Abstract: Vegetation dominated by grasses, which is among the largest ecosystems in the world, has great environmental significance as well as providing feed for livestock and wildlife. Grassland types vary according to climatic zones as do their utilization and wildlife. Competition between species is affected by herbivory and disturbance. Grasslands often result from the arresting of plant succession due to fire, grazing and other anthropic intervention.
Abstract: The idea of degradation of arid and semi-arid lands, often termed desertification in its irreversible form, due to human impact and/or climatic change has been much debated since the mid-1970s. From the time of the United Nation's Conference On Desertification in Nairobi, 1976, certain areas of northern Burkina Faso have been pointed out as examples of severe desertification. Several studies demonstrated that revitalization of a series of E-W oriented fossille dunes in the Oudalan province was ongoing. The present study includes an analysis of the trends of vegetation development in the region, covering the period 1955 to 1994, with emphasis on the fossile dunes. It is demonstrated that desertification and revitalization of dunes were phenomena associated with the period between the early 1970s and the mid-1980s, and that the decline in vegetation cover on the dunes seems to have been reversed in recent years. The analysis is based upon time series of aerial photos and satellite images, field studies of vegetation, interviews with local people and review of relevant literature. The findings are discussed with reference to the debate concerning desertification and land degradation, as well as to the current revisions of the [`]range management paradigm'. The observations indicate that the environmental history of the region is complex and cannot be boiled down to [`]human-induced irreversible degradation'. Rather they support the idea of semi-arid cultural landscapes undergoing constant change in response to both human impact and climatic trends and fluctuations.
Abstract: Acacia nilotica is a tree of international significance both as a beneficial plant and as a species prone to thicket formation and negative impacts on savannas throughout much of its range. While fire has been identified as a useful tool for controlling negative impacts of some Acacia species in Africa, A. nilotica adult trees are apparently fire tolerant. The effects of fire on seed bank mortality, viability and germination, and on juvenile plants of this species are unknown. We undertook a study to investigate the impacts of fire on seeds and first and second year seedlings in Australian Astrebla savannas. The primary objective was to determine the effects of control burns applied during the early stages of invasion and thicket formation. Because of high rates of seedling dessication post fire in 1997, supplementary watering was undertaken until fire mortality could be measured the following year. High seed mortality occurred for seeds located either in cattle dung (100%) or on the soil surface (c. 80%). Germination of those seeds that survived was enhanced following exposure to fire. Very high fire mortality (99%) was observed among first year seedlings and moderate mortality (60%) for second year seedlings even after a low intensity burn. Negative impacts on major pasture species were minimal. The implications of these findings are discussed in relation to A. nilotica fire ecology and to the efficacy of fire as a tool for managing this species.
Abstract: The adoption of ecosystem-based management strategies focuses attention on the need for broad scale estimates of ecological conditions; this poses two challenges for the science community: estimating broad scale ecosystem conditions from highly disparate data, often observed at different spatial scales, and interpreting these conditions relative to goals such as sustainability. The Interior Columbia Basin Ecosystem Management Project (ICBEMP), estimated relative composite ecological integrity by clustering conditions among proxy variables representing three component integrity ratings (forestland, rangeland, and aquatic integrity). Composite ecological integrity provides an estimate of relative system condition within the interior Columbia River basin assessment area that is responsive to changes in broad scale land management practices. Broad-scale measures can be used to assess progress toward land management goals or as an aide for managers in selecting or prioritizing areas (watersheds) for treatment. Currently, federal land managers are using estimates of current composite ecological integrity and trends in ecological integrity to prioritize management activities and understand effects of management actions.
Abstract: Flight behaviours of 23 butterfly species were mapped to establish the effect of both pine afforestation and different-sized grassland linkages on localised butterfly movements. Blocks of pine trees caused most butterflies to change direction and move away from the pine edge. Only four species crossed the grassland/pine edge, and of these, only two flew farther than 20 m into the pine forest. The adjacent grassland/indigenous forest edge had a higher number of species, but very few of these entered the forest. Movement rates were significantly faster in the narrow and highly-disturbed linkages, than in the wide and open grasslands, with the linkages acting as conduits between the preferred grassland patches. However, only highly vagile and eurytopic species actually entered the narrower grassland linkages. In contrast, the wider linkages hosted a significantly higher species diversity and functioned as habitats per se and not just as movement corridors, with butterflies frequently stopping to nectar, oviposit, drink and sunbask. Knowledge of butterfly responses to different landscape structures has important conservation and management implications. From the results here, it is recommended that, for these butterflies, the natural grassland linkages should be wider than 250 m.
Abstract: Abstract. South Africa has an important responsibility to global biodiversity conservation, but a largely inadequate conservation area network for addressing this responsibility. This study employs a coarse-filter approach based on 68 potential vegetation units to identify areas that are largely transformed, degraded or impacted upon by road-effects. The assessment highlights broad vegetation types that face high biodiversity losses currently or in the near future due to human impacts. Most vegetation types contain large tracts of natural vegetation, with little degradation, transformation or impacts from road networks. Regions in the grasslands, fynbos and forest biomes are worst affected. Very few of the vegetation types are adequately protected according to the IUCN’s 10% protected area conservation target, with the fynbos and savanna biomes containing a few vegetation types that do achieve this arbitrary goal. This investigation identifies areas where limited conservation resources should be concentrated by identifying vegetation types with high levels of anthropogenic land use threats and associated current and potential biodiversity loss.
Abstract: Influx of aeolian pollen trapped in marine sediments off Namibia provides a wind variation record for the last 135 kyr. The influx of major pollen components is derived from the southwest African desert/semi-desert zone and shows six periods during which enhanced southeast trade winds contributed to strong upwelling and reduced sea surface temperatures. The most prominent of these occurred during 17-23 cal. kyr, 42-56 kyr and before 130 kyr B.P. Correspondence between the pollen influx record and the Vostok deuterium isotope record suggests that pronounced glacial Antarctic cooling was accompanied by intensification of the southeast trades throughout the Late Quaternary. However, during 42-23 kyr B.P. the combination of strong Antarctic glaciation with a decrease of wind zonality induced by low latitude precessional insolation changes caused strong alongshore winds and Ekman pumping that resulted in strong upwelling and reduced sea surface temperatures without pollen influx enhancement.
Abstract: After-ripening of Cenchrus ciliaris L. spikelets was modelled during storage at various temperatures and equilibrium relative humidities (e.r.h.). At 40 and 50% e.r.h., the rate of after-ripening increased linearly with increase of storage temperature. The highest after-ripening rate was achieved by storing the seeds in 40°C and 50% e.r.h. At 70% e.r.h., however, seeds remained viable at 20 and 30°C but largely failed to after-ripen. Use of the model to predict the storage period required for decreasing dormancy to any desired level is described. The application to re-seeding degraded rangelands in arid areas is discussed.
Abstract: A GIS approach was used in the determination of soil fertility status in the Jhikhu Khola watershed. The watershed was stratified by topography, climate, soil type and land use using GIS overlay techniques. A (2 × 2 × 2 × 4) factorial approach served as the sampling framework to produce single and combined nutrient deficiency GIS maps. Soil acidity, phosphorus availability and lack of base cations were identified as the key soil fertility issues, with forests having the poorest overall soil nutrient status, followed by rangeland, rainfed agriculture and irrigated agriculture. Nutrient budget calculations revealed significant annual deficits in phosphorus for maizerotations but only minor deficits for rice rotations. The effect of inherited biophysical conditions on nutrient deficits were analyzed statistically and displayed using the GIS overlay method. Poor fertility and annual deficits were linked to erosion and sedimentation by documenting annual erosion losses from rainfed agriculture and degraded areas. Over a 7 year period, typical erosion from maize rotations in rainfed agriculture averaged 19 t/ha annually, while erosion from degraded sites were 75-100 percent higher. Significantly different sediment rating curves were obtained from two micro-watersheds, one with 14 percent and the other 25 percent degraded areas. Annual sediment contributions to the micro-watersheds confirmed that degraded sites increase the suspended sediment load, particularly under lower stream flow conditions. The discharge-sediment regression line was significantly higher during the pre-monsoon period than during the monsoon season. GIS tools were found to be useful in all parts of the analysis.
Abstract: At the end of 1997, the Western Division of New South Wales had 22 reserves with a total extent of 9458 km2 or 2.9% of the region. We used five measures to follow the effectiveness of the reserve system as it developed between 1960 and 1997. Two of the measures -- number and total extent of reserves -- are basic statistics in any review of protected areas. The other three measures concern how well the reserve system sampled the region's land types (e.g. ecosystems, vegetation types), defined here as land systems mapped at 1:250,000. The first of these measures was representativeness -- the number of land systems sampled to a threshold level. The second was efficiency -- the proportion of the reserve system contributing to, but not in excess of, conservation targets set for each land system. The third measure of sampling effectiveness was vulnerability bias -- the extent to which reserves have been dedicated in parts of the region with most risk of vegetation loss. The representativeness of the reserve system at the end of 1997 was very low. Results for efficiency showed that a substantial part of the reserve system was not contributing to conservation targets. This partly reflected extensions of reserves to improve their design, highlighting the trade-off between design and efficiency. Values for vulnerability bias were close to those expected if reservation had been indifferent to risk of vegetation loss from clearing or cropping. Higher values would be expected if reservation had been intended to secure good examples of the more vulnerable land systems before clearing or cropping compromised conservation targets. Fluctuations in efficiency and vulnerability bias since 1960 can be related to the establishment and extension of individual reserves. We finish the paper by placing our measures of effectiveness in the context of a more comprehensive list needed to deal with issues such as environmental gradients and species' requirements for long-term persistence.
Abstract: Scheduling conservation action is necessary when the available resources for conservation are insufficient to adequately protect all of the natural features (e.g. species, vegetation types, ecosystems) in a region, at least in the short-term. We propose an approach to scheduling conservation action in production landscapes. It is based on two characteristics of potential conservation areas. The first is vulnerability -- the likelihood or imminence of destruction or alteration of native vegetation. The second is irreplaceability -- the likelihood that an area will be needed to contribute to a set of conservation targets nominated for the region's features. We argue that highest priority for conservation action should go to those areas with both high vulnerability (urgent protection needed to avoid destruction) and high irreplaceability (few or no alternatives if destroyed). To establish the context and rationale for our approach, we review some previous methods for scheduling nature conservation. We then apply our approach to the Western Division of New South Wales, a region of about 325,000 km2, by deriving information on the vulnerability of 248 land systems to two threatening processes (clearing and cropping) and measuring the irreplaceability of potential conservation areas. Our results are maps of areas where conservation action is most urgently needed if regional conservation targets are not to be compromised.
Abstract: This study outlines the development of an approach to evaluate the sources, sinks, and magnitudes of greenhouse gas emissions from a grazed semiarid rangeland dominated by mulga (Acacia aneura) and how these emissions may be altered by changes in management. This paper describes the modification of an existing pasture production model (GRASP) to include a gas emission component and a dynamic tree growth and population model. An exploratory study was completed to investigate the likely impact of changes in burning practices and stock management on emissions. This study indicates that there is a fundamental conflict between maintaining agricultural productivity and reducing greenhouse gas emissions on a given unit of land. Greater agricultural productivity is allied with the system being an emissions source while production declines and the system becomes a net emissions sink as mulga density increases. Effective management for sheep production results in the system acting as a net source (~60-200 kg CO2 equivalents/ha/year). The magnitude of the source depends on the management strategies used to maintain the productivity of the system and is largely determined by starting density and average density of the mulga over the simulation period. Prior to European settlement, it is believed that the mulga lands were burnt almost annually. Simulations indicate that such a management approach results in the system acting as a small net sink with an average net absorption of greenhouse gases of 14 kg CO2 equivalents/ha/year through minimal growth of mulga stands. In contrast, the suppression of fire and the introduction of grazing results in thickening of mulga stands and the system can act as a significant net sink absorbing an average of 1000 kg CO2 equivalents/ha/year. Although dense mulga will render the land largely useless for grazing, land in this region is relatively inexpensive and could possibly be developed as a cost-effective carbon offset for greenhouse gas emissions elsewhere. These results also provide support for the hypothesis that changes in land management, and particularly, suppression of fire is chiefly responsible for the observed increases in mulga density over the past century.
Abstract: We investigated the incidence of endozoochory in the semi-arid South African Karoo shrubland and Kalahari savanna by dissecting and germinating seed from dung samples from a wide range of wild mammals and domestic livestock. Intact seeds occurred at a mean density of 1575 seeds kg-1in livestock air-dried dung and 3613 seeds kg-1in air-dried dung of indigenous animals. Seedlings emerged from dung at an average density of 153 kg-1air-dry dung. Seeds of Aizoaceae, Mesembryanthemaceae, Chenopodiaceae and Poaceae were abundant in the dung of wild and domestic herbivores as well as such ant- and termite-eating insectivores as aardvark (Orycteropus afer) and bat-eared fox (Otocyon megalotis). Seeds of fleshy-fruited shrubs occurred in dung of browsing herbivores and the bat-eared fox. Five non-indigenous weeds were found in the dung samples. Although the floras of the Kalahari and Karoo are considered to be largely wind and water-dispersed, endozoochory is a primary or secondary dispersal mechanism in many plant families and for many plant life-forms. Animals dispersed seeds of many species characteristic of fertile and disturbed habitats. In Mesembryanthemaceae, a family in which seeds are primarily dispersed very short distances by raindrops, endozoochory enables occasional long-distance dispersal.
Abstract: Although acacias are ecologically and economically important, their demography is poorly known. In part this is because few field experiments have been undertaken. Also, a bewildering diversity of factors have been suggested to determine their demography. These factors include disease, fire, large and small browsers and grazers, climatic variation, competition with grass, seed predation and anthropogenic impacts. This synthesis concentrates on the life-history period from seed to adult plant and indicates that important hurdles have been demonstrated for some species in some habitats. Seed and seedling limitation have not been clearly demonstrated, nor has the value of dispersal been quantified. In contrast, the impacts of herbivores and fire in affecting the escape or release of resprouts has been repeatedly demonstrated. Whether fire and herbivory merely slow down the rate of promotion through size-classes or actually prevent it, needs further work. We note that very little comparative work amongst Acacia species has taken place. Most studies have concentrated on single aspects of their life history (especially seed predation), and have not been analysed in relation to population growth. Few field experiments, especially concerning seedling biology, have been performed. We conclude with some suggestions of a framework for interpreting acacia demography.
Abstract: Continuous measurements of the surface energy balance components (net radiation Rn, sensible heat flux H, latent heat flux LE, ground heat flux G, and CO2 fluxes began in early June of 1995 at the Little Washita Watershed, near Chickasha, Oklahoma. A severe drought during 1998 provided a unique opportunity to evaluate the range of fluxes that can be expected during the summer period. Data obtained during four continuous summer periods were used to evaluate the year-to-year variability in summertime energy and CO2 fluxes. During the summer period (day 150-240), total evapotranspiration for non-drought years ranged from 224 to 273 mm with a mean and standard error of 253±12 mm. The mean and standard error of the net ecosystem exchange (NEE) rate of carbon dioxide for the same summer period was -120±36 gC/m2. In a year with severe drought (1998) total evapotranspiration for the summertime period was 145 mm. The lack of precipitation during this time resulted in total losses to the atmosphere of 155 g C/m2 from soil respiration.
Abstract: Summary * 1Seasonal rivers in semi-arid African savannas support riparian woodland and hydromorphic grassland, key habitats for wildlife or livestock. We investigated the effect of numerous, small, agricultural dams built on low-order streams within the Kolope–Setonki subcatchment of the Limpopo river. We examined how reducing or changing the pattern of water flow in the main rivers will affect the riparian or hydromorphic vegetation. * 2Existing hydrological models demonstrate a mean annual water flow of 7·6 × 106 m3, ranging from zero to 215 × 106 m3. The catchment area affected by agricultural dams increased from 2% to 50% between 1955 and 1987. Dams are believed to have curtailed the flow during years of low flow. * 3The water requirement of four key species was assessed from their elevation above and distance from the river such that Faidherbia albida > Schotia brachypetala ~ Xanthocercis zambesiaca > Combretum imberbe. This order did not accord with the relative degree of mortality and canopy dieback. Twenty-nine per cent of F. albida trees were dead and the remainder had lost an average of 31% of canopy volume; S. brachypetala and X. zambesiaca exhibited negligible dieback and no mortality; whereas 10% of C. imberbe were dead and the remainder had lost an average of 8% of canopy volume. * 4Tree size and water availability influenced mortality and canopy dieback of F. albida and C. imberbe. Mortality of F. albida affected trees of all except the smallest size, although dead trees were on average larger than living trees. Dead trees of C. imberbe were at a greater elevation above or distance from the river. The likelihood of F. albida experiencing dieback was greater at higher elevations above the river and for larger trees, whereas that of C. imberbe was greater at greater distances from and higher elevations above the river if a tree was large. * 5Woody cover on hydromorphic grasslands, mainly of Acacia tortilis, increased from 8% to 37% between 1955 and 1987. Most of the increase occurred between 1965 and 1977, coincident with the extended 1960s drought and the above-average rainfall of the 1970s in a system that had been exposed to sustained, severe grazing by livestock. * 6The cumulative impact of many small farm dams on downstream rivers is apparently to reduce flow during critical dry years to levels causing dieback of F. albida and C. imberbe and desiccation of hydromorphic grassland. The water requirements of this vegetation need to be determined for policy makers to address the conflicting water needs of agriculture and indigenous vegetation.
Abstract: Drought is the single most important environmental factor that causes cattle population fluctuations in northern Kenya. The way the grazing lands and animal populations are affected by drought requires long-term monitoring. However, in northern Kenya, patterns of cattle mortality following multiple drought episodes and recovery have not been compared before. This study compared effects of two droughts (1983/1984 and 1991/1992) and three recovery periods (1984, 1992 and 1996) on cattle population in Obbu, northern Kenya. Cattle mortality in terms of age-sex classes; calves, immature animals, breeding females and mature males were compared to understand drought impacts, while relative growth rates of herds and percentage of recovery to pre-drought cattle population levels were determined to understand recovery. The droughts altered herd structure and resulted in greater mortality among calves and breeding females (especially during 1983/1984) than immature animals and mature male cattle. Drought stress in terms of cattle mortality varied from area to another but at the regional level it was less during the 1983/1984 drought (69·8±2·0%) than 1991/1992 (86·8±1·9%). The pre-1983/1984 drought herd size for the Obbu region explained 12·4% of the variation of the post-drought cattle population, while the pre-1991/1992 drought population explained <1% of the variation. Although cattle mortality was weakly linked to the pre-drought population, it was influenced by factors such as disease epidemics and poor nutritional quality in forage. Relative growth rates of herds in Obbu averaged 3·5% year-1after the 1983/1984 drought leading to full recovery in 7 years, while, after the 1991/1992 drought, mean relative growth rate was 2·8% year-1, which after 5 years only achieved ca.32/ recovery of the pre-1991/1992 drought cattle population.
Abstract: Over 120,000 non-native species of plants, animals and microbes have invaded the United States, United Kingdom, Australia, South Africa, India, and Brazil, and many have caused major economic losses in agriculture and forestry as well as negatively impacting ecological integrity. Some introduced species, like corn (Zea mays L.), wheat (Triticum spp.), rice (Oryza sativa L.), plantation forests, domestic chicken (Gallus spp.), cattle (Bos taurus), and others, are beneficial and provide more than 98% of the world's food supply. Precise economic costs associated with some of the most ecologically damaging alien species are not available. Cats (Felis cattus) and pigs (Sus scrofa), for example, are responsible for the extinction of various animal species, however, it is impossible to assign monetary values to species forced to extinction. The estimate is that non-native species invasions in the six nations are causing more than US$ 314 billion per year in damages.
Abstract: Due to the great diversity and complex interactions of vegetation, soils, and climate on rangelands, process-based models designed to evaluate rangeland hydrology must include sophisticated plant and animal components that simulate changes in vegetation over space and through time. An infiltration-based submodel similar to that used in WEPP (Stone et al. (1995) USDA-Agri. Res. Service, NSERL Report No. 10, Chap. 4) was dynamically linked to the SPUR2.4 rangeland ecosystem model (Foy et al., Ecol. Model. 118 (1999) 149) to provide the framework for future model enhancement and investigation of the impacts of management on the rangeland ecosystem. Model description and documentation of model modifications are presented for SPUR 2000. A sensitivity analysis and initial test of SPUR 2000 were performed using rainfall simulation plot and micro-watershed data from Idaho sagebrush rangeland. The sensitivity analysis showed improved sensitivity of runoff and erosion to various vegetation parameters. The long-term simulations demonstrated good representation of soil water content, peak standing crop, and evapotranspiration. SPUR 2000 did a better job of predicting individual thunderstorm runoff events, and estimated 15-year runoff within 12% compared to SPUR2.4, which grossly overestimated runoff. Neither model accurately predicted sediment loss, but predicted values did demonstrate the relatively small amount of erosion that occurs from these rangelands. Neither model could reasonably estimate the snow-driven runoff that dominates these types of western rangelands. Additional research needs to explore the degree of influence that vegetation has on infiltration and runoff and how it varies for different plant communities. Development of specific Ke estimation equations based on this information will strengthen the vegetation-hydrology linkage within the model.
Abstract: Summary * 1The influence of botanical composition on annual phytomass production of a semi-arid grassland in response to precipitation was tested with a 19-year experiment. Three compositional states reflecting good, medium and poor rangeland condition, whose basal cover increased from poor through to good, were created in 1978. * 2Multiple regression models were developed for assessing whether phytomass was influenced by precipitation, composition, phytomass of the previous year, basal cover, abundance of individual species, or diversity. Composition and precipitation accounted for 66% of the variation in phytomass, but a separate model of basal cover by precipitation was equally successful. The linear effect of rainfall on phytomass was enhanced as composition improved from poor (0.076 g m−2 mm−1) through medium (0.197 g m−2 mm−1) to good (0.277 g m−2 mm−1). Phytomass increased for low precipitation if it had been high the preceding year. Phytomass was more variable over time with deteriorating condition. * 3Species’ complementarity ensured greater and more stable production. Setaria sphacelata, Eragrostis chloromelas and Digitaria eriantha increased phytomass on the good or medium condition grasslands during drier years, whereas Themeda triandra had this effect during wetter years. * 4Precipitation-use efficiency (PUE) was influenced mostly by composition and a linear and quadratic effect of precipitation (63% of variance). Optimum PUE of 0.308, 0.203 and 0.096 g m−2 mm−1 for the good, medium and poor condition grasslands, respectively, occurred at intermediate amounts (±680 mm) of precipitation. PUE was increased if phytomass had been high the previous year. * 5Species’ complementarity of PUE in response to precipitation was evident for all compositional states. Ten, mostly uncommon, species and their interaction with precipitation explained an extra 21–42% of the variance. Stability of production was related to PUE for medium and poor condition grassland. Uncommon species therefore ensured growth efficiency and stabilized production as condition deteriorated. * 6Diversity had no influence on phytomass or PUE except for a small to moderate effect, respectively, for the medium condition grassland. * 7Vegetation structure, through limiting runoff and promoting infiltration, is an important control on the amount and efficiency of plant production under variable precipitation, whilst composition further influences the amount and stability of production.
Abstract: Molecular statigraphic records of core SU94-11K (21°N, 18°W, 1200 m water depth) were reconstructed for organic carbon (OC), carbonates, alkenones, n-alkanols and sterols over the last 70 ky to study past changes of production and paleoceanographic conditions in the coastal upwelling of Northwest Africa. UK'37-derived sea surface temperatures (SST) show a 2.5 °C warming during the last deglaciation. Surprisingly, they also indicate that during the last glacial period, between 24 and 15 kyear, SST rose by 1 °C. It can be seen from the values of marine and terrigenous biomarker mass accumulation rates (MAR) that this time interval was also the period of lowest marine production and dust supply suggesting a major change in the North East Trade Winds system. This situation would have lasted until the onset of the deglaciation from which upwelling progressively intensified to produce highest marine biomarker MAR at the Holocene. Our data also show a reduced terrigenous supply in late Holocene sediments that may reflect lower emission rates from the vegetation and/or changes in the wind conditions.
Abstract: Atmospheric CO2 concentrations have increased because of changes in land use and burning of fossil fuels. Grasslands are important terrestrial ecosystems that, along with other temperate and arid rangeland resources, comprise more than 50% of the world's land area. Even though grasslands dominate the world's landscape, their role in the global C budget has not been adequately documented. The objective of this study was to determine the relationship of vegetation structure and dynamics to CO2 fluxes for a grass and a sagebrush-dominated Southern Plains mixed-grass prairie (latitude 36°36'N, longitude 99°35'W, elevation 630 m) and evaluate their potential for carbon sequestration. The CO2 flux calculated at 20-min intervals was measured from mid-February to early May through mid to late December in 1995-1997 on both sites using Bowen ratio/energy balance instrumentation. Plant measurements included aboveground and belowground biomass, leaf area, and canopy height. Estimated annual net CO2 fluxes into these systems were 257 and 23 g m-2 yr-1, respectively, for the grass and sagebrush-dominated sites. Average daily flux during the sampling period and estimated annual rate of daily CO2 flux for the grass-dominated prairie site were greater (1.54 and 0.70 g m-2 per day) than the sagebrush site (0.01 and 0.06 g m-2 per day). Water-use was similar for these two mixed-grass prairie sites. This study indicates that these Southern Plains mixed-grass prairie communities have the potential to sequester C.
Abstract: A diverse assemblage of terrestrial plant palynomorphs is reported from Koingnaas, a site in the Namaqualand region of the Northern Cape Province, South Africa. In excess of one hundred palynomorph types are recognised from three peaty clay horizons contained within a fluviatile sediment suite filling a palæochannel of Tertiary age. No stratigraphically significant differences occur between the three horizons. Angiosperm pollen dominates the assemblage, with a lesser contribution of gymnosperm pollen, and spores make up a significant although small component. The presence of podocarp pollen, angiosperm pollen with modern arboreal counterparts and fossilised wood suggests that the palæoflora consisted of a forested temperate to subtropical environment. The Koingnaas assemblage contains little evidence of the modern regional flora, but links with the Cape Floristic Region are indicated by pollen related to the Proteaceae and possibly the [`]palæoendemic' Bruniaceae. Previously, the palæochannel sediments were thought to be Pliocene, but an early Tertiary age is preferred for the Koingnaas site, supported by similarities with the Palæocene Arnot Pipe assemblage and the position of the palæochannel relative to early Tertiary palæodrainage patterns.
Abstract: Several studies in arid ecosystems have demonstrated that seedling establishment and survival were greater underneath the canopies of shrubs than in the open spaces between shrubs. These results led to the formulation of the hypothesis that seedling recruitment and survival were dependent on the shelter provided by shrub species (nurse-plant hypothesis). Seedling emergence and survival beneath and between the canopies of selected perennial shrub species were investigated at five localities in the Strandveld Succulent Karoo, each dominated by a different shrub species. Seedling emergence and survival were also examined at three localities dominated by annual species. In general, species richness and seedling densities were significantly higher in open areas than underneath shrubs, while seedling survival percentages did not differ significantly between microsites. Therefore, no evidence could be found to support the hypothesis that seedling recruitment and survival were facilitated by the presence of shrub species. Although most species will be able to establish in the absence of shrubs, the presence of woody species may have other advantages when restoring vegetation in mined areas.
Abstract: Arid rangelands host a variety of drought-tolerant wildlife species, many of them requiring conservation efforts for the survival of their populations. The development of drinking water sources for people and livestock forms one of the main development interventions in these rangelands. However, the impact of availability of permanent drinking water on wildlife remains unknown. In this study we analyzed the distribution of wildlife and livestock in northern Kenya in relation to distance to permanent water. Livestock were concentrated in areas close to permanent water, while wildlife were frequently farther away from water; their distributions were inversely correlated. In addition, wildlife assemblages were more diverse farther from water. These results suggest that livestock and human activities related to water points negatively affect the distribution of wildlife.
Abstract: Fires can mediate switches between alternative vegetation types which may be more flammable and thus reinforce fire spread. We tested if there is a positive feedback between the expansion of the tussock grass Ampelodesmos mauritanica (hereafter Ampelodesmos) and fire hazard in Mediterranean Basin communities and its relation to tree cover decline. The effect of fire on Ampelodesmos population structure was analysed by surveying stands burned at different fire frequencies. The effect of vegetation dominated by Ampelodesmos on fire behaviour compared to other species coexisting in the community was predicted by the Rothermel fire propagation model BEHAVE. There was a negative correlation between pine cover and percentage of Ampelodesmos plants. Ampelodesmos mortality after fire is very low. Recently burned stands had a higher proportion of reproductive plants and higher seedling density than unburned stands. The high temperatures reached during fire may kill seeds, the higher seedling recruitment results from fast resprouting and higher seed production of burned plants compared to unburned plants 1 year after fire. Simulations with the BEHAVE fire model predict that Ampelodesmos increases fire intensity and spread because of its high accumulation of fuel load and standing dead material. The results suggest that there is a positive relationship between Ampelodesmos abundance and fire regime which increases the invasive potential of this grass and the fire risk of the community where it dominates.
Abstract: The dynamics of savannah vegetation are still poorly understood. This study aims at analysing land cover changes over the past 20 years in the rangelands area of Narok District, Kenya. To analyse the impact of inter-annual climate variability and human activities on land cover modifications in the area, change detection techniques based on remote sensing data at different spatial and temporal resolutions were used. Coarse spatial, high temporal resolution NOAA (National Oceanic and Atmospheric Administration) data were analysed to investigate the role of inter-annual climate variations on the ecosystem. A combination of time contextual and spatial contextual change detection approaches was used on a set of three high spatial resolution Landsat images to map land cover modifications over the past 20 years. Both datasets are highly complementary in the detection of land cover dynamics. On the one hand, the coarse spatial resolution data detected areas that are sensitive to inter-annual climate fluctuations, but are not subjected to land cover conversion. On the other hand, the high spatial resolution data allowed the detection of land cover conversions or modifications between two consecutive dates that have a more permanent character and are independent of climate-induced fluctuations in surface attributes.
Abstract: The development of cropping systems simulation capabilities world-wide combined with easy access to powerful computing has resulted in a plethora of agricultural models and consequently, model applications. Nonetheless, the scientific credibility of such applications and their relevance to farming practice is still being questioned. Our objective in this paper is to highlight some of the model applications from which benefits for farmers were or could be obtained via changed agricultural practice or policy. Changed on-farm practice due to the direct contribution of modelling, while keenly sought after, may in some cases be less achievable than a contribution via agricultural policies. This paper is intended to give some guidance for future model applications. It is not a comprehensive review of model applications, nor is it intended to discuss modelling in the context of social science or extension policy. Rather, we take snapshots around the globe to [‘]take stock 039; and to demonstrate that well-defined financial and environmental benefits can be obtained on-farm from the use of models. We highlight the importance of [‘]relevance 039; and hence the importance of true partnerships between all stakeholders (farmer, scientists, advisers) for the successful development and adoption of simulation approaches. Specifically, we address some key points that are essential for successful model applications such as: (1) issues to be addressed must be neither trivial nor obvious; (2) a modelling approach must reduce complexity rather than proliferate choices in order to aid the decision-making process; (3) the cropping systems must be sufficiently flexible to allow management interventions based on insights gained from models. The pro and cons of normative approaches (e.g. decision support software that can reach a wide audience quickly but are often poorly contextualized for any individual client) versus model applications within the context of an individual client 039;s situation will also be discussed. We suggest that a tandem approach is necessary whereby the latter is used in the early stages of model application for confidence building amongst client groups. This paper focuses on five specific regions that differ fundamentally in terms of environment and socio-economic structure and hence in their requirements for successful model applications. Specifically, we will give examples from Australia and South America (high climatic variability, large areas, low input, technologically advanced); Africa (high climatic variability, small areas, low input, subsistence agriculture); India (high climatic variability, small areas, medium level inputs, technologically progressing; and Europe (relatively low climatic variability, small areas, high input, technologically advanced). The contrast between Australia and Europe will further demonstrate how successful model applications are strongly influenced by the policy framework within which producers operate. We suggest that this might eventually lead to better adoption of fully integrated systems approaches and result in the development of resilient farming systems that are in tune with current climatic conditions and are adaptable to biophysical and socio-economic variability and change.
Abstract: Although soil erosion is a serious environmental problem in many African countries, its assessment using traditional techniques is hampered by a range of problems. Reliable information on soil erosion rates is, nevertheless, an essential prerequisite for the design of targeted erosion and sediment control strategies. This contribution reports the use of 137Cs measurements to quantify medium-term ( 40 years) soil erosion and redistribution rates in both cultivated and uncultivated areas within the Upper Kaleya River basin in southern Zambia. Typical net soil erosion rates are estimated to be 4.3 t ha-1 year-1 for areas under commercial cultivation, 2.9 t ha-1 year-1 for bush grazing areas and 2.5 t ha-1 year-1 for areas under communal cultivation. Although these erosion rates reflect land use in these broad areas over the past 40 years, rather than present land use, they are nevertheless thought to also be representative of current conditions. The findings indicate that any attempt to develop effective erosion and sediment control strategies in the study area should involve all land use types and should aim to reduce both on-site erosion and sediment delivery from the slopes to the stream channel.
Abstract: This study examined the reproductive performance of dihydroxy pyridone (DHP)-inoculated South African indigenous (SAIG) female goats maintained on two dietary treatments: (i) Leucaena leucocephala/grass mixture and (ii) natural pasture prior to conception, and during gestation. Leucaena leucocephala/grass mixture was nutritionally superior (crude protein and mineral elements) than the natural pasture. The average daily gain, products of pregnancy and foetal development in gravid goats raised on leucaena/grass mixture were significantly (P 60;0.03, P 60;0.009 and P 60;0.005, respectively) higher than those raised on natural pasture. Conception rate of goats fed natural pasture was higher than the band fed Leucaena leucocephala/grass mixture. Leucaena/grass mixture fed goats had kids that were heavier at birth than their counterparts on natural pasture. Pre-weaning kid mortality over the period of study was significantly (P 60;0.01) higher in the Leucaena leucocephala/grass mixture treatment. Colostrum from kidded goats fed leucaena was viscous and difficult to sample. The absence of mimosine toxicity symptoms suggests a possibility of safe use of leucaena as a feed resource to DHP-inoculated SAIG.
Abstract: Summary * 1The effects of agricultural intensification on biodiversity in arable systems of western Europe have received a great deal of attention. However, the recent transformation of grassland systems has been just as profound. * 2In Britain, the management of grassland has changed substantially in the second half of the 20th century. A high proportion of lowland grassland is managed intensively. The major changes include a doubling in the use of inorganic nitrogen, a switch from hay to silage, and increased stocking densities, particularly of sheep. Structurally diverse and species-rich swards have been largely replaced by relatively dense, fast-growing and structurally uniform swards, dominated by competitive species. * 3Most of these changes have reduced the suitability of grassland as feeding and breeding habitat for birds. * 4The most important direct effects have been deterioration of the sward as nesting and wintering habitat, and loss of seed resources as food. Short uniform swards afford poor shelter and camouflage from predators, whereas increased mowing intensities and trampling by stock will destroy nests and young. Increased frequency of sward defoliation reduces flowering and seed set, and hence food availability for seed-eating birds. * 5The indirect effects of intensification of management on birds relate largely to changes in the abundance and availability of invertebrate prey. The effects of management vary with its type, timing and intensity, and with invertebrate ecology and phenology, but, in general, the abundance and diversity of invertebrates declines with reductions in sward diversity and structural complexity. * 6Low input livestock systems are likely to be central to any future management strategies designed to maintain and restore the ecological diversity of semi-natural lowland grasslands. Low additions of organic fertilizer benefit some invertebrate prey species, and moderate levels of grazing encourage sward heterogeneity. * 7There is now a need to improve understanding of how grassland management affects bird population dynamics. Particularly important areas of research include: (i) the interaction between changes in food abundance, due to changes in fertilizer inputs, and food accessibility, due to changes in sward structure; (ii) the interaction between predation rates and management-related changes in habitat; and (iii) the impact of alternative anti-helminithic treatments for livestock on invertebrates and birds.
Abstract: The community structure and abundance of plant-feeding nematodes were studied in four grasslands, which had not been fertilised for 6, 10, 23, and 28 years, respectively. We hypothesised that nutritional impoverishment of the grasslands would result in a decrease in the nematode density and biomass, and a shift in the nematode community structure towards species that are better adapted to nutrient-poor conditions. Furthermore, we expected that plant-specific nematode communities are present in the rhizosphere of different dominant plant species. Multivariate analyses showed gradual changes in the nematode fauna after the cessation of fertiliser application. Particularly, during the first 10 years of succession the density and species number of large endo- and ectoparasites strongly decreased resulting in a lower diversity of nematode genera. Root biomass, plant species, and season had a minor effect on the nematode numbers and community composition. However, within the rhizosphere of single plant species clear community changes were observed with time of non-fertilisation, indicating that qualitative changes within a plant species rather than qualitative differences between plant species affected the nematode community. Most likely, lower nutritional quality of the nematode food source, due to decreased nutrient concentrations and increased levels of defensive compounds in plant tissues under nutrient-poor conditions, was the major factor affecting the plant-feeding nematode community. Average nematode body size, which is constrained by the absolute amount of food necessary for growth and maintenance, decreased at lower nutrient availability. However, the results suggest that evolutionary adaptation of feeding strategies that reduces the energetic costs of feeding and movement, such as endoparasitism, a longer stylet, and the modification of feeding cells, enabled certain nematode species to support a relatively large body size under conditions of low nutrient availability.
Abstract: The term [`]global change' is used to encompass all of the significant drivers of environmental change as experienced by hosts, parasites and parasite managers. The term includes changes in climate and climate variability, atmospheric composition, land use and land cover including deforestation and urbanisation, bio-geochemistry, globalisation of trade and transport, the spread of alien species, human health and technology. A subset of land use issues relates to the management of protective technologies in relation to residues in food and the environment and the emergence of resistance. Another is the question of changing biodiversity of both parasites and their associated natural enemies, and the effects on the host-parasite relationship and on parasite management. A framework for studying impacts of global change is proposed and illustrated with field data, and CLIMEX and simulation modelling of the cattle tick Boophilus microplus in Australia. Parasitology suffers from the perception that the key impacts of global change will be driven by changes at lower trophic levels, with parasitic interactions being treated as secondary effects. This is incorrect because the environment mediates host-parasite interactions as much as it affects parasites directly. Parasitologists need to strive for holistic solutions to the management of animal and human health, within a wider context of overall management of those systems, if they are to make a meaningful contribution to global efforts aimed at coping with global change.
Abstract: Low winter temperature in Mediterranean rangelands delays the growth of most pasture and forage plants and, in particular, annual Medicago (medics). Finding proper associations of medic-Rhizobium, capable to grow and fix nitrogen at low temperature, is necessary to extend the grazing period. In this paper, we studied the performance of three Medicago cultivars: M. aculeata accessions 80 (A) and 5099 (B) and M. rigidula accession 716 (R), grown in the field with three different nitrogen sources. The first treatment (N) was obtained through fertilization, while the second (I) was ensured by inoculation with different strains of Rhizobium meliloti (M620, M508 and BZI). A third treatment (C) was used as a control, neither inoculated nor fertilized. The trial was repeated for 2 consecutive years (1998 and 1999) at ICARDA research station (Aleppo, Syria). Plant development, dry matter production and nodule initiation were investigated. The percentage of fixation-derived shoot nitrogen was also quantified using 15N dilution technique. Our results indicate a genotypic variation in low-temperature tolerance of annual medics. Accession A had a slow growth pattern with low dry matter production compared with B and R over the two seasons. In the two seasons and at the early growth stages, Rhizobium strain played a key role in plant growth, where both inoculated and fertilized plants of accession R had a comparable dry matter. Furthermore, the proportion of nitrogen derived from fixation in A was very low, which was reflected, in turn, on the total amount of fixed nitrogen. The proportion of fixed nitrogen of the association R-BZI was high for the 2 years, where it reached 72 and 87% of the total N in the plant, respectively. It is suggested that associations differed in their response to low winter temperature. Among those we studied, M. rigidula accession 716, inoculated with the strain BZI, proved to be the most adapted association to our environment. In addition, M. aculeata accession 5099 seems to be promising for winter growth, but it needs to be inoculated with a strain more adapted to low temperature.
Abstract: This paper presents a simulation model to project land-cover changes at a national scale for Sudano-sahelian countries. The aim of this study is to better understand the driving forces of land-use change and to reconstruct past changes. The structure of our model is heavily determined by its spatially aggregated level. This model represents, in a dynamic way, a simplified version of our current understanding of the processes of land-use change in the Sudano-sahelian region of Africa. For any given year, the land demand is calculated under the assumption that there should be an equilibrium between the production and consumption of basic resources derived from different land-uses. The exogenous variables of the model are human population (rural and urban), livestock, rainfall and cereals imports. The output are the areas allocated to fuelwood extraction, crops, fallow and pasture for every year. Pressure indicators are also generated endogenously by the model (rate of overgrazing and land degradation, labour productivity, average household "budget"). The parameters of the model were derived on the basis of a comprehensive review of the literature, mostly of local scale case studies of land-use changes in the Sahel. In agreement with farming system research, the model simulates two processes of land-use change: agricultural expansion at the most extensive technological level, followed by agricultural intensification once some land threshold is reached. The model was first tested at a national scale using data from Burkina Faso. Results simulate land-use changes at two time frequencies: high frequency, as driven by climatic variability, and low frequency, as driven by demographic trends. The rates of cropland expansion predicted by the model are consistent with rates measured for several case studies, based on fine spatial resolution remote sensing data.
Abstract: It is often assumed that displacement of native perennial vegetation by exotic annuals will alter nutrient cycling. Nitrogen dynamics of native bunchgrass vegetation and adjacent stands of the exotic annual grass Bromus tectorum were compared on three sites in south-eastern Washington, U.S.A. The stands of B. tectorum had dominated the sites for at least 40 years. It should be emphasized that these sites were not prone to frequent wildfires as can be the case in some B. tectorum -dominated ecosystems. Over a 2-year period very few consistent differences were found between the two vegetation types in above-ground standing crop, root mass, in situ N mineralization, extractable soil N, or total soil C or N. Bromus tectorum above-ground plant mass and litter tended to have lower C/N ratios than did the native vegetation, but the results were not consistent over time or site. It appears that the exotic annual adapted to the resources on the site and, at least at the fairly gross level measured, had little impact on soil nitrogen. These results suggest that caution must be taken when assuming that a change in vegetation type and growth form will necessarily alter soil N levels.
Abstract: The livelihoods and life chances of pastoral communities in the West African Sahel are linked to: the complexity of the activities they must engage in to insure access to resources; to the nature of conflicts and co-operation between ethnic groups; to the inconsistent role of the state in assisting or constraining pastoral livelihoods; and to the negative discourse surrounding pastoralism that still circulates in some government and development policy circles. The paper reviews pastoral livelihoods systems in eastern Niger to illustrate changing modes of access to water and pasture, culminating in present-day tensions and conflict between pastoral groups. State development efforts to provide secure watering points for pastoral herds have initiated social conflicts and violence, rather than creating security. No viable solution has yet been found to control the use of public wells and boreholes. Enabling frameworks for negotiation and conflict resolution must be developed locally, and centrally enforced in this, and many other regions of uncertain climatic change and overlapping systems of resource exploitation.
Abstract: The South African Country Study on Climate Change was hosted by the South African National Research Foundation in Pretoria, Gauteng, South Africa, on 22 August 2000.
Abstract: Very little is known about the chemical composition of Carpobrotus edulis, also known as Hotnotsfig or sourfig. However, some claims have been made in the past by traditional healers, regarding its usage as a medicinal plant. In this investigation it was initially illustrated that a crude methanolic extract of the plant exhibits strong anti-bacterial activity. Subsequently, the crude extract was fractionated by means of liquid-liquid chromatography, tannins removed by means of LH20 column chromatography and bioactive fractions with antibacterial properties isolated by means of preparative thin layer chromatography. Five bioactive compounds, individually or collectively responsible for the antibacterial property of C. edulis, were purified from an active ethyl acetate fraction. These compounds were initially identified as flavanoids using standard fingerprinting methods and eventually identified as rutin, neohesperidin, hyperoside, cactichin and ferulic acid using flavanoid standards. A sixth flavanoid with antibacterial activity was also purified but could not be identified in this way. The latter is currently isolated in larger volume for identification through nuclear magnetic resonance spectroscopy.
Abstract: Global debates surrounding the management of natural resources in protected areas advocate greater involvement of local populations in order to maintain sustainable resource use and conserve biological diversity. For this involvement to be effective, and for development to be truly participatory, a deeper understanding of people's relationships with the environment is needed. This paper explores the society-environment interactions of people in a newly established Wildlife Management Area in western Botswana, illustrating the complexity and diversity of resource use and livelihoods that must be addressed by development interventions.
Abstract: The paper begins by examining the importance of southern African Quaternary environmental change. The Quaternary is characterised by repeated climatic changes of considerable amplitude; analysis of these fluctuations reveals the ubiquity of change and the fundamental dynamism of earth systems. Change is normal and, despite the fact that southern Africa was not subject to Quaternary glaciation per se, the influence of variations in, say, amount and seasonality of rainfall, has been very marked indeed. The Quaternary also represents the time period during which people have become a dominant environmental agent in the subcontinent; southern Africa has played a crucial role in the evolution of hominids and their development has been influenced strongly by accompanying environmental change. The relationship between geomorphology and climate in southern Africa is explored, revealing the degree and extent to which its landscapes are determined by changing environmental conditions, especially during the Tertiary and Quaternary; how apparent is the legacy of the past? This leads to a consideration of the types of geomorphological evidence, some more reliable than others, that can be utilised in order to reveal the details of Quaternary environmental change. Arid and semiarid landscapes appear to preserve more evidence of former environmental conditions, although high contemporary erosion rates and the paucity of long terrestrial-sedimentary sequences hinder their complete elucidation. Two case studies of Quaternary change in the subcontinent are presented, from the southwestern Cape and Namibia. These examples document the increasing intensity of human impact on landscapes to the extent that people now play the dominant geomorphological role, especially in semiarid and coastal areas. The conclusion offers pointers as to how geomorphological evidence of Quaternary change can be used to assist in the better management of contemporary and future environmental conditions.
Abstract: An assessment of changes in soil properties associated with land-use and management practices is vital for the selection and establishment of appropriate sustainable practices under different agroecosystems. This study compared soil properties between land located on an abandoned kraal site (KS), under fallow (FL) and one that was continuously cropped to maize (CC) for over 12 years. Aggregation and aggregate stability as measured by both dry and wet sieving showed large differences between land-use systems. The soil under CC had a higher proportion (26.4%) of micro aggregates (<0.25Â mm) compared with that of FL (10.1%) and KS (6.9%). The dry mean weight diameter (DMWD) was larger in KS (3.03Â mm) than in FL (2.17Â mm) and CC (1.38Â mm). Soil aggregates in CC were the least stable with a wet mean weight diameter (WMWD) of (1.61Â mm) compared with those of FL (2.18Â mm) and KS (2.89Â mm). Reduced stability of aggregates in CC is likely due to the lower organic carbon content of soil in this land-use (1.7%) compared with that of FL (2.5%) and KS (3.2%). The soil under KS had lower bulk density (BD), penetration resistance (PR) and aggregate tensile strength (ATS) than that of FL and CC. Soil moisture content (MC) and available water capacity (AWC) showed an opposite trend. The soil in KS had a higher concentration of total N (TN), available P and exchangeable K, Ca, Mg and Zn. Soil on CC, on the other hand, had a higher concentration of Mn than that from FS and KS possibly because of its acidic nature. There were significant strong correlations between soil organic carbon and BD (-0.86***), PR (-0.61*), MC (0.82**), ATS (-0.62*), WSA (0.79***), AWC (0.91***), pH (-0.61**) and TN (0.76***). Grain yields of maize were highest in KS followed by FL and least in CC. The high yields were attributed to improved soil properties in plots of KS compared with both FL and CC. In conclusion, the findings suggested that organic matter had a major influence on soil properties and fertility.
Abstract: Multivariate analyses and complementarity-based reserve selection algorithms were used as tools for delimiting representative conservation areas in KwaZulu-Natal, South Africa, based on environmental variables and records for 566 breeding and non-breeding birds. The relationships between species assemblages and 20 environmental variables were investigated; including climate, topography, vegetation, landscape attributes, and land-use. Detrended correspondence analysis, canonical correspondence analysis, and hierarchical classification suggested that the major gradients of bird species variation are primarily related to climatic variables such as growing season temperature and seasonality of precipitation, reflecting the strong east-west gradient in oceanicity in KwaZulu-Natal, and water balance, reflecting a strong north-south gradient in aridity. Hierarchical classification was applied to the ordination data and revealed five representative types of bird communities. Four of the five bird communities and 37 species are under-represented in the existing reserve system, and the environmental processes required for long-term maintenance of birds have not been adequately sampled, showing that additional reserves are needed to ensure a more functional representative system. As an alternative, the inclusion of species spatial turnover structure together with associated environmental gradients were employed in both rarity and richness-based complementary reserve selection algorithms to provide a better representation of birds and environmental processes. Improvements on the current generation of reserve selection techniques derived by including ordination analysis and spatial structure are discussed.
Abstract: Measurements of daily actual evaporation, streamflow, rainfall and soil water storage were measured for a two-year period in a 97Â ha grassland catchment located in the Natal Drakensberg. Actual evaporation was measured using the Bowen ratio energy balance technique. Annual precipitation and discharge data were also used to estimate evaporation over a number of years. Results show that in normal years precipitation is equally split between evaporation and streamflow. In dry years evaporation is the dominant component of the water balance. The data were used to develop simple expressions to calculate annual streamflow and evaporation. Good agreements between actual and modelled trends of streamflow using the ACRU hydrological model were found (r=0.80). In general ACRU underestimated streamflow by 15%.
Abstract: With an increased emphasis on the tangible demonstration of the socio-economic benefits of research the need arises for impact evaluation. Impact assessment is a form of evaluation that deals with the effects of research output on the target beneficiaries. This paper reports on the use of indicators within a comprehensive impact assessment approach applied to three case studies of the Agricultural Research Council (ARC) of South Africa. Three broad categories of impact assessment form part of a comprehensive approach, which is the direct outcome of research activities, institutional impact and the people level impact. Indicators are essential for measuring impacts on various levels. The choice of indicators should depend on the objectives of the project, which is usually linked to the broader social and development objectives of a country, and the level of evaluation. Two major groups of indicators can be defined within the comprehensive approach of impact assessment namely: impact indicators and performance indicators. Some problems related to indicators such as the availability of data, the validity of indicators and correction factors are demonstrated. The paper shows that whilst it is important to evaluate or "measure", it is also important to use this impact information in management decisions for better allocation of scarce resources.
Abstract: In ago-pastoral systems of the semi-arid West African Sahel, targeted applications of ruminant manure to the cropland is a widespread practice to maintain soil productivity. However, studies exploring the decomposition and mineralisation processes of manure under farmers' conditions are scarce. The present research in south-west Niger was undertaken to examine the role of micro-organisms and meso-fauna on in situ release rates of nitrogen (N), phosphorus (P) and potassium (K) from cattle and sheep-goat manure collected from village corrals during the rainy season. The results show that (1) macro-organisms played a dominant role in the initial phase of manure decomposition; (2) manure decomposition was faster on crusted than on sandy soils; (3) throughout the study N and P release rates closely followed the dry matter decomposition; (4) during the first 6 weeks after application the K concentration in the manure declined much faster than N or P. At the applied dry matter rate of 18.8 Mg ha-1, the quantities of N, P and K released from the manure during the rainy season were up to 10-fold larger than the annual nutrient uptake of pearl millet (Pennisetum glaucum L.), the dominant crop in the traditional agro-pastoral systems. The results indicate considerable nutrient losses with the scarce but heavy rainfalls which could be alleviated by smaller rates of manure application. Those, however, would require a more labour intensive system of corralling or manure distribution.
Abstract: Crinums are large, showy plants with umbels of lily-like flowers. They are found in tropical and subtropical regions throughout the world, where, for centuries, they have been used traditionally to cure ailments and diseases. Sometimes they are prescribed for the same medicinal purpose. This would suggest that they contain a common ingredient. Phytochemical analysis has recently yielded a vast array of compounds, including more than 150 different alkaloids. These are of the Amaryllidaceae type, whose most noted effects are: analgesic, anticholinergic, antitumour and antiviral. Even though much has been reported on the medicinal properties of Crinum, only an estimated 20% of the species worldwide are represented in these analyses, as reviewed in this paper.
Abstract: Siwalik paleosol and Bengal Fan sediment samples were analyzed for the abundance and isotopic composition ofn-alkanes in order to test for molecular evidence of the expansion of C4 grasslands on the Indian subcontinent. The carbon isotopic compositions of high-molecular-weight alkanes in both the ancient soils and sediments record a shift from low [delta]13C values (ca. -30[per mille sign]) to higher values (ca. -22[per mille sign]) prior to 6 Ma. This shift is similar in magnitude to that recorded by paleosol carbonate and fossil teeth, and is consistent with a relatively rapid transition from dominantly C3 vegetation to an ecosystem dominated by C4 plants typical of semi-arid grasslands. The n-alkane values from our paleosol samples indicate that the isotopic change began as early as 9 Ma, reflecting either a growing contribution of C4 plants to a dominantly C3 biomass or a decrease in water availability to C3 plants. Molecular and isotopic analyses of other compounds, including n-alcohols and low-molecular weightn-alkanes indicate paleosol organic matter contains contributions from a mixture of sources, including vascular plants, algae and/or cyanobacteria and microorganisms. A range of inputs is likewise reflected in the isotopic composition of the total organic carbon from these samples. In addition, then-alkanes from two samples show little evidence for pedegenic inputs and we suggest the compounds were derived instead from the paleosol's parent materials. We suggest the record of vegetation in ancient terrestrial ecosystems is better reconstructed using isotopic signatures of molecular markers, rather than bulk organic carbon. This approach provides a means of expanding the spatial and temporal records of C4 plant biomass which will help to resolve possible tectonic, climatic or biological controls on the rise of this important component of the terrestrial biosphere.
Abstract: A cutting experiment was carried out in BahÃa Blanca (Argentina) during 1998 and 1999 using a randomized block design in a 23factorial experiment: (1) the species Digitaria eriantha and Eragrostis curvula, (2) 0 and 60 kg Nha-1fertilizer treatment and (3) deferred harvesting on 1 June and 15 July. The existing forage was cut in mid-February, the N was distributed and the deferred treatment was initiated. Dry matter yield (DM), dead (DF) and green (GF) fractions, crude protein (CP) content, nitrogen utilization efficiency (NUE), nitrogen recovery (NR) andin vitro DM digestibility (IVDMD) for each year were determined. A treatment by year interaction in DM yields (p<0·05) was found. The deferment date was not found to have any effect (p>0·05). The DM yields were substantially increased by fertilization (p<0·05). Mean DM for the control and the fertilized treatments were 942 and 2430 kg ha-1for D. eriantha and 846 and 1958 kg ha-1for E. curvula, respectively. Similarly, CP for D. eriantha was 5·2 and 6·0%, and 4·2 and 5·2% for E. curvula, respectively. The IVDMD had a small response to the fertilization (p<0·05): the average for D. eriantha was 51% and for E. curvula 39%. The quality of the forage was not influenced by the percentage relationship between DF and GF (p>0·05). The NUE (kg DM kg N-1) and the NR (%) were 24·8 and 25·4 for D. eriantha and 18·6 and 17·6 for E. curvula, respectively. Fertilization must be implemented depending on the costs and the expected increase in income due to the increase in forage production. Marked leaf lodging of D. eriantha may restrict the grazing ability of the animals.
Abstract: Several of the problems associated with grazing animals in extensive settings are related to their uneven patterns of use across the landscape. After fencing, water and salt are two of the most frequently used tools for affecting cattle distribution in extensive settings. Cattle are attracted to water in arid regions, but mixed results have been obtained with salt and mineral supplements. The goal of this study was to evaluate the efficacies of salt and water manipulations for affecting cattle distribution in large (>825Â ha) pastures. This was accomplished by fitting cattle with global positioning system (GPS) collars and monitoring their travels and activities in a three pasture, Latin-square design where water and salt shared a common location and water or salt were moved individually to distant areas. Mean distance of cattle from water (Â km) was unaffected by treatments (P=0.79) suggesting that cattle followed movements of water tanks. Distance traveled daily (Â km), time devoted to grazing (11.0Â h per day), time devoted to resting (10.1Â h per day), and the area (Â ha) of minimum convex polygons were also unaffected by treatment implying that cattle did not compensate for separated water and salting areas with increased travels or disruptions of habitual grazing and resting activities. Centers of activity for cattle shifted further (P=0.02) when water (Â km) was moved than when salt (Â km) was relocated. Mean distance of cattle from salt increased from 1.03Â km, when salt and water were together, to 1.73Â km (P=0.08) when salt and water were separated. This implied that cattle made less effort to remain near salt. Also, when water and salt were separated, cattle were found within 250Â m of water 354 times and close to salt only 38 times. Movement of drinking water to distant points in pastures was the most effective tool for altering cattle distribution. When cattle and salt were introduced to a new portion of a pasture, cattle used the new area for about 2 days, and then began drifting back toward previously used portions of the pasture. Manipulations of salting stations will not significantly rectify serious livestock distribution problems in extensive arid-land pastures.
Abstract: Agricultural systems in South Africa have been developed under primarily arid and semi-arid climatic conditions where droughts are common. Adoption of agricultural practices by farmers maximizes precipitation utilization, ensure production, economic and social sustainability. Precipitation use efficiency (PUE, kg produce ha-1 mm-1 rainfall plus the change in soil water content of the root zone) proved to be a valuable parameter for comparing the level of precipitation utilization of different production or management practices for dryland crop production or rangeland utilization. Increasing the length of the fallow period before planting increased the amount of pre-plant stored water in the soil thereby reducing the risk of drought damage to crops that resulted also in better yields. Deep drainage occurred only on sandy soils during wet seasons and values as high as 20% of the annual precipitation were measured during years of above average precipitation. In the experiments reported soil cultivation generally increased runoff. The retention of large amounts (>6 t ha-1) crop residue on the soil surface is required to decrease runoff from cultivated fields. Between 50 and 75% of the annual precipitation is lost through evaporation from the soil surface thus resulting in relatively low PUE-values.
Abstract: Soils of arid and semi-arid Australia are typically low in both N and P relative to arid zones elsewhere. We examined relative limitations of N and P on productivity of two native perennial grasslands of sub-tropical, semi-arid, north-west Australia. Effects of single and combined additions of N (50 kg ha-1) and P (25 kg ha-1) on growth and plant nutrients were documented over 2 years. Addition of N alone significantly increased total cover, above-ground biomass, N concentrations and N content, in the first year following above-average summer rains. These effects persisted into the second growing season but were of reduced magnitude. Addition of P alone increased P concentrations and aboveground P content but had negligible effects on biomass, indicating luxury consumption. Combined addition of N and P had similar effects to addition of N alone, strengthening the argument that N and not P was limiting to growth. Nitrogen limitation was clearly indicated by low N to P ratios (<7) in aboveground plant components.
Abstract: During the continuous monitoring of atmospheric parameters at the station Cape Point (34°S, 18°E), a smoke plume originating from a controlled fire of 30-yr-old fynbos was observed on 6 May 1997. For this episode, which was associated with a nocturnal inversion and offshore airflow, atmospheric parameters (solar radiation and meteorological data) were considered and the levels of various trace gases compared with those measured at Cape Point in maritime air. Concentration maxima in the morning of 6 May for CO2, CO, CH4 and O3 amounted to 370.3 ppm, 491 ppb, 1730 ppb and 47 ppb, respectively, whilst the mixing ratios of several halocarbons (F-11, F-12, F-113, CCl4 and CH3CCl3) remained at background levels. In the case of CO, the maritime background level for this period was exceeded by a factor of 9.8. Differences in ozone levels of up to 5 ppb between air intakes at 4 and 30 m above the station (located at 230 m above sea level) indicated stratification of the air advected to Cape Point during the plume event. Aerosols within the smoke plume caused the signal of global solar radiation and UV-A to be attenuated from 52.4 to 13.0 mW cm-2 and from 2.3 to 1.3 mW cm-2, respectively, 5 h after the trace gases had reached their maxima. Emission ratios (ERs) calculated for CO and CH4 relative to CO2 mixing ratios amounted to 0.042 and 0.0040, respectively, representing one of the first results for fires involving fynbos. The CO ER is somewhat lower than those given in the literature for African savanna fires (average ER=0.048), whilst for CH4 the ER falls within the range of ERs reported for the flaming (0.0030) and smouldering phases (0.0055) of savanna fires. Non-methane hydrocarbon (NMHC) data obtained from a grab sample collected during the plume event were compared to background levels. The highest ERs ([Delta]NMHC/[Delta]CH4) have been obtained for the C2-C3 hydrocarbons (e.g. ethene at 229.3 ppt ppb-1), whilst the C4-C7 hydrocarbons were characterised by the lowest ERs (e.g. n-hexane at 1.0 and n-pentane at 0.8 ppt ppb-1).
Abstract: The %N and [delta] 15N values of soils and plants were measured along a chronosequence spanning 3 to 3000 Ky in a California annual grassland. Total soil N decreased with increasing soil age (1.1 to 0.4 kg N m-2) while the mean [delta] 15N values of the soil N increased by several [per mille sign] from the youngest to oldest sites (+3.5 to +6.2 [per mille sign]). The [delta] 15N values of plants varied along the gradient, reflecting changing soil N pools and differences in the form of N uptake. The decline in total N storage with time is hypothesized to be due to a shift from N to P limitation with increasing soil age. The general increase in [delta] 15N values with time is interpreted using a N mass balance model, and appears to reflect a shift toward an increasing proportional losses of inorganic mineral forms of N (vs. organic forms) with increasing soil age. We develop a quantitative index of this trend (mineral vs. organic forms of N loss) using mass balance considerations and parameters. The %N and [delta] 15N values along the California age gradient were compared to the published data for a comparably aged chronosequence in Hawaii. Most striking in this comparison is the observation that the California soil and plant [delta] 15N values are several [per mille sign] greater than those on comparably aged Hawaiian sites. Multiple explanations are plausible, but assuming the sites have a similar range in [delta] 15N values of atmospheric inputs, the isotopic differences suggest that N may be, at least seasonally, in greater excess in the strongly seasonal, semi-arid, California grassland.
Abstract: The altitudinal vegetation distribution in the northern Andes during glacial time differed from the present-day conditions as a result of temperature and precipitation change. New evidence indicate that as a response to a reduced atmospheric partial CO2 pressure (pCO2), the competitive balance between C3 and C4 plants have changed. Effects may have remained virtually undetected in pollen records, but can be observed using a stable carbon isotope analysis. Vegetation dominated by C4 taxa, belonging to the families Cyperaceae (e.g. Bulbostylis and Cyperus) and Poaceae (e.g. Muhlenbergia, Paspalum and Sporobolus), may have been able to replace for a significant part the modern type C3 taxa (e.g. species belonging to Carex, Rhynchospora, Aciachne, Agrostis, Calamagrostis, and Chusquea). Impact of reduced glacial atmospheric pCO2 levels and lower glacial temperatures on the composition and the elevational distribution of the vegetation types is discussed. The present high Andean vegetation communities may differ from the glacial equivalents (non-modern analogue situation). We identified dry Sporobolus lasiophyllus tussock grassland and Arcytophyllum nitidum dwarfshrub paramo as the possible relict communities from glacial time. The effect on previous estimates of paleo-temperatures is estimated to be small.
Abstract: Sandy soils formed from granitic rocks on Miocene-aged and older land surfaces cover a large area of central Zimbabwe. These deeply weathered soils are an important agricultural resource for the country yet susceptible to erosion with agricultural use, and decreases in productivity and sustainability have been documented. Regional-based surveys of Zimbabwe have evaluated the general extent of erosion, but site-specific data to determine soil properties related to erosional susceptibility and influence of management are lacking in this area. This study measured physical and chemical properties of five sites (10 pedons) in an area of granitic soils east of the city of Harare. Sites were from university research, commercial, and communal farms. Pedons were paired to determine soil property differences in row crop vs. pasture management. The objectives of this study were to (a) verify important soil properties that influence erosional susceptibility and productivity of these granitic soils, and (b) determine differences in those properties as related to agriculture management. Results indicate important properties that favor high erosional susceptibility in these soils are coarse textures and high degree of weathering (resulting in extractable bases and cation exchange capacity<10 cmol kg-1), and low organic C (ranging from 2.5 to 23.5 g kg-1 C in surface horizons). Pedons in pasture have 2 to 19 cm thicker A horizons, water dispersible to total clay ratios 3% to 17% lower, and greater aggregate stability relative to the paired, cropped pedons. Saturated hydraulic conductivity (Ksat) at 15 to 30 cm depth ranges from 0.2 to 23.4 cm h-1 for all pedons. Greater Ksat in cropped pedons relative to the pasture pair is likely temporal and influenced by tillage. Bulk density and extractable-P exhibit no trends with management and such results are likely confounded by management history such as crop-pasture rotations and fertilization. This study has shown the importance of increasing and maintaining soil C levels to minimize agricultural-induced erosion of these granitic soils. Results suggest that soil textures and the weathered nature of these soils in this semitropical climate produce conditions where organic matter is generally low even in soils maintained in pasture. Therefore, use of conservation management practices will be required to maintain and build adequate soil tilth and fertility for sustainable crop production.
Abstract: This paper introduces a special issue of Global Environmental Change: Human dimensions on the Sahel of West Africa. It reviews the seminar to which the papers were presented, and brings together some conclusions. Despite the quarter century of research into the West African Sahel that followed the great droughts of the 1970s, there are still strong disagreements about how to achieve more prosperous, yet sustainable livelihood systems in the region. There are conflicts between those who believe in indigenous capacities to maintain rural livelihoods, those who believe that various forms of external support are necessary, and those wedded to a vision of a Sahel directed by regional urban growth. Under economic and cultural globalisation, the future of this region is, at best, unclear. The papers in this collection do agree that Sahelian environments are diverse, and that Sahelian people cultivate and exploit diversity and flexibility. They also suggest that there are no quick-fix development solutions, except to build upon this historical diversity with renewed purpose.
Abstract: Both intensity and type of habitat management in grasslands and heathlands affect spider communities. With high intensity management, spider communities often lack diversity and are dominated by a few r-selected species affiliated with bare ground. Low intensity management produces more complex communities introducing more niches for aerial web spinners and climbing spiders. The preferred management will be site-dependent and may not be appropriate for all spiders in all situations, particularly for some rare or threatened species. Providing natural cover is recommended when using extreme forms of management or intensive grazing (particularly by sheep). In extreme cases, or where trampling is heavy, the litter layer should be conserved. We advocate research and survey before and after major management implementation. Habitat management for spiders should not be considered alone, but integrated into a holistic plan. Management for spiders may conflict with rare plant conservation and small reserves should examine the viability of providing two contrasting regimes.
Abstract: This article examines the relation between poor women and men and common property resources (cprs). It locates poor people's use of cprs within a wider focus on sustainable livelihoods, which argues that development initiatives need to build on people's assets and strengths, and identifies cprs as a crucial element of poor people's coping and adaptive strategies. The article considers evidence from India and West Africa with a particular focus on poverty reduction, equity, gender and management issues. Development agencies and governments which have re-focused their attention on poverty in recent years will find that cprs provide an entry point to understanding poor people's perceptions of poverty and for building on their capacities.
Abstract: [`]Vegetation thickening' often refers to an increasing shrub and tree density on many grazed rangelands, woodlands and forests that may or may not have supported such woody plant populations in the past. It is one of several ecosystem changes, including post-clearing re-growth, afforestation and reforestation, which are variants of the same biological phenomenon -- the recovery phase of disturbance/recovery cycles that all vegetation undergoes continuously. There are various levels of human influence over both phases. It is important as part of the global carbon cycle and potentially for its implications for implementation of the Kyoto Protocol. Vegetation thickening poses some inventory and carbon accounting challenges in this regard because of difficulties with quantification and attribution. The attribution of carbon sinks to natural, indirect or direct human influence is difficult because of the complex interactions of factors in determining woodland dynamics. The lack of clear scientific distinction of causation requires decisions to be made on how this is calculated in inventories of greenhouse gas emissions. Advantages, disadvantages, workability and dilemmas of five possible accounting approaches to dealing with these human-influenced biological components are discussed. These approaches range from accounting solely for emissions from clearing ignoring complementary re-growth sinks, to full emissions accounting including methane, nitrous oxide and CO2 emissions from the managed animals and land.
Abstract: A methodology was developed for an integrated assessment of land resources and land use, and applied to Ikem, south-eastern Nigeria. Findings from participatory rural appraisals (PRA) were related to two sets of aerial photographs (1962: 1:6000; 1982: 1:40,000). A two level PRA elicited relationships between soil-landscapes, land cover, land use and local classification schemes at both individual and village decision-making levels. At the field scale, local knowledge on the land was coupled with scientific data collected along toposequences and additional verification transects. Individually owned homegardens are agro-forestry systems involving field crops, vegetables and valued multi-purpose trees such as oil palm. The family-owned fields involve a mixture of food and tree crops. The land cover was a good indication of the fallow period used on fields in the communal farmlands as woody species no longer establish in short fallow periods. At the village scale, participatory land resources mapping was combined with aerial photograph interpretation to create soil-landscape and land cover/use maps that can be used for planning purposes at the local government. Additional archival research supported evidence that the growing population and subsequent land scarcity has led to shortened fallow periods and reduced numbers of woody species in the farmlands. The establishment of new settlements and the gradual increase of private land followed by the planting of tree cash crops have intensified agricultural land use resulting in a higher tree density across a larger area. Agricultural expansion predominantly took place on the relatively fertile land along the rivers. Results indicate the need for a non-ambiguous government policy concerning land tenure that recognises traditional land ownership dynamics.
Abstract: San Antonio is one of the fastest growing metropolitan areas in the USA. Urban sprawl may significantly impact ecosystem services and functions but such effects are difficult to quantify and watershed-level estimates are seldom attempted. The objective of the study reported here was to determine whether LANDSAT MSS could be used to quantify changes in land-use and ecosystem services due to urban sprawl in Bexar County, TX, in which San Antonio is centered. The size of six land cover categories in the summer of 1976, 1985, and 1991 were estimated in the 141[punctuation space]671 ha of three watersheds in Bexar County. Coefficients published by Costanza and co-workers in 1997 [Nature 387 (1997) 253] were used to value changes in ecosystem services delivered by each land cover category, and a sensitivity analysis was conducted to determine the effect of manipulating these coefficients on the estimated values. Although we estimated that there was a 65% decrease in the area of rangeland and a 29% increase in the area of urbanized land use between 1976 and 1991, there appeared to be only a 4% net decline in the estimated annual value of ecosystem services in the study area (i.e. $5.58 ha-1 per year, with a 15-year cumulative total value of $6.24 million for the whole study area). This relatively small decline could be attributed to the neutralizing effect of the estimated 403% increase in the area of the woodlands, which were assigned the highest ecosystem value coefficient. When we assumed that the shift of rangelands to woodlands produced no net change in the value of ecosystem services per hectare, the estimated annual ecosystem service value declined by 15.4% ($23.22 ha-1 per year) between 1976 and 1991. When conducting time-series studies of ecosystem services, it is important to identify parallel changes in land cover types in order to quantify the potentially neutralizing influence of positive land cover changes on the negative effects of urban sprawl on ecosystem services.
Abstract: Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples' responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and constraints for new land uses are created by local as well as national markets and policies. Global forces become the main determinants of land-use change, as they amplify or attenuate local factors.
Abstract: Interactions between fire regime, dispersal strategies and patch structure were examined as key issues for the management of floristic composition of grasslands, through a model that simulates the population dynamics of two competing fire-cued and non-sprouting species. The model describes a heterogeneous environment composed by several patches of grassland, only related by seed dispersal. The last burn date at each patch determines the accumulation level of fuel-biomass provided by a third, dominant species, which in turn controls for the exclusion rate of both colonizer species. The population dynamics of both species was approached following density-dependent models and parameterized for two opposite dispersal strategies: low spatial and high temporal dispersion of seeds (type 1), high spatial and low temporal dispersion of seeds (type 2). Only under the most variable scenarios (when non-synchronous and irregular fire regimes were combined with a proportion of patches (p) with initially depleted seed banks) did the relative success of dispersal strategies vary with the length of the fire-free period. Irrespective of p, smaller interval lengths favored the postburn density of the strategy 1. Strategy 2 was favored over strategy 1 when the fire-free interval increased, such difference being maximum for intermediate p-values. These general tendencies agree with those observed from a reference system: the Flooding Pampa grasslands dominated by Paspalum quadrifarium where short no-fire intervals promote the postburn abundance of a type 1 species (Lotus tenuis) over two type 2 species (Carduus acanthoides and Cirsium vulgare) while for long fire-free intervals the opposite is true. This results suggest that frequency, time since last burn, and burning synchrony are useful components of a fire regime to take advantage of variation in dispersal strategies.
Abstract: The diminishing wilderness areas remaining in southern Africa offer opportunities to establish and market ecotourism destinations. It would thus be useful to gain insight into what conditions make certain ventures viable. With the aid of a model and using data from Ongoye Forest in South Africa, the long-term financial viability of three operational ecotourism scenarios is assessed: upmarket lodges, middle-of-the-range chalets, and campsites. The resulting "preferred" scenario depends on a specific weighted interest in favor of the community, the environment, or the investor. The economic realities of southern Africa suggest that without government support, it may be risky to invest extensive initial capital into the larger scale ecotourism projects proposed.
Abstract: At current densities, elephants are having a severe impact on plant community structure and species richness in the Addo Elephant National Park (AENP), Eastern Cape, South Africa. Those species that are particularly vulnerable to elephants comprise the bulk of the regionally endemic, Red Data Book and rare species (special species) associated with succulent thicket, a vegetation type endemic to the Eastern Cape. The AENP is the only national park in South Africa that contains succulent thicket. Other thicket-containing reserves exist but have insufficient management resources. The AENP can be divided into 16 units based on management and grazing history. Using these units, we show a strong relationship between the duration of exposure to elephant impacts and the richness and density of special species in the Park. Using an iterative reserve-selection procedure, we identify a core system of five botanical reserves within the Park. This system would represent 91% of the Park's special plant species in less than 8% of its area. We recommend an implementation strategy based on the irreplaceability and vulnerability values of each unit, and each species. This involves the maintenance of three existing botanical reserves, the establishment of two additional reserves, the deproclamation of one existing reserve, and further conservation actions to ensure the protection of those special species not included within the core system of botanical reserves. We also provide suggestions for the resolution of the conflicts between elephant conservation and maintenance of plant biodiversity in the AENP.
Abstract: As savannas are widespread across northern Australia and provide northern rangelands, the sustainable use of this landscape is crucial. Both fire and grazing are known to influence the tree-grass character of tropical savannas. Frequent fires open up the tree layer and change the ground layer from perennials to that dominated by annuals. Annual species in turn produce copious quantities of highly flammable fuel that perpetuates frequent, hot fires. Grazing reduces fuel loads because livestock consumes fuel-forage. This trade-off between fire and grazing was modelled using a spatially explicit, process-orientated model (SAVANNA) and field data from fire experiments performed in the Victoria River District of northern Australia. Results of simulating fire (over 40 years) with minimal or no grazing pressure revealed a reduction in the shrub and woody plants, a reduction in grasses, and no influence on the tree structure given mild fires. While mature trees were resistant to fire, immature trees, which are more likely associated with the shrub layer, were removed by fire. The overall tree density may be reduced with continual burning over longer time periods because of increasing susceptibility of old trees to fire and the lack of recruitment. Increases in stocking rates created additional forage demands until the majority of the fuel load was consumed, thus effectively suppressing fire and reverting to the grazing and suppressed fire scenario where trees and shrubs established.
Abstract: The possibility of trading greenhouse gas emission permits as a result of the Kyoto Protocol has spurred interest in developing land-based sinks for greenhouse gases. Extensive grazing lands that have the potential to develop substantial woody biomass are one obvious candidate for such activities. However, such activities need to consider the possible impacts on existing grazing and the possible impacts of continuing CO2 buildup in the atmosphere and resultant climate change. We used simulation models to investigate these issues in the mulga (Acacia aneura) woodlands of southwest Queensland. The simulation results suggest that this system can be managed to act as either a net source or a net sink of greenhouse gases under current climate and CO2 and under a range of global change scenarios. The key component in determining source or sink status is the management of the woody mulga. The most effective means of permanently increasing carbon stores and hence reducing net emissions is to exclude both burning and grazing. There are combinations of management regimes, such as excluding fire with light grazing, which, on average, allows productive grazing but transient carbon storage. The effects of increased CO2 on ecosystem carbon stores were unexpected. Carbon stores increased (7-17%) with doubling of CO2 only in those simulations where burning did not occur, but decreased when burnt. This occurred because the substantial increases in grass growth with doubling of CO2 (34-56%) enabled more fires, killing off the establishing cohorts needed to ensure continued carbon accumulation. On average, the doubling of atmospheric CO2 concentration increased grass growth by 44%, which is identical with mean literature values, suggesting that this result may be applicable in other ecosystems where fire has a similar function. A sensitivity analysis of the CO2 response of mulga showed only minor impacts. We discuss additional uncertainties and shortcomings.
Abstract: Data from the 1997 National Resources Inventory (NRI) are used in this study to examine recent trends in the conversion of cropland to urban land with special attention paid to the spatial distribution of these conversions relative to rangeland to cropland conversions. Our findings are that the approximately 11 million acres of cropland converted to urban land between 1982 and 1997 was coincident with an equal amount of rangeland converting to cropland. The rangeland to cropland conversions equate to replacement lands for cropland lost to urban encroachment. Approximately one third of the cropland lost to urban development occurs on prime farmland while the new cropland converted from rangeland is more likely to be irrigated as it resides principally in the arid western United States. The findings are discussed in light of a sustainable land use system perspective.
Abstract: We used an individual plant-based simulation model (ECOTONE) to evaluate the importance of allelopathy and soil texture to the invasion of semiarid grasslands by the non-native perennial C3 forb Acroptilon repens. We also assessed the sensitivity of model results to the negative effects of allelochemicals on recruitment and growth of perennial grasses. ECOTONE simulates the recruitment, growth, and mortality of individual plants on a small plot (0.12 m2) through time at an annual time step. A daily time step, multi-layer model of soil water dynamics (SOILWAT) was incorporated into ECOTONE to represent competition for soil water on a finer temporal scale. The model was parameterized for a shortgrass community in eastern Colorado, USA, using data available from the literature. Experimental simulations examined the effects of four soil textures and a range of levels of plant sensitivity to allelochemicals on the aboveground biomass of A. repens and of native perennial grasses. Simulation results showed that A. repens dominated the aboveground biomass on a plot only if native species were affected by allelopathic interactions. At moderate levels of plant sensitivity, A. repens became dominant faster and reached a higher proportion of the total biomass on fine- than on coarse-textured soils. Community composition and rate of A. repens dominance were more affected by the sensitivity of plant growth to allelochemicals than the sensitivity of species recruitment. Allelopathic interactions were an important component of the invasion dynamics of this perennial invasive weed, and further field investigations are warranted.
Abstract: Although an ever-increasing body of research data has documented the usefulness of goats for controlling brushy and weedy species such as shinnery oak, blackjack, and post oak, leafy spurge, sericea lespedeza, and many other species, this technique remains severely underutilized. Environmental concerns and the increased costs of chemical and mechanical control methods provide greater opportunities to utilize biological control methods such as goats for removal of brush and weeds. Goats have an advantage over other biological control methods in that they can profitably convert brush and weeds into a saleable product and they can graze concurrently with cattle. cript.In addition, goats improve the cycling of plant nutrients sequestered in brush and weeds, enabling the reestablishment of grassy species. The foremost limitation to using goats for brush and weed control is the social stigma cattlemen attached to goats. The lack of an infrastructure (animal markets, source of large numbers of adapted animals, producer experience and knowledge base) to support goat enterprises is a serious constraint which is gradually being overcome as the goat industry expands. Suitable goat production systems need to be developed for specific environments. This involves the modification of existing knowledge, especially in regard to kidding date, parasite management, predator control, fencing, and marketing strategy. The lack of economic data and enterprise budgets also are constraints. Further research is needed to collect economic data and to develop stocking rate criteria and production systems to support the use of goats for biological weed and brush control in a diversity of environments.
Abstract: Significant changes over the past 150 years in aquatic, terrestrial, landscape, and socioeconomic systems have altered biophysical systems in the interior Columbia basin. Changes and conflict in public policy concerns, such as resource use vs. restoration vs. conservation are especially evident in more than 34% of total forest and rangeland in the United States that are federally administered. In the last decade, design and implementation of complex land management strategies has become an issue for public land managers. In turn, the scientific community is often challenged to develop approaches for management of complete ecosystems. This paper discusses the use of science in the assessment and evaluation phases of one large-scale (multi-region) ecosystem management effort on federal lands in the Columbia river basin, the Interior Columbia Basin Ecosystem Management Project (ICBEMP), and briefly describes the evaluations of three alternative management strategies which are detailed by other papers in this issue. This paper contends that understanding the context of land management decisions is essential to defining the veracity or applicability of alternative land management strategies. Evaluating the alternatives is a complicated science process, which requires understanding the effects of each set of direction over both the short and long term, projecting the effects of those directions, making assumptions about pieces not yet developed, and modeling resource change.
Abstract: Farmers play a key role in nutrient cycling within agricultural areas. This study describes an indigenous system of soil fertility management in the Zamfara Forest Reserve, northwest Nigeria. Data were collected between 1996 and 2000, combining qualitative and quantitative methods. Methods applied include transect walks, qualitative and semi-structured interviews with farmers and key respondents, and chemical soil analyses with standard methods. Results show that farmers combine crop planting pattern and the application of organic and mineral fertilisers in an effective way to maintain the fertility of their soils. Intercropping of legumes and cereals is the dominant cropping pattern. The Hausa farmers keep an average of 4.4 tropical livestock units (TLU) which contribute significantly to the farmyard manure. Ingredients of the farmyard manure are animal droppings, feed left-overs, litter, grass, kitchen residues, and ash. Farmers ranked the quality of livestock faeces as fertilisers: cattle>smallruminants>donkey. The average quantity of farmyard manure brought to the fields exceeds by far the amount provided directly by livestock (7.5 vs. 1 Mg ha-1). From all organic and inorganic sources, 87 kg N, 33 kg P and 120 kg K ha-1 are deposited annually on the fields. Soil analyses revealed a satisfactory nutrient status with 0.28 g N and 3.4 g C kg-1, a C:N ratio of 13, 40 mg kg-1 available P and 69 mg kg-1 available K in the topsoil. The impact of manuring on the nutrient status of the soil is more pronounced for P and K than for N and C. Farmer strategies and management make use of and develop diversity.
Abstract: Soil aggregate stability is widely recognized as a key indicator of soil quality and rangeland health. However, few standard methods exist for quantifying soil stability in the field. A stability kit is described which can be inexpensively and easily assembled with minimal tools. It permits up to 18 samples to be evaluated in less than 10 min and eliminates the need for transportation, minimizing damage to soil structure. The kit consists of two 21×10.5×3.5 cm plastic boxes divided into eighteen 3.5×3.5 cm sections, eighteen 2.5-cm diameter sieves with 1.5-mm distance openings and a small spatula used for soil sampling. Soil samples are rated on a scale from one to six based on a combination of ocular observations of slaking during the first 5 min following immersion in distilled water, and the percent remaining on a 1.5-mm sieve after five dipping cycles at the end of the 5-min period. A laboratory comparison yielded a correlation between the stability class and percent aggregate stability based on oven dry weight remaining after treatment using a mechanical sieve. We have applied the method in a wide variety of agricultural and natural ecosystems throughout western North America, including northern Mexico, and have found that it is highly sensitive to differences in management and plant community composition. Although the field kit cannot replace the careful laboratory-based measurements of soil aggregate stability, it can clearly provide valuable information when these more intensive procedures are not possible.
Abstract: Current and potential future conditions of terrestrial plant communities and landscape health were modeled for three alternative public land management strategies in the interior Columbia River basin. Landscape health was defined as an integration of the degree to which vegetation and disturbance conditions resemble native patterns and support levels of human activity. The range of vegetation and disturbance variability for a period before the middle 19th century was used as a basis for comparison of current and future regimes to the "historical" system. Departure from the "historical" regime in wildland environments was found to be related to altered disturbance patterns, especially changed fire regimes, forest insect and disease levels and excessive livestock grazing effects. Overall, mid-seral forests are currently more prevalent than they were in the past and old forests, especially single-layer structural types, are less abundant. Non-native plant species and altered plant community composition conditions exist across broad areas of rangelands. Landscape health has declined substantially in many areas. Proposed management strategies that emphasize maintenance and restoration activities in a hierarchical landscape approach should generate improved landscape health conditions over the next 100 years. However, the massive scale of changes to disturbance and vegetation patterns from historical to current times and the cost of implementing restoration activities make dramatic improvement unlikely.
Abstract: Aim Patterns of species turnover along environmental gradients are better studied than their causes. Competitive interactions, or physiological tolerance are most often cited as determinants of turnover. Here we investigate differential tree species response to disturbance by fire and mammal browsing as causes of changing dominance of species within and among sites along an altitudinal gradient. Methods We documented the distribution of two Acacia species using maps and sample transects. We explored possible causes of species turnover by studying differences between the species in tolerance to grass competition using pot experiments, to browsers by observing patterns of shoot damage, and to fire by comparing the size structure of populations burnt at different frequencies and intensities. Results Acacia karroo woodlands were rare and occur at higher elevations than the much more common A. nilotica woodlands. Woodland composition seems set to change in future since the pattern of dominance was reversed in juvenile stages. A. karroo juveniles were very widespread and far more abundant than A. nilotica juveniles. A. karroo juveniles were most abundant in tall fire-prone grasslands and were rare on grazing lawns whereas A. nilotica showed the reverse pattern. In the pot experiments, growth of both species was suppressed by grasses but there were no significant differences in response between the two species. Juveniles of A. karroo were more heavily browsed than those of A. nilotica. However juveniles of A. nilotica were less tolerant of frequent intense burns than juvenile A. karroo. Main conclusions Disturbance gradients, from high fire frequency and low herbivore density at high altitudes, to lower fire frequency and higher herbivore density at low altitudes, are responsible for the shift in community structure along the spatial gradient. Differential responses to browsing and fire may also explain temporal turnover from A. nilotica in the past to A. karroo in the present. Changes in the area burnt annually, and in faunal composition, suggest a landscape-scale shift from grazing-dominated short-grass landscapes in the 1960s, favouring A. nilotica, to fire-dominated tall grasslands in the 1990s favouring A. karroo. We suggest that species turnover due to differential responses along disturbance gradients may be much more widespread than the current paucity of studies suggests.
Abstract: Summary Grasslands are located in areas with precipitation ranging between 150 and 1200 mm yr-1 and temperature between 0 and 25°C (Lieth and Whittaker, 1975). Along a precipitation gradient, in temperate regions, grasslands are located between forests and deserts. Sites with annual precipitation higher than 1200 mm yr-1 usually support forests whereas sites receiving less than 150 mm yr-1 usually are occupied by deserts. Temperature interacts with precipitation, moving the grassland-forest and grassland-desert boundaries to wetter or drier areas. For example, as temperature and potential evapotranspiration decrease, the grassland-forest boundary occurs at lower precipitation. In the Great Plains of North America where isohyets run in a north-south direction, the boundary between the tallgrass prairie and the temperate forest has a clear SE-NW direction (Barbour and Billings, 1988).
Abstract: Summary The growth of agricultural production worldwide has led to an increasing role of agro-ecosystems within the global carbon cycle. Arable land in the world covers about one-tenth of the 134 × 1012 m2 of total land area (excluding Antarctica). Much of this land area is bare rock, desert, or covered with ice, and about two-thirds can be considered as covered by vegetation. The total annual carbon flux through all terrestrial ecosystems is estimated at about 50 Pg C (Minami et al., 1993). The objective of this paper is to estimate the contribution of agricultural crops in this total carbon flux. In addition to arable land, grasslands are used for agricultural purposes. They are mainly used for grazing by cattle and sheep, at stocking densities that vary enormously, with the extensively managed rangelands of Australia or Latin America on one end of the scale and the "green carpets" of The Netherlands on the other. Grasslands cover about one-third of the vegetated area and contribute about one-fifth to the global carbon cycle (Minami et al., 1993). For further details on primary productivity of grasslands, reference is made to chapter 12, this volume. Here we present some data on the production of the major crop groups in terms of carbon and nitrogen. The decadal time trend is analyzed, the relation with nitrogen fertilizer production is indicated, and productivity is discussed in relation to other growth-limiting factors.
Abstract: Summary The savanna biome is diverse, including formations ranging from almost treeless grasslands to more or less closed-canopy woodlands with considerable variation in plant composition, biomass, and net primary productivity (NPP). Savannas cover an extensive area in the tropics, inhabited by a fifth of the human population and supporting the majority of the world's livestock and large mammals. Population pressure and land use changes are high and are likely to increase in the foreseeable future. Savanna areas are increasing due to deforestation and abandoned agriculture, and decreasing due to cultivation and degradation, the balance is probably a decrease. These changes often occur in remote areas and are poorly documented.
Abstract: Summary In order to obtain a better insight into past vegetational and climatic changes along the Pole-Equator-Pole: Americas (PEP 1) transect, 32 late Quaternary pollen records from savanna and forest-savanna transition regions of the South American neotropics, north and south of the equator, have been compared. During pre-full glacial times, environmental changes in savannas were spatially complex. Some records show either stable grassland where forest exists today or a repeated alternation between forest and savanna. During the full glacial period, neotropical savannas, both north and south of the equator, expanded due to markedly drier conditions. The Amazon rain forest area must have been reduced during this period. In the southern neotropical regions, savanna area was reduced and replaced by subtropical grassland by cold climatic conditions during glacial periods. During the late glacial period, climate changed to wetter conditions north of the equator at 11,500 14C B.P. (or later) and south of the equator earlier at ca. 16,000-14,000 14C B.P. in montane regions. Wetter conditions were not recorded in the high plains or lowlands. During the early Holocene (until ca. 6000-5000 14C B.P.), the climate was drier in most of the South American savannas than during the late glacial and late Holocene. Early Holocene distribution of savanna was much larger than during the late Holocene. The general synchrony of paleoenvironmental changes since the full glacial period, from neotropical savanna sites north and south of the equator, suggests that changes in the latitudinal migration of the Intertropical Convergence Zone (ITCZ) may have played an important role. The movement of the high-pressure cell over the South Atlantic and changes in frequency of the tracks of the Antarctic cold fronts were also important.
