GSSA-Publications-1991-1995

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Abstract: Gramineae is the most widely distributed family of flowering plants. It is of the greatest use to the human race in all plants of the earth. The leaves of all gasses are very similar in gross morphology. but they are very different and more beautiful surface view in microscopical structure of leaf epidermis. The character of leaf epidermis of grasses are not only the more important for identification of species in the leaf stage, but also very important to define the subfamily in systematics. This book contains two parts, the first part deals with general microscopical structure of leaf epidermis; the second part deals with Chinese descriptions of 6 subfamilies, 114 genera 285 species and 15 varieties, each species or variety is illustrated with 2 micro-photographs for the adaxial and abaxial surface, each micro photograph is accompanied with short English note. It will serve as a key reference book to botanists, agriculturists, horticulturists etc. and also as a pictorial source book for artists.

Abstract: Since the mid-19th century settled livestock ranching has been the major form of land use in South Africa, occupying 68% of the land surface. Decreases in livestock densities and ranch numbers during the past century imply that carrying capacities for domestic herbivores are falling. Differences in carbon isotope signals with soil depth and abrupt shifts in dominant plant species across ranch boundaries reveal that southern African rangelands are changing. Case studies suggest ways to control altered grassland composition, bush encroachment in arid savanna, and dominance by toxic and halophytic shrubs in arid shrublands. But climatic and biological factors constrain rates of passive recovery, and guidelines for active restoration are poor and techniques costly. Moreover, conservation of remaining good rangeland is seldom enforced, and economic considerations usually outweigh the land user's desire to sustain diversity and productivity.

Abstract: An approach to combining remote sensing spectral measurements with an ecosystem process model is presented. In this approach, the ecosystem model is not bound by the sole use of satellite data, but integrates the latter in an explicit formulation of the main processes of vegetation functioning. A close analysis of the relationships between processes described by the model and spectral measurements can therefore be carried out, and the capability of the model to be driven by remote sensing can also be investigated. This first article presents a regional ecosystem process model for Sahelian regions. The model describes a herbaceous layer composed of only annual species. The processes of the soil-plant-atmosphere system, such as water fluxes in the soil, evaporation, transpiration, photosynthesis, respiration, senescence, litter production, and litter decomposition at the soil surface, are modeled. Moreover, structural parameters such as vegetation cover fraction, LAI, and canopy height, which are essential parameters for coupling with physical models of reflectivity, are also simulated. Comparison with aboveground biomass measured between 1976 and 1992 at a regional scale in two different regions of the Sahel, namely, Ferlo in Senegal and Gourma in Mali, shows that the model is able to simulate the temporal evolution of the aboveground biomass components.

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Abstract: An approach for combining remote sensing spectral measurements with an ecosystem model was presented in an accompanying article (Mougin et al., 1995). The sahelian grassland ecosystem STEP model developed for that purpose was also described and validated. In order to fulfill a prerequisite for using coarse resolution optical satellite data with the STEP model, the present paper presents i) a modeling of the reflectance which is adapted to the sahelian landscape and ii) a study based on the coupled ecosystem-reflectance modeling to assess the potential of vegetation indices for inferring vegetation parameters. The modeling of the landscape reflectance is based on existing soil and canopy reflectance models, and considers area-weighted contributions from green and dry vegetation, and bare soil components. The ecosystem model provides the landscape reflectance models with inputs like vegetation cover fraction (fv) and leaf area index (LAI) to characterize the vegetation present. Atmospheric effects are also accounted for using an existing simplified radiative transfer model. Simulated top of the atmosphere reflectances confronted to real satellite data during a growing season indicate that the modeling is adequate to reproduce temporal profiles of vegetation indices when atmospheric conditions are not prohibitive. Simulated vegetation indices (NDVI, SAVI, GEMI, SR) compared to vegetation characteristics show that a good tracking of the evolution of LAI and v during the growing season is possible before maturation. A sensitivity study of the four VIs to green biomass, soil brightness, and atmospheric water vapor is carried out for the specific case of the Sahel. The SAW and NDVI are both found to be adequate if atmospheric effects are minimized. NDVI integrated over the growing season is compared to net primary productivity (NPP) for different sites, regions, and growing seasons. A near-linear relationship is found, but the same relationship may not be applicable to different regions or growing seasons. On the whole, the results suggest that vegetation indices contain information which are useful for the ecosystem model, despite the fact that perturbating factors make the retrieval of these informations difficult. The possibility of using satellite data to drive the STEP model, or control its simulations, will be assessed in a forthcoming article.

Abstract: Remote sensing applications used for resource assessment often lack the capacity to test image data against predictions. This article describes remote environment and management assessment (REMA), a new method for the interpretation of rangeland plant cover change, which uses Landsat MSS data and neutral predictions. REMA has been designed to provide a generalized and testable method to assess herbivore impact on potential forage productiveness, even when a plant cover is heterogeneously distributed. In this article, models are constructed to interpret patterns and processes of cover change within paddocks exposed to alternating periods of plant cover increase and decline. Relative cover changes along distance from water point axes are derived to standardize and reveal gradients of cover change and cover resistance to drought. By testing cover changes against neutral predictions, insights are gained into the association between grazing processes, geomorphology, and climatic conditions. Four MSS images of two sheep-grazed paddocks from wooded rangelands in eastern Australia are used to demonstrate that increasing and decreasing linear cover change gradients, and contrasting forage resistances to drought, can be found and assessed. The patterns and levels of cover change due to grazing were found to be different and to have nominally high and low levels of drought resistance that were related to paddock management, geomorphology, and climate.

Abstract: Spatial and temporal subcontinental patterns of fire distribution in Africa, may vary strongly from year to year. These variations may be of climatic or anthropic origin. Global Area Coverage (GAC) data, from the Advanced Very High Resolution Radiometer (AVHRR), are known both to provide a good description of fire calendar and on a continental scale, a good indicator of locations of intense fire activity. In fact, the GAC data, available on a daily basis back to July 1981, is the only source of information actually available to determine burning patterns both on a continental scale and over long periods of time. This study presents the spatio-temporal distribution of vegetation fire in Central Africa, as derived from GAC imagery, over the four 1984/85 to 1987/88 dry seasons of the Northern Hemisphere (November to February periods). The analysis of the mean fire distribution patterns over the four dry seasons, as defined by vegetation cover and pluviometric conditions, shows a north to south gradient of fire activity in the savannah domain: This gradient of fire activity has been previously related to the annual pluviometric calendar and the amount of rainfall. The strong interannual variability in fire activity observed for this four-years-period could not, however, be explained by the monthly pluviometric patterns. The observed fire gradient therefore seems to result from additional meteorological or anthropic parameters. The methodology used in this study demonstrates the potential of GAC data for fire monitoring at a subcontinental scale. Current work is extending the area of interest to the entire African continent using the 10-yr-period of GAC imagery.

Abstract: SUMMARYThe seasonal rate and extent of dry matter (DM) and neutral detergent fibre (NDF) degradation of the African sourveld grasses Alloteropsis semialata, Andropogon appendiculatus, Cynodon dactylon, Elionurus muticus, Eragrostis plana, Harpochloa falx, Heteropogon contortus, Hyparrhenia hirta, Microchloa caffra, Themeda triandra and Tristachya leucothrix in the rumen were measured using the nylon bag technique at the D05) between species, being largest in A. semialata (2201) in spring (218%). Species differed (P < 001) from spring (778 %). The rate of DM degradation (kd) in the rumen also differed (P < 0054) and E. plana and A. appendiculatus the slowest (005) in winter (0048).Neutral detergent soluble (NDS) content was highest in A. semialata (29%) and lowest in E. plana (211%) PDCW content. Mean PDCW content was highest in spring (596%). Cell wall degradation (kc) rates were fastest (003). Overall, kc declined from spring (0029). In general, A. semialata, T. triandra and H. hirta appeared to have the most favourable, and E. plana, A. appendiculatusand M. caffra the least favourable, ruminal degradation characteristics. These differences suggest that species composition is likely to have a major impact on potential animal production on these low quality grasslands.

Abstract: Results of various studies on the origin of Arctic air pollution are reviewed, focusing on what is known about its physical characteristics and chemical composition, as well as on emission sources and major pathways of pollutant transport to the region. Emissions from anthropogenic sources in Eurasia have been found to be a major contributor to Arctic air pollution measured at altitudes of up to 2-3 km in the atmosphere during winter. During sporadic summer transport of pollutants to the region, emissions from sources in Europe seem to be more important than those from other sources. Polluted air masses, carrying a mixture of anthropogenic and natural air pollutants from a variety of sources in different geographical regions, have been identified in the Arctic at altitudes of 4-5 km during both summer and winter. Long-range transport of airborne loess from deserts in Asia and Africa to the Arctic at these altitudes was suggested. Model calculations indicate that <10% of pollutants emitted in the major source regions is deposited in the Arctic, although our knowledge on wet and dry removal processes in this region is very incomplete. Maximum concentrations of sulfates and fine particles in the Arctic were observed at the beginning of the 1980s. No major changes in concentrations were observed during the 1980s and some decrease was measured at selected stations at the end of that period. This decrease, particularly in lead and fine particle concentrations, was related to the decrease in their emissions in some source regions. A meteorological shift was also suggested as a possible cause of the decrease in concentration. Major gaps in information on sources, pathways and behavior of pollutants in the Arctic are identified. Current research programs that should improve our understanding of the origins and environmental effects of Arctic air pollution are presented.

Abstract: This study provides data on plant density, vegetation cover, total and forage phytomass for the main rangelands and shrubs of a [`]pilot zone' (Almeria, Spain) in the south-east of Spain. Carrying capacity has been calculated for each rangeland, and for two different levels of energy requirements: maintenance (from 0·29 to 1·28 goats ha-1) and production (from 0·20 to 0·88 goats ha-1). The nutritive value was determined for the most representative shrubs in the area

Abstract: Two development narratives about Africa cry out for rectification. One is the "Except-Africa" narrative talked about when the techno-managerial elites conclude, "Development works...except in Africa." The other is the elites' neo-Mathusian Doomsday Scenario for countries in Except-Africa. Both development narratives are factually incorrect and do an extremely poor job of stabilizing decision making in heterogeneous and changing African settings. Counternarratives are needed and some are suggested.

Abstract: This study was designed to quantify plant selection by Angora goats on a sagebrush-bunchgrass rangeland and to provide information as to the potential for using goats to rehabilitate sagebrush rangelands in less than optimal condition. Goats were introduced to sagebrush-steppe rangeland at the Squaw Butte Experimental Range in eastern Oregon. Groups were maintained separately to avoid social learning across groups. Diets were ascertained using focal-animal bite-count observations during five consecutive seasons, summer of 1990 through summer 1991. Does and kids were primarily graminivorous; however, there was strong seasonality in species preference and a significant age difference in diets selected. Kids selected a more diverse diet and consumed significantly higher amounts of sagebrush and other woody plants during the initial observation season. Animal age influenced plant selection throughout the study until kids were 18 months old.

Abstract: Stable-isotopic, clay-mineralogic, and bulk-chemical analyses were conducted on paleosols of the Neogene Siwalik sections in northern Pakistan in order to reconstruct floodplain environments over the past ~ 17 Ma. The stable carbon isotopic composition of soil carbonate (mean [delta]13C (PDB) = -10.2%) and associated organic matter (mean [delta]13C (PDB) = -24.1%) in paleosols representing 17- ~ 7.3 Ma reveal that floodplain vegetation was dominated by C3 plants. At 7.3 Ma, a shift toward more positive carbon isotopic values began, signaling the gradual expansion of C4 grasses onto the floodplain. From 6 Ma to present, carbon isotopic values for paleosol carbonate (mean [delta]13C (PDB) = +0.6%) and organic matter (mean [delta]13C (PDB) = -14.4%) are uniformly enriched in 13C, indicating the presence of nearly pure C4 grassland. The scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1.0-1.25 m/yr or less for the entire 17 Ma of record. Paleosols in the lower portion of the section lack organic A horizons but have reddish B horizons often containing secondary iron-oxide nodules. Leaching depths of soil carbonate in these older paleosols are typically greater than those in the Plio-Pleistocene part of the section, where organic A horizons are common, and B horizons are markedly more yellow. The combined evidence suggests that the mature paleosols in the pre-7.3 Ma part of the record are dominantly calcareous Alfisols or Mollisols that once underlay nearly pure C3 vegetation, perhaps trees and shrubs, while calcareous Mollisols underlying C4 grassland dominate the upper part of the record. The carbon- and oxygen-isotopic trends in the paleosol record in Pakistan are also evident in the diet of fossil mammals, and in paleosols from Nepal, thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent-wide. Local effects, such as the development or intensification of the Asian Monsoon driven by uplift of the Tibetan Plateau, may have led to the expansion of C4 grasses. If, however, the expansion of C4 grasses proves globally synchronous, then a larger scale cause, such as a marked decrease in [varrho]CO2, may be the driving mechanism.

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Abstract: This paper describes the development of a model for estimating herbage production from rainfall and evapotranspiration in rangelands and its calibration using a vegetation cover index derived from remotely-sensed data. The model operates on a time unit of 1 month and has a maximum of three calibration parameters: a water use efficiency term, a cover depletion rate and a term describing the percentage of tree and shrub cover present. The model can represent variability at the whole landscape level and is well-suited to calibration. Parameter values derived when the model is inverted show variations which can logically be associated with differences in land condition and grazing pressure. These parameter values make it possible to model differences in herbage production in a particular area under different rainfall conditions and in response to changes in land condition or the level of grazing.

Abstract: Mahjur areas are commonly found in the rangelands of the Dhamar Montane Plains. In various ways their use is integrated in the local agro-pastoral land-use system. They are most importantly used as a forage reserve in the dry season for feeding sheep. Local variation of their role, in that respect, is related to variation in ecological factors and is one measure aimed at optimizing rangeland utilization. It is recommended that their traditional utilization by village communities, of decreasing importance under the current socio-economic conditions, should be reconsidered. The re-introduction of an adapted system to improve livestock production in the dry season and to enhance ecological stability is proposed.

Abstract: The Eastern Cape Subtropical Thicket (ECST) forms the transition between forest, semiarid karroid shrublands, and grassland in the Eastern Cape, South Africa. Undegraded ECST forms an impenetrable, spiny thicket up to 3 m high consisting of a wealth of growth forms, including evergreen plants, succulent and deciduous shrubs, lianas, grasses, and geophytes. The thicket dynamics are not well understood, but elephants may have been important browsers and patch disturbance agents. These semiarid thickets have been subjected to intensive grazing by domestic ungulates, which have largely replaced indigenous herbivores over the last 2 centuries. Overgrazing has extensively degraded vegetation, resulting in the loss of phytomass and plant species and the replacement of perennials by annuals. Coupled with these changes are alterations of soil structure and secondary productivity. This rangeland degradation has largely been attributed to pastoralism with domestic herbivores. The impact of indigenous herbivores differs in scale, intensity, and nature from that of domestic ungulates. Further degradation of the ECST may be limited by alternative management strategies, including the use of wildlife for meat production and ecotourism. Producing meat from wildlife earns less income than from domestic herbivores but is ecologically sustainable. The financial benefits of game use can be improved by developing expertise, technology, and marketing. Ecotourism is not well developed in the Eastern Cape although the Addo Elephant National Park is a financial success and provides considerable employment benefits within an ecologically sustainable system. The density of black rhinoceros and elephant in these thickets is among the highest in Africa, with high population growth and the lowest poaching risk. The financial and ecological viability of ecotourism and the conservation status of these two species warrant expanding ecotourism in the Eastern Cape, thereby reducing the probability of further degradation of ECST.

Abstract: Using standard census data, an index is developed expressing the contribution of range livestock systems to total county incomes. This index is then applied to results of a simulation of the effects of global warming on the productivity of cow-calf range livestock systems in the western USA. Estimates of declining range-based incomes in a southern tier of states coupled with increasing productivity in the middle and northern Great Plains, the inter-mountain Rockies and the Pacific Northwest suggest that significant shifts could occur in the location of feeder calf production if these climate changes occur.

Abstract: River salination due to dryland agriculture was studied between 1985 and 1986 in the 150-km2 large catchment of the Sandspruit river, a tributary of the Berg river in the semi-arid Western Cape Province of South Africa. The study included investigations of all major water bodies within the catchment and aimed to identify and quantify their salinity dynamics. The following results can be presented: 1) The mean annual rainfall is about 400 mm, and has a salt concentration from the ocean of 37 mg/L. 2) Groundwater recharge of the shale aquifer only occurred during the winter season when salts from the soil and the weathered shale were transported into the groundwater. 3) The main salt output occurred between July and September and is associated with floods. A linear regression model was established to estimate salt output from the catchment by using the water level measured at the gauging station. 4) The total salt output in 1986 was 8052 Mg (tons), but bulk atmospheric deposition accounted only for a third of this amount. The remainder salt output was delivered by groundwater and interflow from the weathered shale and the soils within the catchment.

Abstract: The Grasshopper Integrated Pest Management Project (GHIPM) is a $15 million project initiated in 1986 to identify, develop, and implement rangeland grasshopper management tactics within the framework of Integrated Pest Management (IPM) in the Western United States. Computer simulation has been used to fulfill many original objectives for GHIPM. For example, models have been developed and/or used to simulate grasshopper population dynamics, forage growth and destruction, and ranch economics. These models also have been used to structure and deliver knowledge to land managers who make decisions about grasshopper control. In addition, another group of computer simulation studies were developed to probe at basic mechanisms and understanding of rangeland grasshopper ecology. For example, an object-oriented simulation is being developed that can represent any number of unique grasshopper cohorts for specific species, life stages, and disease status. Soil temperature and moisture are also being simulated to support a grasshopper egg hatch model. All of these research models were designed for basic science with a focus on improving management of rangeland grasshoppers.

Abstract: Atriplex nummularia, Atriplex canescens and Cassia sturtii were planted in thenorthern Negev in 1984 in six replicates at five planting densities: 625, 1111, 2500, 4444 and 10,000 shrubs ha-1 . They were left undisturbed for 3 years until July 1987, following which they were summer browsed by sheep and goats until the shrubs were completely defoliated, and summer browsed again 1988, 1990 and 1991. A. nummularia was superior to the other species. It had the highest total and edible biomass after 3 years of undisturbed growth and the best absolute recovery after browsing. Neither of the Atriplex species recovered the initial standing biomass recorded before browsing in 1987, and there was a serious decline in the regrowth of leaf biomass. Cassia sturtii recovered its initial standing biomass at the two highest planting densities but failed to do so at the other densities.

Abstract: In northern intertropical Africa, many geological data have documented several abrupt climatic fluctuations taking place during the time of the last deglaciation. One of them is an aridity event, generally placed in the interval 11,000-10,000 BP, and synchronous with the Younger Dryas cold episode of the temperate regions, that has been explained by the influence of the Atlantic Ocean circulation on global climate. In this paper we present high resolution (50 to 150 years) studies of organic matter and pollen undertaken on a new core from the Rusaka peat bog (3°26' South, 29°37' East, 2070 m altitude), dated by the conventional (l2 dates) and the AMS methods (18 dates obtained on bulk sediment and macroremains). Although the sediment at the bottom of the core was deposited during the last glacial period prior to 21,000 BP, the dating provides a reliable chronology for the last 12,000 BP only. Several vegetational changes are documented in the interval 12,000-9000 BP, but their chronological placement can only be achieved with a few years of uncertainties. A great dispersion of AMS dates is attributed to contamination by charcoal dated between 11,700 and 11,500 BP, and to a possible age plateau at ca. 10,000 BP. Therefore the results are preferably presented versus depth to keep synchronism in the stratigraphic placement of the successive events. At Rusaka, increase in carbon storage, C/N ratio for terrestrial plants, and tree cover began at ca. 12,000 BP, soon after the swamp had been established. This date is in good agreement with a major increased hydrological balance well-documented throughout the intertropical region. The forest installation is progressive, rather complex and seen as a two step process. The first forest phase (11,700 BP to 10,600 BP) is dominated by Hagenia, a montane taxon, in good correspondance with previous records from other authors in East African mountains. The second forest regeneration took place post 10.000 BP, after a clearly reversed trend of tree cover from 10,600 to 10,000 BP, ending with a short episode of minimum trees lasting no more than about 200 years. But there is no indication of cooling whatsoever, and the opening of the forest is better explained by increased aridity, rather than normal pattern of forest succession. This will remain a controversal interpretation among palynologists until high resolution pollen data can be obtained for the 13,000 BP and earlier period. Nevertheless, the timing of the arid episode at Rusaka is in good agreement with other evidence mentioned from highland and lowland pollen data. A detailed comparison with 25 available pollen diagrams is limited by poor or inconsistent dating or low resolution of the pollen data. Nevertheless pollen from four of them document an arid event in good agreement with its timing at Rusaka and high resolution isotopic results from two sites in equatorial lowlands and from the Sahel. This work shows that the arid Younger Dryas occurred at the same time both in lowlands and highlands, and therefore was most likely a precipitation signal rather than a response to temperature decrease.

Abstract: Initiatives to link rural development and species conservation, known as integrated conservation-development projects (ICDPs), have been launched with considerable fanfare and funding around the world. Although ICDPs hold appeal as broader ecological efforts than the conservation and development strategies that preceded them, they also suffer conceptual flaws that may limit their appropriateness and potential sustainability, at least when applied to the protection of large African mammals.

Abstract: This paper describes methods to couple the reflectance-resistance model developed in Paper I with the normalized difference vegetation index (NDVI) data from the advanced very high resolution radiometer (A VHRR) on satellites over the eastern United States. A land use data set was also employed to determine appropriate model parameters suitable for describing differences in characteristics of light scattering and leaf resistance among different plant canopies, especially between forests and short canopies (crop and grass, etc.). As a case study, the biweekly averaged NDVI data for a year with normal precipitation (1987) and a drought year (1988) were selected for analysis to maximize differences in vegetative conditions and canopy conductance for pollutant transfer. The satellite-derived NDVI over the region had a much lower value in summer 1988 than in summer 1987. The depression was especially large for cultivated areas and rangelands, but it was much less significant for forested regions. The NDVI data were incorporated into the model to calculate the regional distribution of canopy conductances for pollutant transfer to the earth's surface.

Abstract: Interspecies differences in voluntary intake and fractional rates of passage and degradation of digesta in goats and sheep grazing on semiarid lands in the south-east of Spain were studied following a 2 (animal species) × 3 (period of the year, i.e., phenological state) × 3 (feed supplementation) factorial design. The animals were on a semi-extensive management system and were fed, from early spring to late summer, pasture unsupplemented or supplemented (88 g DM/animal/d) with barley grain or with barley grain plus urea. The voluntary intake met the energy (ME) requirements for maintenance in goats but not in sheep. The voluntary intake of organic matter of pasture (POMI) was significantly (P < 0.05) affected by the phenological state of the pasture and significantly reduced by supplementation (P < 0.05). The total organic matter intake (TOMI) remained unchanged. Goats had significantly (P < 0.05) faster fractional rates of passage of digesta from the rumen than sheep. Neither the phenological state nor the supplementation affected the particle outflow rate. The fractional rate of degradation of both dry matter (DM) and crude protein (CP) seemed to be slightly higher in goats than in sheep, whereas it was unaffected by supplementation. Effective degradability (Ed) of DM both in goats and sheep decreased from early spring to late summer.

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Abstract: Over the years a number of vegetation management systems has been evaluated and recommended. The Potch system is also a management system which was specifically developed for semi-arid regions where the rainfall is unreliable. The influence of this system on vegetation condition, was evaluated over four seasons. From the results it appeared that the vegetation condition in all paddocks, barring one, improved from commencement of the trial under this system.

Abstract: Grass cover distribution in the northern section of the Namib-Naukluft Park inNamibia was estimated following the rain seasons of 1989, 1990 and 1991. High cover of grass occurred particularly in the vicinity of rocky outcrops and in drainage lines. Grass distribution is related to the gradient of increasing rainfall from West to East, the soil moisture pattern influenced by runoff and the distribution of seeds in and above the soil surface. The spatial distribution of grass patches showed a certain predictability, thus providing baseline data for range management.

Abstract: Trophic structure and composition are examined in two important biotic records, one the Paleogene of Wyoming and Montana, and the other from the Neogene of Pakistan. The Paleogene sequence spans approximately 10 million years and encompasses four North American Land Mammal Ages (Torrejonian, Tiffanian, Clarkforkian, and Wasatchian). The Neogene sequence spans approximately 17 m.y. and includes most of the Miocene and Pliocene with the best documented interval spanning from 16 to 7 Ma. Five basic trophic categories (primary consumers: herbivores, frugivores, omnivores: secondary consumers: insectivores, carnivores) are recognized for Paleogene and Neogene mammals based on tooth morphology, body size, and analogy with modern mammalian groups. The Paleogene mammalian biota is characterized as one in which both trophic structure and taxonomic composition change through the history of the record. The Neogene mammalian biota maintains a relatively consistent trophic structure through most of the record, although taxonomic composition changes substantially through time. Based on comparisons of trophic structure from the Paleogene and Neogene records with that of selected modern mammalian faunas, Paleogene habitats fluctuated between closed, humid forests and more open, drier woodlands. Neogene trophic structure indicates that savanna woodlands were the typical habitat present through most of the sequence. Only after 7 Ma did these woodlands give way to more open grasslands in Pakistan.

Abstract: Economic returns from improved technology for cow-calf, sheep, and goat production at area, farm, and hectare levels were evaluated. Proposed additional investments and cash costs were established comparing current to desirable situations. Production efficiency that could be reached through the proposed technological changes were established from research results in Mendoza and other areas. Net present value (NPV) for each activity was determined. A break-even analysis was carried out to determine activity's sensitivity to varying investments, costs, and product prices. NPV was positive for the three livestock species at all levels. Cow-calf and goat production were the most sensitive to increasing investments and cash costs, respectively. The probability of reaching product prices that would yield negative returns was generally low.

Abstract: Savanna landscapes in the dry communal areas of southern Zimbabwe are highlyspatially heterogeneous. This year-long study explores the responses of cattle to variation in the availability of fodder in different habitat types situated in clay and sandy soil savanna zones. Low land habitat types of relatively small overall area, such as drainage lines, riverine strips and dambos, have the highest availability of herbaceous biomass per unit area in the dry season and in dry years in both savanna types. Browse is available in all habitats, but particularly where there is a low understorey of shrub vegetation. Cattle feeding patterns respond to this heterogeneity of available fodder at the landscape level. Studies of foraging behaviour demonstrate that cattle show high levels of seasonal feeding preference for particular parts of the landscape, notably low lying [`]key resource' habitat types with high levels of available herbaceous biomass. Cattle foraging strategies (through free grazing or herding) involve both concentration on these key resource areas and switching between a variety of habitats and forage sources, including browse. These strategies differ both between savanna types and seasons of the year. Planning for livestock management in the dry areas of Zimbabwe should take into account the importance of landscape heterogeneity in the design of grazing interventions. Policies also need to ensure that flexible movement responses to a highly spatially and temporally variable resource base are possible.

Abstract: As sustainable crop management systems are developed, an assessement of the effects of these practices on the soil microflora is essential to ensure maximum productivity. A 3-year field study was established to determine the effects of crop residue burning, no-till management and four preemergence herbicides on soil microorganisms. Numbers of actinomycetes, algae, bacteria, fungi and nitrifiers were evaluated during the soybean [Glycine max (L.) Merrill] growing season in a wheat (Triticum aestivum L.)-soybean double-cropping system. Residue burning and tillage had no effect on numbers of bacteria and nitrifiers. Non-disturbed (non-burned or no-till) plots had greater numbers of actinomycetes, algae and fungi 7 days after herbicide application each year, but the increases generally did not persist through the season. Herbicide application had no effect on microbial numbers. This is particularly important with recent increased emphasis on protection of soil and water resources from pesticide contamination. As new management systems are developed, their effects on biological properties must be carefully assessed, since the soil microflora play such a vital role.

Abstract: The concept of desertification has recently been re-evaluated with two major outcomes. Firstly, the term itself has been reviewed, with most authors concluding that the emotive implications of [`]desertification' (i.e. advancing deserts per se) are inappropriate in many cases and that the general term [`]dryland degradation' is a more accurate description of reality. Secondly, it has been argued that the extent, nature and apparent irreversibility of the process has been over-estimated and that degradation in some areas may only be temporary, consequent upon an unfavourable combination of climatic and anthropogenic factors. In southern Africa, a reassessment of the concept of desertification is long overdue; the traditional view has prevailed to the extent that grazing management policy in the semi-arid parts of the sub-continent is essentially founded on the premise that widespread, irreversible degradation has occurred in post-colonial times. In this paper, we examine this position in the light of the available published evidence. It is suggested that some changes in the vegetation of the semi-arid Karoo occurred prior to the onset of European colonization, a function of phases of climatic aridification and the impacts of both Kho San hunter-gatherers and Khoi Khoi herders. This argument contextualizes the alleged historical impacts, which are shown to be interpreted along the lines of three competing models accounting for the pattern of assumed vegetation change. The literature concerning Karoo degradation is reviewed and it is revealed that much of the research throws little light on which, if any, of the three competing models most closely approximates reality. Instead, it becomes clear that the recognition of dryland degradation in the Karoo requires further investigation, and several possible approaches are presented by which the hypothesis of irreversible change may be tested and the pattern of vegetation change identified. It is concluded that a more systematic monitoring programme, including the investigation of vegetation and other environmental variables, should be instigated in South Africa.

Abstract: The basic reasons for the present unsatisfactory structure of agricultural R & D in Southern Africa and particularly in South Africa, are the focus of R & D on the commercial sector of agriculture, at the expense of the non-commercial sector, top-down policy decision-making and the institutional separation of research and extension. This has led to the generation of inappropriate technology and ineffective technology transfer particularly for rural or communal farmers. The solution to these problems is a restructuring of agricultural R & D in which R & D for commercial agriculture is privatised enabling all government resources for agricultural R & D to be devoted to the non-commercial sector, a reversal of top-down decision-making empowering stakeholders to take their own decisions, and by making agricultural development, including agricultural R & D, an integral part of rural development structures and decision-making.

Abstract: Current methods to estimate biomass as a basis for carrying capacity and secondary production include biomass measurements in the field, use of rainfall /biomass relations and simulation models. Each of the methods have their drawbacks. Collection of field data is laborious, rainfall /biomass relations lack precision and models, which simulate processes, are highly-demanding in input data, expertise and advanced equipment. An approach is presented to bridge the gap between those simulation models and the need for more accuracy in simple biomass estimates at less detailed scales. Transfer functions are developed using the results of a process-simulation model called SAHEL. The transfer functions allow estimation of the depth of wetting of the soil profile and percolation in relation to the water content at field capacity (pF 2.5). In comparison with simple rainfall-biomass relations, application of transfer functions allow more accuracy in estimating biomass production at a less detailed scale. With the transfer functions length of growing periods could be established more accurately, allowing for more precision in agro-ecological zoning methods.

Abstract: We begin by stressing that relevant and adequate information is an essential ingredient of efficient decision-making processes aimed at optimising the performance of livestock enterprises. Such decisions are universally made, so that though different approaches may be required, animal health and production monitoring (HPM) is as important in sub-Saharan Africa (SSA) as it is in livestock systems in other parts of the world. To set the scene for our discussion of HPM in SSA, we broadly describe the main African production systems in tabular form, categorised by ecological conditions, production goals and input and output relations within a broad fanning systems context. Subsequently, the scope and diversity of HPM in SSA is reviewed. This review reveals that in 2 decades of system monitoring, a wide variety of objectives have been tackled from broad system description and constraint diagnosis to more focused research to identify and quantify the impact of disease and other specific factors on the productivity of cattle and small ruminants. There have been many monitoring clients, ranging from national governments through aid agencies and the scientific community, to individual farmers. To serve these diverse clients and their objectives, a plethora of methods and data collection techniques have evolved, which are briefly reviewed. Methods are often system-specific. As examples, we discuss the specific monitoring needs of two contrasting production systems (pastoralists in the arid and semi-arid zones and smallholder dairy farmers in the highlands of East Africa) to indicate how monitoring has contributed to our understanding of these systems and how monitoring might be better targeted to satisfy future needs. The impact of HPM on the "state of the knowledge' of traditional African production systems are then summarised at two levels. The first includes specific health and productivity information gained while the second considers the more general lessons learned with respect to livestock enterprise functions and their impact on human welfare. Finally, future monitoring needs are discussed relative to changes in African livestock systems. It is anticipated that further specialisation and intensification of livestock enterprises will require decision-support systems, many of which already exist in the developed world and could be adapted to SSA.

Abstract: A general model of rotational grazing is constructed where in each of P consecutive time periods a mob of animals grazes one of m paddocks. The optimal grazing sequence is that which maximises their total herbage intake and satisfies the physical constraints of the grazing system. The total herbage intake is compared for four grazing strategies: continuous grazing, strict cyclic rotation, greedy rotation and optimal rotation. A branch-and-bound algorithm is used to find the global optimum strategy. A 100 ha system is simulated carrying 300-400 dairy cows for 60 days in late winter and early spring with a range of subdivisions and grazing durations to ascertain the effectiveness of the different strategies in maximising intake. It is shown that (1) continuous grazing maximises intake when pasture growth is in surplus to animal requirements, (2) that animals' herbage intake under rotational grazing is likely to be poor unless the rate of rotation is carefully synchronised to the pasture growth rate, (3) that grazing management makes little difference to productivity in comparison to stocking rate and average initial pasture, (4) that there is no reason to expect subdivision of land to increase productivity unless reasons such as pasture trampling on wet soil mitigate against long grazing durations. Greedy rotational grazing is found to increase herbage intake on multipaddock systems with an initially inhomogeneous distribution of pasture.

Abstract: In any heterogeneous environment, classical methods used to estimate daily DMI and daily diets of grazing animals are difficult to implement. To investigate the grazing behavior of a goat and a llama, feeding on the garrigue in their respective flock, we therefore used a technique based on direct observation of biting. The observations were carried out in spring and early summer, and under decreasing vegetation availability conditions for each season. In high vegetation availability conditions, daily DMI at pasture was 44 g DM/kg BW0.75 (6th day in paddock: d6) and 76 g DM/kg BW0.75 (d3) for the goat vs. 42 g DM/kg BW0.75 (d3) and 53 g DM/kg BW0.75 (d3) for the llama during spring and summer, respectively. The goat's diet (% DMI) was mainly composed of browse (89 to 99%), whereas the llama's consisted of grass (55 to 78%). The choices made by the two animals were confirmed by the evolution of the consumption levels of the forage species in each paddock. As vegetation availability decreased, the daily DMI of the two animals fell and their requirements were no longer satisfied. In spite of shifts in daily diets, grass DM always accounted for at least 35% of the llama's diet but never exceeded this value for the goat. Diurnal variations were observed in the diets of both animals, which may reveal differences in grazing strategies: the goat seemed to be selective first, whereas the llama tried to eat quickly first. The morphological structure of browse species influenced instantaneous intake rates in the two animals. Because both animals occasionally focused on plant species that permit high intake rates, the curve of cumulative DMI within a meal vs. time bounced from time to time, and could not be adjusted to a mono-exponential model as with penned animals. The technique we used thus not only provides consistent data on the daily intake and daily diets of goats and llamas grazing a shrubby, heterogeneous environment but also information on the process of diet selection itself along the grazing journey.

Abstract: Strongly developed vegetation banding in desert chenopod shrubland occurs on hillslopes having gradients of as little as 0·5 degrees and displays a stepped microrelief of about 10 cm. Surface runoff is shed from the bare surfaces in rainstorms of as little as 4-5 mm, and infiltrates readily within the vegetated bands. The banding thus functions as an efficient system for water redistribution, the landscape being divided into multiple bare runoff (water source) and vegetated runon (water sink) zones. Patterns of stone distribution across a study hillslope suggest that the vegetation banding is at least Holocene in age. The patterned shrublands thus represent an enduring component of this arid rangeland environment, and one whose unusual microhydrology should be preserved by informed management.

Abstract: The relationships between certain chemical components of fertilized and unfertilized Cymbopogon-Themeda summer veld herbage, herbage intake by lactating cows and steers and daily gain of pre-weaned calves or steers, were determined in the summer rainfall area of the Republic of South Africa. The herbage was represented by a wide range of grass species with, according to the literature, different palatabilities. Negative correlations that were found for the relationships of concentrations of some of the amino acids and sulphur (S) content with crude protein (CP) content of the veld herbage, indicate that supplementation of high quality summer veld herbage with ruminally undegraded histidine, valine, isoleucine and S-containing amino acids may be beneficial for fast growing ruminants. The correlation between digestible dry matter intake by the grazing steers (DDMIW), expressed in g per kg W0.75 day-1, and the average daily gain (ADG) of the steers (g day-1), was highly significant (P 60; 0.01; r = 0.87). The relationship between DDMIW by lactating cows and the ADG of their calves was not significant (P 62; 0.05; r = 0.44). Highly significant (P 60; 0.01) correlations were found between ADG of steers and respectively CP content and acid detergent fibre (ADF) content of the pasture. (r = 0.95; r = -0.86). The relationship between neutral detergent fibre (NDF) content of the herbage and the ADG of the steers was significant (P 60; 0.05; r = -0.68). The CP content of the herbage that the cows grazed was correlated highly significantly (P 60; 0.01; r = 0.69) with the ADG of the unweaned calves. No significant relationships could be found between ADG of the calves and the ADF and NDF contents respectively of the pasture that their mothers grazed (P 62; 0.05; r = -0.36 and r = -0.21). Under the conditions described, some of these relationships can be used reliably for the prediction of potential animal growth on summer veld herbage.

Abstract: Palaeoenvironmental records which include the interval between 11,000 and 10,000 BP have been investigated for 15 sites in South Africa. Less than half of them are well dated and have a resolution adequate for elucidating climatic conditions during the time of the Younger Dryas. A sea surface temperature record from a marine mollusc sequence provides the only unequivocal evidence of cooling during this time. None of the palynological sequences from the interior of the subcontinent suggest consistent deviations in temperature or moisture attributable to a Younger Dryas equivalent. Based on the available evidence, therefore, it seems that if global Younger Dryas conditions influenced the climate of South Africa, the effect was too small to register a spatially consistent pattern in the pollen sequences of the interior of the country.

Abstract: Striga gesnerioides, a plant parasitic phanerogam, is a known constraint to cowpea production in the sahelian and northern guinea savanna zones of West and Central Africa. A survey was done in 1990 across six countries to collect data on soil types, cowpea phenotype, and cropping systems with relation to incidence and severity of striga on cowpea. Of the 153 fields visited, 40% were infested with S. gesnerioides. Generally, the severity of the parasitic weed was light, with a mean rating of 1.5 on a scale of 1 to 5. A high correlation was found between incidence of striga and the amount of sand in the soil. Of the 153 sites only 27 had no sand in the soil. Of those 27, only three (11%) had some S. gesnerioides compared with 50% on sandy soils. A database was compiled on cowpea phenotypes and the cropping systems in which they are used. Severity of striga infestation per cowpea plant decreased somewhat from east to west, though it is unclear whether this was a function of cowpea genotype or striga pathotype. The predominant cropping systems where striga infestation occurred were sole cowpea, intercrop with millet, and with sorghum. Fields in rotation with cotton, or intercropped with vegetables and legumes were always striga-free.

Abstract: Changes in vegetation composition and land condition that occur in response to grazing in natural grassland systems may alter plant and animal production, but the relationships are poorly understood. This study examined the effect of a change in land condition on herbage and animal production in two tropical tallgrass regions of northern Australia. The contrasting land condition classes, selected along fence-lines separating paddocks with different grazing histories, were defined as: State I. Dominated by palatable tussock perennial grasses; State II. Less palatable tussock perennial grasses, annual grasses and forbs as the major species. State II produced considerably less herbage than State I. Cattle grazed the two land condition classes to achieve comparable utilisation rates over the range 5-60% utilisation in a number of 8 week seasonal grazing periods over 2 years. At both Charters Towers and Katherine, steer growth was greater in State II than in State I, most rapid in the early wet season and least in the late dry season, and greatest at low utilisation rates. Differences in liveweight gain due to land condition class were greatest at the lightest levels of utilisation. Owing to the differences in pasture productivity between land condition classes, comparable levels of utilisation were achieved by imposing contrasting stocking rates. Steer growth was higher from State II land at low stocking rates while at high stocking rates State I produced better liveweight gains. The greater liveweight gain by steers grazing State II at low stocking rates can be explained by better diet quality which was reflected in higher levels of faecal nitrogen. The proportion of C3 species (forbs, native legumes, shrubs, eucalypt leaves) in the diet of animals grazing State II vegetation was about twice that of steers in State I. These C3 species were considerably higher in nitrogen than the C4 grasses at the end of the wet season. At high stocking rates, animals in the State II treatment had less available feed on offer, resulting in lower liveweight gains compared with State I. The likelihood of further deleterious changes to land condition and productivity occurring should management attempt to maximise production from State II land are high.

Abstract: To test the effects of shade on understorey herbaceous productivity in tropical savannas, water relations of important grass species that either grow primarily under tree crowns or in open grasslands were studied in Tsavo National Park, Kenya. The relationship of stomatal conductance to light intensity was investigated under well-watered conditions; and the relationship of stomatal conductance to light intensity, vapor pressure deficit, and leaf water potential was studied during a period of decreasing soil moisture. Below-crown species were more responsive to reductions in light intensity than open-grassland species, with stomatal conductance of below-crown species declining linearly with reductions in light intensity. Conductance of open-grassland species was relatively unchanged at all except the lowest light levels. Below-crown species therefore reduced their water loss when shaded, conserving soil water for later growth. Open-grassland species appeared to be more efficient than below-crown species at extracting water from dry soils under full-sun conditions.

Abstract: Global warming is likely to alter natural and agricultural ecosystems, probably causing relocation of some of the major crop-producing regions, and a change in the geographic distribution of rangelands and forests. More important than the direct effect of the temperature increase, would be any alteration in the rainfall pattern in those many regions where rainfall limits crop production. The purpose of this work, which focuses on a traditional, semi-arid, cattle-cereal crop production area in the Central Pampas of Argentina, was to study structural and functional changes in this agroecosystem in response to the measured climate variability over a 30 year period, 1960-1990. Using long-term data, correlation analysis was used to estimate the degree of association between changes in the land use pattern on the one hand, and changes in rainfall, grain price and crop yield on the other hand. Crop yield was the result of an interaction between climatic and technological factors. The analysis also linked climate variability with key agroecological factors such as hydrology, energy flow, and soil nitrogen balance. The results showed that changes in land use were highly correlated with the yield of crops, less correlated with rainfall, and poorly associated with crop grain prices. A positive correlation between the annual rainfall and the relative increase of the crop area was found for all districts analyzed. This change could largely explain the increased energy flow as well as nitrogen loss in the agroecosystem studied. Consequently, land use strategies should be considered with caution, especially during favorable climatic period in semi-arid environments. The same conditions that favor grain harvesting in these environments, may also set at risk the sustainability of a long-term, low-input agriculture.

Abstract: Sap flow gauges were used to measure transpiration from the shrub component of a 7-year-old agricultural fallow in Niger, West Africa. The aim of the study was to provide the data necessary to develop and validate multi-source models of evaporation from semi-arid land surfaces by measuring transpiration from a single component of the vegetation. The vegetation at the study site was a type of savannah, consisting of scattered shrubs, with an understorey of annual grasses and herbs. Sap flow measurements were restricted to Guiera senegalensis J.F. Gmel., the dominant shrub species. Sap flows were measured throughout the wet season of 1990 (June-September), using sap flow gauges operating on a constant power heat balance principle. Sap flow rates measured in individual stems were strongly related to leaf area and net radiation. Strong positive correlations were observed between the hourly mean flow rates measured in different stems. Daily transpiration, T, averaged across a 0.25 ha sample plot was compared with daily total evaporation (measured by eddy correlation), E. T was calculated by scaling up from sap flow measurements in a sample of stems to the whole plot by using the frequency distribution of stem diameter in the plot, and assuming that sap flow in each stem was proportional to its basal cross-sectional area. E varied from about 2 mm day-1 at the start of the wet season to 4-6 mm day-1 during August and September, when maximum leaf area and soil profile water content were observed. E, a measure of evaporation from all plant and soil sources, always exceeded T. At the end of two dry periods in June and July, when soil evaporation and transpiration from the herb understorey probably totalled about 0.5 mm day-1, E was only 0.7-0.9 mm day-1 greater than T, suggesting that the scaling procedure adopted gave reasonable estimates of bush transpiration. Over the whole wet season, transpiration from G. senegalensis accounted for 35% of the total wet season rainfall of 454 mm.

Abstract: The impact of ecological factors such as changes in rainfall could lead to large compositional changes in the diverse indigenous flora of southern Africa. A study was therefore initiated to determine the influence of rainfall conditions on species composition changes, which could serve as a basis for determining the long term influence of rainfall increase (e.g. cloud stimulation) and rainfall decrease (e.g. long term droughts). Certain species were found to occur in all the rainfall zones while others were limited to either the high or the low rainfall area. The reaction of species on the rainfall gradient also differs in vegetation representing different degradation stadia. The predictions of the reactions of key species on rainfall decrease or increase are of special importance for the eventual determination of grazing capacity.

Abstract: Soil moisture can be significantly increased with microcatchments that have 4 to 5 m long water catchment aprons and 7 to 15% slope gradients. The increase was by 59% (from 10·9 to 17·3% vol/vol) from the surface to 15 cm depth, by 63% (from 11·5 to 18·8% vol/vol) from 15 to 30 cm depth, and by 80% (from 11·3 to 20·3% vol/vol) from 30 to 45 cm depth. Increases in soil moisture were found in both the late summer and the late winter season when the highest precipitation is received. There are some year-to-year differences depending on how much precipitation is received each year. Rill erosion on the aprons increased with apron length and gradient. Erosion volumes were quite low (14·9 1 to 26·3 1) considering the amount of area of an apron (120 and 150 m2).

Abstract: The relationship between cover density and soil loss under simulated rainstorms of 30 and 60-minute duration and 33 mm h-1 intensity was investigated. Soil loss varied from 0-7.3 g m-2 for cover of 55-95% and reached maximum values of over 80.0 g m-2 (30-minute storms) and 140.0 g m-2 (60-minute storms) for cover of 25% or less. A critical threshold occurred at 55% cover below which erosion rates rapidly increased to over 15.0 g m-2 (30-minute storms) and 30.0 g m-2 (60-minute storms) during single rainstorm events. Storm duration and frequency were important determinants of erosion over more prolonged time periods. Total calculated soil loss for an 18-year period under 55% cover for frequent 30-minute storms (frequency: 3-4 times a year) was 6 times that for infrequent 60-minute storms (5-year return period).

Abstract: A mass balance approach for nitrogen has been applied to Northern Ireland grassland. The nitrogen flux through grazing animals based on utilized metabolizable energy of forage (UME) was employed in regression analysis of historical data to give a measure of both fertilizer utilization and a background contribution which was equated with the net contribution of soil organic N to the inorganic N pool. This rate (52·0 kg N ha-1) is balanced by the input of plant dead matter and cattle excreta as dung leading to the conclusion that there is no net organic N accumulation in Northern Ireland grassland. Consideration of all known inputs and outputs of N suggests that 78% of the inputs of N are lost to the atmosphere by either denitrification, ammonia volatilization or unknown loss processes. Of the 22% remaining balance of N, only 9% is available as animal products and the remaining 13% is lost as leachate. There does appear to be scope for modifying present intensive systems to take into account the accumulations of N in the inorganic pool where animal products (14 kg N ha-1 represent only 5% of the available N pool (259 kg N ha-1).

Abstract: Ground investigations of rangeland use and condition are restricted by resource and travel limitations. Management of these vast, multiuser resources could be enhanced by information from remote sensing. Microwave radar imagery is becoming readily available and its all weather capability provides greater reliability than visible-infrared (VIR) sensors. The objective of this study was to evaluate a combination of radar and visible-infrared sensors as tools in rangeland monitoring. Data from Landsat Thematic Mapper (TM) and SPOT VIR sensors were compared with data from airborne and ERS-1 synthetic aperture radar (SAR) sensors to determine similarities and contrasts with a view to exploiting any synergism. The study site was the Agriculture and Agri-Food Canada Onefour Research Substation in southeastern Alberta. The TM and SPOT VIR sensor bands were highly correlated. The radar sensors were correlated with each other to a lesser degree. Correlations between VIR and radar were not high. Vegetation type influenced VIR reflectance and radar backscatter. Russian wildrye pastures had high radar backscatter as well as high VIR reflectance. Native range had low VIR reflectance and low radar backscatter. Crested wheatgrass pastures had low VIR reflectance and high radar backscatter. Other features, such as exposed sedimentary Cretaceous softrock, had high values for both sensor groups, while intermittent water bodies or shallow depressions characterized by high clay content and strong microtopography had high radar backscatter but low VIR reflectance. More information can be obtained from the combination of both types of sensor than from either alone.

Abstract: The development and application of an expert system is described for screening alien woody plants for their invasive potential in South African fynbos. The system is proposed for use by potential introducers to demonstrate low invasive risk before importing woody alien species for cultivation. Rules for the system were derived from empirical evidence by quantifying invasion windows and barriers that have limited the set of widespread woody invaders (trees and shrubs) in fynbos to fewer than 20, out of several hundred introduced species. The system first compares broad-scale environmental conditions (climate and soil) between the home environment of a species and fynbos. Features of the plant in its home environment (basic life history traits, population characteristics, regeneration biology, habitat preferences) are then assessed. Finally, an assessment is made of life history adaptations to the prevailing fire regime in fynbos (juvenile period, fire-survival capacity of adult plants, seed bank longevity). The reasoning is explicit and the steps leading to a conclusion (high risk/low risk) can be retraced. Besides the obvious application in identifying species with a high risk of invading, the system has considerable potential for modelling, and for teaching the concepts of biological invasions. The rules provide an explicit conceptualization of invasion processes in fynbos and identify multiple paths to invasive success (not all of which have been realized yet). The system can therefore be used in planning control operations (for optimal allocation of control effort to critical stages in invasion), and for predicting the outcome of changes (e.g. in fire frequency) on the dimensions of invasion windows, and for assessing what changes are needed to prevent or reduce the extent of invasion by a given taxon. Application of the system is demonstrated on Pinus and Banksia taxa and a selection of species from Californian chaparral.

Abstract: Biomass production of different ecotypes within three ecological importantgrass species was determined during cultivation under uniform environmental conditions. Results obtained clearly indicate that ecotypes of these species exhibit a significant degree of variation with regard to biomass production. Furthermore, indications from this investigation are that no correlation exists between production ability of a species and long-term average rainfall, and the effect of both genetic and environmental factors on the production ability of a species determines the eventual biomass production of a species. Biomass production represents one of various ecologically important characteristics to be used in conjunction with other ecological characters to construct a usable, special purpose classification system. This system will assist rangeland ecologists in identifying functional ecotypes within grass species, thus facilitating the understanding and interpretation of vegetation dynamic models and rangeland condition assessments.

Abstract: The Integrated System for Plant Dynamics (ISPD) is a comprehensive system in which new and existing data and knowledge are quantitatively or qualitatively used as a basis for range condition and grazing capacity assessments and for denning appropriate management options to maintain or improve the condition and capability of the range. This study was carried out to investigate the degree to which the qualitative approach in ISPD can be implemented, and to determine the amount and availability of data and expert knowledge in a specific area for the purpose of constructing a database in ISPD. Large quantities of information were available for the construction of vegetation condition and grazing capacity models for direct implementation in the grazing industry. The results generated by the models corresponded to the proposed grazing capacity values for the study area. The models furthermore enable any user to assess rapidly and accurately the range condition and grazing capacity for any vegetation unit in any stage of degradation.

Abstract: Cows are important agents of geomorphological change. On the uplands, heavy grazing compacts the soil, reduces infiltration, increases runoff, and increases erosion and sediment yield. However, light and moderate grazing have effects that are much less significant. In riparian zones, grazing decreases erosional resistance by reducing vegetation and exposing more vulnerable substrate. Trampling directly erodes banks, thus increasing turbulence and consequent erosion. Future studies should be framed within the hydroclimatological, edaphic and geomorphological dimensions of the areas being studied so that controlling variables may be more readily isolated. We believe that both empirical studies and deterministic modeling can provide insights as to the effects of grazing on geomorphology.

Abstract: The percentage of phenolic containing cells (PCC) and total phenolics in the leaves of different ecotypes of three ecological important grass species were determined during cultivation under uniform environmental conditions. Results obtained clearly indicate that ecotypes of these species exhibit a significant degree of variation with regard to percentage PCC and total phenolics. Furthermore, no anti-herbivory function can be assigned to phenolic compounds in these species, as ecotypes with Decreaser-species ecological status (highly palatable) have higher levels of total phenolics, compared with other less palatable ecotypes with lower levels of total phenolics. Percentage PCC and total phenolics represent two of various ecological important characteristics to be used in conjunction with other ecological characters to construct a usable, special purpose classification system. This system will assist rangeland ecologists in identifying functional ecotypes within grass species, thus facilitating the understanding and interpretation of vegetation dynamic models and rangeland condition assessments.

Abstract: This paper evaluates research on herbaceous tropical forage legumes in sub-Saharan Africa and offers two alternative explanations for the lack of adoption of adapted species. There is a considerable volume of literature from sub-Saharan Africa on the evaluation, chemical composition, fertiliser requirements, persistence, management and use of forage legumes. Most legumes tested are exotic and emphasis has been placed mainly on Australian species and cultivars of Stylosanthes, Centrosema, Desmodium, Lablab and Macroptilium. Research programmes have been characterised by cycles of introduction and re-introduction of legumes, and most of the screening has been observational or conducted under cutting on-station. Relatively few accessions of a given species have been tested at any one time and, in total, represent only a small proportion of the collections held in the major forage gene banks. Ignorance of the literature and a failure in communication between forage scientists, even within countries, have resulted in costly duplication of effort. Despite the potential benefits of forage legumes and the availability of species adapted to a wide range of environments, actual use in the livestock sector has been limited, with the exception of dairy production systems in highland areas

Abstract: Densities of large herbivores within distance annuli around drinking troughsin the Kruger National Park were determined by means of aerial counts. A relationship between herbivore use intensity and distance from drinking troughs was tested for and modelled with the logistic curve. A significant negative relationship was found. High herbivore densities within 0·5 km of the troughs dropped off steeply to a more or less uniform density beyond the immediate vicinity of the water. This has major implications for the rangeland condition in the immediate vicinity of troughs.

Abstract: This work reports on a method using fuzzy membership functions to construct an aggregated interaction matrix in which the summation of variables is scaled according to the way rainfall and soil variables affect water availability to plants and hence influence rangeland productivity. Aggregation of the variables gives a comprehensive value which can be used to predict production. The model increases the predicability of production to 81% compared to models using rainfall alone and a multiplicative parametric one which give predictibilities of 61 and 76% respectively. The results showed that (1) the importance of rainfall in determining production was most important at lower rainfalls i.e. <350 mm; (2) soil texture and particularly slope were important through out the rainfall range (149-700 mm) investigated; and (3) soil depth was only important at the higher >350 mm rainfalls. The aggregated interaction matrix gives a measure of land productive capability.

Abstract: Remote sensing data from the NOAA-11 AVHRR satellite were collected over the USDA-Agricultural Research Service Walnut Gulch Experimental Watershed in southeastern Arizona during the MONSOON 90 field campaigns. An energy balance model which relies primarily on remotely sensed inputs was used to extrapolate evapotranspiration (ET) estimates from one location containing near-surface meteorological data to other areas in the basin. Satisfactory results were obtained under a wide range of environmental conditions. However, the ET values are essentially instantaneous and therefore do not necessarily provide reliable estimates of daytime or daily ET fluxes required for many hydrological and resource management applications. An operational technique was developed to extrapolate one time of day ET estimates to daytime averages using the evaporative fraction concept and empirical methods for converting midday available energy to daytime average values. Model derived daytime average ET fluxes were in reasonable agreement with local ground-based measurements. The technique also was used to estimate daily ET at the basin scale.

Abstract: The high elevation shola-grassland vegetation types of the Western Ghats apparently remained in a stable equilibrium for many decades, implying that both vegetational types are highly developed and attained stability under the same climatic regime. Several authors considered these two distinct vegetation formations occurring in juxta-position, as climax formations. According to the Clementsian view of climatic climax, however, two distinctly different vegetation types cannot form climatic climaxes under the same regional climate. Possibly some edaphic or biotic factors are responsible for rendering stability to the grassland in this system. We tested the following three hypotheses in this context. (1) The physico-chemical properties of the soil such as depth, organic matter, nutrient status and water holding capacity are more favourable in the depressions than in the exposed surfaces, which in turn might be responsible for the development of the woody vegetation in the depressions. (2) The shola forests exhibits similar structural attributes and a higher floristic diversity compared with the medium and low elevation wet evergreen forests of the Western Ghats region. (3) The shola trees are characterized by a low regeneration capacity, thus probably making it a shrinking resource base. With its characteristic deep fertile soil and high moisture holding capacity, the shola forests may remain in the same steady climax state, provided anthropogenic and other catastrophic disturbances do not destroy them. The grasslands were, however, characterised by generally shallow soils, low water holding capacity and low site nutrient capital. Hence, the assumption that grasslands are steady state vegetations maintained by edaphic factors, holds good. Structural and floristic elements of the shola forest revealed a very high floristic richness and diversity, probably the highest in the Western Ghats region. A total of 942 stems of at least 10 cm girth at breast height (GBH) and belonging to 53 species were encountered in the 5000 m2 sampling area (basal area 48 m2 ha-1). Contrary to the widely held dogma that shola forest does not possess adequate regeneration potential, the present study reveals that under the forest cover, profuse regeneration of almost all of the overstorey species occur. However, regeneration characteristics were different along the margins and in open grasslands, possibly as a result of differences in ecological conditions.

Abstract: The carrying capacity concept was developed from animal ecology, and applied to rangeland management in order to assess sustainable livestock stocking rates. In it, long-term ecological sustainability was not a well developed criterion. Early applications of carrying capacity concepts to agricultural land-use have been much criticised, but recent developments provide useful insights. The proposed definition of human carrying capacity is [`]the maximum level of exploitation of a renewable resource, imposing limits on a specific type of land-use, that can be sustained without causing irreversible land degradation within a given area'. Hence, it is a property of the ecosystem only. The definition is primarily aimed at maintaining ecosystem productivity and resilience, i.e. avoiding irreversible land degradation. The human carrying capacity is based on the sustainable supply of natural resources and on resilience thresholds of the ecosystem. The level of maximum sustained exploitation of natural resources can also be expressed as maximum sustainable agricultural production levels, or sustainable population densities based on such production levels. Such applications require careful definitions of the assumptions and conditions involved. Absolute assessments of human carrying capacity have limited value only, particularly in semi-arid regions. However, comparing human carrying capacity levels with current exploitation rates of natural resources provides a useful framework to consider the ecological aspects of sustainable land-use.

Abstract: The relationships between daytime averages of net radiation (Rn,dt) and solar radiation (Rs,dt) were investigated with data collected from the MONSOON 90 experiment conducted in a semiarid rangeland basin. Just as in many previous studies, a regression between Rn,dt and Rs,dt was performed. In an attempt to account for more of the variability in Rn,dt, soil moisture was included as an additional independent variable. The behavior of the ratio Rn,dt/Rs,dt was also investigated. It was found that both temporal and spatial variations in this ratio were mainly correlated with surface shortwave albedo and soil moisture. Measurements of microwave brightness temperatures from an L-band (21 cm wavelength) radiometer, sensitive to near-surface soil moisture, also showed a high correlation with Rn,dt/Rs,dt. Estimates of Rs,dt from the GOES-7 satellite were used with the soil moisture data to compute Rn,dt. The results indicate that improved estimates of basin-scale Rn,dt for semiarid rangelands can be obtained by including soil moisture measurements. This may lead to more accurate regional-scale estimates of daily ET with operational methods using satellite-based measurements. Comparisons between Rn,dt and Rs,dt during the dry and wet seasons suggested that the variation in surface albedo and temperature are required in order to fully account for observed differences in equations predicting Rn,dt and the ratio Rn,dt/Rs,dt.

Abstract: This paper examines sensitivity of the Southern African subcontinent to climate change. It shows that the region has particularly sensitive water resources. Aridification of the subcontinent will affect a wide range of ecological processes, due to possible loss of important wetland habitats, reduced stream discharges as well as reduction in extent of shallow lakes. The primary response of terrestrial ecosystems will be a reduction in diversity as sub-humid biomes are replaced by more xeric types with fewer species. Rain-fed agricultural systems will be adversely affected and food security from such systems will be reduced. Other social impacts include impairment of hydroelectric generation, with the attendant economic effects. Populations of disease vectors will multiply more rapidly and the geographical distribution of such vectors could be extended to areas currently free of them. The higher ambient temperature will necessitate high standards of urban sanitation to avoid spread of fly-borne disease such as typhoid, enteritis and meningitis.

Abstract: Hierarchical classification based on proportional species composition of the grass layer was used to identify and classify semi-arid rangeland into range types. The relation between range types produced by the classification and the environmental parameters measured were investigated using a two-group, and a multi-group stepwise linear discriminant function analysis. The first split of the TWINSPAN dendrogram separated savanna from open grassveld. The open grassveld was characterized by Themeda triandra, Microchloa caffra, Eragrostis capensis and E. plana and the savanna by Setaria neglecta, Sporobolus fimbriatus, Panicum stapfianum and Cymbopogon plurinodis. The two range types were best discriminated by rainfall, soil depth and altitude with sites in the grassveld corresponding to deep soils and receiving rainfall of more than 450 mm a-1, and sites in savanna corresponding to shallow soils and receiving rainfall of 400-500 mm a-1. Further divisions within these two range types were related to soil textural and chemical characteristics of the A-horizon. Multi-group discriminant function analysis identified eight environmental variables which best discriminate between range types at level 3 of the hierarchical dendrogram. Rainfall, soil depth and altitude were selected as the most important environmental variables discriminating between range types. Reclassification by discriminant analysis using the eight selected environmental factors resulted in a 67% concurrence with range types. It is proposed that the area be stratified on the basis of the current classification for monitoring and management purposes.

Abstract: Four deterministic rainfall-runoff models are briefly described and applied to a small (0.18 km2) grassland catchment in the Eastern Cape Province of South Africa. The models vary in complexity, from a variable time step model with two soil layers and incorporating probability distribution principles for some of the parameters, through two daily time step models, to a relatively simple, but widely used, monthly time step model. The model parameters have largely been determined from measured physical characteristics (topography, soils, vegetation, etc.) of the catchment and not through calibration. As well as comparing the simulated runoff values, the model performances are compared using observed values of soil moisture measured over a period of some 29 months. Although the four models produce similar results, the variable time step model simulates the observed soil moisture variation most successfully and the monthly model least successfully. Most of the differences in the simulation results can be explained by either the differences in complexity of the modelling approach or the resolution of the input data.

Abstract: This article relates the species pattern and structure of miombo woodland in a deforested peasant farming area of central Zimbabwe to its ecological determinants and its present and past use. Data on species composition, basal area, height and physiognomy of the woody vegetation are presented for different parts of the landscape. The nature and degree of disturbance from harvesting for fuel and timber is quantified. Woodland in the arable areas and close to village lines is shown to be dominated by fruit trees, other trees with cultural controls on their cutting and species which quickly invade disturbed ground. The latter may be highly productive of woody biomass. In the grazing area, deeper soils which were cultivated in the past have retained an open structure and tend to be dominated by heavily coppiced Brachystegia spiciformis and Combretum molle (also dominants of less disturbed miombo woodland). Lithic soils which have not been cleared support denser, coppiced woodlands also dominated by climax species. Woody vegetation on kopjes and along riverine fringes is less disturbed in terms of its distribution, species composition, density and height than woodland in other parts of the landscape. The spatial pattern and nature of cutting is shown to vary between land use categories, between different species and according to the dimensions of individual stems. Miombo woodland shows a relatively high degree of stability in species composition under disturbance by cutting: of the 94 species included in the analysis, relatively few were shown to be significantly associated with a particular soil type, catenal position or land use category.

Abstract: Pollen and dinoflagellate cyst analyses of deep-sea core located off Morocco provide a continuous record of paleoclimatic and paleohydrological change off Northwestern Africa since the last glacial episode. The stratigraphy is given by isotopic analysis ([delta]18O) of planktonic foraminifera, which shows a two-step deglaciation. Xeric conditions on the adjacent land, marked by the increase of steppe taxa (Artemisia, Chenopodiaceae/Amaranthaceae, Ephedra), and the development of the montane taxon, Cedrus atlantica are observed before Termination IA and during the Younger Dryas. These intervals are also marked by a high abundance of Pinus pollen grains, which indicates a strengthening of the northeastern (NE) trade winds. Variations of the surface water temperatures are shown by the fluctuations of dinoflagellate cyst assemblages which reflect a cooling of the surface waters during Termination IA and the Younger Dryas episode. Intensification of the upwelling system off Morocco resulting from enhanced trade winds occurred during these two key-periods. Quercus forests, which are an important part of the present-day vegetation of the Maghreb region, developed around 8500 yr B.P. Dinoflagellate cyst assemblages suggest that present-day oceanic conditions were established during this period.

Abstract: A 200 m long marine pollen record from ODP Site 658 (21°N, 19°W) reveals cyclic fluctuations in vegetation and continental climate in northwestern Africa from 3.7 to 1.7 Ma. These cycles parallel oxygen isotope stages. Prior to 3.5 Ma, the distribution of tropical forests and mangrove swamps reached Cape Blanc, 5°N of the present distribution. Between 3.5 and 2.6 Ma, forests occurred at this latitude during irregular intervals and nearly disappeared afterwards. Likewise, a Saharan paleoriver flowed continuously until isotope Stage 134 (3.35 Ma). When river discharge ceased, wind transport of pollen grains prevailed over fluvial transport. Pollen indicators of trade winds gradually increased between 3.3 and 2.5 Ma. A strong aridification of the climate of northwestern Africa occurred during isotope Stage 130 (3.26 Ma). Afterwards, humid conditions reestablished followed by another aridification around 2.7 Ma. Repetitive latitudinal shifts of vegetation zones ranging from wooded savanna to desert flora dominated for the first time between between 2.6 and 2.4 Ma as a response to the glacial stages 104, 100 and 98. Although climatic conditions, recorded in the Pliocene, were not as dry as those of the middle and Late Pleistocene, latitudinal vegetation shifts near the end of the Pliocene resembled those of the interglacial-glacial cycles of the Brunhes chron.

Abstract: The diet of native goats grazing typical vegetation in the piedmont of Mendoza was monitored for 4 years. Vegetation was dominated by Pappophorum caespitosum, Digitaria californica, Trichomaria usillo, Baccharis salicifolia and Acacia furcatispina. Six goats were maintained yearlong on a 3-ha watershed with slopes up to 30%. Diets were sampled by grazing the goats with esophageal fistulae, once every 4 months. Plant cover was reduced from 62.3 to 23.8% after the 4 years of grazing with little fluctuation in the chemical composition of the diet. Grasses were selected over dicotyledonous herbs and shrubs in most periods throughout the 4-year cycle, except in two of 12 sampling periods. From these results it is concluded, that goats are not primarily browsers and showed the ability to maintain the quality of their diet even though the range condition declined.

Abstract: The middle Miocene represents a major change in state in Cenozoic climatic evolution, following the climax of Neogene warmth in the late early Miocene at ~16 Ma. The early stage of this climatic transition from ~16 to 14.8 Ma was marked by major short term variations in global climates, East Antarctic Ice Sheet (EAIS) volume, sea level, and deep ocean circulation. In the later stage from ~14.8 to 12.9 Ma, climatic developments included major growth of the EAIS and associated Antarctic cooling, a distinct increase in the meridional temperature gradient, large fluctuations in sea level followed by a global sea level fall, and important changes in deep water circulation, including increased production of Southern Component Water. East Antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere, including aridification of mid-latitude continental regions. Increased stability of the EAIS after 14.8 Ma represents a crucial step in the establishment of late Neogene global climate systems. What controlled these changes in polar climates and the East Antarctic ice sheet? Deep ocean circulation changes probably played a major role in the evolution and variation in polar climates, as they have throughout the Cenozoic. Oxygen and carbon isotopic evidence for warm, saline deep water production in the eastern Tethyan/northern Indian Ocean indicates that meridional heat transport to the Antarctic inhibited Cenozoic polar cooling and EAIS growth during the early middle Miocene from ~16 to ~14.8 Ma. Inferred competition between warm low-latitude sources (derived from the eastern Tethyan-northern Indian Ocean) and a cold high-latitude source (Southern Component Water) from ~16 to 14.8 Ma may have been associated with instability in the Antarctic climate and cryosphere. Reduction of warm, saline deep water flow to the Southern Ocean at ~14.8 Ma may have decreased meridional heat transport to the Antarctic, cooling the region and leading to increased production of Southern Component Water. These middle Miocene climatic and cryospheric changes in the Antarctic had profound effects on marine and terrestrial climates. As the meridional surface temperature gradient increased, boundaries between climatic zones strengthened, leading to increased aridification of mid-latitude continental regions in Australia, Africa and North and South America, enhancing the development of grasslands and stimulating the evolution of grazing mammals.

Abstract: Although ecological, economic and social conditions vary from country to country, the quandary of increasing pressure on limited tropical savanna resources is universal. This article reviews some of the characteristics of tropical savannas, competing land uses, and the effects of some of the land use decisions. It examines the potential role of science in improving the quality of land use policy formulation and implementation, particularly in the areas of land use allocation and management.

Abstract: A geographically referenced data base, including time series of land use and population information in a standardized format, is now available for 13 South and Southeast Asian nations: India, Bangladesh, Sri Lanka, Myanmar, Thailand, Laos, Cambodia, Vietnam, Malaysia, Singapore, Brunei, Indonesia and the Philippines. Data are available for five dates (1880, 1920, 1950, 1970, and 1980), and the 13 countries have been subdivided into a total of 94 zones. Sources, methodology, and limitations of these data are reviewed. Between 1880 and 1980, the regional population of humans increased by 262%, the area of cultivated land expanded by 86%, and the area bearing grass and shrub vegetation increased by 20%, while total forest cover decreased by 29%. Expansion of arable land, and biomass removal driven by both local and external economic demands, were both linked to deforestation. The data indicate that even in 1880 (when much of the region was effectively in a preindustrial state), anthropogenic activity had already caused enormous modifications of the natural vegetation. Land use changes that occurred before the preindustrial period must therefore be taken into account in the development of carbon cycle models.

Abstract: The diversity of rangeland ecosystems makes application of remote sensing data difficult. This study was conducted to determine the effects of plant surface residue on rangeland canopy radiometric measurements. Measurements were made on moderately and heavily grazed native rangeland pastures. Standing senesced plant residue was collected and spread in the autumn to establish treatments of 0%, 33%, 66%, and 100% ground cover. Canopy radiometric measurements were made weekly the following grazing season using the red (RED) (0.63-0.69 [mu]m) and near infrared (NIR) (0.76-0.90 [mu]m) wavebands of a Mark II radiometer. We examined relationships between wavebands, ratio vegetation index (R = NIR/RED), the normalized difference vegetation index [ND = (NIR - RED)/(NIR + RED)] and forage dry matter accumulation and surface plant residue. All wavebands and indices were significantly related to dry matter accumulation on both moderately and heavily grazed pastures. Separation of residue treatments by radiometric measurements was more evident on moderately grazed than on heavily grazed pastures. Red reflectance was most sensitive to surface residue treatments and separated residue from no residue plots until early June when green growth became dominant. Vegetation indices R and ND tended to be lower for the 100% surface residue treatment for both pastures and higher for the 0% treatment for the moderately grazed pasture. Results suggest that different amounts of surface residue would not greatly interfere with using radiometric measurements to predict dry matter accumulation on Northern Great Plains native rangeland.

Abstract: Botanical composition of steer diet (fecal sampling with microhistological analysis) and availability of grasses and forbs (clipping method) and shrubs and trees (dimension analysis) in pastures stocked at 25, 50 and 80% use of perennial grasses were determined during two 120-day grazing periods under a four-pasture, one-herd grazing system. Diet composition was not different (p < 0·01) when grass use was <= 50%. Steers were forced to significantly alter (p < 0·01) diet selection patterns from the beginning to the end of grazing periods in all treatments by consuming less grasses and more browse. Diet content was closely related to the live herbage available.

Abstract: Plant density and tiller counts were done in several Sahelian rangelands in Mali, under a variety of soil, rainfall and grazing situations. Numeric models were developed to explain the dynamic relationship between grass tillering and herb density. Tests of application of these models to the plant and tillering density data justify the selection of the maxima function model. Discussion of the results leads to an ecological interpretation of the parameters of the model which relate the dynamics of tillering to the concepts of ecological niche and inter-plant competition for resources. The application of the model helps in assessing the role of grass tillering in the structure and productivity of Sahelian rangelands and in their response to drought and pastoral management changes.

Abstract: The effects of soil texture and grassland management, i.e. rate of fertilizer N input, mowing vs grazing, and the number of years the site is under grass, on the amounts of soil organic C and N and on the rates of C and N mineralization were investigated. A positive relationship was found between the amount of organic N in the soil and the clay + silt content. The relationship was affected by the groundwater table. There was a negative relationship between the percentage of soil N mineralizing during incubation and the clay + silt content of the soil. The amount of organic C was only positively correlated with soil texture in the soils with a high water table, but the relationship was less clear. Except for the groundwater table, differences in the C-to-N ratio of the soil organic matter in sandy soils confused the relationship of soil organic C with soil texture. Organic matter in podzol soils had C-to-N ratios between 15 and 20 while in other sandy soils the C-to-N ratio ranged from 10 to 18; in loams and clays the C-to-N ratio was ca 10. The percentage of soil C mineralizing in sandy soils was negatively correlated with the C-to-N ratio of the soil organic matter. The sandy soils with a C-to-N ratio 16 that were used for incubation contained black humus including small charcoal particles; both other sandy soils with a lower C-to-N ratio contained brown humus without visible charcoal particles. So we hypothesize that sandy soils with a high C-to-N ratio contained more inert C than sandy soils with a low C-to-N ratio. The rate of N fertilization had no effect on soil organic C and N nor on the rates of C and N mineralization. Differences between the effects of grazing and mowing on soil organic C and N and the rate of C and N mineralization were very small and not very consistent. Both the amounts of soil organic C and N found and the rates of C and N mineralization were significantly higher in old grassland (10 yr) than in young grassland (1-3 yr). The increases in the mineralization rates were larger than the increases in soil organic C and N.

Abstract: A simulation model of the pastoral production system for a chenopod pasture type was used to evaluate pasture and animal production responses to a range of alternative management systems, stocking rates and initial pasture condition states. The management systems evaluated included the Merrill four-pasture, three-herd system, deferred rotation, the Annean system (involving winter grazing only), and continuous grazing. These systems were evaluated at five stocking rates and for four levels of initial pasture condition. Simulations were based on historical rainfall data from a station in the Western Australian arid zone for the period 1963-1987. Formal systems of rotational resting appear to have little prospect for application in this environment. Although animal production in winter was high under deferred rotation, overall these systems were inferior to the Annean and continuous grazing systems in terms of both animal production and pasture response (change in density of desirable perennial plants). In most instances the best pasture response resulted from the Annean system which also achieved levels of animal production (in winter) which were generally second only to deferred rotation. However, at low stocking rates, continuous grazing produced similar pasture and animal production responses to the Annean system for range varying from excellent to poor condition. For range in very poor condition, continuous grazing limited the rate of recovery relative to the Annean system. Although the latter is particularly beneficial under these circumstances, its application depends on the ability to distribute animals at low stock density over summer in order to avoid the potentially serious consequences of heavy grazing pressure at this time.

Abstract: A simple model of soil moisture balance and herbage production in the arid and semi-arid rangelands of central Australia is presented. The model has few parameters and only requires inputs of rainfall and potential evaporation to model daily soil moisture and plant growth. Five landscape types were studied for over 2 years, and for up to four major growth events, to provide data for estimating parameters in the model. Moisture loss in the 0-500 mm soil profile has been modelled using an negative exponential function which depends on available soil moisture and is driven by daily rainfall and potential evaporation. The growth of herbage, whilst soil moisture is above wilting point, is a linear function of actual evapotranspiration, with the decay of plant material represented by a logistic curve.

Abstract: In south-western Co^te d'Ivoire mature forest is felled and burned and one crop of upland rice is grown. Forest is then allowed to regenerate for 15 or more years before being cropped again. Soils are very gravely, clayey, acid, thoroughly leached and chemically poor. Forest, soil, rice, weeds and regrowth were studied in the fields of local farmers in permanent plots during 2-5 years. The fields (16) covered all currently cultivated soil types and forest types. Burning leads to an instant mineralisation of organic matter and the ashes produce a marked decrease in acidity (before burning pH 4.4-5.2, after burning pH 5.4-6.2). The nutrient availability is further stimulated by the reduction of Al activity in the soil solution. Fire is a decisive factor in cultivation: slightly burnt or unburnt areas are wholly unproductive. The rice thrives on the nutrients contained in the ash of the burnt forest rather than on the nutrients of the mineral soil: the nature of the soil is of relatively little importance, as long as large quantities of biomass are burnt. A fire of normal intensity destroys enough buried seeds and vegetative parts of forest plants to avoid weed stress, yet allows the survival of a sufficient number of forest plants for forest regrowth after the rice crop. Excessive burning kills sprouts and buried seeds. Regeneration comes then from seeds dispersed into the field after the fire, mainly grasses and forbs. Grassy shrub land or thickets are thus formed.

Abstract: In semi-arid and arid magisterial (administrative) districts (n = 45) in the Cape Province, South Africa, there has been a mean 44·4 ± 14·6% (S.D.) reduction in the stocking rates of domestic livestock over the period 1911-81. In five savanna districts there has been a mean 36·8 ± 8·5% increase in stocking rate. For all districts during the period 1911-30 the mean stocking rate was 12·5 ± 8·6 large stock units/100 ha, and for 1971-81 the mean rate was 8·4 ± 7·7 LSU/100 ha (one bovid weighing 420 KG = 1 LSU). The reduction in stocking rate differs significantly between biomes and shows a general trend towards being greater in the more arid districts. The reduction is significantly greater in the succulent Karoo where seven of eight districts have experienced stocking rate reductions > 50%. Districts with a rainfall variability index > 4·0 (i.e. with lowest recorded rain only 25% or less of highest recorded rain) show a significant trend towards larger reductions in stocking rate than do all the other districts. Reductions in stocking rate, however, are not significantly correlated with the index of rainfall variability or with an index of drought, suggesting that changes in stocking rate are not influenced only by higher probabilities of drought. Past and present stocking rates are significantly correlated with mean annual rainfall in the eastern Karoo, central Karoo, succulent Karoo and Savanna districts. The total number of stock-water points in each district in all biomes increased over time. In Gordonia, Kuruman, Mafeking, Taung and Vryburg, where stocking rates have increased, they are positively correlated with stock-water points, but in all other districts, this relationship is negatively correlated. We conclude that the current livestock stocking rate in the semi-arid and arid rangelands of the Cape Province is unrelated to market forces or state policy but is determined by utilizable primary productivity of rangelands. This study provides evidence that the production potential of drylands has decreased markedly in semi-arid and arid rangelands throughout the Savanna, Nama-Karoo and succulent-Karoo biomes of the Cape Province.

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Abstract: The composition of the anthophilous insect fauna of a plant community in the north-western Cape, South Africa, has been investigated. During a 3-year survey more than 300 species belonging to four orders and 41 families have been identified as day-active floral visitors. The vast majority are solitary bees (136 spp.), but masarine wasps (14 spp.), bombyliid flies (53 spp.), and monkey beetles (20 spp.) are also well represented. The anthophilous insect fauna of Goegab appears to be far more diverse than those of desert scrub communities in California and Chile, but equally diverse as that of a Californian Chaparral site. Compared to the latter, Goegab seems to be particularly rich in bee flies, Masarinae and possibly Eumenidae, but poorer in bees and butterflies.

Abstract: The Pliocene epoch represents an important transition from a climate regime with high-frequency, low-amplitude oscillations when the Northern Hemisphere lacked substantial ice sheets, to the typical high-frequency, high-amplitude Middle to Late Pleistocene regime characterized by glacial--interglacial cycles that involve waxing and waning of major Northern Hemisphere ice sheets. Analysis of middle Pliocene (~3 Ma) marine and terrestrial records throughout the Northern Hemisphere forms the basis of an integrated synoptic Pliocene paleoclimate reconstruction of the last significantly warmer than present interval in Earth history. This reconstruction, developed primarily from paleontological data, includes middle Pliocene sea level, vegetation, land--ice distribution, sea--ice distribution, and sea-surface temperature (SST), all of which contribute to our conceptual understanding of this climate system. These data indicate middle Pliocene sea level was at least 25 m higher than present, presumably due in large part to a reduction in the size of the East Antarctic Ice Sheet. Sea surface temperatures were essentially equivalent to modern temperatures in tropical regions but were significantly warmer at higher latitudes. Due to increased heat flux to high latitudes, both the Arctic and Antarctic appear to have been seasonally ice free during the middle Pliocene with greatly reduced sea ice extent relative to today during winter. Vegetation changes, while more complex, are generally consistent with marine SST changes and show increased warmth and moisture at higher latitudes during the middle Pliocene.

Abstract: Much of the spread of participatory rural appraisal (PRA) as an emerging family of approaches and methods has been lateral, South-South, through experiential learning and changes in behavior, with different local applications. Rapid spread has made quality assurance a concern, with dangers from 34;instant fashion 34;, rushing, formalism and ruts. Promising potentials include farmers 039; own farming systems research, alternatives to questionaire surveys, monitoring, evaluation and lateral spread by local people, empowerment of the poorer and weaker, and policy review. Changes in personal behavior and attitudes, and in organizational cultures, are implied. PRA parallels and resonates with paradigm shifts in the social and natural sciences, business management, and development thinking, supporting decentralization, local diversity, and personal responsibility.

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Abstract: Mixed grazing groups of 15 bonded ewes and five cows consistently (100%) remained together in one of two adjoining arid rangeland paddocks during each of three seasons beginning in September 1991. The paddocks were separated with only two strands of wire fence, the bottom wire being 0.7 m off the ground. In contrast, non-bonded ewes (controls) were found in the adjoining paddock without cattle 54% of the time. This created a mean separation distance between non-bonded ewes and cattle of 977 m. Locating ewes in the non-bonded treatment required additional time, thus reducing management efficiency and increasing costs by approx. $0.10/hd/d. In a separate study begun in January 1992 an enduring bond between sheep and cattle was produced by confining 65 to 86 day-old lambs with cattle in pens for 55 d at a cost of approx. $0.51/hd/d. Bonding may provide an economically viable alternative to conventional wire fencing on many properties as a means of controlling the spatial distribution of sheep under mixed grazing.

Abstract: The temporal and spatial distribution of African savanna grassland fires has been examined, and the areal extent of these fires has been estimated for the subequatorial African continent. African savanna fires have been investigated using remote sensing techniques and imagery collected by low-light sensors on Defense Meteorological Satellite Program (DMSP) satellites and by the Advanced Very High Resolution Radiometer (AVHRR) which is aboard polar-orbiting National Oceanic and Atmospheric Administration (NOAA) satellites. DMSP imagery has been used to map the evolution of savanna burning over all of the African continent/1/ and the analysis of AVHRR imagery has been used to estimate the areal extent of the burning in the southern hemispheric African savannas. The work presented primarily reflects the analysis completed for the year 1987. However, comparisons have been made with other years and the representativeness of the 1987 analysis is discussed.

Abstract: Aspects of the relationships between the plants and the flower-visiting insects of the north-western Cape, South Africa, based upon a 3-year study on permanent plots, are examined. The vast majority of plant species of the study area show entomophilous pollination syndromes. Particularly noteworthy is the preponderance of large open brightly coloured blossoms, especially of Asteraceae and Mesembryanthemaceae, most of which show allophilous to melittophilous pollination syndromes. Flower-visiting records are given for more than 300 day-active insect species belonging to four orders and 41 families. From the flower-visiting records and the analysis of pollen loads of selected bee specimens it is concluded that the anthophilous insect fauna is dominated by generalist foragers. Most flower/insect associations are not exclusive and frequently overlap.

Abstract: Methane is the most abundant organic chemical in the earth's atmosphere, and its abundance is increasing with time and has reached levels not seen in recent geological history. Methane is produced both naturally and anthropogenically. One of teh sources of anthropogenic methane is manure from domesticated animals. A methodology has previously been developed to estimate the amount of methane generated from this source. This was done by estimating the methane conversion factor (MCF) typically achieved by various waste management systems. The present study was conducted to evaluate these MCF assumptions using dairy manure as the representative livestock manure. The MCFs for the most dominant of disposal methods, rangeland/pasture disposal, were much lower than the earlier estimates. Other waste management systems, such as solid storage and liquid slurry storage had much higher MCFs, at 20 and 30°C. However, these waste management methods are more prevalent in parts of the world where the average annual temperature is closer to 10°C. At that temperature, the MCF is negligible in all waste management systems. This study showed that the previously reported estimates of MCF for some waste management systems were higher than was actually the case. Consequently earlier estimates of the amount of methane generated globally from manures were higher than those found in this study.

Abstract: In Tunisia, the rehabilitation of overgrazed and degraded rangelands is being attempted through the reintroduction of various native perennial plant species. We studied plant--water relations in two of the leading candidate species, Seriphidium incultum (syn: Artemisia herba-alba) and Anthyllis henoniana, under conditions of water stress. Anthyllis was found to be adapted to water stress through rapid water uptake ability and a deep root system allowing access to water reserves lying deep in the soil. In contrast, Seriphidium has adapted to drought by tolerating very severe desiccation of its above-ground parts. Moreover, Seriphidium individuals consist of several hydrologically independent subunits, with the result that one part of the plant can die without damaging the rest of the plant. Relationships between xylem potential in the two species and soil water potential are also discussed.

Abstract: Development and use of crop growth simulation models has increased in the last decades. Most crop growth models require daily weather data as input values. These data are not easy to obtain and therefore in many studies daily data are generated, or average values are used as input data for these models. In crop growth models non-linear relations often occur. Thus the simulation result with average data can be different from the average result with daily data. In this study the effects of using average weather data on simulated potential and water-limited yields were investigated with a spring wheat crop growth model. It was expected that deviation in simulation results was related to the variability of the weather. Therefore effects were studied for sites in three different climates: temperate maritime, mediterranean and humid tropical. Variability of the weather during the growing season on these sites was quantified. Intuitively the weather in the mediterranean and humid tropical climates is far more constant than the weather in the temperate maritime climates. However, for all locations the variability of the weather during the growing season was nearly the same. The explanation for this unexpected result was found in the fact that on all sites crops were grown in that part of the year in which it rains. The existence of dry and wet days during the growing season causes a large day-to-day variation in weather. For all sites an overestimation of the simulated potential yield of 5-15% was found as a result of using average weather data. For water-limited production the use of average data resulted in overestimation of yield in the wet conditions and underestimation of yield in dry conditions (up to 50%).

Abstract: This study examines the variability of the normalized difference vegetation index (NDVI) over Bostwana during the period 1982-1987. Its relationship to rainfall is evaluated from 26 stations representing six vegetation formations and six soil types. The study demonstrates a linear relationship between rainfall and NDVI as long as rainfall does not exceed approximately 500 mm/yr or 50-100 mm / month. Above these limits, a "saturation" response occurs and NDVI increases with rainfall only very slowly. This occurs at much lower thresholds of rainfall over Botswana than over East Africa or the Sahel. The ratio of NDVI to rainfall in Botswana is several times higher than in savannas in these other two regions. Both this ratio, which represents the rain-use efficiency, and the total productivity of vegetation, as assessed from NDVI, vary with vegetation and soil type. The highest productivity and efficiency occur on the clay-rich vertisols, the lowest on the sandy arenosols and solonchaks. In general, the rain-use efficiency appears to be more a function of the underlying soil than of the vegetation formation.

Abstract: Using the methods of direct gradient analysis, we investigated some of the factors responsible for species turnover in the dwarf shrubland/grassland interface of the eastern half of the Nama-Karoo biome, South Africa. The analysis suggested that taxa are distributed along topographic/moisture gradients, with two broad syntaxonomic classes differentiated from one another by substratum. If the patterns of species turnover on the two major substrata (sandstone and dolerite) differ significantly, taxa may be responding to environmental stresses other than elevation and rainfall. The null hypothesis being that if the two substrata parallel one another along a topographic/moisture gradient, the species replacement rates should be similar. The null hypothesis was rejected as species replacement rates on sandstone at high rainfall and high elevation are higher than on dolerite at comparable environmental conditions. The differences are attributable to species-poor degraded sites in topo-moisture class C (1200-1300 m elevation and 300-350mm median annual rainfall). The topo-moisture class has a high coefficient of variation in mean annual rainfall. Topo-moisture class C on sandstone pediments supports a degraded flora. The high entropy of the samples suggests that the flora is well-adapted to coping with the climatic uncertainty of this region. There does not appear to be an encroaching karoo front, but rather a flora of generalist species which are successful at coping with the high coefficient of variation in precipitation. It is suggested that if environmental conditions change due to global warming, the intruding front will only extend into areas of increased climatic uncertainty. Pastoral management strategies which increase environmental uncertainty should also be discouraged.

Abstract: This paper presents results of a deforestation experiment carried out with the general circulation model of the Laboratoire de Météorologie Dynamique coupled to the Schématisation des Echanges Hydriques à l'Interface entre le Biosphère et l'Atmosphère (SECHIBA) vegetation model. An integration of 1 year was carried out in which the tropical forests of Amazonia, Africa and Indonesia were replaced by grassland. It was found that the model produces a reduction in evaporation and an increase in soil temperature. In contrast to similar experiments, a significant increase in moisture convergence was obtained; this increase is attributed to an enhancement of the convective activity of the Intertropical Convergence Zone (ITCZ).

Abstract: The experiment was conducted in the protected grazing land at Rajkot with eight male goats of the Zalawadi breed (average body weight 14.3 ± 2.6 kg) to study feeding habits and grazing behavior. Goats spent 76.6% of observation time in grazing. Grazing goats showed a distinct diurnal pattern for selectivity of types of forage. During morning hours grasses were preferred more than 80%, followed by thorny bushes (18%), whereas in the evening bushes were preferred 69% and grasses 30%. Bite rate at different hours was not significantly different among plant species. Bite size varied significantly (P < 0.01) among grasses, bushy and other miscellaneous forage species. Herbage intake/day calculated for grazing animals was 0.23 kg/kg BW0.75. Of the total biomass consumed, 44% grasses, 52% thorny bushes and 4% were miscellaneous forbs.

Abstract: Diets of angora goats (Capra hircus) positively conditioned to eat big sagebrush (Artemisia tridentata subspp. wyomingensis) were contrasted with control groups to assess the effects of positive conditioning. Goats were conditioned by including ever-increasing amounts of sagebrush in the daily ration, to a maximum of 25% by weight as fed. Conditioning effects were evaluated by comparing relative consumption of big sagebrush in a rangeland setting. Field trials were conducted at the Squaw Butte Experimental Range, a shrub steppe rangeland in eastern Oregon. Our results indicate that neither conditioned does nor kids had significantly different intake of sagebrush when compared with control animals. Young animals consumed shrub species sooner than adults and ate significantly more shrubs throughout all seasons until the second summer when diets did not differ between age groups.

Abstract: The cycling of biomass through livestock into manure and urine that fertilise the soil is an important linkage between livestock and soil productivity in semi-arid West Africa. This study was conducted to determine the effects of different forage leaves on the amounts and forms of nutrients excreted by sheep, the relationship between diet quality and nutrient voidings, and to evaluate the potential impact of these effects on the release of nutrients from urine and faeces when used as organic fertilisers. Five diets consisting of Pennisetum glaucum (PG), Vigna unguiculata (VU), Acacia trachycarpa (AT), Guiera senegalensis (GS) and Combretum glutinosum leaves were fed to growing sheep. The total amount and proportion of nutrients voided in faeces and urine was highly influenced by the N and P contents of the feeds, and the lignin: neutral detergent fibre, lignin:N, and polyphenol:N ratios. Sheep fed VU leaves excreted significantly more total-N than sheep fed any of the browse leaves. Feeding browse caused a general shift from faecal-soluble N (microbial and endogenous N) to faecal-insoluble N (undigested plant N). Animals fed VU leaves voided large amounts of urine N which would be susceptible to large volatilisation losses. Sheep fed browse leaves voided less urine N, and therefore produced excreta less susceptible to volatile-N losses. The estimated 45-54 kg N and 5.1-7.8 kg P ha-1 released from the various faeces would provide an important contribution to the annual requirements of millet of 36 kg N and 6.1 kg P ha-1. Selecting feeds that not only satisfy the nutrient requirements of livestock but produce animal excreta less susceptible to losses may improve nutrient cycling in mixed farming systems of semi-arid West Africa.

Abstract: Soil erosion by wind or water is a serious problem in North and South America. When no-till or reduced tillage is used to control erosion, the density of certain annual and perennial weeds can increase and new weed control techniques are usually required. The effects of conservation tillage on annual and perennial weeds, weeds that are spread by wind, plants from rangelands and pasture as weeds and volunteer plants as weeds are reviewed. Current weed control methods with minimum tillage, herbicides, cover crops and other cultural practices in conservation tillage systems in North and South America are described. Some producers are successfully controlling weeds in continuous summer cropping systems in North America and in double cropping systems that include wheat in the winter and soybean or corn in the summer in Brazil, Argentina and southeastern United States. Successful conservation tillage systems usually involve cropping sequences of three or more crop types and several herbicides. In these cropping sequences, the ground is covered with a crop during most of the period in which the climate is favourable for weed growth. Perennial weeds are a problem in all tillage systems and there is a general dependence on glyphosate for perennial weed control. In successful conservation tillage systems, the amount and cost of herbicides used is similar to that for herbicides used in conventional tillage systems.

Abstract: In African semi-arid savannas livestock production frequently dominates human activity, but it has been claimed that wildlife ranching can be more profitable than extensive beef production. Traditional accounting methods generally exclude the biological costs of stocking effects on rangeland productivity. This paper presents a framework for evaluating overstocking effects on the financial profits (based on market prices) and economic profits (estimated from the opportunity costs of inputs and outputs) of alternative range-based animal production systems. The method was applied to 50 commercial cattle, wildlife, and mixed ranches in the Zimbabwe Midlands using 1989/90 data. Level of overstocking was estimated from positive differences between grazer stocking rate and rangeland carrying capacity, which was predicted from long-term mean annual rainfall. Since it is generally impossible to accurately quantify stocking effects on rangeland productivity, and thus to confidently evaluate overstocking costs, values ranging from Z$0.00 to Z$0.50 kg-1 ha-1 overstocking were used. The resulting range of costs were subtracted from financial and economic profits. Cattle ranches were significantly overstocked while mixed and wildlife ranches were not. Thus cattle ranch profits decreased more rapidly with increasing simulated overstocking cost. In other words, with increasing sensitivity to overstocking, wildlife and mixed ranches had a higher probability of remaining financially and economically profitable than did cattle ranches.

Abstract: This article is the continuation of a study of the relationship between NDVI and rainfall in semiarid Botswana. That study notes significant differences in the NDVI-rainfall relationship for various soil types and a much higher ratio of NDVI to rainfall over Botswana than over comparable regions of the Sahel or East Africa. The current article examines the extent to which differences in the rate of soil moisture generation, as a function of soil type or locality, can account for these results. It concludes that they cannot. This study demonstrates that the five soil types do differ significantly with respect to both the rate of soil moisture generation per unit rainfall and the ratio of NDVI to soil moisture. The most productive soils are the clay-rich vertisols; the arenosols are the least productive, although the rate of soil moisture generation is about the same for both soil types. The results also suggest that over Botswana NDVI may be significantly influenced by soil reflectivity and that the vegetation growth is promoted by exogenous soil water originating as runoff in the surrounding higher terrain.

Abstract: Plant-derived smoke and aqueous extracts of smoke stimulate germination of dormant seed of the important fire-climax grass Themeda triandra (redgrass). The positive germination response to smoke increased as the state of seed imbibition increased. Furthermore, aqueous smoke extracts significantly increased seed germination at optimum and sub-optimum germination temperatures. Ethrel and ethylene, at a wide range of concentrations, failed to increase T. triandra seed germination, indicating that ethylene is not the active component of plant-derived smoke. Similarly, ash or aqueous ash extracts failed to stimulate germination. In contrast, aqueous smoke extracts prepared from burning fynbos vegetation and grass leaf material stimulated T. triandra seed germination. The bioactive component of plant-derived smoke may originate from a commonly occurring source, possibly being a thermal breakdown product of hemicellulose or cellulose.

Abstract: Carbon monoxide (CO) is one of the main reactive trace gases in the earth's atmosphere: it influences both the atmospheric chemistry and the climate. In order to evaluate the atmospheric budget of CO, knowledge of the emission rates from, and the, geographic distribution of, the individual sources are required.

Abstract: A three-year experiment for the determination of deposition fluxes on heathland was conducted at the Elspeetsche Veld involving several research groups. Micro-meteorological measurements of SO2, NH3 and NO2 were made using different techniques. Furthermore, throughfall and bulk precipitation fluxes of SO42-, NH4+ and NO3- were also measured. From these measurements, deposition parameters were derived to yield a generalized description of the surface exchange of these trace gases, including possible interactions. For SO2, generally low surface resistances were found; the annual average dry deposition velocity ranged from 0.8 to 1.0 cm s-1. The annual flux of SO2 was estimated as 250 mol ha-1 yr-1. For NH3 also, low Rc values were observed, yielding annual average Vd of 0.8 cm s-1. The annual flux of NH3 was estimated as 850 mol ha-1 yr-1. Under the environmental conditions prevailing in the Netherlands, co-deposition between SO2 and NH3 was estimated to be irrelevant. Surface wetness was found to be the dominating factor influencing dry deposition of the two gases. Rc values for NO2 stomatal behaviour, Vd for this gas ranged from 0.1 to 0.4 cm s-1. Fluxes measured with the throughfall method are compared with fluxes derived using micro-meteorological methods. The yearly average net throughfall flux for SO4 and the dry deposition flux (SO2 and SO4 particles) amounted 500 and 350 mol ha-1 yr-1, respectively. For NH4 this was 1180 and 930 mol ha-1 yr-1, respectively. The correlation between the two on a monthly basis is significant (r=0.50 for SO4 and r=0.52 for NH4, n = 12, p<0.05).

Abstract: Rates of soil loss were determined using erosion pins on a severely eroded surface in a small (19 km2) arid rangelands catchment in western New South Wales, Australia, over a 10-year period. Rates of up to 209 t ha-1 year-1 on rilled surfaces, 59·5 t ha-1 year-1 on flat surfaces, and 30·6 t ha-1 year-1 on vegetated hummocky surfaces were calculated. The initiation of this erosion is attributed to overgrazing by sheep and rabbits in the late nineteenth century, and its amelioration is precluded by hydraulic factors which prevent the use of reclamation techniques like waterponding.

Abstract: The Hakea seed-moth, Carposina autologa Meyrick was released in South Africa for the biological control of Hakea sericea Schrader. The impact of the moth on the canopy-stored seeds of H. sericea was evaluated in the southwestern Cape over 3 years. The moth has reduced the mean accumulated seeds at the two study sites by 64.2% and 50.6%. It has shown a surprising ability to disperse and establish new colonies at low population levels. Although seed destruction is not severe, it is expected to contribute to the control of the weed.

Abstract: A utilitarian simulation model of botanical composition of ruminant diets on rangelands is proposed. It emphasizes the use of forage resource diversity within the range ecosystem context. The forage species, within a plant community, are taken as the functional unit of the model. Four indices are defined: (a) a probability of encountering forage i in the plant community, (b) a structural index of bite taken in forage i, (c) a quality index of forage i, and (d) a selectivity index of the animal foraging. These indices are combined to calculate potential alimentary capacities of forage species (PAC), and to estimate their contribution to the diet taken from a particular plant community. An extrapolation to the overall habitat is then made, by an estimation of relative feeding times spent within the various plant communities of the rangeland.

Abstract: Simultaneous measurements of SO2 and NH3 dry deposition using the micrometeorological gradient method were performed continuously at two heathlands. It is concluded that dry deposition of both SO2 and NH3 at the two locations in general is limited by aerodynamic resistance during conditions with wet surfaces. The results of the measurements are used to investigate the influence of pollution climates on the dry deposition of SO2 and NH3. It is demonstrated that low surface resistances of SO2 and NH3 will occur in humid regions, as surface wetness is found to be the most important parameter. A high flux of one gas relative to the other can increase its surface resistance through saturation of the surface and lower the resistance for the other gas. During dry conditions, SO2 and NH3 uptake is controlled by stomatal behaviour of the heather plants. Upward fluxes of NH3 have been observed during these periods. It is furthermore suggested that fog composition has a large influence on Rc values, resulting in both high and low values. Frost was demonstrated to increase Rc values of both gases.

Abstract: The effect of climate change on plant and livestock production in the Great Plains of North America is an important issue. The purpose of this study was to modify an existing rangeland ecosystem model and to simulate a cow/calf production system under different climate scenarios. The project required the capability of simulating rangeland livestock production under different ambient CO2 concentrations, temperatures and precipitation patterns. Climate change scenarios were created from three general circulation models (GCMs): GISS (Goddard Institute for Space Studies model), GFDL (Geophysical Fluid Dynamic Laboratory model), and UKMO (United Kingdom Meteorological Office model). Results from the GCMs were used to modify the climate record for a site in northeastern Colorado. Concomitantly, modifications were made to the SPUR model to help predict the effect of predicted climate change on selected variables of the range/livestock ecosystem. Simulation runs showed that predicted climate change will affect plant and animal production for rangelands. Changes in production were more closely related to changes in temperature and precipitation than to enhanced [CO2] alone. The effect of climate change on livestock production was very complex and results were dependent on the particular GCM scenario being simulated.

Abstract: Historical grasshopper survey data were used to relate grasshopper densities to ecological condition classes on the Bureau of Land Management's Shoshone District in Idaho as part of an effort to identify areas prone to high grasshopper densities and to understand the effects of range management practices on grasshopper populations. A MOSS-based Geographic Information System was used to overlay maps of ecological condition, elevation, and grasshopper density to test the hypothesis that grasshopper density was the same for all ecological condition classes. Areas that had been severely disturbed by wildfires and invasion of exotic annual vegetation had significantly higher grasshopper densities over the 3 years examined than less severely disturbed area that retained some sagebrush cover. This suggests that shrub loss due to wildfires or other causes may lead to greater grasshopper densities. The techniques and applicability of geostatistical spatial analysis to these questions is also discussed.

Abstract: The advantages of incorporating variable length time steps into deterministic hydrological models are discussed and a method based on the use of rainfall thresholds to determine appropriate length steps automatically is presented. The method has been incorporated into a continuous catchment hydrology simulation model that was developed from an earlier version of a single-event flood model. The model, data preparation, and results analysis and display functions are all contained within a more general model application software package (HYMAS -- Hydrological Modelling Application System), which is currently being developed. A brief description of the components of the model is provided, with emphasis on the effects on their operation using different length time steps of modelling. Data from a semi-arid grassland catchment in South Africa and an arid catchment in Arizona, USA, are used to illustrate that a variable time interval approach can improve the overall efficiency of a model.

Abstract: Crete has a very long history of human intervention in the natural environment which has resulted in physical and cultural diversity exemplified by a large variety of landscapes; all this diversity, however, has been threatened in the last few decades. To identify and investigate the effects of the economic development applied over the last years, statistical data on forests, rangelands, livestock, agricultural lands and human population have been collected from the village communities and the towns included in the study area and analysed. Evolution of the population indicates a 47% and a 36% decrease in the number of inhabitants in the mountainous and hilly communities, respectively, as opposed to an 8.7% increase in the plain communities from 1951 to 1991. This depopulation of the mountainous area has led to the abondonment of the traditional land uses in the uplands at the same time as the intensification of agriculture in the lowlands, which has involved the development of tree monocultures, use of artificial fertilizer irrigation and spraying over large areas (18.8% of the total area is cultivated land). On the other hand 1.75% of the area is residential, with massive commercial tourist development leading to all kinds of intrusive and discordant buildings. Forestry has limited importance as an economic activity, even though land classified as forest occupies 20.9% of the whole area. Livestock grazing is a dominant activity on all wildlands (57.6% are classified as rangelands) including forest. There was a 71% increase in the number of livestock from 1981 to 1991 giving a 50% increase in the stocking rate (animals ha-1 year-1). Overstocking, coupled with free and uncontrolled grazing as well as with frequent pastoral wildfires, has resulted in severe degradation.

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Abstract: Fire is a major threat to many national parks worldwide. Social research in the savanna woodland biome of northern Benin shows that in addition to the commonly cited reasons for setting bush-fires--tradition, clearing fields, hunting, and improving dry season grazing--villagers burn to deter wild animals, to increase the supply of certain forest products, and to take revenge on the national parks. Villagers' perceptions of the effects of fire often correspond to our scientific understanding. With an appreciation of the villagers' logic we can predict that the establishment and protection of national parks will increase the incidence of human-caused bush-fires. To counter this, parks need to promote changes in long-standing traditions, encourage more intensive land-use practises, assist in protecting crops and livestock against wild animals, and improve relationships with the surrounding villagers.

Abstract: We investigated the plasticity of seedlings to shade in six shrub species common in subtopical thicket, in order to assess their microhabitat preferences for regeneration. Cassine peragua and Sideroxylon inerme, which also occur in adjacent forests, were the most shade tolerant and would be unlikely to require canopy gaps for recruitment: their relative reduction in growth in dense shade was slight, as was their increase in leaf weight ratio (LWR); leaf inclination was adjusted to near horizontal in dense shade and maximum net photosynthetic rate (Amax) remained fairly low in sun-acclimated plants. Rhus glauca, which also occurs on forest margins, demonstrated the highest growth rates, especially in the open, and together with its high potential Amax is well-equipped as a pioneer, and would benefit from canopy gaps for establishment. Cassine aethiopica, which is also common in coastal forests, was slower growing than Rhus, but less shade tolerant than C. peragua and Sideroxylon and would probably benefit from canopy gaps for establishment. Pappea capensis and Schotia afra, which also occur in open savanna vegetation, demonstrated a growth and morphological pattern indicative of species adapted to periodic drought, in having a high ratio of woody conductive tissue to leaf tissue with accompanying slow growth. Their relatively poor performance in deep shade suggests that canopy gaps would benefit their recruitment. We concluded that canopy gaps may be essential for recruitment of the full species complement in sub-tropical thickets.

Abstract: Comparison of a set of paleogeographic maps of Africa for the Last Glacial Maximum (LGM) and the Holocene Climatic Optimum (HCO) allows us to discuss the contribution of paleocontinental proxy-data in paleobiomass calculations and their accuracy. Maps show considerable shifts in the area covered by the main ecosystems. In this study we have quantified these areal changes, from the LGM to the HCO, in terms of variations in carbon storage. Each biome has been assigned a carbon density in living and soil organic matter. From desert to tropical forest the mean carbon densities vary from 0 to 20 kg m-2 for phytomass and from 0 to 13 kg m-2 for soil (peat excluded). During the world deglaciation Africa was a sink for 154 Gt (standard deviation 42 Gt) of atmospheric carbon. Since the HCO Africa has been a source of carbon. More recently human deforestation is responsible for a carbon flux towards the atmosphere which is ten times the mean annual flux due to vegetation change in response to climate change. Extended to a global scale this regional test shows that the paleoenvironmental approach is more appropriate for paleobiomass estimates than calculations based only on oceanic data.

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Abstract: Ground data from the Central Plains Experimental Range in northeast Colorado and Landsat satellite images of that area acquired in August 1989, June 1990, and September 1990 were used to evaluate the level of association that can be expected from a univariate model relating spectrally derived vegetation indices (difference, ratio, and normalized difference vegetation indices) and dried green vegetation biomass. The vegetation indices were related to the ground sample estimates using a sample point, spectral class, and greenness strata approach. No strong relationships were found between the vegetation indices and sample estimates of dried green biomass using the sample point approach. The spectral class approach produced significant results only for the June 1990 sample period (r=0.96). Significant relationships were found for the August 1989, June 1990, and September 1990 samples periods (r2=0.95, 0.71, and 0.95, respectively) when the data were aggregated by greenness strata. The high degree of association between green biomass and the NDVI, obtained when the data were combined into greenness strata, indicated that it is possible to predict green biomass levels on semiarid rangelands using univariate regression models.

Abstract: The paper describes the natural framework of the Booro-Borotou (1.36 km2) basin: geomorphology, geology and soil, vegetation and surface features, precipitation and evapotranspiration. Several experiments (rainfall simulation, surface runoff traps), together with the observation of internal storage and floods, show the complexity of runoff processes. Discussion confirms that, in this elementary watershed, water emerging as runoff travels by multiple routes.

Abstract: Soil and crop growth micro-variability, which reduce crop yield and complicate interpretation of agronomic field experiments, are traditionally seen as problems. Data are presented that suggest that, in subsistence farming systems in the semi-arid tropics of West Africa, where nutrient and water availability alternate in limiting agricultural production, soil and crop growth micro-variability may be an asset to farmers. These farmers are more interested in relatively good yields in poor rainfall years (a satisfactory level of [`]assured' production) than in good average yields. Although soil and crop growth variability limit bumper harvests, they may also reduce the risk of poor harvests and consequent food supply problems. Soil and crop growth micro-variability in the semi-arid tropics of West Africa should be studied more systematically, as part of a systems approach to agricultural research which includes the use of simulation models.

Abstract: This paper analyses the role of agriculture in the economic development of West Asia and North Africa, with special reference to the interactions between oil wealth, population growth, agricultural development and the need for agricultural research. Since the 1960s agricultural supply lagged behind demand, which grew rapidly as a result of population increases and rising incomes. Following the oil recession of the 1980s it was felt that the development of the agricultural sector should be less dependent on other sectors, particularly oil. The possible roles of agriculture in the region's future economic development are outlined, with the implications for agricultural research. Special attention is given to the natural resource constraints affecting the region's agriculture (particularly water), and to the issues influencing the identification of research priorities.

Abstract: The preservation of the non-renewable soil resource is a vitally important aspect of the long-term development of conservation tillage and pasture production systems in the Pacific region. Improved grasses and legumes are commonly sown in New Zealand and Australia to increase pasture and animal production. Pastures sown by conventional cultivation are becoming increasingly expensive and time consuming. Crops and pastures sown in rotation by conservation tillage methods (including no-tillage) are becoming more common. This paper summaries major soil and plant management factors and their interactions with the environment and machinery, which improved biological reliability and sustainability of no-tillage in the Pacific region. Collectively the research has demonstrated that the habitat of seeds under no-tillage together with their resulting seedling microenvironments, are pivotal to yield and are influenced by micromanagement of the soil, surface residues and soil fauna in the sown slot zone. These parameters are themselves influenced by the action and the design of seed drill openers. Soils under sustained no-tillage systems, involving organic matter return, contain vapour-phase moisture even in dry soils, often together with oxygen-enhanced diffusion potential largely unmatched by tilled soils. Description of technology designed to create and exploit such environments is made. The causal processes of failures and the high biological risks associated with conventional no-tillage drills are also explained. Provided appropriate pest control measures are taken, this technology has resulted in biologically predictable, reliable and sustainable crop establishment and production systems.

Abstract: West African soil resources have high potentials for enhancing agricultural productivity, if well-managed and restored. In this context, the importance of tillage systems have not been fully appreciated as an integral part of good farming systems in order to tally with the peculiarities of the soil, crops and the environment. Most improved tillage systems are not widely used, although the relatively small-scale uncontrolled application of mechanical tillage has had untold adverse effects on properties and productivity of soils in the humid and subhumid regions. In contrast, mechanical soil tillage involving deep plow-till and soil inversion has proven beneficial on compact soils of arid and semi-arid regions. The plow-based systems not only reduce soil bulk density and soil strength but also improve the efficiency of water and nutrient use. The exposure of structurally unstable Alfisols and Ultisols predominant in the humid and sub-humid regions by mechanical tillage can cause more adverse effects than beneficial effects on soil properties and crop yields, especially on a long-term basis. On the other hand, the no-till system with crop residue mulch can maintain favorable soil properties. The conservation tillage system, however, requires more research to make it applicable to diverse soil types, crops and ecoregions. Apart from the long-term effects of tillage on the level of soil organic matter and the attendant release of nutrients, the effects of tillage systems on the chemical properties of soil are often contradictory and are confounded by many other factors so that clear-cut cause and effect relationships are not obvious. The interactions between fertilizer application, liming, soil organic matter content and tillage systems, especially on acid soils, are such examples. More detailed studies on nutrient dynamics under different tillage systems are necessary. The interactions between the relatively new technologies of alley cropping and agroforestry which allow a more continuous use of the land should be investigated vis-à-vis tillage systems. Long-term, well-designed, adequately equipped experiments (which are scanty in West Africa) should be encouraged to elucidate and confirm results of many short-term experiments.

Abstract: Spatial dependence is a fundamental structure of spatial data that can be readily measured. Change in landscapes can be monitored effectively using measures of spatial dependence. Scale of fluctuation analysis estimates the dimensional extent to which data are significantly autocorrelated by observing the behavior of sample variance under extended local averaging. Algorithms to estimate the one-dimensional scale of fluctuation (correlation length) and two-dimensional scale fluctuation (correlation area) in image data are described. The approach is demonstrated with an analysis of a 9-year TM image series of a tallgrass prairie preserve, Konza Prairie Research Natural Area, to assess the impact of bison on the spatial patterning of vegetation.

Abstract: An analysis tool was developed to simulate primary productivity and crop yields for both present and possible future climate conditions. Southern Africa was delineated into 712 relatively homogeneous climate zones, each with specific climate, soil and vegetation response information. The primary productivity and crop yield models were linked with the climate zones via a cellbased agrohydrologlcal model, with the final output coordinated using a Geographic Information System. The results of this preliminary study show a large dependence of production and crop yield on the intra-seasonal and inter-annual variation of rainfall. The most Important conclusion from the study is the readiness of the developed tool and associated infrastructure for future analysis into social, technological and political responses to food security in southern Africa.

Abstract: Introduction of mechanized agriculture induces profound changes in soil characteristics. Soil compaction originating from mechanical land clearing, mechanized cultivation, and continuous cropping is aggravated by crusting and hard-setting phenomena of soils, and widespread occurrence of naturally compacted upland soils and subsoil gravel horizons. Natural and anthropogenically induced soil compaction has detrimental effects on growth and yields of a wide range of crops. Furthermore, compaction can persist for a long time if no adequate measures are taken to minimize or alleviate it. In humid and subhumid regions of Africa, the no-tillage system with crop residue mulch is an important method of controlling soil compaction, followed in significance, by biological and mechanical loosening where motorized land clearing is the causative agent. Biological methods involve cover crops and alley cropping or agroforestry. Where new land areas need to be opened up, land clearing should be done by the slash-and-burn method, so that most of the nutrients in the vegetation are returned to the soil. Where mechanical land clearing is inevitable, forest removal should be done by the use of shear blade, whereby most of the roots and stumps are left in the ground intact, and the forest litter is not removed. In semi-arid and arid regions of Africa, alleviation of soil compaction can be done by two methods. One method is to use the controlled traffic tillage system. Controlled traffic results in both a loose-rooting zone and a firmed traffic lane, thereby providing good plant growth and trafficability for timely field operations. The second method is to use mechanical loosening techniques, i.e. ploughing by animal traction or tractor power, chiseling, deep ripping, subsoiling, and tied-ride system. The effect of mechanical loosening, however, tends to be of short duration if the ensuing field traffic is not controlled.

Abstract: Evidence is accumulating that land use changes and other human activity during the past 100 to 200 years have contributed to decreased CH4 oxidation in the soil. Recent studies have documented the effect of land use change on CH4 oxidation in a variety of ecosystems. Increased N additions to temperate forest soils in the northeastern United States decreased CH4 uptake by 30 to 60%, and increased N fertilization and conversion to cropland in temperate grasslands decreased CH4 uptake by 30 to 75%. Using these data, we made a series of calculations to estimate the impact of land use and management changes which have altered soil the CH4 sink in temperate forest and grassland ecosystems. Our study indicates that as the atmospheric mixing ratio of CH4 has increased during the past 150 y, the temperate CH4 sink has risen from approximately 8 Tg y-1 to 27 Tg y-1, assuming no loss of land cover to cropland conversion. The net effect of intensive land cover changes and extensive chronic disturbance (i.e., increased atmospheric N deposition) to these ecosystems have resulted in about 30% reduction in the CH4 sink relative to the soil sink assuming no disturbance to any of the temperate ecosystems. This will impact the global CH4 budget even more as atmospheric CH4 concentrations increase and as a result of further disturbance to other biomes. Determining the reasons for the decreased CH4 uptake due to land disturbance is necessary to understand the role of CH4 uptake in conjunction with the increasing atmospheric CH4 concentrations. Without accounting for this approximately 20 Tg y-1 temperate soil sink, the atmospheric CH4 concentration would be increasing about 1.5 times the current rate.

Abstract: In the framework of the Netherlands Remote Sensing Program, a system for monitoring of actual evapotranspiration and biomass development on the basis of METEOSAT is developed. Because of its operational characteristics, the method is such that it requires minimal input other than the METEOSAT data and can run fully automatic on a microcomputer. In this article, the methodology, including: calibration, atmospheric correction, radiation and energy balance mapping, and biomass simulation is described. The method has been applied during a complete growing season to a part of West Africa, with Burkina Faso in the center. Processing results in the form of METEOSAT-derived evapotranspiration (MDE) and METEOSAT-derived herbaceous biomass (MDB) maps are presented. They are compared with NOAA-NDVI data and verified with rainfall and biomass "ground truth." A new methodology--"triangular regression analysis"--is introduced to assess the stochastic errors in the satellite and ground data. It is finally concluded that METEOSAT can provide precise estimates of areal evapotranspiration and biomass. In terms of areal biomass, the stochastic errors in MDB and NDVI are both small compared to the pixel sampling error in the biomass field data.

Abstract: Polleniferous sediments from southern Africa associated with past warm episodes before the Last Glacial Maximum, are rare. Interpretation of environmental conditions during these phases are complicated by difficulties of dating. In sediments from the northern areas, north of 28°S, the prominence of tropical woodland pollen suggests that the period between 7000 and 6500 yr B.P. was associated with optimal temperatures during the Holocene. Identifying the warmest phase in the southern high-lying grasslands and semi-arid Karoo shrublands south of 28°S is difficult, because unlike the savanna areas of the north, they do not yield good pollen indicators for changes in temperature such as those of frost sensitive trees. However, some pollen sequences from further south along the southern coast of Africa (34°S) and at Marion Island in the Southern Ocean (47°S), suggest that the Holocene temperature optimum occurred at about the same time in the sub-antarctic area in the south and the subtropical regions in the north. The advent of moister conditions in southern Africa during the early to middle Holocene, is generally recorded earlier (ca. 7500-6500 yr B.P.) in the north at ca. 26°S, than around 31°S, (ca. 5000 yr B.P.). This change is provisionally associated with a relative shift in seasonality from a predominance of all-season precipitation to a greater proportion of summer rainfall, which apparently reached the southern Karoo areas two thousand years later than the northern Bushveld region.

Abstract: Multiple land-use designs are becoming increasingly necessary in semi-arid Africa as growing populations focus numerous production systems onto spatially limited arable lands. Engineering distinct land uses into a single area ideally requires that land-use components complement each other, and operate in predictable magnitudes. Quantitative evaluations of components to be included in multiple land-use designs are necessary to determine both how components would [`]fit' together, and how these would serve populations participating in distinct production systems. With data gathered in Somalia, this study considers a design in which fodder-producing trees and irrigated agriculture could be integrated. Following a discussion of the benefits of such an integration, this analysis focuses on a quantitative examination of potential livestock carrying capacity from Acacia albida trees in an irrigated area. Comparisons are made with observed livestock numbers in order to determine if such a design could accommodate the seasonal influx of nomadic herds. The land-use elements that comprise carrying capacity are themselves examined to see which elemens might be managed to offset or take advantage of those which are not easily managed.

Abstract: Population pressures within southern Africa are forcing people to increasingly crop land of a diverse and fragile nature where the risk of environmental degradation is high and current yields are low. Much of the earlier tillage research is not applicable to these conditions as efforts have concentrated on commercial farming with tractors for the higher potential regions. It is only in the last 10-20 years that attention has increasingly focused on the tillage requirements of small-scale farmers in these harsh water-scarce semi-arid regions. There is now a clearer understanding of the basic environmental constraints to crop production in terms of climate, poor soil fertility and structure and considerable advances have been made towards improved systems but there is still a lack of appropriate tillage system recommendations. All too frequently researchers have omitted the farmer input from their considerations and endeavours. Consequently limited consideration has been given to the social (e.g. land tenure), economic (e.g. credit), energy (labour and draught power) and technical constraints experienced by the small farmers they are trying to help. The need to develop more adoptable interim systems is therefore indicated but the slim margins within which small farmers must operate highlight the continuing need for sound tillage research to backstop the development of sustainable conservation systems.

Abstract: Subshrubs are the dominant plant type of rangeland in the north-western coastal zone of Egypt. As animal husbandry depends to a large extent on this feed source, effects of grazing on plant growth were investigated. Experimental results showed that grazing extends the growing period of subshrubs. the mechanism underlying this phenomenon is lower water use by plants in the rainy season and the consequent higher availability in the dry season. Owing to the characteristic growth form of the subshrubs, leaves are protected inside their dense structure, ensuring plant growth while grazing takes place. Simulations suggested that water storage in deeper soil layers is a function of grazing intensity and annual precipitation. It is suggested that a considerable grazing pressure is necessary to maintain the rangeland. Regeneration of the rangeland is a problem and physical removal (firewood) is a greater danger to its persistence than is grazing.

Abstract: The enormity of the African refugee problem underscores the importance of resettlement issues in land use planning. Efforts to resettle subsistenceoriented agricultural populations have often come into conflict with host or in-place land uses as competition for scarce resources leads to land degradation, violence and the failure of resettlement schemes. The success of refugee resettlement will depend to a large extent on the degree to which host and refugee land use patterns become integrated or reconciled. The majority of African refugee populations reside on the Horn and in the Sahel, where arid and semi-arid ecologies predominate and pastoralism is a major form of land use. This study considers a resettlement design that integrates refugee agricultural land use patterns with those of the host pastoralist land use in the context of the frequent droughts that visit the area. Given the magnitude of dislocation problems on the continent, successful resettlement will play an important role in African agriculture and development.

Abstract: Changes in vegetation cover over time in arid rangelands can be used to monitor land condition and to identify processes of land degradation. This article describes how a cover index can be derived from Landsat MSS data and how the index can be standardized to remove atmospheric effects and differences in sensor calibration between spacecraft. Tests carried out on 1-m-diameter radiometer targets show that the best separation between soil, rock, or stone and vegetated surfaces occurs in the Band 4-Band 5 data space. This separation includes both dry and green vegetation whereas in the commonly used Band 5-Band 7 data space the separation is much less clear if the vegetation is not green. We have therefore developed a vegetation cover index in the Band 4-Band 5 data space. This index, known as PD54, has a similar form to the perpendicular vegetation index of Richardson and Weigand (1977). It is calculated by identifying a soil line or, more correctly, an upper soil band limit, and then determining the perpendicular distance of each pixel from that line. The perpendicular distance is scaled using distances calculated for points or pixels which have 100% cover. In the normal mix of rangeland vegetation at the pixel scale, these reference pixels occupy a very limited area of the Band 4-Band 5 data space and can be treated as a point or as a line of limited length and with a slope similar to that of the soil line. PD54 performs better than several other indices when tested at the Landsat MSS pixel scale using aircraft-mounted radiometer data. It is also less subject to systematic errors when shifting from one vegetation type to another. The principal difficulty in using PD54 as a cover index arises because there is no single soil line. Instead, the position of that line varies with both Munsell soil hue and chroma. Attempts to standardize PD54 for Landsats 1, 2, 4, and 5 showed that the commonly used approach of converting data to exoatmospheric reflectance based on published radiometer gains and offsets does not work. Furthermore, the dark pixel subtraction method of haze correction does not remove all atmospheric effects. It is, however, possible to remove the effects of differences between the different Landsat MSSs and inadequate haze correction by identifying the extremes of the Band 4-Band 5 data space on a particular scene and using them to scale PD54. Once this is done, PD54 gives substantially better estimates of cover from MSS data than Band 5 values which have supposedly been radiometrically standardised.

Abstract: The role of empiricism in predicting mean annual primary production at the mesoscale is demonstrated through development of a simple model (RESAP) for application over all land surfaces within a given savanna region. The model is necessarily pragmatic and constrained by availability of standardized data on a network scale. The model was applied to a large test area in southern Africa and provides results using a SYMAP routine for representing spatially continuous information. The model discrimates between woody and herbaceous plant components and also assesses the effects of anthropogenic disturbance on plant productivity. Productivity of natural vegetation was found to be remarkably equitably distributed across the diverse conditions which suggests various compensatory production mechanisms at the mesoscale. Model output graphically indicated that intensive agriculture successfully converts total productivity into both a more usable and more accessible form at the apparent cost of long-evolved total production levels.

Abstract: Firmly based palaeoenvironmental data for southern Africa prior to 40,000 yr B.P. are sparse. The only site which is likely to be able to provide useful information for Isotope Stage 6 is the Pretoria Saltpan; warming at the end of this stage appears to have been rapid and to have been associated with increased precipitation in the interior of the sub-continent. In contrast, dry conditions appear to have prevailed in the southwestern areas during the warmest phases of Isotope Stage 5. This regional difference first became apparent during the Pliocene. During the Last Glacial Maximum temperatures based on isotope ratios reached their lowest values of 5-6°C below present, in the southern part of the subcontinent, and widespread dryness prevailed. Warming became quite rapid after 16,000 yr B.P. and was almost everywhere associated with a marked increase in wetness to around (or even above) present levels. This warming phase continued until the beginning of the Holocene; the terminal Pleistocene was, however, marked by desiccation in the arid western areas. Of special interest is the Holocene altithermal, which can be placed between 7000 and 6500 yr B.P. The extent of the temperature rise cannot be specified with any precision, but probably did not exceed the Holocene mean by more than 2°C. In the southern Cape and Karoo more summer rain apparently occurred than during Isotope Stage 2 and in the early Holocene, and this trend towards year-round rainfall appears to have become increasingly pronounced through the later Holocene until about 2000 yr B.P. This argues, in a general way, for an increase in the proportion of summer rainfall with rising temperature in the present winter rainfall areas of southern Africa.

Abstract: The response of six forage crops to salinity was investigated in the field by means of a double-line source experimental design. The crops were Rhodes grass (Chloris gayana Kunth) cv. common, Bermuda grass (Cynodon dactylon L. Pers.) cv. Suwannee, Kallar grass (Leptochloa fusca L. Kunth), salt (spike) grass (Distichlis spicata L.), seashore paspalum (Paspalum vaginatum Swartz), and alfalfa (Medicago sativa L.) cv. Gilboa. The trial was carried out over two growing seasons, 1990 and 1991. The electrical conductivity of the irrigation water (ECi) ranged from 1.2 to 9.5 dS/m, and the mean seasonal electrical conductivity of the saturated soil paste (ECe) from 3 to 14 dS/m. The salt tolerance of the six forage species was found to be: salt grass > Bermuda grass > seashore paspalum > Rhodes grass > Kallar grass = alfalfa. In the first season, dry matter yields of salt grass, Bermuda grass and seashore paspalum were not affected by a soil ECe of 14 dS/m. In the second season, only the yield of salt grass was unaffected. Rhodes grass had, in the second season, exceptionally high annual yields (5.0 kg/m2) with fresh water irrigation. Thus, even though in comparison with most other grasses the yield of Rhodes grass was reduced by salinity (about 6% yield reduction with every unit increase in ECe above a threshold of 4.0 dS/m), its yield exceeded that of most species at an ECe of 8 dS/m. There was no consistency in the effect of salinity on crude protein, fiber and ash contents among the six forage grasses. In the second season ash content varied from 8% for Bermuda grass to about 15.5% for seashore paspalum. Crude protein content varied from ~11.5% for Rhodes grass to ~16% for Bermuda grass and 22% for alfalfa. Both Bermuda grass and salt grass had a relatively high fiber content (40-42%). When brackish water supply was limited, dry matter yield of salt grass was double the yield of the other species, indicating an advantage of this species under non-irrigated rangeland conditions. This work shows that brackish water with an ECi of>=10 dS/m may be used for irrigation of certain forage crops without any yield reduction.

Abstract: Charred Gramineae (grass) cuticle stomatal cells and pollen have been recorded in many well sections of Early Miocene to Pleistocene age from the coastal and offshore region of the Niger Delta. Gramineae microfossils were examined from approximately 4000 samples during the course of a palynological study aimed at establishing a high resolution biostratigraphic zonation scheme for the Niger Delta. Opaque (charred) cuticle, formed as a result of savanna fires, is intermittently abundant from the basal Middle Miocene and provides an excellent tool for stratigraphic correlation and palaeoclimatic interpretation. Intervals of abundant charred cuticle are considered to represent essentially dry periods when savanna vegetation extended over most of the delta. The Gramineae cuticle and pollen record suggests that climates became increasingly dry from the latest Early Miocene and that Late Miocene climates were particularly arid. After a return to a mainly everwet regime in the earliest Early Pliocene, the Late Pliocene and Pleistocene climates were characterised by alternating dry and uniformly moist climates. The pollen record suggests an expansion of Gramineae into swamp habitats during the Pleistocene. The period of Late Miocene dessication may have been responsible for the extinction of much of the West African humid tropical flora.

Abstract:

Abstract: Food plant selection by herbivorous mammals and by harvester ants Messor capensis was compared for three sites differing in past and present management in the southern Karoo, South Africa. At all three sites the ants collected an estimated 4·1 million seeds (5·2 kg)/ha/y which amounted to 10% of the seeds and 18% of the annual seed biomass production of common plants. Seed removal by M. capensis did not appear to compound the effects of herbivorous mammals on the reproductive potential of plants, because ants concentrated on the most abundant seeds > 0·3 mg. Ant granaries on degraded rangeland contained more seeds of ruderals and of plant species unpalatable to sheep.

Abstract: The endemic seed plant flora of the north-eastern Transvaal Escarpment (part of the Afromontane Region) is assessed in terms of the region's lithology (mainly rocks of the Transvaal Sequence). A total of 81 species and infraspecific taxa are endemic or near-endemic to the quartzitic and related rock types of the Black Reef Quartzite Formation, Wolkberg Group and Timeball Hill Formation (c. 3880 km2) and a total of 32 species were recorded as endemic or near-endemic to the dolomitic Chuniespoort Formation (c. 2100 km2). As a major centre of biodiversity, we propose to name this escarpment region of Transvaal Sequence, the Wolkberg Centre. Two subunits of endemism are recognized: the Blyde Subcentre in the south, and the Serala Subcentre in the north. Although the number of endemics on dolomite is less than half the number on quartzite-derived substrates, the degree of endemism is higher on the former. The majority of dolomite epidemics are confined to the drier areas and are not of such strong Afromontane affinity as the quartzite ones. Nearly all the endemics are herbaceous, confirming to the observation that regional endemism levels in the Afromontane Region are high in grassland, but low among the tree flora of the patches of undifferentiated evergreen forest. The vegetation of the Wolkberg Centre, especially the grassland, is under considerable pressure, particularly from the timber industry and invasive alien plants. Existing and proposed conservation areas in the centre are listed.

Abstract: The Pretoria Saltpan is a circular crater 1130 m in diameter and is situated some 40 km N of Pretoria (lat. 25°34'30''/long. 28°04'59''E). A recent tube sampling and core drilling programme has revealed an infilling consisting of some 90 m of fine lacustrine sediments (chiefly organic muds, underlain below 30 m depth by micrites) which rest upon a further 61 m of coarse clastic debris. Granite bedrock was encountered at - 151 m. Broad sedimentary zones correspond with major phases in the evolution of the crater lake. Superimposed cyclical patterns of accumulation reflect environmental changes on millenial to seasonal timescales. 14C age determinations on algal debris from the upper 20 m of the core indicate a mean rate of sedimentation of about 1 m/2000 yr, suggesting that the lacustrine sequence may span almost 200,000 yr. Over this period major environmental changes are apparent from sedimentological, chemical, mineralogical and isotopic analyses of the core and studies of the pollen spectra and diatom assemblages present within it. This long continental sequence is therefore providing a high-resolution palaeoenvironmental record for southern mid-latitudes over much the same period as is covered by the Vostok ice-core in Antarctica.

Abstract: A multiple-source surface energy balance model for use in general circulation models (GCMs) is developed. The model recognizes three biome architectures: closed canopies (e.g. forest), biomes with two distinct canopies (e.g. savannah) and agricultural crops. The model is based on the Penman-Monteith approach and solves for latent and sensible heat flux without the need to specify a surface temperature or humidity. The two canopies and soil layer are allowed to interact through the specification of a within-canopy saturation deficit and temperature. One or two canopy surface resistances and a soil surface resistance can be specified. The model is calibrated for tropical rainforest, tropical savannah and an agricultural crop. Good agreement is obtained for both hourly and long term evaporation. Two responses to soil moisture were identified for the savannah: a long term one and a short term one. The latter relates to the switching of evaporation from a demand controlled to a supply controlled process. Some problems in the specification of roughness lengths for sparse crops lead to errors in the calculation of momentum exchange. Suggestions are made for improvement. Possible applications of the model are discussed.

Abstract: The Namib and Kalahari deserts preserve evidence of a long history of aridification in southern Africa. The earliest sedimentation within the Kalahari Basin dates to the Late Cretaceous, but the first onset of arid conditions probably occurred in the Early Tertiary; other arid episodes recurred throughout the Tertiary but the development of the Kalahari Sand Sea, with its linear dune system, is unlikely to predate the Late Pliocene. This, the largest single body of aeolian sand in the world, is now largely stabilized by vegetation, but evidence exists for its periodic reactivation throughout the Quaternary. Although episodes of dune building are evident within the Namib region as early as the Eocene, the Namib Sand Sea, represented by the now consolidated Tsondab Sandstone Formation and the overlying active dunes of the Sossus Sand Formation, does not predate the Upper Miocene. Evidence from the Upper Pleistocene suggests, however, that there were significant fluctuations in the degree of aridity which prevailed during and after the last glacial period.

Abstract: A development path for South Africa that will create jobs and reduce poverty must include the encouragement of greater labor intensity in agriculture, especially of smallholder farming, which was suppressed under apartheid. There is, however, widespread skepticism -- on both the left and the right -- about the prospects for more labor-intensive farming. But this skepticism is called into question by both theory and evidence of the advantages of small-scale production in certain products and circumstances; there are now numerous examples of this in many parts of the world. The paper discusses the preconditions for the development of such farming in South Africa, including land reform and the need to reorient investment and supporting economic and technical services (research, training, marketing, credit) from the privileged, large-scale "white" farms to the undercapitalized and neglected black smallholders.

Abstract: Generally, Rb-Sr biotite and phlogopite ages range from ~ 2050 Ma to ~ 1950 Ma between the Murchison-Thabazimbi and Triangle-Tuli-Sabi shear zones of southern Africa in the rocks comprising the Central and Southern Marginal Zones of the Limpopo Belt and adjacent portions of the Kaapvaal Craton. In some shear zones, however, similar ages ocurr as young as ~ 800 Ma. In contrast, within the Kaapvaal Craton south of the Murchison-Thabazimbi Shear Zone, Rb-Sr biotite ages range between ~ 3150 Ma and ~ 2100 Ma and show no regular distribution. In all cases, the ages are interpreted to indicate the time elapsed since the biotite last cooled below its closure temperature, approximately 320°C. The regular pattern of 2050 Ma to 1950 Ma Rb-Sr biotite ages north of the Murchison-Thabazimbi Shear Zone suggests that the present erosional surface approximates a paleo-isothermal surface. This surface was exposed by uplift and erosion which was completed by ~ 1900 Ma to 1800 Ma ago when the sedimentary and volcanic rocks of the Soutpansberg Group were deposited. The regional uplift was accommodated by motion on the Murchison-Thabazimbi and Triangle-Tuli-Sabi Shear Zones and probably was related to tectonism associated with the emplacement of the anorogenic Bushveld and Phalaborwa complexes. Other anorogenic granitic magmatism accompanied uplift. The depth represented by the paleo-isothermal surface and the magnitude of the uplift that exhumed it cannot be constrained precisely. It is suggested, however, that the majority of the 10 to 15 km by which crust in this area is thinner than that of the adjacent cratons is the manifestation of this uplift.

Abstract: Methods used in the analysis of 1163 pieces of charcoal from Elands Bay, South Africa, are described. Results from three archaeological sites (Tortoise Cave, Spring Cave and Mike Taylors Midden) show that the most common woody species at Elands Bay today also occurred in the archaeological record over the last 4000 years. This would suggest that climatic change over the last 4000 years has not been sufficient to influence the species composition of wood brought into the sites by people. There are, however, differences in species composition of the charcoal from Tortoise Cave on the one hand and Mike Taylors Midden (MTM) and Spring Cave on the other. These differences reflect fundamental differences in environment between the sites.

Abstract: A deterministic simulation model (FORAGE) has been developed as an interface between the plant and animal components of a general rangeland ecosystem model (SPUR). The model predicts forage intake and diet selection of grazing beef cattle by simulating the mechanistic components of grazing behavior. Bite size, rate of biting, rate of intake and grazing time are modified by changes in sward characteristics. Sensitivity analyses revealed that the model is sensitive to underestimation of critical parameters. The model suggests that, when forage availability is limited, intake is limited by rate of intake and grazing time.

Abstract: Poverty in Africa is primarily a rural phenomenon. Its growing incidence is partly due to slow growth in GDP induced by economic policies that discriminated against agriculture. Urban bias in social spending has left the rural poor with little or no access to basic needs. Technological change, improved rural infrastructure and an efficient marketing environment are needed to enhance agricultural growth and maximize returns to the rural producer. Improving the human capital of the rural poor will expand their employment opportunities. Cost-effective transfer programmes would provide a safety net for the vulnerable poor.

Abstract: Now that governments are beginning to consider actions to respond to the potential threat of global warming (even if they do not yet believe that it will definitely occur), their representatives search the scientific literature for [`]clues' about the positive or negative impacts of a few degrees Celsius increase in global temperature. There is a growing number of [`]guesstimates' (often called scenarios) about climate change impacts in sub-Saharan Africa. A review of the existing scenarios highlights conflicting, if not opposing, views about those impacts. Such scenarios must be used with caution and labelled as speculation. No single scenario should be used for determining irreversible policy responses to the potential regional consequences of global warming.

Abstract: Since its beginning about ten thousand years age, agriculture has spread steadily around the world to become a dominant form of land management on all continents. Agricultural practices have affected the welfare of many organisms other than the primary targets of its manipulations. Prior to the 1960's, with the slow rate at which new land was brought under cultivation, there was little concern about the relation between agriculture and conservation. Low intensity agricultural management systems allowed survival of nontarget economic species which also gave relatively higher value to their indirect benefits (recreational, aesthetic, economic). But the dramatic increase in intensity of management and capital investment in agriculture after World War II heralded in a new era in which the multiple use of the land declined as the intensity of management, and, hence, the value of the market crop, increased. Little attention has been paid to ways changes in agricultural practices might have beneficial consequences for conservation. Agricultural practices can be used as key experimental variables and as laboratories to provide conservation biology with systems to investigate many ecological processes. The goal of the discussion is to provide an overview of conservation biology and agriculture and the relationships that could help determine how agricultural objectives and practices could be modified to enhance the conservation of biological resources for the long-term viability of agriculture. Traditional and modern technological practices both can contribute to the development of new systems. A provisional classification of organisms is offered to assist in the analysis of the interactions between agricultural practices and the organisms. Agricultural systems are classified into monoculture, mixed farming, pastures and rangelands, forestry, intensive animal production systems, and integrated systems. An identification of key techniques and practices within each type of agriculture, the spatial scale of agriculture, lead to a clarification of how agricultural operations could be changed and how such changes would affect non-target species, management options, and research opportunities.

Abstract: Small East African goats (191) were observed for over 3 months while foraging in their natural environment. The vegetation composition of 48 plots measuring 10 × 10 m was assessed quantitatively. From recordings of feed selection and vegetation availability, preference indices were calculated for groups and individual plant species. Green vegetation covered 79% of the total sample area in the wet and 40% in the dry season. Goats spent 33 and 37% of their grazing time actively eating in the wet and dry period, respectively. The average preference index for browse was stable, whereas it declined considerably for grass with progressive dryness. Animals gained weight throughout the experiment. Highest variability was found in acid detergent lignin (ADL) of foraged browse species. Digestibility in vitro of organic matter (IVOMD) varied from 38 to 65% and content of metabolizable energy (ME) from 5.2 to 9.7 MJ kg-1 DM. Goats selected a ration containing 13.5% crude protein and 7.24 MJ ME in DM. No significant correlations were found between IVOMD, ME and preference index. Multiple correlation for crude fat and hemicellulose with preference index was highly significant (r2 = 0.67, n = 21). The ranking order for browse emerging from in vitro results did not match with animals' choice.

Abstract: The aftermath of fire was examined in a New Zealand grassland reserve, dominated by the tall tussock Chionochloa rigida. Deliberate fire has not previously been used in reserve management in New Zealand. Following an accidental fire in part of the reserve in autumn 1976, part of the remainder was deliberately burnt in the following spring for an experimental comparison. Vegetation changes were monitored until 1988. After both fires, the exotic grass Agrostis capillaris was abundant. Shoot frequency of Chionochloa rigida was low after fire due to the loss of the canopy, but generally increased. Twelve years after the fire, the vegetation was still different between areas of different burning history. In the unburnt area, the shrub Leptospermum scoparium was replacing Chionochloa. Species frequencies were used to classify the vegetation by Cluster Analysis. A transition matrix was calculated for the communities so derived, and a Markovian model used to predict future vegetation changes. Medium-term replacement of exotic grassland by native tussock grassland was predicted, with replacement by native Leptospermum scrub after several decades. Native forest species, some now present in small amounts, could eventually replace the Leptospermum. It is recommended that Chionochloa grassland at this altitude should be burnt every 15-40 years to maintain the community. Chionochloa rigida is expected to tolerate this regime. Burning would prevent loss of the tussock grassland by scrub invasion and consequential scrub fires. Such fires would probably result in the replacement of most native vegetation by aggressive exotic shrubs, or, if they were controlled, by exotic grassland.

Abstract: The development of savanna-type grasslands is a relatively recent phenomena in East Africa. The stable carbon isotopic composition of paleosol carbonates from fossil localities in East Africa show that C4 vegetation was present by amout 8-9 Ma but made up only a relatively small proportion of the total biomass. Although the proportion of C4 vegetation increased in the Pliocene and Pleistocene there is no evidence for the development of virtually pure C4 grasslands, as is characterized by tropical grasslands today, until Middle Pleistocene times. This has important implications concerning the evolution of mammals in Africa, including hominids.

Abstract: Snakeweeds, Gutierrezia spp. (Compositae), are native plants that are serious weeds in rangelands of the southwestern United States and northern Mexico. Although the genus apparently originated in North America, 7 species occur in Argentina and 5 in Chile. In Argentina, we found 79 species of insects, 1 mite, and 1 plant pathogen on the 3 species of Gutierrezia most similar to the North American snakeweeds; 33 of these species were observed feeding or had a high probability of feeding on Gutierrezia. Of these, 17 species of insects appear to have narrow host ranges and are possible candidates for biological control of snakeweeds in the southwestern United States. The insects that caused the most obvious damage were 5 species of root borers: the sesiid moth Carmenta haematica (Ureta); the weevil Heilipodus ventralis (Hustache); and 3 buprestids, Dactylozodes alternans Chevrolat, D. okea Gory, and Agrilus leucostictus Klug. Other insects that may have biological control potential were two species that fed on flowers and seed heads, a pyralid moth (Homoeosoma n. sp.) and a tephritid fly (Trupanea patagonica (Brethes)); a leaf beetle (Stolas ingrata (Boh.)); and 2 species of stem-gall formers, an unidentified gelechiid moth and a tephritid fly, Strobelia baccharidis Rondani. The factors that may limit control, the ecosystem effects of controlling these native plants, and the approaches that can be taken are discussed.

Abstract: In this paper, the second part of a two-part series, the performance of a quasi-physically based rainfall-runoff model (QPBRRM) is evaluated for a set of 39 events from a small rangeland catchment (R-5) using a suite of alternative antecedent soil water content estimates. The data set used to glean antecedent conditions for the R-5 events, described in the companion paper contains 22 848 observations of soil water content made over a 4 year period. The performance of the model is improved by using estimates of antecedent soil water content that include consideration of spatial variability.

Abstract: Disease of domestic animals on rangelands is caused by a wide variety of agents (some infectious and some non-infectious). Disease is primarily a function of the ecosystem, where a shift in the relationships of the system components has led to an imbalance between the animal and its environment. The control and prevention of diseases is by interventions that change the system 039;s composition and/ or function so that the imbalance is corrected. Medicinal interventions play a major role, but may be costly and sometimes are ineffective and deleterious to the environment. Non-medicinal interventions may be just as effective where appropriate, mostly use resources from within the ecosystem and so have the advantage of often being more readily available and cheaper. This is particularly advantageous in the developing world.

Abstract: The profitability of animal traction technologies in semi-arid West Africa continues to generate much debate. The specific objective of this paper is to determine the profitability of, and the constraints to the adoption of, oxen traction technologies on smallholder farms in South-West Mali. A farm-level programming model of a representative smallholder farm was used to determine farm level adoption patterns, the impacts and the constraints to the adoption of alternative combinations of oxen traction technologies (i.e. oxen with plough and oxen with plough and weeder). The cropping system scenarios under which oxen tillage technologies are profitable for farmers in this zone are derived. Financial analysis of the multi-year net cash flows from adopting the oxen, plough and weeder technical package was performed. Modelling results show that the complete oxen-plough-weeder technology is financially profitable for farmers in the zone, but its profitability by being conditional on the expansion of peanut (cash crop) area requires structural changes in the product markets to allow farmers the opportunity to expand and market their output.

Abstract: A review is presented of dambo properties and hydrological data relevant to the determination of runoff response. The review focuses upon dambo distribution, topographic location, soil water regime, vegetation and channel characteristics, and the hydrological mechanisms reported to be operating within dambos. Collated statements on the influence of dambos on river flow regimes from 25 reports in seven different countries illustrate an absence of consensus on the influence of dambos on flood flows, low flows and total catchment runoff. A case has been established for dambos to be considered to reduce low flows in certain regions of Africa, by combining results from regional flow regime analysis and regional evaporation data from Zimbabwe, and by reassesing past studies of dambo hydrology in Malawi and Zambia.

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Abstract: Abstract. A review is presented on the literature about the distribution of savannas in humid climates in Africa and Asia and their vegetation dynamics. Sections are devoted to African lowland and montane savannas (the latter divided into southern, eastern, western and northern African), Madagascar, Indian subcontinent, SE Asia and New Guinea. It is concluded that the extension of savannas under humid climatic conditions and the relation to the distribution of forests is a function of cultivation, grazing by domestic and wild animals, present and previous climate, geomorphology and soil characteristics. Once established, savannas are often maintained by fires, both natural and man-made. Montane savannas are generally brought about by man's clearing, cultivation and burning. Fire is a stochastic variable; it creates an ecotone sensu stricto (an environmentally stochastic stress zone) at the forest/savanna border. On the other hand, if geomorphology and soil are the determinants, the transition between forest and savanna would have the character of an ecocline (a gradient zone) with fundamentally different conditions. In humid African lowland climates forests expand into savannas if the latter are not maintained by man. Whether forests also expand in less humid climates is disputed. In montane areas forest expansion may be delayed on degraded soils and when diaspores are lacking.

Abstract: This paper, the first part in a two-part series, is concerned with the interpretation of spatial and temporal variations in soil water content across a small rangeland catchment; two data sets are examined. The first data set is comprised of 25 728 soil water content measurements made at 34 sites over an 8 year period. The second data set consists of individual soil water content measurements made at 247 sites over a 6 day period. Geostatistical methods are used to describe variations in soil water content; general characterizations are made. In the companion paper the impact of antecedent soil water conditions is investigated for a suite of R-5 event simulations with a quasi-physically based rainfall-runoff model.

Abstract: The development of savanna-type grasslands is a relatively recent phenomena in East Africa. The stable carbon isotopic composition of paleosol carbonates from fossil localities in East Africa show that C4 vegetation was present by amout 8-9 Ma but made up only a relatively small proportion of the total biomass. Although the proportion of C4 vegetation increased in the Pliocene and Pleistocene there is no evidence for the development of virtually pure C4 grasslands, as is characterized by tropical grasslands today, until Middle Pleistocene times. This has important implications concerning the evolution of mammals in Africa, including hominids.

Abstract: Environmental effects on the variability of herbage production and nitrogen uptake of an ungrazed annual Mediterranean sward were studied with a well-tested simulation model. Meteorological data for a 21 year period were from a semi-arid site in the northern Negev of Israel and the observed daily rainfall was multiplied by 0.5, 1.0, 1.5 and 2.0 to simulate different rainfall zones. Rainfall regime, nutrient level and soil depth accounted for 83-91% of the variation in the standard deviation of herbage production (SDh) and of nitrogen uptake (SDn), respectively, while rainfall and nutrient level alone accounted for more than 95% of the variation in the coefficient of variation (CV) of both herbage production (CVh) and nitrogen uptake (CVn). Distribution of the accountable variation in SDh was divided among the three factors (24% rainfall, 40% nutrient availability and 18% soil depth), while the variation in CVh was the result predominantly of rainfall (93%), to a much smaller extent to nutrient availability (3%) and to a negligible degree to soil depth (0.1%). Greater nutrient availability tended to increase both SDh and CVh. SDh in relation to rainfall was highest in the intermediate semi-arid zone, but relatively low in both the drier and wetter zones. On the whole, CVh and CVn decreased with higher rainfall, even though the CV of rainfall was held constant. CVh and CVn sharply distinguished between the zone with less than 264 mm rainfall and higher rainfall areas. This, indeed, is the approximate dividing line between relatively reliable conditions for arable agriculture and submarginal conditions in the region. It is shown that the lower stability of herbage production, expressed as CVh, in drier regions is not so much a consequence of greater rainfall CV as of lower absolute amounts of rainfall. Under more humid conditions, greater stability (i.e. lower CVh) can be a result of nutrient deficiency, and not only a consequence of lower rainfall CV.

Abstract: This paper describes the development and initial validation of a simulation model designed to predict patterns of landscape use by cattle as a function of environmental conditions and spatial distribution of key landscape attributes. The model consists of environmental, physiological, behavioral, and landscape submodels. Information on climatic conditions from the environmental submodel is used by the physiological submodel to determined current physiological status of animals in terms of heat balance, water balance, and hunger status. Information on physiological status is used by the behavioral submodel to select and subsequently perform activities. Performance of activities then affects physiological state. The landscape submodel provides information concerning spatial relationships among and within different habitat patches. Landscape attributes influence animal behavior, and animal behavior then influences landscape characteristics. Several aspects of model performance were evaluated using new field data and literature information. Predicted animal water losses via respiration, sweat, urine, and feces, total time spent in various daily activities, and the sequence of these activities all are in general agreement with field data and literature information. However, more accurate prediction of respiration rate, which controls shade seeking behavior in the model, may require more sophisticated representation of the combined effect of temperature and relative humidity. Initial simulations, which examined seasonal differences in the effect of distance between shade and water on landscape use, demonstrated the capability of the model to address a wide variety of questions concerning utilization of heterogeneous landscapesby grazing animals.

Abstract: A pollen sequence in a relatively young hyrax dung midden in the Orange Free State, South Africa, shows marked changes in composition which can be related to environmental fluctuations. The midden from Clarens was dated by radiocarbon to the last thirty years on the basis of recent radiocarbon concentration levels of the atmosphere, which were artificially increased by extensive nuclear arms testing after 1954. Fluctuations in the pollen contents of the dung sequence conform with recent vegetation changes between 1947 and 1990, which are revealed by a series of air and other photographs. Details of the fluctuating pollen sequence can further be interpreted in terms of short-term meteorological changes which have been recorded at a nearby weather station in Bethlehem, Orange Free State, and in terms of the effects of stock grazing on vegetation of the area.

Abstract: Improved farming systems are needed to enhance productivity and reduce degradation on hardsetting Alfisols in the semi-arid tropics. A long-term experiment was started in July 1988 at ICRISAT, Hyderabad, India, to evaluate practices to improve infiltration and reduce erosion by stimulating biological activity and protecting soil in the rainy season. This paper outlines the rationale for the experiment, describes it, and summarises early results. Fifteen treatments in a randomised block design were applied to plots 28.5 m long by 5 m wide on a 2% slope. Nine annual treatments made up a factorial sub-set: tillage by tined implement to three depths (0, 10 and 20 cm) combined with three mulch treatments (no mulch, farmyard manure (FYM) at 15 t ha-1, and rice straw at 5 t ha-1). Pearl millet (Pennisetum glaucum) was sown in the factorial sub-set in July 1988. Six perennial species ley treatments (combinations of perennial pigeonpea (Cajanus cajan), verano stylo (Stylosanthes hamata), and buffel grass (Cenchrus ciliaris)) completed the randomised block design. All treatments were replicated three times making 45 plots in total. Plots were instrumented to measure runoff and soil loss. Millet straw yield was reduced by tillage to 20 cm and grain yield was significantly reduced by tillage to both 10 and 20 cm. Mulches had no effect on millet straw yield but FYM significantly increased millet grain yield. The proportion of rainfall running off plots ranged from 15.8 to 39.1%. Perennial species treatments tended to have higher runoff than treatments under millet, but this was not consistent as zero tillage without mulch, and tillage to 10 cm either with mulch or with FYM mulch, also had relatively high runoff. Rice straw mulch significantly reduced runoff by comparison with FYM and no mulch. Soil was lost mainly as suspended load, indicating that raindrop detachment was the main erosion process. Effects of perennial species were variable and probably reflected the degree of surface protection provided in this establishment phase. Tillage significantly increased suspended load concentration in the first major runoff event but not in an event later in the season. Rice straw mulch significantly reduced bed load concentration in the first event and reduced suspended load in the later event. The ability of straw mulch to reduce runoff volume and sediment concentration suggests mulch-based systems may be able to contribute to sustainability of farming systems in the semi-arid tropics. The lack of beneficial effects from tillage suggests a limited role for tillage-based systems. Results from subsequent years are needed to form definite conclusions and to show effects of slower biologically-induced changes in the soil.

Abstract: SUMMARYGrassland productivity was studied for four years near Terbol, Lebanon. In the first year pasture availability and plant numbers were monitored along transects, and in the following three years the effects of sowing four Mediterranean annual legumes (three cultivars of subterranean clover and a local ecotype of Medicago rigidula) and top-dressing with super-phosphate were studied. The results indicated that natural grasslands were dominated by annual grasses (Aegilops, Hordeum, Bromur, Lolium and Poa). Legume density was low, which resulted in poor legume productivity, especially in winter. Exotic legumes only resulted in a slight improvement in pasture productivity even when phosphate fertilizer was added. However, partial protection from grazing (for one or two months in late winter and spring) more than doubled the number of legume seeds in the seed bank compared with full protection and open grazing. The build up of seeds in the soil is an essential step towards the improvement of productivity in these degraded pastures, which form a large part of the land surface in Lebanon and on which small ruminant production largely depends.

Abstract: This article attempts to provide a preliminary assessment of how agricultural and related policy research has generally neglected biological conservation, the significance of the policy changes now underway, and the need for further policy changes. Policy changes are identified which could promote increased cooperation between agricultural and conservation biology researchers and practitioners. The policy and policy research implications of seriously pursuing a new and challenging goal for agriculture are explored. A review and examination of past U.S. agricultural goals, institutions, and policies suggests that the legacy of agriculture's gradual transformation over the past two centuries, and particularly the past several decades, has led to an increasing genetic impoverishment of farm habitats and rural landscapes. New national goals concerning genetic diversity of farm habitats and rural landscapes are defined as ecological goals and point to developing and adaptive and resilient food and agricultural system as part of the larger need to develop a more adaptive and resilient society. Agricultural goals, and the institutionalization that has led to the attainment of goals for great crop productivity and high labor efficiency of industrial agriculture, have been achieved through very high energy inputs. Such agriculture is based on the availability of fossil fuel and is vulnerable to climate changes. Examples of ways to modify policy to enhance diversity include making changes in current set-aside policies, credit programs, and rangeland management. In developing policies, current paradigms should be reexamined and issues of water and energy should receive highest priority. The aesthetic value and diversity of rural landscapes should also be considered. Strategies need to be developed for setting changes in agricultural policies that will lead to more diversified, lower-input agricultural systems.

Abstract: Abstract. The physiognomy of dry savannas is described as a combination of discontinuous woody perennials and a continuous grassland matrix. Interactions between these two components are of vital importance for the persistence of a savanna landscape. Earlier savanna models have emphasized competitive interactions for water between the two components. Recent studies have argued that small-scale facilitating interactions between woody perennials and the herbaceous understorey are also important. This phenomenon has been given little theoretical consideration in the savanna literature, but it has been an important topic in agroforestry and arid-grassland ecology. This paper reviews some of the evidence for micro-site effects of trees and shrubs, and attempts to integrate their interactions with the surrounding open grassland. Woody perennials modify the microclimate by interception of solar radiation and rainfall. Their root systems extract nutrients horizontally and vertically, which are concentrated in the sub-canopy soil from litter decomposition and root turnover. Legumes are abundant in dry savannas, and may have symbiotic relationships with Rhizobium bacteria. This symbosis increases the availability of nitrogen in the soil. Isolated trees and shrubs initiate feedback mechanisms in their interactions with other organisms, and contribute to an uneven distribution of water and nutrients in dry savanna. This influences the species composition, and community diversity. Small-scale facilitating interaction between the woody and herbaceous components and competitive interaction on larger scales, are complementary processes which together explain a dynamic coexistence.

Abstract: Many black South African women use traditional herbal remedies as antenatal medications or to induce or augment labour. Very little is known about the pharmacology and potential toxicity of the plants used in these herbal remedies. The ethnic background and traditional usage of these remedies was researched and a literature survey revealed that 57 different plants were used in herbal remedies during pregnancy and childbirth. Several of these plants are poisonous and details of their toxicity are given.

Abstract: The economic effects of alternative destocking tactics in the face of drought for a sheep enterprise on semi-arid rangelands in South Australia were investigated. Tactics of taking no special action and of destocking the property's 14 600 sheep by 20% and 40% as soon as seasonal rains fail were considered. By examining all possible 10-year sequences of good, average or drought years, a tactic of substantial destocking was shown to have a better long-term expected economic return, with less variance, than a policy of hopeful inaction. A more detailed examination of drought sequences showed that at least 20% immediate destocking is sensible if the drought lasts only 1 year but that 40% is sensible if the drought lasts longer; given that the first year of drought can be recognised by the end of the winter growing season, 40% destocking is economically worthwhile overall (regardless of ecological implications). A sensitivity analysis showed that, although the economic returns were sensitive to market prices for wool and for the animals sold during drought, the general result remained valid over a very wide range of market conditions for the property considered. On the basis of today's prices and costs, a policy of substantial immediate destocking in drought would also have been best in almost all of the decades of real weather records from 1885 to 1985, and is likely to become increasingly appropriate with forecast climatic change.

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Abstract: Effective integration of the three main goals of rangeland management - economic gain through livestock production, management of game animals for recreational use, and conservation of biological diversity - is essential and will form a cornerstone of conservation of biological diversity for future generations. Rangelands encompass nearly 50% of the earth's land area and is defined as land where people have intervened to manage the vegetation with livestock for economic gain. The introduction of domestic animals to a natural plant community has profund effects on the composition of the vegetation, soil erosion by wind and water, and on the population density and species compositions of native organisms. Ranglands vasry in their biological and economic productivity throughout the world and the greatest impacts on biodiversity usually occur onsites with the highest productivity. Worldwide overgrazing is the primary issue in range management. The basic tenet of range science is thatthe reduction of number of livestock animals will lead to greater productivity per unit area. Other factors affecting rangelands are discussed including perturbations by traditional grazing practices, management of western rangelands, problems with animal management, introduced domestic animals, and management of native animals for meat production. A classification into four categories is presented with opportunities for proper management to enhance biological diversity and range productivity discussed for each type. Ways to manage rangelands for biodiversity include fire and utilization of restoration techniques.

Abstract: Abstract. Savanna-grassland ecosystems are highly interactive due to effects among interconnected trophic elements. This can cause disturbance at one level in the trophic web to be propagated through that web to have effects far removed from the initial locus of disturbance. The reconstructed effects of rinderpest upon African savannas, acting directly upon susceptible grazers and browsers but in directly upon many other ecosystem components, are used as a case history illustrating the propagation of disturbance in savanna ecosystems.

Abstract: The objectives of this study were to simulate diet selection by sheep grazing on rangelands and to explore how changes in forage harvestability of different forage pools may affect diet selection. This was done by calibrating linked forage dynamics, diet selection, and sheep production models for three sites in the Edwards Plateau region of Texas. The forage dynamics model simulated the accumulation, removal, and quality dynamics for 33 different forage pools. Harvestability, preference, avoidance, and palatability parameters were associated with each forage pool through the diet selection model. The sheep model was used to calculate intake and to set grazing pressure. Diet selection was adequately represented by the models on each of the three sites. Interaction of forage quality and availability resulted in complex diet selection responses that were strongly tied to seasonal forage dynamics. Sensitivity analyses on harvestability emphasized periods when supplementation may be necessary due to restricted forage availability. The linked models provide an aid to understanding the relationships between forage dynamics and diet selection, especially when used in conjunction with field studies.

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Abstract: The relationships coupling ecologically important processes to pattern formation at different spatial and temporal scales can be explored through a multidisciplinary approach that involves observation, experimentation, and theory. We are using this approach in the study of a serpentine grassland located in the Jasper Ridge Biological Preserve of Stanford University, and we present preliminary results for that system to illustrate the approach. We argue that the development and analysis of simplified null models is an essential precursor to the successful development of more detailed models. Field and experimental studies can be used to examine the mechanisms producing pattern at small spatial and temporal scales; these then form the basis for spatially explicit, landscape level models. Simplified versions of the models can be used as computational experimental tools to explore the consequences of varying disturbance regimes and other critical influences on pattern formation; more detailed versions can be used as limited predictive tools and to guide experimental work.

Abstract: Partitioning available energy between plants and bare soil in sparsely vegetated rangelands will allow hydrologists and others to gain a greater understanding of water use by native vegetation, especially phreatophytes. Standard methods of conducting energy budget studies result in measurements of latent and sensible heat fluxes above the plant canopy which therefore include the energy fluxes from both the canopy and the soil. One-dimensional theoretical numerical models have been proposed recently for the partitioning of energy in sparse crops. Bowen ratio and other micrometeorological data collected over phreatophytes growing in areas of shallow ground water in central Nevada were used to evaluate the feasibility of using these models, which are based on surface and within-canopy aerodynamic resistances, to determine heat and water vapor transport in sparsely vegetated rangelands. The models appear to provide reasonably good estimates of sensible heat flux from the soil and latent heat flux from the canopy. Estimates of latent heat flux from the soil were less satisfactory. Sensible heat flux from the canopy was not well predicted by the present resistance formulations. Also, estimates of total above-canopy fluxes were not satisfactory when using a single value for above-canopy bulk aerodynamic resistance.