the changes in [delta]18O values of East African pedogenic carbonates through the Plio-Pleistocene.

Abstract: Abstract Aim Wildlife and pastoral peoples have lived side-by-side in the Mara ecosystem of south-western Kenya for at least 2000 years. Recent changes in human population and landuse are jeopardizing this co-existence. The aim of the study is to determine the viability of pastoralism and wildlife conservation in Maasai ranches around the Maasai Mara National Reserve (MMNR). Location A study area of 2250 km2 was selected in the northern part of the Serengeti-Mara ecosystem, encompassing group ranches adjoining the MMNR. Emphasis is placed on Koyake Group Ranch, a rangeland area owned by Maasai pastoralists, and one of Kenya's major wildlife tourism areas. Methods Maasai settlement patterns, vegetation, livestock numbers and wildlife numbers were analysed over a 50-year period. Settlement distributions and vegetation changes were determined from aerial photography and aerial surveys of 1950, 1961, 1967, 1974, 1983 and 1999. Livestock and wildlife numbers were determined from re-analysis of systematic reconnaissance flights conducted by the Kenya Government from 1977 to 2000, and from ground counts in 2002. Corroborating data on livestock numbers were obtained from aerial photography of Maasai settlements in 2001. Trends in livestock were related to rainfall, and to vegetation production as indicated by the seasonal Normalized Difference Vegetation Index. With these data sets, per capita livestock holdings were determined for the period 1980�2000, a period of fluctuating rainfall and primary production. Results For the first half of the twentieth century, the Mara was infested with tsetse-flies, and the Maasai were confined to the Lemek Valley area to the north of the MMNR. During the early 1960s, active tsetse-control measures by both government and the Maasai led to the destruction of woodlands across the Mara and the retreat of tsetse flies. The Maasai were then able to expand their settlement area south towards MMNR. Meanwhile, wildebeest (Connochaetes taurinus) from the increasing Serengeti population began to spill into the Mara rangelands each dry season, leading to direct competition between livestock and wildlife. Group ranches were established in the area in 1970 to formalize land tenure for the Maasai. By the late 1980s, with rapid population growth, new settlement areas had been established at Talek and other parts adjacent to the MMNR. Over the period 1983�99, the number of Maasai bomas in Koyake has increased at 6.4% per annum (pa), and the human population at 4.4% pa. Over the same period, cattle numbers on Koyake varied from 20,000 to 45,000 (average 25,000), in relation to total rainfall received over the previous 2 years. The rangelands of the Mara cannot support a greater cattle population under current pastoral practices. Conclusions With the rapid increase in human settlement in the Mara, and with imminent land privatization, it is probable that wildlife populations on Koyake will decline significantly in the next 3�5 years. Per capita livestock holdings on the ranch have now fallen to three livestock units/reference adult, well below minimum pastoral subsistence requirements. During the 1980s and 90s the Maasai diversified their livelihoods to generate revenues from tourism, small-scale agriculture and land-leases for mechanized cultivation. However, there is a massive imbalance in tourism incomes in favour of a small elite. In 1999 the membership of Koyake voted to subdivide the ranch into individual holdings. In 2003 the subdivision survey allocated plots of 60 ha average size to 1020 ranch members. This land privatization may result in increased cultivation and fencing, the exclusion of wildlife, and the decline of tourism as a revenue generator. This unique pastoral/wildlife system will shortly be lost unless land holdings can be managed to maintain the free movement of livestock and wildlife.

Abstract: In order to track changes in the relative abundance of C3 and C4 plants in savanna vegetation, C/N and [delta]13C values were measured on bulk organic material in an 8840 14C-year record from Lake Tilo, Ethiopia. Between 8840 and 2500 BP, high C/N ratios suggest that input to the lake was predominantly from terrestrial plants. The corresponding [delta]13C values thus provide a proxy for changes in catchment vegetation that are supported by pollen data. [delta]13C values in the early Holocene are relatively low, reflecting the dominance of C3 vegetation (woody plants) and a more humid climate. [delta]13C shows no response to a known regional arid interval at 7800 yr BP, suggesting that woody vegetation was able to survive relatively prolonged dry periods. A gradual, rather than sharp, [delta]13C response to the end of the early Holocene humid interval at ~4500 yr BP further supports this. Higher [delta]13C values at ~2800-2300 and ~1000 yr BP correspond to increases in sedge pollen, thought to be growing in freshwater springs, exposed as lake-level fell. The C/N and [delta]13C composition of bulk organic material complements the pollen evidence and may be useful in other lakes in savanna regions as indicators of terrestrial vegetation change.

Abstract: Shrub encroachment into arid and semi-arid grasslands in the southwestern United States is of concern because increased shrub cover leads to declines in species diversity, water availability, grazing capacity, and soil organic matter. Although it is well known that shrubs have increased over time, we have little quantitative information related to the non-linear nature of this vegetation change over a particular period. On the Jornada Experimental Range (JER; USDA-ARS) and the adjacent Chihuahuan Desert Rangeland Research Center (CDRRC; New Mexico State University) in southern New Mexico, shrub increase has been measured with various ground survey techniques extending back to 1858. For this study, we used 11 aerial photos taken between 1937 and 1996 that covered a 150-ha study area and had sufficient resolution for shrub detection. A QuickBird satellite image provided coverage for 2003. We used image segmentation and object-based classification to monitor vegetation changes over time. Shrub cover increased from 0.9% in 1937 to 13.1% in 2003, while grass cover declined from 18.5% to 1.9%. Vegetation dynamics reflected changes in precipitation patterns, in particular, effects of the 1951-1956 drought. Accuracy assessment showed that shrub and grass cover was underestimated due to the constraint of the pixel size. About 87% of all shrubs >2 m2 were detected. The use of object-based classification has advantages over pixel based classification for the extraction of shrubs from panchromatic aerial and high-resolution satellite imagery. Incorporating both spectral and spatial image information approximates the way humans interpret information visually from aerial photos, but has the benefit of an automated classification routine. Combining several scales of analysis in a hierarchical segmentation method is appropriate in an ecological sense and allows for determining shrub density in coarser level classes. Despite encountering difficulties in analyzing a greatly varying aerial photo data set, including variability in spectral and spatial resolutions, moisture conditions, time of year of observation, and appearance of grass cover, aerial photos provide an invaluable historic record for monitoring shrub encroachment into a desert grassland.

Abstract: Vegetation change, particularly from the grass to shrub life form, is a critical issue on the world's semiarid rangelands. Stable carbon isotope ([delta]13C) values and associated radiocarbon ages from soil organic matter (SOM) were used to evaluate vegetation change across five landscape positions at a small enclosed basin in southeastern Arizona. Light and dense SOM fractions were separated to distinguish recent vegetation changes. The direction and timing of vegetation change differed with landscape position along a gentle elevation gradient from the basin outlet to a nearby volcanic ridge top. C4 perennial grasses have dominated the basin outlet, center, and toe slope landscape positions since at least 5000-6000 years BP, except for the dominance of C3 plants at the bottom of the outlet excavation at 5000 years BP. This isotopic change is associated with rounded cobbles that may have been a stream channel, suggesting the presence of C3 herbaceous or woody riparian vegetation. On mid-slope and ridge top landscape positions, where semidesert shrubs now dominate, the proportion of plants with C4 metabolism calculated from mass balance mixing formulas decreased from approximately 60% as recently as 400 years BP to only 1.5% observed today. The light SOM fraction from mid-slope and ridge top surface soil horizons was approximately 30% C4 and had a post-bomb date, suggesting that the conversion from grass to shrub occurred over the last several decades.

Abstract:

Abstract: Soil life depends on water, inorganic chemical elements and organic matter. Due to photosynthesis there is the growth of vegetation, primary production. The role of vegetation and humus in relation to their function and the many characteristics of their composition have been described in relation to soil quality and soil health. Soil is an environmental component and is permanently changing due to the often cyclic processes of litter supply. This chapter focuses on vegetation and humus and their various interacting components. The overview looks at present day knowledge and classical scientific knowledge. Moreover, it emphasizes the possibility of applying neglected data to present day soil management. Differences in the chemistry and structure of soils and litter cause great diversity in vegetation types. The way plants cope with various concentration of nutrients in the soil is partly formalized in the indicator values for plant species (Ellenberg) that can be deduced from soil type, moisture regime and nutrient regime. In general higher nutrient levels as well as chemically extreme environments result in lower plant diversity. The adaptation of plants to changing environmental components is a permanent process, resulting after decennia or centuries in resistant ecotypes, as in the case of a surplus of heavy metals in specifically metal-resistant ecotypes of the grasses Agrostis and Festuca, or in endemic species such as the Zinc violet. Mycorrhiza can protect roots against a surplus of heavy metals. The role of organic matter, its quantitative production and the various humus forms such as Fulvic Acid (FA) and Humic Acid (HA) have been evaluated. Soil types have been arranged according to organic matter conversion types in Mull with very active fauna and microflora, Mor that is the opposite, and Moder which lies between both types. The functionality of soils and their vegetation are often evaluated on a very limited spatial scale. They should be considered in the spatial context of a landscape above and below the soil surface. Several very specific indicators can be applied for chemical changes in the soil. A very general indicator of soil quality is the change in plant species composition, evaluated by Ellenberg's indicator values and related to the effects of manure, heavy metals, acidification and desiccation. The chemical composition of macro-elements and metals of the above ground vegetation and its analysis can provide information on the behaviour and availability of metals in the underground. This may reflect the position and capacity of the root and mycorrhiza system especially in buried (or covered) soil areas. The species-specific accumulation of chemical elements in leaf and above ground tissues and in litter has to be incorporated in the evaluation of soil quality and health, but is still missing in most ecological soil studies and in soil legislation as far as ecological risk assessment is concerned. There is hardly any vegetation and soil in any ecosystem that has escaped mechanical damages as a result of heavy machines, and modification to its chemistry by human activities. Physical impacts on the soil, resulting in soil compaction can be evaluated by root and mycorrhiza development that is restricted in compacted soil. In evaluating soil vitality, past, present and future land use has to be defined. Also impacts of physical, chemical and biological disturbance and the consequences for vegetation, soil organic matter, decomposition rate, and the impact on the soil profile have to be characterized. In general, plants and micro-organisms and to a lesser degree animals, have sufficient genetic potential to colonize each soil if water is available and changes occur slowly. The biodiversity of vegetation and fauna on soils with extreme saline and heavy metal-enriched environments may be very low. Such soil will not support the growth of edible plants, but the soil itself is still very vital.

Abstract:

Abstract: This thesis uses the sustainable rural livelihoods framework to investigate the livelihoods of communities residing adjacent to a remote protected area on the Wild Coast. The communities living in the area are among the poorest in South Africa and are largely dependent on migrant remittances and state welfare grants for their survival. Soon after South Africa�s first democratic elections in 1994, the communities lodged a land claim against the protected area on the basis of past removals. In 2001, their land rights to the protected area were restored, opening up new avenues for the development of the area. It is argued that livelihood systems in the area are complex, varied and dynamic, and that for development to be sustainable, it needs to be informed by a thorough understanding of the many factors that shape the context in which livelihoods are generated. The research is based primarily on �in-depth� micro-studies of two villages in the area - Ntubeni and Cwebe. It includes a detailed assessment of the extent and distribution of poverty and the various factors that make households vulnerable to livelihood shocks. The role of the rich and diverse natural resource base, the property rights associated with it, and the under-development of infrastructure and services in the area, are discussed in relation to livelihood prospects. A systems approach is used to examine the various ways in which livestock husbandry, cropping, natural resource use, employment and welfare dependence interact. Finally, the thesis examines in some detail the distribution of household assets, livelihood strategies and livelihood outcomes between the two villages, and between households in different income groups.

Abstract:

Abstract:

Abstract: The principal objective of this investigation, was to collect the family Cyperaceae and to study their leaf, bract and culm anatomy. The second was to examine the collection for unique structures or forms, whilst a third was to classify the Cyperaceae according to their photosynthetic structures and types. Distribution of the Cyperaceae within the broad region defined as the Eastern Cape would be influenced by rainfall pattern. It was expected that C� species would predominate in more mesic environments and habitats, whilst the C� species would be found in drier less favourable habitats. Collection within the region (November 1993 to late January 1997), yielded 106 species, totalling some 600 specimens. Both sub-families of the Cyperaceae (Caricoideae and Cyperoideae), eight tribes (Abildgaardieae, Cariceae, Cypereae, Hypotvtreae, Rhynchosporeae, Shoeneae, Sirpeae and Slerieae) and twenty five genera were found to be present. Sixty percent of the species were C� and forty percent were C�. Sixteen new species, which had not been collected within the boundaries of the region previously were also found. Over 43 percent of the species collected had unique anatomical characteristics that appeared to be influenced by habitat and or climate influenced. These are the characters influenced by hydromorphic, mesomorphic and xeromorphic environments. These anatomical characters: Thickness of leaves and bracts; thickness of the adaxial and abaxial epidermis of the leaves and bracts; flush, sunken and raised stomata; presence or absence of bulliform cells; presence and distribution of sclerenchymatous structures; presence or absence of a hypodermis; presence or absence of cavities in the leaves, bracts and culms; mesophyll or ground tissue structure, and the presence or absence of secretary structures. A few noteworthy anatomical characters that are influenced by climate are present in Cladium mariscus subsp. jamaicense (Schoeneae), the Cariceae, the Cypereae and the Sclerieae. Within Cladium mariscus subsp. jamaicense the pseudo-dorsiventral leaves and bracts, as well as the large lamina cavities, containing trans-lamina girders are unique. Papillate epidermal cells are limited to the tribe Cariceae. In the Cypereae many of the species lack bulliform cells and hypodermal layers. In Pycreus cooperi (Cypereae) the vascular bundles of the leaves and bracts, appear to be stacked in rows, that are inter-spaced with lamina cavities. In the Sclerieae the mesophyll structure is specific to the species level. Unique anatomical characteristics were also present in the leaves, bracts and culms of the genus Carpha. In this genus distinctive lateral vascular bundles were present abutting the large bundles and/or midrib bundle. The most distinctive anatomical characteristics that could be used to separate the members of the Cyperaceae were the structures and associated structures related to the photosynthetic pathway. The Eastern Cape Cyperaceae could be divided into three distinct groups based on photosynthetic structure, namely one C�, a C� and a potential C�-C� intermediate group. The C� group was found to have non-radiate mesophyll and an outer parenchymatous sheath with small chloroplasts (Cariceae, Cyperaceae [in part], Hypolytreae (Chrysithrix capensis], Rhynchosporeae [R. brownii], Schoeneae, Scirpeae and Sclerieae). The C� group has radiate mesophyll and an inner parenchymatous sheath with enlarged chloroplasts (Kranz or PCR sheath). The C� species are present in tribes Abildgaardieae, Cypereae (in part) and Rhynchosporeae (R. barrosiana). In the Eastern Cape, a few species with C� anatomy have anatomical characteristics that are similar to the species with C� anatomy (Cyathocoma hexandra [bracts], Cyperus tennellus var. tennellus [leaves and bracts], Ficinia bulbosa [leaves], F. dura [leaves and bracts], F. lateralis coastal [leaves and bracts], F. oligantha [bracts], F. pingiour [bracts], F. stolonifera [leaves and bracts], F. tribracteata [leaves and bracts], F. zeyheri [leaves and bracts], Isolepis cernua [leaves and bracts], I. costata var. macra [bracts], Schoenus nigricans [leaves], Scirpus nodosus [bracts] and Tetraria cuspidata [leaves and bracts)). The vascular bundles within this intermediate group, fall within the Hattersleyand Watson (1975) minimal cell lateral count and maximal cell distal count criteria for C� grass species. However, no biochemical data exists to see whether they are C�-C� intermediates or whether the Hattersley and Watson (1975) C� criteria for grasses applies to smaller, or scutiform Cyperaceae or not. Based on the results presented here, five distinct structural forms/types were found to be present in the C�, C� and C�-C� intermediate groups. The C� and the potential C�-C� intermediate species may be divided into two types, based on the number of vascular sheaths present. In the first or A-type, vascular bundles are surrounded by two sheaths and in the more dominant B-type, by three. The A-type was found in the Cypereae (Cyperus denudatus and C. textilis) and most of the Scirpeae. B-type anatomy occurred in the Cariceae, Cypereae (c. difformis, C. pulcher, C. sphaerospermus, C. tennellus var. tennellus and P. mundii), Hypolytreae, Rhynchosporeae (R. brownii), Schoeneae, Scirpeae (Bolboschoenus maritimus, Ficinia cinnamomea, F. fascicularis, F. lateralis both, F. pingiour, the genus Fuirena, I. diabolica, I. fluitans, I. prolifera and Schoenoplectus paludicola) and Sclerieae tribes. Based on the vascular sheath structure, the C� species could be divided into three groups, namely bulbostyloid, chlorocyperoid and fimbristyloid, where the bulbostyloid structure occurred in Bulbostylis schoenoides. Cyperus (in part), Kyllinga, Mariscus and Pycreus (except P. mundii) had a chlorocyperoid structure. Genera with fimbristyloid structure were recorded in the genera Abildgaardia, Bulbostylis and Fimbristylis. The bulbostyloid type represents a potential a fifth C� anatomical type within the C� Cyperaceae. As a result of this observation, it is possible that the C� syndrome may have evolved five times in the Cyperaceae and not four as previously suggested by Bruhl and Perry (1995) and by Soros and Dengler (2001). The C� Cyperaceae species within the Eastern Cape are more dominant in higher elevation habitats the C� species, similar to the C� grasses. The only C� species that occur at high elevations are those with three sheaths. The C� and C� species within the region occur in similar low rainfall habitat ranges, where the C�'s are more dominant in xeric habitats on drier soils than the C� species, similar to the grasses. Where more C� species occur in higher rainfall habitats than the C� species. With the exception of the Afromontane Bulbostylis schoenoides and R. barrosiana, the C� species similar to the grasses are dominant in high light and temperature habitats with low rainfall, unlike the C� Cyperaceae of Japan and America. Only five species occur in the desert like conditions of the Karoo-Namib biome (Cyperus laevigatus, C. rupestris var. rupestris, I. cernua, M. capensis and M. uitenhagensis), which have less than 250mm of rainfall per annum. Only three species are habitat-specific or may be endemic to a specific area within the Eastern Cape, namely A. capensis, Chrysithrix capensis and R. barrosiana. A. capensis in marshes on the Amatole mountains near Alice and Hogsback. C. capensis to the Tstsikamma mountains of the Wite Els Bosch forests. R. barrosiana to the marshlands of the Cape Morgan coastal Nature reserve at Kei Mouth. The anatomical types of the C� and more especially C� Cyperaceae are not specifically found in a particular rainfall regime or habitat type, which is contrary to the thesis hypothesis. However, the C� species are mostly correlated with hydrophytic to mesic habitats, with the exception of Ficinia and the two sheathed species. Ficinia is dominant in mesic grasslands and halophytic habitats. The two sheathed C� species are mostly present in halophytic habitats. The C� species are also more dominant in mesic to xerophytic grasslands, as expected in the hypothesis. Where only a few species occur in habitats correlated with increasing rainfall and temperature similar to the C� Cyperaceae of Japan and America. It may thus be that the development and evolution of the different C� anatomical forms (or phylogenetic forms) within the Cyperaceae may have enabled these species to establish themselves in habitats that were alien to their origins. It may be that the ability to regulate photoassimilate and water transport within the Cyperaceae enables their success in a dynamic and unpredictable climate, such as the Eastern Cape. Many of the anatomical characteristics reported in this thesis and its appendices are unique to the tribes, genera and/or species of the Eastern Cape Cyperaceae and thus may be valuable to future taxonomic classifications of the family. The research presented here should provide a good working platform for future, more detailed research on this often forgotten component of the vegetation.

Abstract: The factors that influence the invasion of hillslopes by the shrub Pteronia incana in the communal rangelands of Ngqushwa (formerly Peddie) district were investigated. Mgwalana, one of the catchments in the district where encroachment by the species is widespread, was chosen. The study combined field observations with image analysis based on high resolution infrared imagery. The catchment was flown and high resolution infrared images (1mx1m) were taken using a Kodak DCS420 digital, colour-infrared camera. The images were analysed using Idrisi32 and Kilimanjaro GIS versions. The ability of different vegetation indices to separate P. incana from the other cover types was investigated. Field observations of the degree of P. incana invasion in relation to, inter alia, soil surface conditions, slope angle and visible forms of erosion were made. A Digital Elevation Model (DEM) of 20m spatial resolution was used to derive terrain parameters. The presence and absence of P. incana in relation to slope gradient and aspect were determined. The combined influence of the two terrain parameters and land use on the invasion was also investigated. The Topographic Wetness Index (WI), a component of the TOPMODEL was derived from the DEM and its relationship with the spatial distribution of P. incana was explored. Soil moisture dependencies for P. incana and grass species as well as surrogates for runoff under the shrub and adjacent bare areas were determined in the field. A high level of classification accuracy confirmed the reliability of digital camera imagery for spatial analyses. Distinct spectral separability for the surface vegetation cover types was achieved by means of the Perpendicular Vegetation Index (PVI) as opposed to the ratio based vegetation indices (NDVI, SAVI and MSAVI). The absence/presence of P. incana was noted to be strongly influenced by slope angle and aspect. The probability for P. incana occurrence increased with slope steepness and southerly slope orientation. Abandoned and grazing lands were identified as the main invasion hotspots. Blanket invasion of the former signified the high susceptibility of abandoned land to P. incana invasion. The combined influence of land use, slope gradient and aspect was also noted to have promoted the invasion. This is borne out by the concentration of the invasion on abandoned steep slopes with a southerly orientation. Local topographic variations were identified as having a strong bearing on P. incana spatial distribution. The topographically driven WI confirmed this relationship, such that P. incana was associated with the low WI values of convexities. Differences in the moisture dependencies between P. incana and grass species were demonstrated by the greater rooting depth of the former. During field surveys, soil surface crusting was noted as inherent to P. incana patchiness. The coupling between local topography and soil surface crusting underpins soil moisture variability at hillslope and patch scales respectively. This in turn determines the competition between P. incana and grass species and the eventual replacement of the latter by the former. A close spatial correlation between fully established P. incana and severe forms of soil erosion was observed. Loss of patchiness and expansion of inter-patch bare areas promote runoff connectivity erosion. As most of the runoff becomes run out, hillslopes tend towards dysfunctional systems. Greater soil moisture storage after rainstorms under P. incana tussocks than the adjacent bare areas signifies the shrub�s water harvesting capabilities. The tussocks could thus serve as a starting-pointbuilding- block for the rehabilitation of dysfunctional hillslope systems.

Abstract: