GSSA-Publications-1986-1990

Abstract:

Abstract: Main Contents 1. The ecological environment of rangeland 2. The classes of rangeland (1) Map of rangeland distribution in Qinghai province I. Wood land and coarse grasses type II. Shrub and coarse grasses type III. Dry pastureland type IV. Desert rangland type V. Meadow rangeland type 3. The main plant resource of rangeland (1) Appendix a. The index of plant Chinese name b. The index of plant Latin name (2) Acknowledgement

Abstract: Interpretation of large-scale color infrared and color aerial photography can be a labor-and cost-effective means to make inventory of and monitor rangelands while maintaining accuracy. Ground measurements of total vegetation cover, tree, shrub and cacti cover at Organ Pipe Cactus National Monument were taken in 1975 and 1984. Estimates of ground vegetation cover made using large scale (1:1200) color and color infrared aerial photography were compared to these ground measurements. High correlation coefficient values exist between color infrared transparency estimates and ground measurements of total vegetation cover (r=0·972) and shrub cover (r=0·891). Correlation coefficients were similarly high when matching color prints against ground measurements of total cover (0·976) and shrub cover (0·858). Estimates from color infrared film transparencies corresponded better with ground measurements for both tree and cactus cover, with r values of 0·685 and 0·812 respectively, than the estimates from color print photographs with r values of 0·501 for tree cover and 0·246 for cactus cover.

Abstract: A mathematical model is presented of the subsistence pastoral system on the Makatini Flats surrounding the Pongola floodplain just south of the Mozambique border in north-eastern South Africa. The model takes into account the quality and quantity of the different vegetation types. With the impoundment of the Pongola river a number of management issues have arisen relating to the use of land and water resources. The model is used to analyse the effects on the economic returns from the pastoral system of reductions in water and traditional grazing land. It is concluded that, at a regional level, the expected returns from agriculture on irrigated land on the Makatini Flats will more than compensate for the consequential fall in returns from the pastoral system. Whether the cultivation of maize on the floodplain should be encouraged or not is less conclusive.

Abstract: Seed pods of kadad (Dichrostachys cinerea), collected immediately after they matured in December, were fed to male goats; undigested seeds were removed from faeces and allowed to germinate. Seeds were also removed from seed pods and scarified in concentrated sulphuric acid before germination. In addition, scarified seeds were germinated in media of different NaCl and pH concentrations. Germination was significantly increased in acid-scarified seeds and reduced in seeds passed through goats' digestive systems. Seed germination was inversely related to NaCl concentration, and was high between pH 3 and pH 11, but no germination occurred at pH 1 and pH 13. Kadad seeds were polyembryonic, with 72.6% of the seeds with single embryos, 19.1% twin embryos, and 8.3% triple embryos.

Abstract: Land-sea correlation off NW Africa is investigated from both modern and late Pleistocene/Holocene pollen records. Pollen spectra from modern soil surface samples from Senegal and Mauritania and from modern bottom sediment samples from the offshore eastern Atlantic (21-12°N) record accurately the latitudinal vegetation zonation of West Tropical Africa, by showing the maximum percentages of the phytogeographical groups and the same characteristic taxa as the adjacent vegetation zones. A strong correlation between marine (core M-16017-2 near Cap Blanc) and continental (sebkha of Chemchane, Mauritania) pollen signals is also observed for the evolution of the late Glacial/Holocene vegetation zonation at 21°N. The differing sensitivities of each sedimentary environment for recording local and/or subcontinental vegetation changes are discussed.

Abstract: ABSTRACTFlooded savannas in south-west Venezuela consist of seasonal, marshy and flooded grassland communities, the distribution of which depends on soil level. Seasonal grasslands are dominated by tuft-forming, rhizomatous C4-grasses (exemplified by Paspalum chaffanjonii in this study), while flooded grasslands are dominated by stoloniferous grasses which develop rooted, floating culms during the rainy season (Leersia hexandra and Hymenachne amplexi-caulis). The interface between these two communities is a marshy grassland dominated by stoloniferous grass species which tolerate flooding to a depth of 10 to 25 cm (Panicum laxum and Leersia hexandra). All perennial grass species in flooded grasslands behave as typical C3 plants, while marshy grasslands are dominated by Panicum laxum, a species with reduced photo-respiration, low RuBP/PEP-carboxylase ratios, and low absolute RuBP-carboxylase activity compared to C3 grasses. It also has lower photosynthetic rates than the other grass species. Hymenachne amplexicaulis appears to be the least drought tolerant from the species selected, in accordance with its distribution in the wettest side of the flooding gradient studied. The other species showed marked reduction in relative water content and pronounced increase in leaf proline content in drought experiments lasting 6 to 30 days. Alcohol dehydrogenase increased markedly in response to anaerobiosis in the root environment in the tuft forming grasses, while the stoloniferous species with ascending culms were least affected by this treatment, probably as a result of better aeration inside the culms and also to the production of adventitious roots in upper nodes. Nitrate reductase activity increased as a result of anaerobiosis in the roots but not in the leaves, of all species except Leersia hexandra. No difference among the species was found in malate accumulation, or the activity of malic enzyme.

Abstract: The value is discussed of a soil water balanceg accounting model (WATBAL) based on rainfall and used to predict plant growth periods in the arid zone of Western Australia. However, this model fails to simulate differences in plant growth periods where soil amelioration measures have been undertaken. To overcome this limitation, the model was modified by adjusting the runoff component and the maximum water holding capacity to allow for the evaluation of differences in growth periods due to range improvement measures. A comparison in growth periods for treated and untreated sites was made. The validity of these changes was compared against observations over a 2-year period on a rehabilitation site at Wooramel, Western Australia. Using the modified WATBAL program with rainfall data over a 30-year period, the simulation showed that soil amelioration techniques (e.g. water-ponding and chisel ploughing) may increase the growth periods on degraded rangeland. Such an appraisal may provide useful guidelines for evaluating and adopting specific rehabilitation treatments in rangelands.

Abstract: Agaricus goossensiae var. pseudolutosus var. nov., Conocybe cylindracea, Coprinus megaspermus C. ovatus, C. vosoustii, Lepiota locquinii f. rioussetiae, Leucoagaricus macrorrhizus, Mycena chlorantha, M. olivaceomarginata and M. pseudopicta are reported from xerophytic grasslands in central Spain.

Abstract: Strains of Cynodon dactylon (L.) Pers. were collected from six different climatic localities in South Africa. Under controlled conditions the strains were submitted to various environmental stress factors. Experiments were conducted to ascertain their sexual and vegetative reproductive potencies. The drought resistance test revealed that the Augrabies strain is best adapted to tolerate severe moisture stress. All strains survived a soil pH (HZO) of 2.7. The average biomass production of the Delareyville strain, at 2096 fertilizer application, was double that of the Klawer strain. Vegetative reproductive faculties of stolon scions outstripped those of rhizomes by an average ratio of 3.6:1. A seed viability ranging from 0 to 3.596 was obtained. The low percentages of seed viability indicate that the best results will be obtained if stolon scions are used to establish C. dactylon strains in denuded areas. The results indicate that no strain is superiorly adapted to resist all environmental stress factors. Consequently, strain selection for reclamation purposes will depend on the specific environmental conditions prevailing at the reclamation site. All results yielded differences between the six strains which are symptomatic of ecotypification. A hypothesis which implies that in situ studies are sufficient to predict ecotype suitability for reclamation is presented.

Abstract: An extensive search was made for distinctive shock-metamorphic effects in order to test the theory that the Bushveld Complex (BC) was formed by the impact of large extraterrestrial objects. Field and petrographie studies concentrated on two geological environments in which current impact cratering theories predict the formation and preservation of such shock-metamorphic effects as shatter cones, unusual fragmental or melt breccias, and shock lamellae in quartz. These are: (1) pre-BC quartzite xenoliths in the Rooiberg Group, a thick sequence of acid lavas (rhyolites and rhyodacites) and related rocks, proposed by earlier workers as a possible crater-filling impact melt; and (2) the locally observable contact between the Rooiberg Group and the underlying pre-BC basement (Pretoria Group), a contact possibly corresponding to the original crater floor in established impact structures. More than 320 samples of pre-BC quartzite were collected and examined petrographically for shock-metamorphic effects. No megascopic shock-metamorphic effects (shatter cones or unusual breccias) were observed in any outcrop. In thin section, no petrographic shock effects (e.g., shock lamellae hi quartz and kink bands in biotite) were observed in any sample. The quartzites from both the basement (80 samples) and the Rooiberg xenoliths (245 samples) are virtually undeformed. Cataclastic textures are rare, and individual quartz grains show only normal metamorphic deformation lamellae (Böhm lamellae) and single or multiple sets of fluid inclusions arranged along irregular planes which appear to be healed fractures. Although some of these parallel sets superficially resemble so-called "decorated" shock lamellae, universal stage measurements of their orientation demonstrate that they are totally different. The absence of both megascopic and microscopic shock-metamorphic effects in a large suite of carefully selected samples strongly indicates that impact models for the BC are not correct and that the BC is not an impact structure. This conclusion also agrees with: (1)the complex stratigraphy now recognized in the lower Rooiberg Group, which is not consistent with an impact melt origin, (2) the absence in the Rooiberg Group of any of the distinctive melt-rich fragmentai breccias which dominate the crater-filling deposits in established large impact structures, and (3) the undeformed character of the basement rocks below the Rooiberg Group and the apparently concordant contact between them.

Abstract: Lake Baringo and its environs are an incongruous landscape, an archetypal example of landscape degeneration, a laboratory for scientific research and a playground for the moderately prosperous. Landscape degeneration has resulted from natural processes of drought, deluge and locusts working in concert with overgrazing induced by land use changes accompanying colonialization. Scientists have concentrated on natural history topics as well as problems associated with land abuse. The landscape's recreation component is not readily explainable. It is based on Kenya's indigenous and resident middle class now supplemented by increasing numbers of birders and package tourists. The infrastructure supporting recreation eases the difficulty of scientific research, thus tending to stimulate it. Evidence suggests that the local population, though thoroughly grounded in pastoralism, nevertheless understands the various components of its landscape and exploits them accordingly. Lake Baringo and its environs are unsuitable for designation as a national park or equivalent reserve, and landscape restoration techniques may be broadly considered. So far however the area has been regarded only as degraded pasture, a single dimension that leaves little room for hope. Viewed as a landscape of several dimensions including pasture, research and recreation, the situation, particularly in light of the residents' reaction to the complex, is considerably more hopeful.

Abstract: Pollen-bearing lake, bog, and spring sediments are relatively scarce in many arid and semiarid regions of the world, and few are dateable beyond the 14C range. We have obtained pollen spectra from speleothems collected from caves in the Somali-Chalbi and Kalahari deserts suggesting that these deposits may be an important future source of desert paleovegetation data. As cave speleothems can be dated by the 230Th/234U method to c. 350,000 yr B.P., and by the TL and ESR methods potentially to 1 m.y. B.P., and can sometimes give paleotemperature and paleohydrologic data, they could provide a first glimpse of desert paleoenvironments during isotope stages 4-9. Ages of speleothems from the Chihuahuan, Kalahari, and Somali-Chalbi deserts suggest that there was more available moisture in the southwestern U.S.A. and in northwestern Bostwana during glacials and interstadials of the last c. 300,000 years, but that wetter conditions in the Horn of Africa corresponded with interglacials and perhaps to a lesser extent with interstadials. Pollen from three northern Somalia speleothems indicate more mesic conditions in the Horn of Africa at 10,000, 11,800, and 176,500 yr B.P., while speleothem pollen spectra from Matupi Cave in northeastern Zaire, presently surrounded by tropical rainforest, suggest a savanna grassland at this cave c. 14,000 yr B.P.

Abstract: The use of hydrologic modeling and simulation in range management has been increasing. Models provide effective and efficient tools for range management and research. As management tools, they are used to make long-term predictions and to determine the responses of rangelands to management practices. As research tools, they are used to conceptualize, organize and synthesize the available information; they are also used to focus research. Several models of rangeland hydrologic processes have been used, especially for runoff, evapotranspiration and erosion. This paper reviews and summarizes the performance of these models. The paper also discusses the problems involved with some of the techniques used to model the hydrologic processes. Recommendations for improving runoff prediction are included.

Abstract: Within a study of grazing behaviour in 12 cattle herds (mean size 45 head) kept by Fulani pastoralists, the diurnal pattern of grazing activity during 5 herd-days per month over 1 year was analysed. Herding restricted animal access to pasture to only 8.4 h day-1 as an annual average. The herding period was longest (>10.5 h) in the transition from dry to wet season and shortest (< 7h) in the late wet season. The peaks in grazing activity observed in free-ranging herbivores were not evident in the herded cattle, whose grazing activity remained at a high level throughout the herding day. Resting, including ruminating, accounted for only 5% of herding time. Other studies of restricted grazing by African cattle revealed a reduction in animal production only if forage was scarce or of low quality. The Fulani herds had access to a variety of grazing resources throughout the year. Any possible limitation in animal production due to restricted grazing time must be seen in the wider context of the land-use system, in which the Fulani herding practices permit an integration of cropping and livestock husbandry.

Abstract: The relationships between resource availability and the requirements of ungulate species were approached by assessing the habitat preferences of three ungulate species, namely roan Hippotragus equinus, sable H. niger and tsessebe Damaliscus lunatus, in relation to the classification of their available habitats. Cluster analysis distinguished between five habitat types. Roan and tsessebe were generally associated with habitats forming a large portion of the total area, whereas sable were associated with confined habitats. Selectiveness and possible resource limitation were, however, indicated for tsessebe as they attained higher correlations with particular habitat features which were relatively scarce in the study area.

Abstract: A comparison of eight improved management technologies was made for a typical Northern Australian beef cattle property carrying about 3000 breeding cows located in the Katherine district of the Northern Territory. RANGEPACK HerdEcon, a computer package which links a dynamic herd model with farm enterprise costs, was used to progressively implement various property development strategies. These included combinations of cow and steer supplementation, and pasture improvement with Stylosanthes spp. Over a 20-year period the predicted accumulated cash surplus for the superior cow herd supplementation, cow and steer herd supplementation, and pasture improvement options were $0·66m, $1·12m and $1·32m respectively. After real interest rates of 6% were charged on borrowed capital and company taxation was levied, however, the 20-year net surpluses were $0·40m, $0·66m and $0·35m respectively. Annual turnoff rates were 24, 21 and 19% of herd numbers, but 33, 37 and 36% of herd value respectively. These figures compare to an expected 20-year loss of $1·40m for an undeveloped property in the same area, with a turnoff rate of 14% of herd numbers, and 17% of herd value. Successful pasture improvement can result in a productive enterprise, but there are major capital investment costs during implementation, as well as risks of pasture failure. As a result, supplementation strategies are more attractive, because they require less capital investment, and can be suspended in difficult circumstances. However, supplementation without good land management can cause pasture and landscape degradation. Because the beef industry in Northern Australia will continue to rely mainly on native pastures, research and development should reorientate to emphasise the long-term maintenance of native pastures, rather than their replacement. This study shows the advantages of a whole property approach to research and development, and the usefulness of a dynamic model to investigate the implementation phase of a new technology.

Abstract:

Abstract: Hyrax middens in relatively dry parts of Africa preserve plant material which includes pollen. The bottoms of two stratified hyrax dung middens from Blydefontein Basin in the Karoo shrubland of South Africa, were dated by radiocarbon to ca. 300 yr B.P. and ca. 1130 yr B.P. Comparison of midden pollen spectra with pollen from alluvial sediments near one of the hyrax middens, and in modern surface samples, indicates that middens contain pollen which reflects local vegetation, and that diet probably does not have a major influence on pollen spectra. Changes in pollen composition probably reflect climatic conditions during the early history of the older midden profile. Grass dominated spectra suggest moist conditions existed between 1200 and 300 yr B.P., and an interval of slightly more shrubby karoid vegetation possibly points to a minor dry spell at 1000 yr B.P. A sharp increase of karoid shrub vegetation, and a decrease of grass since 300 yr B.P. is reflected in both middens. The change was apparently triggered by relatively dry conditions, and later, during the last 150 years, it was enhanced by overgrazing from European domestic stock.

Abstract: A combined ecological and economic approach was used to assess and compare the productivity of 44 maize farms located in two different ecological zones in south-western Nigeria. First, the technique of investigation involved, the identification of the ecological parameters in particular soils and climatic variables that significantly influence the crop's production in the two zones; secondly, it involves the estimation of the costs and revenues accruing from cultivating a hectare of land for maize production for each ecological zone. Using a rating procedure developed in this study, four parameters were used to assess the sampled maize farms in the two ecological zones: nitrogen, phosphorus, number of rainy days and Gross Margin Analysis. The results of the assessment indicate that it is more profitable to produce maize in the savanna zone than the forest zone. In addition, all the farms sampled in the savanna zone but only 65% of the farms in the forest zone were rated fairly suitable to very suitable for maize production.

Abstract: The Karoo Sequence spans an age ranging from Carboniferous to Jurassic and occurs in intra-cratonic and graben-rift basins throughout southern Africa. All of the subcontinent 039;s bituminous, anthracite and coking coal reserves are contained in Early Permian to Triassic Formations of the Karoo Sequence. The most complete assemblage of these upper Paleozoic strata occurs in the Karoo Basin, an asymmetric, epicratonic depository now covering over half of the surface area of the Republic of South Africa. The large aerial extent of these strata belies the potential coal resources as the coals are confined to specific geographic localities, determined by the coal seams confinement to within particular stratigraphic intervals. Two major geographic coal regions are described: (1) the Witbank/Highveld/Eastern Transvaal coalfield in the extreme northern basin areas; (2) the Natal coal fields located southeast of the Witbank region and also more distal to the proximal northern basin coal deposits (Fig. 1). In the Witbank region, coal seams occur in a 80-180-m clastic sequence of the Vryheid Formation. Basal coals overlie post-glacial tillite, glaciofluvial outwash braid-plain conglomerates and sandstones, and minor glaciolacustrine and glaciodeltaic sequences. The lowermost coals often lie directly on pre-Karoo basement with no other intervening strata. The coals overlying these lowermost glaciogenic strata are interbedded with lobate delta and bed-load fluvial sequences. In addition, fine- to coarse-grained anastomosed river deposits are contained within some coal seams and these paleochannel lithologies now locally deleteriously affect coal distribution and quality, i.e., coal beneath paleochannel axes, which were dip-parallel, is thinned due to channel incision and erosion. The coal contains a high percentage of ash immediately above paleochannel axes and up to several kilometers adjacent to paleochannel margins (Cairncross and Cadle, 1988; Cairncross et al., 1989). Paleotopography directly controlled sedimentation patterns in the Witbank coalfield regions. Permo-Carboniferous glaciers scoured valleys into the pre-Karoo basement and the Vryheid Formation sediments and peat initially infilled these paleovalleys. Consequently, coals thin, pinch-out and shale-out against relatively steep-sided valley flanks. Directly above paleotopographic highs, coal and associated strata are attenuated due to compaction, or may be absent due to non-deposition. In the Highveld coalfield, paleotopographic relief was so severe that the total coal-bearing succession is accommodated in paleovalleys, leaving prominent basement highs projecting through the entire sequence (Winter et al., 1987). Paleovalleys were, moreover, the initial sites of clay and silt deposition. These argillaceous sediments infilled depressions and were subjected to differential compaction, thereby providing favorable, low-relief sites for peat accumulation. However, superimposed on these depressions and paleolows, were syn- and post-deposition low-sinuosity, bedload fluvial systems. These originated in the northern granitic source terrain and flowed southward down the paleovalleys, channeling arkosic sediment through the peat swamps. Peat accumulation was therefore interrupted by clastic contamination, channel scouring and erosion. Post-depositional compaction of these paleochannel sandstones was negligible and coal deposited in sequences above paleochannels is thinner than the stratigraphic equivalent coal overlying adjacent fine-grained flood plain sediments. In contrast to the Witbank region, the coal-bearing succession in the Natal coalfields overlies substantial thicknesses of glacial moraine (Dwayka Formation) and distal shelf shale (Pietermaritzburg Formation). The paleotopographic controls evident in the Transvaal coalfields are therefore insignificant and dampened by these thick underlying strata. The fluviodeltaic coals which formed in these areas developed in broad featureless plains and are therefore laterally persistent (Roberts, 1986). Tectonic subsidence was however more rapid in the eastern Natal regions than in the more stable northern platform localities. As a result, the Vryheid Formation is considerably thicker in Natal and in places exceeds 500 m. Greater tectonic instability produced higher geothermal gradients and a general increase in coal rank from the stable cratonic platform in the west to the Natal region in the east is evident. Locally, anthracite has resulted from increased thermal gradients produced by Jurassic dolerite dykes and still intrusions. The southern limit of the Vryheid Formation is defined by the southerly basinward shale-out of the clastic sequence, several hundred kilometers south of the Transvaal coalfields. This distal extent of the coal-bearing succession is, in places, defined by clastic paleoshoreline sequences which fronted the landward positioned fluviodeltaic systems. Breaching of this paleoshoreline did however periodically take place and basin waters transgressed over the swamps terminating peat accumulation and depositing glauconite-rich sediment now preserved as transgressive siltstone and sandstone overlying the coal seams.

Abstract: The conventional view of 34;traditional 34; or informal systems of African land rights is that they impede agricultural development, and that land titling or registration is needed to encourage land transfers to more productive farmers, improve farmer access to credit, and create incentives for investment in land improvement, soil conservation and new technology. In spite of growing pressure on land resources and on existing land tenure systems, there is much evidence from many parts of Africa which calls into question this conventional view. The costs of land titling may be quite high, and its effects contrary to expectations. A number of cheaper alternatives to land titling may be more effective in guaranteeing the land rights of African farmers in situations of growing land tenure change and uncertainty.

Abstract: Structural and stratigraphic aspects of the Lebowa Granite Suite (the granites) and Rustenburg Layered Suite (the basic rocks) are examined and compared in various compartments of the Bushveld Complex, South Africa. The coeval Molopo Farms Complex–located largely in Botswana–is included in this examination. Structural features are evaluated in terms of relationships to major structural features of the Kaapvaal Craton, such as the Thabazimbi-Murchison lineament, and its extension in Botswana, the Kgomodikae lineament, the Melinda, Abbotspoort, Rustenburg and Steelpoort faults, and the Barberton lineament in the south. Histories of structural development in the eastern and western compartments indicate a pre-Bushveld age of some structural features and models are proposed of recurring movements along pre-existing fundamental lines of weakness. It is concluded that features such as the Thabazimbi-Murchison lineament are lithospheric in extent and that they played an active role controlling the emplacement of the Bushveld and Molopo Farms complexes.

Abstract: A multivariate analysis of the current South American Land-Mammal Ages is used to reanalyse the recognized 34;faunistic (mammal) units 34; or chronofaunae that appear related to radical environmental and climatic changes, which we characterize as Faunistic Cycles and Subcycles. The compositional changes recorded in the successive Faunistic Cycles reflect regional environmental and climatic variations, thus patterns of climatic change. Basically we used cheek teeth of ungulates–natives and immigrants–as an indicator of dietary preference. We then try to infer the structure of successive fossil ungulate communities to deduce the structure of their associated vegetation, and thus the prevailing climatic conditions. We also used other native mammals that followed similar dental modifications, e.g., some rodents and some marsupials, and various types of biological and/or geological evidence. These include climate-sensitive or ecologically specific animals or plants, changes of regional distribution and lithological features of the mammal-bearing formations, diastrophic events, changes in global marine temperatures, and sea-level changes, to contrast those climatic and environmental inferences. We conclude that: (1) From the oldest to the youngest cycles the ungulates changed from browser sylvan types to predominantly open country and grazer types as warm, humid sylvan environments became drier and more temperate. (2) The earliest mammal communities (Paleocene-Eocene), excluding the peculiar Cochabambian Cycle, show a higher diversity but are composed of taxa with less extreme morphological differences. Even mammals placed in different orders were not nearly as dissimilar as their later counterparts. This relationship gradually became reversed within the later communities, i.e., lower diversity but taxa with more extreme morphological differences; that is, mammals placed in separate orders became more divergent. (3) According to the record of mammals as well as other climate-sensitive organisms, warm and relatively humid forested environments had a wider latitudinal range, stretching at the very least to the northern part of the Antarctic Peninsula. (4) With some regional range fluctuations, Palcogene and Early Miocene tropical to subtropical environments remained very well represented as far as the southern tip of the continent. (5) The Middle Miocene mammals (beginning of the Panaraucanian Faunistic Cycle) indicate that favorable environments were shifted to northern Patagonia and that many climate-sensitive mammals (including platyrrhine monkeys) disappeared from Patagonia, in correlation with the waning or extinction of many taxa related to subtropical woodlands. (6) Mammals of the Panaraucanian Cycle and the Pampian Subcycle clearly indicate that this was the time of the most extensive open-country environments, progressively ranging from wetter subtropical savannas to cold-temperate steppe-like habitats. Most of the mammals of this time were savanna-adapted or steppe-adapted elements. (7) Mammals representing the Postpampian Subcycle attest to the wide swings and cyclicity of the Cenozoic climates. (8) According to the Brazilian mammal records, as well as other biological evidence from the isthmian region, the rainy forested areas characterizing those regions evolved quite recently, by the latest Pleistocene to Recent times.

Abstract: The large human and livestock populations in relation to the land area, coupled with the [`]user-right' land tenure system, makes the land use planning process in the communal lands of Zimbabwe a special case. Problems are associated with the historical and legislative background of the land issue in Zimbabwe. The initial problems involved boundary disputes between kraalheads, the balance of power between the traditional leadership and local government leaders and inadequate data collection. Within the planning process the problems hinged on reconciling an [`]ideal plan' with one acceptable to the community. It also depended on the community appreciating that their land comprised a finite resource. Therefore a compromise land reorganization plan was produced in which the land use planning principles remained in the background as a referral point. This plan gives the community a chance to revitalize their communal land resources, something that was only reflected in the principles of the 1951 Native Land Husbandry Act.

Abstract: Compared with monospecies stocking, numerous studies substantiate that multispecies stocking can efficiently increase use within and among the mosaic pattern of rangeland plant life forms. However, multispecies stocking may fail to bring anticipitated biological and financial results because of severe small ruminant losses, often because of coyote (Canis latrans) predation. Previously published data have demonstrated that when young lambs are bonded to cattle, they will follow cattle under free-ranging conditions. This close association under free-ranging conditions has been shown to reduce coyote predation on lambs. However, in addition to protection, lambs that stay with cattle may have their diet selection influenced. Differences between cattle and sheep diets were estimated using microhistological analysis of heifer and lamb feces. The data indicated differences between pastures, animal species, and bonded and non-bonded lamb diets. Lambs bonded to cattle grazed 7% more grass, 5% fewer forbs and 4% fewer shrubs between April and June than non-bonded lambs. Cattle diets were not influenced by either bonded or non-bonded lambs grazing in the same pasture and averaged 57% grass, 35% forbs and 8% shrubs. In contrast, bonded sheep diets averaged 35% grass, 59% forbs and 5% shrubs. The relatively large differences between heifer and lamb diets, and the relatively small differences between bonded and non-bonded lamb diets, do not negatively impact the potential benefits to be gained from multispecies stocking using bonded sheep. Managing bonded sheep with cattle under free-ranging conditions may result in more uniform spatial use of the vegetation than would occur if either species were managed alone.

Abstract: Broad conservation objectives for the lands of Western Australia have been endorsed by State Government. The implications of particular objectives are discussed for pastoral land within the sector of the arid zone dominated by winter rainfall, in the light of current knowledge on the essential ecological processes, the status of flora and fauna, and degradation problems resulting from post-settlement land usage. Experience of the inter-relationships between grazing stock and resource management in arid winter rainfall areas suggests that, in order to achieve consistent, sustained animal production, the producer 039;s land management objectives must be aimed at conserving and improving key perennial elements of the vegetation. Perennial pastures exist as many different suites of palatable native perennials (mainly shrubs plus some grasses). They can be promoted as a consequence of tactical grazing, protection or mechanical regeneration and reseeding of degraded assemblages. Poor though the research base is, management for quality perennial forage reserves should largely satisfy conservation objectives as applicable to such environments, while conferring distinct economic benefits for the individual pastoral business. The environmental progress of such management can be measured and demonstrated at range monitoring sites which have begun to provide detailed information on the vegetation and soils of entire regions of the arid zone. Measures of the extent and severity of accelerated soil loss and changes in composition and density of perennial communities provide the most practical and easily comprehended measures of pastoral impact. Other measures, such as gauging extinctions of changes in species diversity, are neither sensitive nor reliable as indicators of environmental degradation, system stability or vegetation recovery in the region. The popular conception that formal conservation objectives for arid pastoral lands can be achieved only by the removal of grazing has little empirical basis. It should be viewed as an understandable prejudice which reflects the degree to which pastoral misuse has discredited conservation-oriented pastoralism as a legitimate land use. The whole pastoral industry of the region thus needs to embrace perennial pasture management, and to publicize its problems and successes through range monitoring or other evidence of conservation action, in order to redress its poor community image in land management.

Abstract: A transition from shifting cultivation towards more intensive types of agriculture necessitates the introduction of alternative systems of cultivation. Since this change is often followed by deforestation, systems which are sustainable in treeless surroundings are worth searching for. An agricultural system where mound-cultivation is combined with green manuring is presented. It is based on the spreading of an initial compost-mound for a cereal-legume crop rotation on mounds, alternating with flat cultivation. The effect on soil nutrient stores was followed for 2 years as well as in mounded fields of various ages. Both pH and effective cation exchange capacity (ECEC) increased following compost-mound cultivation, and the content of P and Ca doubled. After 4 years of legume-cereal crop rotation on mounds alternating with flat-cultivation, more nutrients had accumulated in the soil than were present before in the fallow.

Abstract: The SPUR (simulation of production and utilization of rangelands) model was evaluated for use on eastern hill land pastures. The model was calibrated using the first year of soil fertility, weather, and animal data collected from a four-year study involving crossbred beef cattle grazing tall fescue. Calibration involved adjusting of plant inputs for maximum photosynthetic rate, leaf area index, root to shoot ratio, and the effect of trampling on biomass. Once calibrated, SPUR was used to simulate animal weight gains and biomass production using data collected in the last three years of the study. Simulated animal gains agreed well with the observed animal gains. However, simulated plant biomass did not agree with observed plant biomass.

Abstract: Crop coefficient (Kc) curves for grain sorghum, cotton, maize, groundnut and millet were developed for the Nigerian semi-arid tropics (8 176; to 13 176;N; 5 176; to 15 176; E) based on grass reference 0 determined with the FAO-24 (Penman) procedure and lysimeter measured crop water use data at Samaru, Nigeria (11 176;11 039;N; 7 176;38 039;E). The recommended equation for estimating solar radiation from relative sunshine hours was determined to be Rs = [0.28 + 0.46(n/N)Ra] using measured solar radiation data. A value of 1.6 was obtained for the ratio of day to night time wind speeds for the growing season (May to October) using an automatic weather station. A procedure was also developed to estimate daily minimum and maximum relative humidity from daily minimum and maximum temperatures and the usual relative humidity records. The Kc curves developed can be recommended for use in farm water management decisions throughout the semi-arid tropics of West Africa south of the Sahara.

Abstract: Changes in village farming systems brough about by population growth and continuing low rainfall, are described for the three main agro-ecological zones in Burkina Faso. The toposequential landuse and cropping patterns were used as the basis for a model, which describes the long-term ecological degradation from declining proportions of fallow land and over-cropping. The implications of these changes for land tenure systems have also been considered. The result provide a human and ecological setting for th current land degradation problem in the West African savanna and thereby indicate possible directions and priorities for future agricultural research.

Abstract: The numbers of dead cattle in 1977/1978-1985/1986, expressed as a percentage of the total cattle numbers, for six regions in Botswana and for the country as a whole, were analysed as a function of a simple 10-day water-balance model which contains only estimated potential evapotranspiration, rainfall, one single rangeland-cattle factor and one maximum available soil moisture reserve as input parameters. The output of the model is a livestock performance index, which expresses (as a percentage) the extent to which the assumed water requirements of cattle and range were satisfied by rainfall. It was found that, depending upon the area, between 75% and 90% of the variability of the cattle death ratios is accounted for by the index calculated for the past, the second last and part of the third last season. On a national scale, 93% of the interannual variability of cattle death ratios and 93% of the variability of the percent departure of cattle numbers from the normal cattle population growth curve is accounted for by the livestock performance index calculated for the above-mentioned period. Further analysis of the results obtained for each area and tests of accuracy and precision of the model show that the index can be used as a qualitative indicator of rainy season qualities for livestock performance on an areal scale and as a quantitative indicator for the assessment of cattle death ratios and numbers on a national scale.

Abstract: Structural and stratigraphic aspects of the Lebowa Granite Suite (the granites) and Rustenburg Layered Suite (the basic rocks) are examined and compared in various compartments of the Bushveld Complex, South Africa. The coeval Molopo Farms Complex--located largely in Botswana--is included in this examination. Structural features are evaluated in terms of relationships to major structural features of the Kaapvaal Craton, such as the Thabazimbi-Murchison lineament, and its extension in Botswana, the Kgomodikae lineament, the Melinda, Abbotspoort, Rustenburg and Steelpoort faults, and the Barberton lineament in the south. Histories of structural development in the eastern and western compartments indicate a pre-Bushveld age of some structural features and models are proposed of recurring movements along pre-existing fundamental lines of weakness. It is concluded that features such as the Thabazimbi-Murchison lineament are lithospheric in extent and that they played an active role controlling the emplacement of the Bushveld and Molopo Farms complexes.

Abstract: The assessment of the suitability of land for specific uses is a vital part of land use planning and agricultural development. The FAO Framework for land evaluation provides a good basis for determining physical land suitability and for extending the information base into yield potential for different management levels and farming systems. In this paper the FAO procedure is demonstrated for farming systems which include coconuts in the Coastal Belt of Tanzania. An extract of the land suitability map and legend are given. Yield potential for coconuts varies from 5 nuts per palm per year on unsuitable land with poor management practices to 80 nuts on the most suitable land with good management. To assess optional land uses, cashewnuts, maize and rangeland were also considered alongside coconuts. Planners and decision-makers can now use the results to target scarce resources to optimal areas and to design viable farm units and farming systems for local physical, social and economic conditions.

Abstract: Regional water budget tendencies reported by 14C-dated field data are correlated with Late Quaternary cooling and warming phases. Areal frequency distribution analysis of these correlations shows cooling phase negative and warming phase positive water budget tendency to be negatively correlated, with a significantly larger area reacting in cooling phases. Six main phases of climatic and environmental change are deduced from functional time and elevation plots. The only clear phase dislocations of positive and negative water budget tendency in all climatic zones are identified for the period before 23,000 yr B.P. and for the Full Glacial 20,000 to 17,000 yr B.P. There are clear differences in chronological sequences between the subtropics and tropics, but during Holocene very complex time and elevation patterns are apparent. This implies a strong cooling phase intensification of subtropical anticyclonic belts. The aridification gradient rises exponentially from subtropical arid to humid innertropical Africa wheras the humidification gradient shows a reverse structure. Humid tropical Africa is less susceptible to climatic change than semiarid regions and the arid zone is least affected. In those regions being susceptible to both cooling and warming trends non-climatic factors may play an important role in ecosystem fluctuations. Water budget tendency analysis does not indicate large-scale glacial and interglacial dislocations of continental atmospheric circulation patterns.

Abstract: Paleohydrological and palynological data from the three major ecoclimatic zones in modern tropical west Africa -- the Guineo-Sudanian, Sahelian and Saharan -- have been summarized to provide a 12,000 year history of paleoclimatic variation. On the basis of 54 limnological sites and 16 pollen sequences, past rainfall patterns can be distinguished with a 500 year resolution. Paleohydrological data indicate several periods with higher rainfall than present. Those at 9.5 ka-7 ka BP and 4 ka-2.5 ka BP occurred in both the Sahelian and Saharan zones. Two abrupt changes in the vegetation are evident in the palynological data, and these confirm the importance of hydrological fluctuations. At 9 ka BP, the vegetation suddenly responded to an abundant increase in rainfall. At 2 ka BP, the vegetation changed quickly to its modern distribution in response to generally drier conditions. Although evidence exists for a temperature increase at 9 ka BP and increased seasonality in precipitation at 7.5 ka BP, the details regarding these events must be refined.

Abstract: In four field experiments, carried out in The Netherlands, small wind-tunnels were used to make direct measurements of ammonia (NH3) volatilization from different types of slurry and manure applied to the surface of grassland. During periods of up to six days following application, losses of NH3-N often amounted to more than 40% of the NH4-N applied. Percentage loss was highest (83%) from a poultry slurry and least (21%) from an air-dried poultry manure. Losses of NH3-N were generally greater from pig slurry (36-78%) than from cattle slurry (41%). In most cases 80% or more of the total NH3-N loss occurred within 48 h of application. Estimates were made of total annual NH3 emissions from four systems of poultry housing. The highest total loss (50% of the N voided in droppings) occurred with a battery house producing a slurry with a low content of dry-matter; most of the loss took place after spreading. With a second battery house, in which the droppings were air-dried, the total loss was only 12%, with much lower emissions from the housing and during spreading.

Abstract: Aeolian dust processes have played an important role in the evolution of the Australian landscape, yet little is known of the processes and their sediments. Two major dust transport pathways are described, based upon paleo-dune patterns and present day dust storms and related processes. These dust pathways have been fed by alluvium deposited in internally-draining river basins. During the period leading up to and including the Late Pleistocene Aridity rates of dust entrainment, transport and deposition were significantly higher than at present. The ocean sediments of the Tasman Sea, the Pacific and Indian Oceans received massive amounts of aeolian sediment. Dust contributions to some Australian soils have also been considerable.

Abstract: Buried lake sediments and tufa strandlines of Holocene age provide evidence of a former lake in the Selima Oasis depression, northwest Sudan, near the hyperarid core of the eastern Sahara Desert. A 1.6 m section through laminated lake muds and precipitates has been analysed in detail, and 30 radiocarbon dates, geochemical, sedimentological, diatom and pollen analyses indicate that the unit dated from approximately 8.4 ka BP to <6 ka BP, and was deposited in an environment that passed through one arid-to-humid-to-arid cycle. The arid episodes, from prior to 8.4 ka BP, and subsequent to 7 ka BP, are characterized by high CaCO3 deposition, abundant diatom indicators of relatively high salinity and well developed periphytic communities, and pollen spectra dominated by desert-grassland indicators. A humid period centered on 8 ka BP is indicated by low CaCO3 deposition, high organic rich mud and Al and Si oxide deposition, diatoms indicating a fresh, deep (20 m) lake, and a pollen assemblage with maximum values for Sahelo-Sudanian tree taxa suggesting a thorn tree and shrub savanna vegetational mosaic. This reconstruction, concordant with higher groundwater table and precipitation between 9.3 and 7 ka BP, agrees with palaeoecological inferences from other sites in North Africa.

Abstract: Petrographical and palynological coal-quality investigations relating to variations in one of the best-known and well-researched coalfields in Africa, the Witbank coalfield, and one of the most commercially important seams within this coalfield, the No. 2 seam, are highlighted in this paper. The investigations were based on 14 channel samples covering a 40 × 20 km2 area in the Witbank coalfield. The results indicate that the coals in the No. 2 seam were formed at the stage of major change-over from Dwyka to Ecca floras as illustrated by the progressive dying-out of Dwyka pollens and spores and the introduction of Ecca floral elements. This also suggests a rapid amelioration of climate over the period of peat accumulation, following a period of continental glaciation. Furthermore, it is proposed that the in-seam horizons reflect fluctuating of cyclic environments (probably due to changing water level) and plant communities (due to changing growth environments). Saccate pollens appear to occur in association with vitrinite-rich microlithotypes, trilete spores with inertodetrite and carbominerite-rich microlithotypes, and plicates with inertite semifusite/inertodetrite microlithotypes. Acritarchs (nonspinose) are present in parts of the seam where inertodetrite is common and in association with unusual suites of trace and major elements (possibly indicating changing geochemical environments in high groundwater conditions). Petrographic results indicate that the coals are medium rank (hypobituminous) and show wide variations in maceral, mineral, and microlithotype compositions, both vertically and laterally. On the basis of microlithotype and mineral-group analyses, investigations were undertaken to establish vertical subdivisions (by the study of historical patterns) and possible lateral correlations of these subdivisions in the area under investigation. These methods were then compared with distribution of selected chemical and geochemical parameters. The evidence suggests that a common sequence of major events (and some minor events) occurred during the accumulation of the No. 2 seam, as manifested by petrographic and palynological facies. Three major periods or zones are recognized. These tepresent periods of relatively stability (quiescence) separated by major in-seam disruptive events, namely, flood deposits bearing high proportions of detrital organic material or minor clastic sedimentation. These zones are subdivided into several subzones representing periods of reworking, local flooding or rise in ground water levels, and/or changing geochemical environments. These events can be recognized throughout the area under investigation, but the manifestation of these events varies from area to area, depending upon topographic situation, proximity to river channels, valley flanks or palaeoshorelines, degree of subsidence and compaction, geochemical environment, and length of time under a specific set of conditions. Thus, channels in close proximity to one another, or in similar positions relative to valley flanks or axes, appear to be remarkably similar to one another. Direct correlation of stratigraphic zones and sub-zones from sample site of sample site was therefore possible, although the methods to achieve this are complex and require the support of several supplementary/complementary interpretative techniques. Coal-quality variations and distribution within the original seam are therefore explicable in terms of the detailed factors listed above.

Abstract: This article addresses the potential land use conflict between trees and cattle. The search for pasture frequently leads to the large-scale destruction of trees yet, paradoxically, when grazing land is under stress the retention of trees becomes ever more important to sustain the productive capacity of the land. Communal grazing is a vitally important land use in southern Africa, but it is increasingly under stress. Through a series of case studies, the article explores ways of maintaining a productive environment by turning the potential adversaries of cattle and trees into allies. To achieve this goal will require an integrated land use approach which overcomes the institutional boundaries of rangeland management, forestry, energy planning and agricultural extension.

Abstract: Land use policy is often developed without regard to historical considerations, even though policy may fail because it is familiar to local people who have found it to be inaccurate and inappropriate. Between 1931 and 1981 officials consistently described north-eastern Botswana as severely overgrazed and in imminent danger of ecological disaster unless destocking took place. Over the same period the cattle population tripled, while enforced destocking caused hardship to local cattle holders. The contrast between local experience and official prescription over 50 years suggests why present-day residents are sceptical of official rangeland policy. The design of rangeland policy and range and livestock management projects would benefit from considering the history of local experience with official policy and advice.

Abstract: Effects of extreme livestock pressure on the abundance and distribution of a drought-deciduous shrub Sericocomopsis pallida, and effects of the shrub canopy on microclimate, soil fertility and grass production, were studied in savanna grasslands of southern Kenya. Canopy volume declined with increasing herbivore pressure, but shrub density was not systematically affected, suggesting strong resilience against destruction by herbivores. However, shrubs became more aggregated with increasing herbivory, suggesting that clumps of individuals are more resilient to destruction than are isolated individuals. Grass production was three times greater under the canopy of S. pallida than in the open. Comparisons of physical-chemical properties among soils derived from four microsites revealed far higher nutrient levels in sub-canopy soil than in soil derived from open ground between canopies, and radically different properties compared to soil heavily enriched with livestock dung and urine. Higher nutrient levels beneath the canopy most likely resulted from Utter decomposition.A pot experiment, designed to simulate shading and soil conditions in the field, showed that grass growth promotion was largely due to a substantial increase in soil fertility beneath the canopy of S. pallida, comparable to grass productivity in soil enriched with livestock excreta. However, this increase in sub-canopy grass production did not significantly increase regional grass layer production.

Abstract: Rangeland areas are characterized by sparse and limited hydrological data that make the use of existing mathematical runoff models difficult and impractical. A simple rational mathematical model was developed to predict runoff in three Oregon semiarid rangeland watersheds, using daily precipitation and mean daily temperaturs. The model consists of three main components to estimate snowmelt runoff due to thawing and rainfall, and rainfall runoff. The model calculates daily flows on a continuous basis. Comparison with measured flows for monthly predictions gave coefficients of determination (R2) varying from 0.67 to 0.81 for different basins and different periods of observation, including verification periods. The predicted timing of monthly flows was consistent with observed data. Using the Curve Number method, new approaches are suggested for snowmelt runoff calculations.

Abstract: Information from the literature about forage conservation losses in the field has been reviewed, contrasted and analysed in the categories respiratory loss, leaching loss and mechanical loss. An attempt has been made to summarise the information in terms of relationships with various climatic, crop and machinery factors, suitable for incorporation in an operational research model of forage conservation. An equation developed to relate respiratory loss to the temperature, moisture content and water soluble carbohydrate content of forage material gives a good representation of results of a range of laboratory studies, and is in reasonable agreement with less accurate field studies. A relationship between leaching loss for a given quantity of rain and moisture content is proposed, but on the basis of very limited information. It was found helpful to regard mechanical loss as the sum of two processes, namely true shatter loss and pick-up loss for windrowing, baling and forage havesting operations. An equation relating shatter loss to moisture content and severity of mechanical treatment is proposed. It is suggested that a roughly constant level of pick-up loss per unit area of stubble cleared by the operation might be assumed, because this is the only conclusion justified on the basis of the rather varied information available.

Abstract: Winter foraging behaviors of pregnant crossbred beef cows grazing Montana native rangeland were examined over a continuous 46-day period in January and February. The objective was to examine daily estimates of two principle grazing behaviors, forage intake and time spent grazing, in response to fluctuations in acclimated thermal environments. Sixteen 5-year-old cows (525-575 kg) were fitted with vibracorders to monitor daily grazing time (DGT). Fecal organic matter output was estimated using total fecal collections and a Cr2O3 dilution technique. In vitro organic matter disappearance (IVOMD) was determined from extrusa obtained from four rumen-fistulated cows. Mean daily forage intake expressed as a percentage of body weight day (% BW per day) increased (P 60;0.05) when present day ambient air or wind-chill temperatures deviated (either an increase or a decrease) from temperature averages of 1, 2 or 3 previous days, but the magnitude of response was small ( 60;0.0005% BW per day per 176;C deviation). Daily intake was unresponsive (P 62;0.05) to deviations from acclimated temperatures calculated for the previous 4-20 days. Dietary extrusa IVOMD averaged 34.5% and remained consistent (P 62;0.05) during the winter grazing period. Daily grazing time decreased (P 60;0.05) with ambient or wind-chill temperature deviations from acclimated thermal regimes of the past 1-3 days, and the magnitude of response was also small ( 60;0.01 h per day per 176;C deviation). The slight responses of these two principal foraging behaviors indicated thermal fluctuations (8 to -16 176;C) within a familiar winter environment were minimally stressful with no resulting adverse effects upon the animal.

Abstract: In South Africa, organized dune stabilization began in 1845 in the western Cape with the introduction of Australian Acacia species which were regarded as the most useful plants for this process. Initially, seed was sown directly onto the sand, but in 1875 this was modified by spreading city refuse over the bare sand to temporarily stabilize the sands before seeding with Port Jackson Wattle and a few other species. This proved uneconomical because of the need to construct a railway line, and in 1896 a French technique was introduced. A foredune was formed at the source of the drift sand by constructing barriers with wooden poles or Marram Grass. The area behind this was then thatched with brushwood or seeded with grass before introducing alien woody species. Later the area was simply covered with seed-bearing Acacia branches. In the late 1940s it was realized that the ability of alien species to oust indigenous species posed a threat to the natural vegetation. However, it was not until 1974 that their use was curtailed. The present policy is to only stabilize areas when absolutely necessary, using indigenous species. An artificial foredune is no longer constructed, but brushwood packing prior to seeding is still undertaken. Indigenous seedlings, grown in nurseries, are also planted under the brushwood and successful stabilization takes at least five years. Harmful effects which arise from the use of alien species are discussed and include the ability of species to produce impenetrable thickets and suppress the growth of indigenous vegetation, the increase in the periodicity of fires, the draining of soil water resources and loss of cultivated land. The problem associated with stabilizing large sand drifts is the net loss of sand from beaches. Dune stabilization is an important management tool in the coastal zone, but there is a need for greater awareness of the problems associated with both stabilization using alien species and with badly planned development.

Abstract: Soil loss models are commonly applied to obtain estimates of erosion for planning purposes. This paper asks whether it is safe to utilise two widely-used models, the Universal Soil Loss Equation (USLE) and the Soil Loss Estimation Model for Southern Africa (SLEMSA), to conditions for which they were not designed. Three mini-catchment erosion plots in semi-arid SE Spain are reported, which between them gave 24 measured storm soil loss events. Comparing this actual soil loss with what would be predicted by USLE and SLEMSA indicated that neither model can completely be applied with current knowledge of equation factor values. USLE gave approximately the right magnitude for prediction but with too low a spread in values and SLEMSA gave the better prediction of rank order of soil loss but greatly underestimated magnitude. It must be concluded that the blind application of empirical models to unmeasured situations will not give reliable predictions of soil loss.

Abstract: During the past decade, Africa, more than any other continent, has been associated with famine and malnutrition. The Sahelian drought of the early 1970s, the Wollo and Karamoja famines and most recently, mass starvation in Ethiopia, have followed one another in rapid succession. The term [`]food crisis' continually crops up in the popular and academic press. An increasing number of researchers probe possible causes; many seek a systemic reason for the present situation. One working hypothesis is that increasing commoditization of food has undermined Africa's food systems. This paper does not purport to prove or disprove this. Less ambitiously, its aim is to draw attention to inter-relationships between commoditization and physical and social aspects of African food systems, tracing their possible effects on the nutritional status of the African population. In so doing, some of the complexities of developing food production and consumption in the transition from peasant societies to more urban-based national economies become evident. The paper is divided into three main parts: a discussion of conceptual categories and general background information about sub-Saharan African food zones and commodity and factor markets; a review of literature on rural food availability and nutrition; and a review of urban food availability and nutrition.

Abstract: Prescribed fire in Arizona chaparral can be used to obtain temporary improvements in forage supplies and a mosaic of uneven-aged stands of chaparral to reduce risks of widespread wildfires. A paired-watershed study demonstrated that prescribed fire had a negligible effect on the ionic composition of streamflow from a chaparral watershed that had been converted by means of a herbicide to grasses, forbs, and scattered shrubs. Before the prescribed fire, nitrate concentrations from the converted watershed were about 10 × greater than those from the control watershed because of nitrate release associated with the conversion process. The fire did not cause further increases in nitrate concentration. Concentrations of sulfrte, bicarbonate, and chloride anions and of calcium, magnesium, sodium, and potassium cations were not affected by the fire. Electrical conductivity and pH also were not influenced. Seasonal fluctuations in ionic concentrations coincided with seasonal variations in rainfall and streamflow. Nitrate concentrations increased during periods of high streamflow, but other anions and all cations decreased during periods of high flow. Electrical conductivity and pH remained relatively constant during the study.

Abstract: The different approaches to control of weeds by biological methods are reviewed. The methods depend upon the techniques used and the control desired. These approaches are classified as follows: the classical or inoculative method, based on the introduction of host-specific exotic natural enemies adapted to exotic weeds; the inundative or augmentative method based on the mass production and release of native natural enemies usually against native weeds; the conservative method based on reducing numbers of native parasites, predators and diseases of native phytophages that feed on native plants; and the broad-spectrum method based on the artificial manipulation of the natural enemy population so that the level of attack on the weed is restricted to achieve the desired level of control. Examples of each of these different methods are presented and the advantages and disadvantages are discussed. The greatest development for the future potential usage of biological control will be the use of biotic agents in an integrated approach to weed management.

Abstract: A review of Late Quaternary palaeoclimatic data derived from several pollen sequences, between ca. 22 and 34°S in Southern Africa, shows a degree of similarity in temperature and moisture variations between the various site. Pollen data from sites such as Wonderkrater and Rietvlei (Transvaal), Tate Vondo (Venda), Elim (Orange Free State), Equus Cave (Southern Kalahari) and Boomplaas (Cape Province) suggest relative dryness during the Last Glacial Maximum, wet conditions during the Late Glacial, and dry conditions during the Early Holocene ca. 8000 yr B.P., followed by progressively moister conditions peaking soon after the development of a temperature optimum ca. 6500 yr. B.P. Problems with radiocarbon dating of polleniferous spring deposits, however, prevent precise correlations of especially Late Pleistocene sequences. Different seasonal patterns in the Late Glacial and Early Holocene may explain palaeobotanical data and are partly compatible with simulations of past climates of Kutzbach and Guetter (1986).

Abstract: A well-tested simulation model of annual herbage growth limited by water and nitrogen availability was used to examine possible interactions between nitrogen availability, soil depth and rainfall in a Mediterranean-type environment. Meteorological data for a 21-year period were taken from a semi-arid site in the northern Negev of Israel, and the measured rainfall was multiplied by 0.5, 1.0, 1.5 and 2 to simulate different rainfall regimes, under otherwise similar meteorological conditions. It was found that, whereas total production increased with greater soil depth, the qualitative response of herbage production to nitrogen was not affected by soil depth, but was strongly affected by rainfall: in the dry, 132-264 mm mean annual rainfall range, the response to added nitrogen was negligible; in the intermediate range (between 264 and 396 mm annual rainfall) production responded to both nitrogen and water; in the [`]wet' range (396-528 mm) the response was mainly to added nitrogen. These results would explain why production is so variable in the arid and semi-arid regions but fairly uniform, although much below potential yields in the more humid Mediterranean regions.

Abstract: Previously described forage and beef models were used to investigate the biological productivity of continuous (CG) and rotational grazing (RG) systems on common bermudagrass (Cynodon dactylon (L.) Pers.) in the southern USA. Simulated factorial experiments allowed examination of the interacting effects of agronomic practices and grazing system variables on cattle (yearling steer) production per area and average daily gains. Cattle production-stocking rate curves were compared to determine (1) the stocking rate (Smax) at which peak cattle production (Gmax) occurred and (2) which grazing system class was potentially more productive. Results indicated that RG permitted greater Smax, particularly at low fertilization levels. However, the grazing system class which yielded greater Gmax was a function of the number of paddocks used in the RG system. RG systems with less than 8 paddocks generally produced less beef per area than CG; those with more than 8 paddocks were more productive. High fertilization levels favored RG systems with large numbers of paddocks and rapid rotation. The paddock number effect resulted from increasing production efficiency (ratio of animal production to herbage production) with increasing numbers of paddocks. The exercise corroborated a hypothesized stocking rate by grazing system class interaction but also indicated that biological productivity of grazing systems may be influenced by multiple interacting effects of input variables.

Abstract: Pollen analysis of vlei or swamp sediments from the Nuweveldberg Mountains in the Central Karoo yields a vegetation history spanning the last 760 years. It sheds light on the local vegetation shifts in response to fluctuations in climate and the possible effects of changing land-use, particularly when Khoi-Khoi herders began occupying the area which was previously inhabited by San hunter-foragers. Multiple discriminant analysis, which compares Holocene fossil pollen assemblages with modern pollen spectra, is used as a tool in palaeovegetational reconstruction. Visual, subjective zoning of the pollen diagram is substantiated by multiple discriminant analysis. This technique is shown to be useful in determining whether modern analogues exist for the fossil pollen assemblages and for identifying misclassified vegetation zones and zones not identified during the initial subjective zoning. Used in this way, multiple discriminant analysis can considerably enhance the interpretation of fossil pollen spectra.

Abstract: Large quantities of coal are extracted in New Mexico by surface mining that results in large areas of surface disturbance. Some goals of reclaiming these disturbances are to control erosion and consequent sediment yields by recontouring and revegetation. This study investigates the rates of infiltration and sediment removal on successfully reclaimed coal mine areas, and their relationship with analogous undisturbed rangeland. Reclaimed areas that had been revegetated for one, three and five years, and a nearby natural rangeland, were subjected to simulated rainfall. Ponding time and runoff time were similar between the non-disturbed lands and the areas reclaimed one and five years before for both dry and wet soil moisture scenarios. The area revegetated three years before required substantially longer time to pond and yield runoff than the rangeland. The reclaimed areas with three and five growing seasons displayed greater infiltration rates than the rangeland area on dry soils and wet soils. Infiltration rates for the reclaimed area with one growing season were similar to the natural rangeland area for both soil moisture conditions. Sediment production and concentrations on the newly reclaimed areas were equal to, or greater than, that for the rangeland on dry and wet soils, respectively. The reclaimed area with the most established vegetation yielded the least sediment of all the reclaimed sites, and significantly less than the rangeland site, regardless of soil moisture situations. Various vegetation, rock, soil, and surface roughness variables were found to influence ponding and runoff times, infiltration rates, sediment production, and sediment concentration. These variables include, in decreasing importance: foliar grass cover, grass production, bulk density, foliar shrub cover, shrub production, horizontal roughness, litter cover, vertical roughness, rock cover and organic matter content.

Abstract: Near-infrared and mid-infrared spectroradiometric reflectance variables were studied for estimating grass phytomass production within grass plots fertilized with five rates of nitrogen. Nine difference vegetation indices, five single wavelengths, and one waveband were correlated with phytomass. Among the 15 variables studied, TM5 (1550-1750 nm), reflectance at the 1100 nm (R1100), 1650 nm (R1650), and 2200 nm (R2200) wavelengths, and five indices [R1100-R1200, R1100-R1650, (R1100-R1300)-TM5, R1100-R2200, and R1200-R1650] had significant coefficients of determination (r2) ranging from 0.83 to 0.92. The spectral variables involving the mid-infrared wavelengths generally yielded the highest r2 coefficients. These results suggest the potential for estimating grass phytomass production over large and inaccesible rangeland areas using Thematic Mapper (TM5 and TM7) satellite data.

Abstract:

Abstract: This paper aims, first, to examine critically Kenya's economic, political, and planning systems, since they can be identified as the causal factors producing many of Kenya's environmental problems and as the frameworks that constrain the identification and implementation of effective environmental policies. The second intention is to demonstrate through a case study that the spatial relationships between physical environment, rural economy, tribe and politics may interact to thwart local participation in solving the environmental problems of the marginal areas.

Abstract: A plant growth model has been developed as a component of a general rangeland production and utilization model (SPUR). The carbon and nitrogen content of standing green, live roots, propagules, standing dead, litter, dead roots, soil organic matter and soil inorganic nitrogen are simulated. The model can simultaneously simulate up to seven plant species or species groups on a total of nine heterogeneous range sites. It incorporates processes which are common to C3 and C4 plants but does not consider plants with Crassulacean Acid Metabolism. When coupled with the other components of the SPUR model, the plant component allows testing of grazing management, environmental variation, and fertilizer application.

Abstract:

Abstract: The past and present distributions of Rudd's lark are reviewed, and recent claims concerning range reduction examined. The species occurs within a geographically and altitudinally restricted range and conforms closely to the boundaries of a restricted group of grassland vegetation types. Its presence within these is determined by local vegetation floristics and structure, and sites with moderately or heavily grazed grassland without forb invasion are preferred. Changing land-use practices have probably adversely influenced the distribution of Rudd's lark in parts of the Transvaal, but populations were discovered in Natal and rediscovered in East Griqualand, an area where the species was thought to be extinct. Distribution in the Orange Free State is reassessed, and the western limits of the species' range are redefined.

Abstract: The author contends that Geographic Information System (GIS) technology can help lending institutions better understand the long-term consequences of economic development projects on African land and climate resources. Issues that are specifically addressed include: the application of GIS to investment plans for the agriculture sector, what can go wrong in agriculture planning when environmental data are not included, how scientific data bases and ADP system software can be used by economists and other social scientists to anticipate the impact of bank projects on natural resource systems, and what can be done to minimize environmental damages in agriculture development. Inputs to the [`]ideal' investment process include: geocoded satellite, climate, environment and demographic data.

Abstract: Seed crop and seed weight of the dominant deciduous tree species in African miombo woodland, Brachystegia spiciformis, varied between years. Seeds possessed no dormancy and germinated completely after imbibition. First phase of seedling growth (2 weeks) is completely based on energy and nutrients allocated in the large cotyledons. The scarcity of stomata on cotyledons did not allow an important net photosynthesis of these plant parts. Low seed weight gave slow-growing seedlings. Optimum temperature for photosynthesis was at 30°C; photosynthesis at higher temperature interfered with the closing movements of the leaflets. At the time of abscission of the cotyledons (38-75 days after germination) nearly 80% of nitrogen and potassium, 65% of magnesium, and 50% of phosphorus and copper had been exported from the cotyledons to the seedling. Late abscission of the cotyledons was negatively correlated with growth performance, being a good and early selection criterion for forestry.

Abstract:

Abstract: This paper discusses options for improvement of the Borana pastoralist system. Overall, the prospects for increasing offtake of livestock or milk, by improvements in marketing facilities alone are not promising. National policies to avoid serious adverse shifts in the exchange rate of cattle for cereals would reduce suffering in drought years, however. Assessments of primary dry matter production suggest that more livestock could be carried in the north and west of the study area if dry-season water supplies could be improved. Against this, evidence of rangeland degradation in these zones suggests dangers in increased stocking. The Borana practice of 3-day watering of cattle during the dry season is beneficial in reducing water and primary dry-matter requirements during these periods of shortage. Desilting of existing surface ponds and construction of new ones could be beneficial if sited in areas of underutilised rangeland. Borana cattle are generally more productive than other forms of livestock, with quite high rates of reproduction and milk yield and low mortalities. The practices of relying on milk for subsistence and disposing of young males, to maintain a high proportion of cows in the herd, appear rational. The only apparent aspect of productive performance with scope for improvement, is in cattle growth rates. The production of small areas of leguminous fodder is recommended for the supplementary feeding of calves.

Abstract: Annual wool production of 120 native Corriedale ewes (age, 2.5-3.0 years; mean weight, 30 kg) was monitored from 1981 to 1983 in two experiments: (1) a rotational grazing system at three stocking rates (two, four and six ewes per hectare), and (2) continuous, rotational and common use rotational (with cattle) management systems at a stocking rate of three ewes per hectare. Greasy fleece weights, staple lengths and fiber diameters were recorded after shearing in 1982 and 1983. Stocking rates had no significant effect on greasy fleece weights per ewe. Greasy fleece weights per hectare increased proportionally with stocking rate. Fiber diameter decreased significantly (P 60;0.05) as stocking rate increased. Grazing strategy did not significantly affect staple length or fiber diameter between continuous and rotational grazing with sheep only, but greasy fleece weight was 9% greater (P 60;0.01) under continous grazing. The common use rotational grazing system produced the lowest wool production with a significantly smaller (P 60;0.05) fiber diameter than the continuous and rotational grazing strategies with sheeo only. Care should be taken to prevent overstocking with cattle under common use grazing if wool production is to be maintained. A reduction (P 60;0.05) in greasy fleece weight was noted in lactating ewes compared to non-lactating ewes. The results indicate that ewes producing lambs are more sensitive to different grazing strategies than are open and dry ewes. Wool production did not appear to be a sensitive indicator of grazing treatment differences.

Abstract: Rainfall and the length of the growing seasons are highly variable in the semiarid East African rangelands such as Borana. Dry years occur about one year in five and droughts one year in twenty. Survival is possible in dry years by spending the entire household cash income on food. In drought years, livestock losses and rangeland degradation are mitigated by extensive migration of animals. There is greater dependence on smallstock and camels, and in some instances food crop production. Nonetheless, there is widespread suffering due particularly to loss of calves and milk supplies and deteriorating terms-of-trade for cattle exchanged for cereals. Complete recovery of livestock numbers and human living standards may take many years. The effects of drought may be mitigated by supplementary feeding of calves, or of cows, and production of cereal crops immediately the rains resume.

Abstract: A trial was conducted on Montana native rangeland to examine the effects of cow age and ambient air temperatures on mid-winter grazing activity of pregnant beef cows. Cows were fitted with vibracorders and pedometers for 50 continuous days in January and February to monitor daily grazing time (DGT) and distance traveled. Three-year-old cows grazed 0.7 h day-1 longer (P 60;0.005) and traveled 0.85 km day-1 further (P 60;0.05) than 5-and 7-year-old cows. Total DGT averaged 8.8 h day-1 across ages and was insensitive (P 62;0.05) to mean ambient temperature departures (either increases or decreases) from average temperatures of the previous 1-20 days. DGT did not remain below 8 h day-1 for more than one successive day. However, examination of grazing times within daily periods indicated significant linear respones to temperature changes. Morning (07.01-13.00 h) grazing times exhibited variable responses (P 60;0.05) to temperature departures from averages across the previous 17, 19 and 20 days. Grazing times during afternoons (13.01-19.00 h) and evenings (19.01-07.00 h) declined (P 60;0.05) when temperatures either increased or decreased from averages of the previous 6-10, and 1, 2 and 4 days, respectively. Only 17% of DGT occurred during the evening period. We concluded that in the foothill grasslands of the Northern Rockies, range beef cows maintained consistent total grazing time despite fluctuating mid-winter temperatures (8 to -26 176;C) and that cow age influenced grazing activity.

Abstract: A continuous pollen record from a central African highland site (3°28'S, 29°34'E) with 15 radio-carbon dates spans at least the last 40,000 yr. Both modern and fossil pollen have been investigated. A clear pattern of changes in vegetation and climate is suggested. Prior to 30,000 yr B.P., the occurrence of the montane conifer forest, including the upper forest limit, indicates climatic conditions colder and drier than now, but more humid than in late-glacial time. Between 30,000 and 15,000 yr B.P., grassland with afroalpine indicators expanded down to 2500-2000 m altitude as a result of dry, and most probably cool, climate; the montane forest persisted in refuges, although much reduced. Forest vegetation with the same floristic composition as today appeared after 13,250 ± 200 yr B.P., suggesting more humid conditions. The occurrence of a possible short-term humid episode about 21,500 yr B.P. is correlated with some high lake-level stages in East Africa and with organic deposits in deep-sea cores from the Mediterranean and the Atlantic Ocean.

Abstract: The improved understanding of the pollen signal in the marine sediments offshore of northwest Africa is applied to deep-sea core M 16017-2 at 21°N. Downcore fluctuations in the percentage, concentration and influx diagrams record latitudinal shifts of the main northwest African vegetation zones and characteristics of the trade winds and the African Easterly Jet. Time control is provided by 14C ages and 18O records. During the period 19,000-14,000 yr B.P. a compressed savanna belt extended between about 12° and 14-15°N. The Sahara had maximally expanded northward and southward under hyperarid climatic conditions. The belt with trade winds and dominant African Easterly Jet transport had not shifted latitudinally. The trade winds were strong as compared to the modern situation but around 13,000 yr B.P. the trade winds weakened. After 14,000 yr B.P. the climate became less arid south of the Sahara and a first spike of fluvial runoff is registered around 13,000 yr B.P. Fluvial runoff increased strongly around 11,000 yr B.P. and maximum runoff is recorded from about 9000-7800 yr B.P. Around 12,500 yr B.P. the savanna belt started to shift northward and became richer in woody species: it shifted about 6° of latitude, reached its northernmost position during the period of 9200-7800 yr B.P. and extended between about 16° and 24°N at that time. Tropical forest had reached its maximum expansion and the Guinea zone reached as far north as about 15°N, reflecting very humid climatic conditions south of the Sahara. North of the Sahara the climate also became more humid and Mediterranean vegetation developed rapidly. The Sahara had maximally contracted and the trade winds were weak and comparable with the present day intensity. After about 7800 yr B.P. the southern fringe of the Sahara and accordingly the savanna belt, shifted rapidly southward again.

Abstract: Rangelands, though marginal for arable agriculture, are an important agricultural resource in many countries. They also represent a particular challenge for extension services: there are conflicts of interest between different categories of user, and agricultural research does not yet give many definitive technical points of intervention. Common interpretations of extension such as [`]technology transfer' to individual farming families are inadequate in these circumstances, as the case of the Yemen Arab Republic illustrates. A wider understanding of extension is needed, one which recognizes the variations in, and adaptability of, local farming systems. Basic principles of good land and livestock husbandry can be taught; communities and individuals who have proved more successful than others can be identified and their practices tested, refined and made more widely known; and extension workers can play an important part in the search for suitable institutional arrangements for the management of communally held resources.

Abstract: This exercise investigated the effects of short-duration grazing (SDG) variables on herbage production and cattle production on desert foothills. The hypothesis that stocking could be increased under SDG while maintaining grass stand integrity was also examined. Number of paddocks, length of stay per paddock and stocking rate were systematically varied under dry, average and wet years. Simulations of season-long grazing under various stocking rates and precipitation regimes provided a series of control runs. Factors controlling biological productivity of SDG systems were climate, stocking rate and number of grazing rotations per season. The latter two factors gave rise to two functional attributes, frequency and intensity of herbage defoliation, both of which decreased herbage production. Livestock production per area displayed a quadratic response to stocking rate and declined as the number of rotational cycles increased. In dry and average precipitation years, cattle production per area was higher under SDG than under season-long grazing; in wet years, production in season-long and SDG systems was similar. When seasonal herbage utilization was constrained to the maximum permissible for stand replacement (70%), SDG systems with one grazing rotation per season were able to carry 40% and 15% more animals than season-long grazing systems under dry and average herbage growth conditions, respectively. This exercise suggested that stocking rates can be increased slightly under SDG, but only under a limited range of conditions. Increased stocking rates under SDG were due to a predicted increase in efficiency of forage harvest by livestock.

Abstract: The deep-sea cores M 16415-2 and M 16416-2 at about 9°N off Sierra Leone were analysed palynologically for the time interval 140,000-70,000 yr B.P. Results were presented in absolute (pollen concentration and pollen influx) and relative diagrams (pollen percentage). In a previous study it was evidenced that in northwest Africa pollen is mainly transported to the Atlantic by wind, so that the efficiency of aeolian pollen transport (pollen flux) could be used to evaluate changes in the intensity of the northeast trade winds. The glacial episodes (represented by the oxygen isotope stages 6 and 4) are characterized by strong northeast trade winds, whereas the last interglacial (stage 5) is characterized by weak trace winds. The pollen influx diagram shows that the intensity of the trade winds increased slightly during the relatively cool intervals of stage 5 (viz. 5.4 and 5.2). Tropical forest had maximally expanded around 124,000 yr B.P. (stage 5.5), around 98,000 yr B.P. (transition of stage 5.3 to 5.2), and around 70,000 yr B.P. (first part of stage 4): an increasing delay of the response of tropical forest to global intervals with maximum temperature is apparent during the last interglacial. As tropical forests need continuous humidity, the record of tropical forest monitors changes in climatic humidity south of the Sahara. During the last interglacial, the southern boundary of the Sahara shifted only little: expansions and contractions of the tropical forest area are correlated with contra-oscillations of the grass-dominated savanna zone. Great latitudinal shifts of the desert-savanna boundary, on the contrary, occurred during the penultimate glacial-interglacial transition (around 128,000 yr B.P.) to the north, and during the last interglacial-glacial transition (around 65,000 yr B.P.) to the south.

Abstract: The semi-arid lands of the world are characterized by low and unreliable rainfall, with lack of soil moisture during all or part of the year being the predominant limitation to vegetative growth. Soil erosion, salinity, nutrient deficiencies and soil texture may also limit tree establishment. These lands are often quite fragile systems, where agriculture is frequently a marginal economic prospect. Yet the pressure to expand agricultural production in these areas is increasing rapidly, and the results of imprudent expansion are often quite damaging to the long-term productive capacity of the land. Establishment requirements for shelterbelts in semi-arid areas are similar to those encountered everywhere, with a general need for good site preparation, effective control of competing weed and grass growth before and after planting, and protection of plants from domesticated stock and vermin. The limitations of available moisture in this zone require special importance to be attached to plant/water relationships at the time of establishment. Consideration should be given to supplementary watering by hand methods or by establishing irrigation systems, including drip or trickle irrigation. Tree establishment methods which may be considered include hand- and machine-planting, as well as direct seeding and natural regeneration. The long-term survival and effectiveness of shelterbelts in semi-arid areas depends on proper establishment, good designs and careful choice of species. It is evident from published reports that there is a common range of species used in many parts of the world, including in particular, species of the genera Acacia, Casuarina, Leucaena, Pinus, Prosopis and Tamarix. A number of individual species are listed and classified for locality and primary uses. Indigenous species should always, however, be the first to be considered in any planting project. The need for planting of new shelterbelts in semi-arid agricultural areas could be reduced if proper land-use planning is applied during the initial development phase of the farmland. Much of the shelterbelt planting in these areas is required to redress particular problems arising from unwise clearing of native vegetation. Frequently, these problems, especially erosion and salinity, could have been avoided if the nature of the land was given proper consideration prior to development, and native tree or shrub cover retained and managed in sensitive localities. The most effective and economical land protection will, in the long term, be provided through proper land use, with the integration of forest or woodland management with agricultural production.

Abstract: Four grassland types at Cherrapunji, in northeastern India, namely the Osbeckia, Arundinella, Ischaemum, and Eragrostiella, types, were studied for soil nutrient losses through their hydrology and related soil-fertility changes. Losses through water and the consequent soil-fertility depletion were shown to be related to the frequency of the burn to which these grasslands are subjected. The Ischaemum type, with regular burning at 2-years' intervals, was the most adversely affected, compared with the Osbeckia type, which had not been burnt for the past 6 years.In all the grassland types which were studied, the losses through water were high during the early part of the monsoon period, owing to the poor vegetation cover at that time. A desertified site with the Eragrostiella type of grassland had the lowest soil-fertility level, and had losses through removal in water that far exceeded the prevailing soil-nutrient level.Fire can help in stabilizing the seral grassland vegetation if the soil is sufficiently deep and the frequency of the burn is not too great. On the other hand, too frequent perturbations by fire are apt to result in a desertified landscape that is difficult to restore.

Abstract: Results of an extensive experiment at five sites in Victoria, Australia, during the 1985-1986 summer are presented, and a modified vegetation index observed by the AVHRR is related to "grassland" fuel-moisture content. This relation is used as a basis for an operational system by which the Country Fire Authority uses AVHRR imagery as an objective input to decisions on the declaration of total fire ban regions in Victoria.

Abstract: The late Miocene (Turolian) localities of Pikermi and Samos in Greece present numerous ruminant species which have been interpreted to represent savanna-adapted taxa. The masticatory morphology of these extinct ruminants is compared qualitatively to twenty-seven extant ruminant species from Asia and Africa using thirteen masticatory features. Statistical analysis of these features on the modern species shows significant differences between the morphology of browsers, intermediates and grazers and suggests that intermediate and grazing adaptations evolved independently more than once. In addition, certain extant ruminant browsers and intermediates may have assumed such diets from ancestral grazing species recently. Application of this method to the extinct species from Pikermi and Samos shows that, with the exception of one species, the bovids were either browsers or intermediates. Parurmiatherium rugosifrons from Samos was probably the only grazer. Pachytragus laticeps, a presumably advanced species, has masticatory morphology very similar to Miotragocerus species, commonly interpreted as primitive species. Samotherium boissieri and Helladotherium duvernoyi were intermediate feeders, although giraffids. We propose that the absence of grazers at these localities suggests that savanna-like dietary adaptations for ruminants were not as widespread as now. The presence of savannas similar to those of East Africa at Pikermi, Samos and other Miocene localities is unlikely. Such savannas were originally proposed because of modernization of fossil taxa, the presence of numerous ungulate and hyaenid species, the misconception that hipparions represent zebra-like species, and the abundance of fossil specimens. Ruminant faunal comparisons using masticatory morphology point out a greater similarity of Pikermi and Samos to extant forest and woodland ruminants; the extinct ruminant faunas were not similar to extant savanna-adapted species. A good physiognomic model for the Pikermi-Samos ruminants is the forest-woodland ruminants of Sichuan, China, Southeast Asia, and Kanha, India. The hypothesis that the Pikermi ruminants evolved in forested environments is supported by analysis of the local paleofloras. The Pikermi is similar to modern warm mixed riparian evergreen and broadleaf deciduous temperate woodland-forest. The Turolian mountains near Pikermi had mixed forests, although evergreens dominated.

Abstract: Summary 1. The origin and history of aridlands and their vegetational cover is closely related to geological history, especially in relation to plate tectonics, mountain building, land-and sea-level changes and ice ages, and the arrival of modern humans and their subsequent development. 2. A close relationship exists between world temperatures and precipitation. Therefore, the development of present-day zonal, aridland vegetation and climate cannot be divorced from the history of the latest ice age. 3. The combined geological and palaeobotanical evidence demonstrate that whilst the origin of modern openland and aridland vegetation went back to the time of the origin of angiosperms during the Cretaceous, its subsequent expansion went hand in hand with the lowering of world temperatures during the Palaeogene and Neogene, when a series of angiospermous families having dominantly herbaceous and openland taxa, as members, appeared successively in the stratigraphic record. 4. The successive lowering of world temperatures had the overall effect of reducing precipitation levels all over the globe. Consequently, high rainfall areas, bearing closed forests, became progressively smaller and smaller and the decreased rainfall promoted the evolution and expansion of low biomass, openland and aridland vegetation. 5. The break-up of regional closed forests had started from the middle Miocene but the main expansion of zonal, aridland vegetation, in low and middle latitudes, appears to have taken place, together with the expansion of tundra vegetation, at high latitudes, from the late Pliocene. Glaciations of a magnitude of at least two-thirds that of the late Pleistocene glacial maxima started to occur about that time, 25 Ma ago. 6. The alternations between cold, glacial and warm, interglacial periods, during the late Neogene, especially with increased amplitude during the last 0.4 Ma, allowed less and less time for forest vegetation to expand and stabilize during the warm intervals, with the result that openland and aridland vegetation was able to expand to unprecedented levels. 7. Further, as man increased fire frequencies during the late Pleistocene, the relatively fire-sensitive and mesophytic taxa were selectively eliminated and more and more forests were opened to invasion by openland taxa in low and middle latitudes. Later on, with the clearance of forests for agriculture, the overall effect on vegetation was to create open landscapes which favoured the expansion of openland taxa at low, middle and high latitudes, during an interglacial, that is, the Holocene, a feature that is unprecedented in the entire earlier geological record.

Abstract: An interactive beef production system model is outlined. The beef component is based on the Kahn model. The structure of the model is flexible, allowing mob grazing, grazing of multiple resources and rotational grazing. Animals may be culled, weaned, sold or bought as required, or decision rules may be implanted in the model. Validation work, performed for Colombian conditions, is described. The sensitivity of the beef component was examined with regard to small changes in important parameters. It is concluded that the model reacts reasonably to changes in plane of nutrition at the prevailing levels of forage quality. The forage component is concerned with grass-legume mixtures; it is based on a small number of functions, and is pending validation. Economic modules generate cash flows and standard economic investment criteria. For any particular simulation, economic reanalysis may be carried out to investigate the effects of changes in price or in other economic parameters. The potential uses of such a system are sketched.

Abstract: A trial was conducted on Montana native rangeland to examine the effects of cow age and ambient air temperatures on mid-winter grazing activity of pregnant beef cows. Cows were fitted with vibracorders and pedometers for 50 continuous days in January and February to monitor daily grazing time (DGT) and distance traveled. Three-year-old cows grazed 0.7 h day-1 longer (P<0.005) and traveled 0.85 km day-1 further (P<0.05) than 5-and 7-year-old cows. Total DGT averaged 8.8 h day-1 across ages and was insensitive (P>0.05) to mean ambient temperature departures (either increases or decreases) from average temperatures of the previous 1-20 days. DGT did not remain below 8 h day-1 for more than one successive day. However, examination of grazing times within daily periods indicated significant linear respones to temperature changes. Morning (07.01-13.00 h) grazing times exhibited variable responses (P<0.05) to temperature departures from averages across the previous 17, 19 and 20 days. Grazing times during afternoons (13.01-19.00 h) and evenings (19.01-07.00 h) declined (P<0.05) when temperatures either increased or decreased from averages of the previous 6-10, and 1, 2 and 4 days, respectively. Only 17% of DGT occurred during the evening period. We concluded that in the foothill grasslands of the Northern Rockies, range beef cows maintained consistent total grazing time despite fluctuating mid-winter temperatures (8 to -26°C) and that cow age influenced grazing activity.

Abstract: The invasions of introduced species into five reserves in tropical savannas and dry woodlands are described. Vascular plants are the group having the most introduced species; invasions are least important in dry, regularly burned savannas, more important in moist, derived savannas (where scrambling shrubs are invading) and most important in wetlands (where trees, shrubs, herbs and aquatic macrophytes are invading). Control, which should be initiated early in an invasion, is being implemented for only a few species. Water-dispersed plants and herbaceous weeds are generally impossible to control using current technology. Biological control measures are urgently required for some invasive shrubs (e.g. Chromolaena odorata). Introduced vertebrates are generally less important, but exceptions are large mammalian herbivores in Australia and several near-native ungulates in southern Africa. Predation apparently limits the number of successful vertebrate invasions. Introduced mammalian pathogens have had severe ecological effects in Africa. Invertebrate invasions require more research.

Abstract: Results of fossil pollen studies in Eastern, Central and Southern Africa covering the last 32,000 years are surveyed in this paper. This research, conducted between 1951 and 1985, was mostly concentrated in East and Southern Africa, but a number of pollen sequences from intervening sites provide some links between the data of these two regions. In all this immense region, of half the African continent, information from fossil pollen is available only from some 30 sites. In addition to problems with absolute dating, the interpretation of the results in terms of former vegetation poses difficult questions. While it is far too early to draw detailed maps of former vegetation some very general conclusions can be inferred from the data presented. At two sites in East Africa pollen evidence has been found for the existence of a warmer and more humid period from ca. 32,000 to 28,000 yr B.P., an episode known as the Kalambo Interstadial. During the period from ca. 28,000 to 20,000 yr B.P. the climate in East and Central Africa was fairly similar to that during the Holocene moist period. In Southern Africa during the same period palynologic and geologic results indicate that cold episodes occurred while higher rainfall in East Africa, the Kalahari and adjacent regions caused high lake levels. During the last glacial maximum from ca. 20,000 to 16,000-14,000 yr B.P. aridity spread over nearly the whole region. The Zaire rain forest was considerably reduced and the tree line on the East African mountains was depressed by 900-1100 m, indicating a drop in mean temperature of 5-8°C. Lakes in East Africa and the Kalahari dried out, except for the southern Kalahari, its surroundings, and the SW Cape, where humidity was high. The general causes for aridity were the low evaporation at the ocean surface and the strong upwelling of colder waters. More humid conditions which have been postulated for the central part of southern AFrica could have been the result of lower evaporation in lake basins while the penetration of winter rainfall in the area has also been proposed. An abrupt change to warmer and more humid conditions in East Africa at ca. 12,000 yr B.P. reversed all the former processes. Rainfall also penetrated the Kalahari from the NW, NE and SW sides. Remarkable fluctuations in climate at this juncture could be demonstrated by pollen evidence in South Africa only at Aliwal North. During the Holocene, humid conditions persisted in East Africa until ca. 4000 yr B.P., when the climate became drier. Insufficient dated evidence in southern Africa makes it difficult to compare the various climate chronologies. In general the climate may have been wetter until about 4000 B.P. when a dry interval occurred. In East Africa pollen data point to deforestation by man during the last two millennia.

Abstract:

Abstract: The Richtersveld area, bounded by 16° and 18° E and 28° and 29° S, has been mapped geochemically using stream sediment samples collected from first-order streams on a one-kilometre grid. The samples have been analysed for 20 elements and geochemical maps on a scale of 1:250,000 have been prepared. The basement consists of the Orange River Group which has been intruded by the Vioolsdrift Suite between 1700 and 1900 Ma. Intrusive into the Vioolsdrift Suite is the Richtersveld Suite, consisting of alkaline granite, syenite and diorite, which intruded at 970 Ma. The basement and the Richtersveld Complex are overlain by the younger Gariep Complex and in the south the Vioolsdrift Suite is overlain by the still younger Nama basin. The last intrusive event was the emplacement of three granitic plutons at 550 Ma. Geochemical maps for Rb and Y are used to characterize the geochemistry of the basement rocks. These maps show that the northern portion of the Vioolsdrift Suite is granodioritic whereas the southern portion is granitic. The boundary between the two granitic terrains is delineated. The distribution of Rb in the sandstone of the Gariep Complex reflects the Rb variation in the Vioolsdrift Suite and the Richtersveld Complex from which it was derived. The Rb in the sandstone occurs in feldspar thus demonstrating that mechanical weathering dominated during the its formation. The distribution of Y confirms both the proposed source areas and weathering conditions. Yttrium occurs in placer deposits in the sandstones of the Gariep Complex. The deep water facies of the Gariep Complex reflects the provenance areas vaguely, but due to homogenization in the basin the distribution of Y is more homogeneous in the shale. The effect of chemical traps such as dolomitic limestone is, however, apparent. The sporadic high concentration levels of Rb and Y in the sandstone of the Nama basin indicate that the granitic portion of the Vioolsdrift batholith was the source area, that mechanical weathering dominated and that placer deposits formed during the deposition of the fluvial sandstones. The dolomitic limestones, however, show evidence of the chemical fractionation of Y, indicating that chemical leaching and concentration took place during this phase. Elements such as Sn, W, Be, B, Th, Nb and Ta, all of which occur in the southern Vioolsdrift batholith, could have concentrated as placers in the Gariep and Nama sandstones. Elements such as U, Y, P, and Cu, of which substantial deposits are known, did not concentrate in the sandstones, but formed accumulations in the limestone and carbonaceous limestone of the younger sediments. Geochemical maps for Y, P and U show examples of hitherto unknown metallogenic provinces in the deep water sediments. Geochemical maps for Ti, Zr and P can be used to define the boundaries and relative concentration of diamonds within individual deposits and to identify new exploration targets. The pegmatite metallogenic province is divided into a northern P-enriched province containing accumulations of Y, Zr, Th, U and rare-earths, and a southern Nb-enriched province. The latter contains several Ta- and Be-producing pegmatites. The extension of these two pegmatitic provinces, which are also associated with the widespread W-mineralization, to the west of the Nama basin is also suggested.

Abstract: This paper outlines the use of Landsat MSS for cover monitoring on sparsely vegetated landscapes grazed by cattle in central Australia. For important pastoral landscapes, a 5/7 ratio based on absolute reflectance was found to be linearly related to total plant cover, with correlation coefficients (r) varying from -0.90 to -0.98. The strength of this relationship was notable in that the predictive regressions used data from Landsats 2, 3, and 4 and had sun angles varying from 32° to 46°. Prediction of cover change on some landscapes was difficult because response to rainfall was confined in limited locations, or occurred at a subpixel level. Yearly or twice yearly cover measurement at a regional level is now feasible, but implementation depends on successfully blending the technology into the decision making processes of government agencies and pastoral managers. This blending will determine whether the coarser scale NOAA imagery will be more cost-effective than Landsat MSS, considering the scale at which decisions are taken.

Abstract: The characteristics of the arid rangelands of Australia that have influenced the application of remotely sensed data from the currently accessible satellites (Landsat and NOAA) are those intrinsic to the landscape, i.e., the nature of the soils and vegetation, and the extrinsic factors of pattern and dynamics of pastoral use. Both sets are examined within the sociopolitical context of contemporary Australia. To date, digital processing of satellite data has found little application to rangeland inventory and is unlikely to do so in the future, notwithstanding the future availability of increased spatial and spectral resolution from SPOT and Landsat TM. Most applications are currently directed towards assessment and monitoring of rangelands with a requirement for quantitative rather than qualitative information. Because of the nature of the rangelands and the pattern of pastoral use, information relating to land degradation is of greater interest than pasture productivity, though this may change in the future. Also because of the nature of the soils and vegetation, spectral modeling and the derivation of vegetation- or soil-related indices within a GIS appears to offer the greatest potential for the routine application of both Landsat and NOAA AVHRR data. Initially it was the availability of Landsat data that catalyzed the application of satellite data to rangeland assessment, monitoring, and management. However, NOAA AVHRR data appear capable of replacing Landsat MSS in providing cost-effective information about pasture productivity but not for land degradation where the higher spatial resolution is required. In the foreseeable future Australian rangeland applications will most likely use high frequency/low spatial resolution data (e.g., NOAA AVHRR) as a complement to low frequency/high spatial resolution data (e.g., Landsat MSS/TM, SPOT).

Abstract: This paper reviews the current capability of video imagery for rangeland management assessment. Three video systems are described and evaluated: 1) a black-and-white four-band system with visible/near-infrared (0.4-1.1 [mu]m) sensitivity, 2) a selectable three-band color system, and 3) a black-and-white monoband system with midinfrared (1.45-2.0 [mu]m) sensitivity. These systems have provided near-real-time imagery that could be useful to detect differences among many variables such as plant species, phytomass levels, fertilized and drought-stressed grass, heavy grazing, and burned areas. The computer compatibility of video imagery also has been demonstrated. Finally, results have shown that video systems may have considerable application to integrate the above-listed variables for rangeland resource management assessment.

Abstract: A method for grouping soils for specific purposes is presented using the example of maize in the savanna ecological zone of south-western Nigeria. The technique involves two important stages. The first is the identification of the crucial soil properties influencing maize production in the study area while the second is the actual rating of the soils based on the relevant soil properties identified. Using an index of soil variable contribution to the growth and yield of maize in the area, only two soil properties, the organic matter and the available moisture contents of the soils, contribute significantly (58·4% and 13·1%, respectively) to the growth and yield of the crop, out of the twenty soil parameters analysed. With respect to the second stage, six soil productivity classes ranging from A (Excellent) to E (Poor) were arrived at as far as maize production in the area is concerned. The assignment of scores to the two soil properties used in rating the soils was based on their relative contribution to the growth and yield of the crop. However, the results of the application to, and comparison of the rating scheme with, 29 local soil series previously assessed for rainfed maize production by Murdoch et al. (1976), largely indicate that, after carrying out the special purpose soil classification, there is still the need to engage in capability assessments of the land using other environmental parameters apart from the soil attributes.

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Abstract: Summary The grasslands of Urhobo plains occur within the humid forest zone of south-western Nigeria in discontinuous patches. They are almost treeless and are dominated by grasses such as Imperata cylindrica, Loudetia arundinacea, Panicum maximum and Hyperrhenia sp. Many of the grass species are suitable for feeding livestock. The suggestion is made that the grasslands can be used for livestock production. Urhobo plains grasslands lack the typical tree species present in the drier grassland belts of northern Nigeria mainly due to geographic isolation within the forest zone. Also, tree species present in adjacent forest and forest regrowth are absent in Urhobo plains grasslands. The soils are sandy, acidic and deficient in plant nutrient.

Abstract: Abstract The main factors affecting the abundance and composition of the invertebrate fauna in grassland are reviewed. Old grasslands with species-rich swards and complex structure support an abundant and diverse fauna compared with uniform leys with few species. Seasonal and successional changes in the sward are accompanied by equally marked changes in the invertebrate community. Climate and weather have a major influence, but their effects may be modified locally by the availability of shelter. Soil physical and chemical characteristics influence the soil fauna directly and the above ground fauna indirectly through the vegetation. Food quality as determined by physical and chemical plant characteristics strongly influences invertebrate growth, reproduction and mortality. The main biotic factors affecting abundance are natural enemies and disease; these, in combination with weather and food quality, are often the main agents in determining population density in natural communities. Management practices such as grazing, cutting, fertilizer application, burning, soil water control and pesticide use profoundly influence the sward and induce correspondingly great changes in the invertebrate community.

Abstract: This paper, based on the Joint Ethiopian Pastoral Systems Study (JEPSS) conducted from the International Livestock Centre for Africa (ILCA), describes the Borana System of Southern Ethiopia. The supply of dry-season well water in the Borana rangelands allows a semi-settled existence. However, while milking herds (warra) are kept at the settlement, dry cattle (forra) travel further afield in search of dry-season grazing. Stocking densities are reasonably close to the maximum potential except in areas not supplied by wells. Reproduction rates, and milk yields of the Boran cattle, are quite high for pastoralist herds, while mortalities are low. Sheep, goats and camels supplement production from cattle. Although milk is the staple food of the Borana, grain purchased with the proceeds of livestock sales meets over 30% of dietary energy requirements. Overall, the Borana are efficient rangeland and livestock managers, who manage to survive in a tightly constrained environment. These findings suggest that the scope for improvement is limited.

Abstract: Overgrazing of pastures, particularly in the spring period of seed production, is the major reason for low forage production and land degradation in the Middle East and North Africa. Conventional policies for increasing livestock production by using cereal grain can cause further degradation of rangeland areas and are expensive. Pasture development using medics and other annual pasture legumes can provide a quantum leap in forage production that will solve the problem of overgrazing. There is a need for grazing management particularly during the transitional phase of pasture establishment. A series of case studies illustrates alternative models of grazing management that have been developed from local grazing traditions.

Abstract: Efficient land use and farming systems are essential if agricultural production is to be increased substantially in Africa on a sustainable basis. Land use and farming systems in the Horn of Africa -- Sudan, Somalia, Ethiopia and Djibouti -- are analysed in this article. Policy options and recommendations to improve the situation in the four countries are outlined.

Abstract: The unfenced ranges of Botswana support large cattle herds, which are operated on a commercial basis, and small herds, which are managed in order to meet family subsistence needs. The distinctive herding practices and sales strategies associated with large and small herds are suited to the variable amounts of human labour, cash and saleable animals at the disposal of herd owners. If they are to operate permanently on a commercial basis, small herds must grow in size. The process of commercialization will not, therefore, alleviate overstocking on communal rangelands and the majority of small herd owners are not likely to endorse any programme of voluntary destocking.

Abstract: Distribution trends are reviewed among 1808 plant species known to be in the IUCN Red Data Book categories and which occur in the fynbos and karoo biomes of the Cape Province, South Africa. The field-search and taxanomic limitations of the data are noted. Aspects of extinction biology are considered in relation to natural and human-caused factors which increase rarity. The genetic biogeography of the isolation of the plant populations in the region is discussed as a guide to future research. The priority ranking of species for conservation treatments is critically examined and a method for its evaluation is proposed.

Abstract: On semi-arid rangelands, stems and other standing dead material may accumulate in bunch-grasses and restrict access to new growth by grazing animals. We found that the presence and heights of residual stems in Lehmann lovegrass (Eragrostis lehmanniana Nees) increased the times between successive bites taken by grazing cows, thus decreasing biting rates when compared to bites taken where these stems were reduced. As new tillers elongated, biting rates increased but remained lower on those plants with the greatest amounts of residual stems. Ingestive behavior of cows may be influenced by distinctive features of the vegetation available at each bite taken. The number of bites cows take on grass plants containing large amounts of residual herbage could influence the average biting rate during a foraging bout. Methods of collecting biting-rate data should account for these influences.

Abstract: The literature suggests that two different approaches have been applied to problems of rangeland monitoring using MSS data. These are referred to as the near infrared over red ratio which has been successfully applied to areas of relatively dense vegetation in the humid zone, and the darkening effect which is applicable in the sparsely vegetated semiarid zone. Data from Botswana suggests that neither of these is singularly appropriate in the savanna woodland zone of southern Africa. In the Botswana hardveld the measured vegetation cover consists of green vegetation which generally occupies less than 60% of the cover in a given area. The soil component is dominant. This, in addition to other vegetation components which produce a darkening effect, results in high reflectance values in the red and infrared parts of the spectrum for areas with a low vegetation cover and low reflectance values in both wavebands for areas with a high vegetation cover. In savanna woodland environments which contains elements of both the near infrared to red ratio and the darkening approach, the most suitable indicators of range condition and degrees of desertification can be obtained by directly applying spectral ranges from the red band. The range of values used is heavily ecosystem, therefore soil-type-dependent, and is referred to as the savanna woodland model.

Abstract: Pollen spectra in a peat deposit from a mountainous area near Tate Vondo in Venda have been grouped into three zones. The oldest zone of c. 12,000-10,000 yr B.P. contains mainly grassland and fynbos elements, as well as forest pollen consisting mainly of Podocarpus. These spectra suggest that the vegetation on slopes was open, but that forests were well developed in mountain ravines. This scenery is suggestive or relatively cool, sub-humid conditions. The second zone, which dates between c. 10,000 and 6500 yr B.P., contains increased savanna elements and local Psoralea pollen, while forest and fynbos pollen types are reduced. The pollen spectra in this zone are suggestive of gradually increasing temperatures and dryness. On the basis of prominent warm savanna and reduced fynbos pollen a temperature optimum is indicated at the boundary between this and next pollen zone, representing the last c. 6500 years. More swamp and mesic woodland elements in this youngest zone are suggestive of relatively moist conditions. The upper part of the zone, which represents the last c. 1500 years, shows a sharp decline in tree pollen which may be attributable to burning and clearing of woody vegetation by Iron Age people moving into the area. The general palaeoenvironmental changes indicated by the Tate Vondo pollen sequence is consistent with pollen evidence found along a transect from north to south through the Transvaal, suggesting that these changes were of regional significance for the province.

Abstract: Satellite imaging systems do not produce images that are in perfect planimetric accord with the Earth's surface, nor do the images coincide with the deliberately distorted geometrics of various map projections. For many purposes there is a requirement that satellite images be georeferenced or transformed according to the constraints of some convenient map projection. Other requirements may call for one satellite image to be transformed to the geometry of another. In this paper consideration is given to the geodetic correction and registration of polar-orbiting satellite data with particular reference to the monitoring of vegetation over large areas. Attention is given to the variation of the field of view with change in sensor view angle associated with the Advanced Very High Resolution Radiometer (Avhrr) on the Tiros-n series of meteorological satellites. Avhrr data, with a nominal resolution of 1.1 km on the ground, have been compared with multi-spectral scanner (Mss) data from the Landsat series of satellites which have a resolution of approximately 80 m on the ground. As the deterministic correction of image distortions is limited by nonsystematic deviations of the satellite from its known position, methodologies have been developed for emperically determining the appropriate transformation with optimal accuracy. The results presented suggest that polar-orbiting meteorological satellite data enable the monitoring of vegetation over vast areas. Such monitoring, not conceivable previously, could contribute to a timely and appropriate response in the case of calamitous drought, given the experience of Ethiopia and the Sahel in recent years.

Abstract: Visible and near infrared spectral reflectance values were recorded from Nevada rangeland plant communities using both low flying aircraft and ground measurement approaches. The individual spectrum values, four-band signatures and infrared: red scatterplots were used to compare 5 × 5 m aerial pixels with data from various ground components. Results show that vegetation and soil do not account for the integrated aerial spectra. The composite ground signatures indicate that spectrally dark components exist in rangeland plant communities which decrease the brightness of a scene measured from the air. Shadow and litter are presumed to be the primary sources of spectral darkening. An estimate of the overall signature of the shadow/fitter component was calculated.

Abstract: Remote sensing in aridland/rangeland regions has developed to meet the need for low cost management information over large expanses of land. Applications include rangeland management, watershed analysis, antidesertification, wildlife habitat management, mine waste reclamation, management of the arid land-irrigated agriculture interface, and outdoor recreation. Unique remote sensing problems in arid regions are related to sparse vegetation, multiple species, and considerable bare ground. Thus spectral interpretations must consider: multiple intermingled green and senescent species; considerable bare ground which includes cryptogamic soil crusts and powdery, endurated, or salinized surfaces; standing dead vegetation; litter; and shadows. Pixel modeling will be required in these heterogeneous environments. In particular, the lack of greenness tends to preclude the application of vegetation indices based on infrared/red ratios. New interpretation approaches to scene understanding, such as those included in this issue, should lead to useful procedures for aridlands.

Abstract: Learning early in life may play an important role in the development of dietary habits and foraging skills of domestic ruminants. In this review we (1) explore the theoretical and empirical bases of early dietary learning, (2) examine constraints on such learning, and (3) discuss the implications of diet learning for livestock production and range management. Ruminant livestock select a diet from a wide variety of potential foods; some are appropriate while others are nutritionally poor or even harmful. Because of these complexities, evolutionary processes should favor animals whose diet selection is based on generality and flexibility. Learning which foods to eat and which to avoid is such a system. One way for individual animals to discover the value of food is through trial and error learning. Their preferences for, or aversions to, foods may result from trial and error learning based on cautious sampling and resultant nutritional and physiological consequences. Additionally, evolutionary processes could provide selective pressure for herbivores that feed in large, mixed-generation groups to rely on social learning, where foraging information is passed from experienced to inexperienced foragers. Recent research suggests that the mother may greatly influence her offsprings' dietary habits. As a result, dietary learning may be more pronounced in early, as opposed to later, life and there may be a sensitive period that coincides with the transition from monogastric to ruminant; i.e. weaning. There are genetic, metabolic and morphological constraints on dietary learning. Plant olfactory and gustatory characteristics that ruminants have consistently associated with negative consequences may be genetically fixed, and it is often possible to explain avoidance of plant species and parts by herbivores in terms of deterrent phytochemicals and physical plant characteristics. It is considerably more difficult to identify feeding attractants in plants. In addition, small ruminants are constrained nutritionally to select diets of higher quality than large ruminants, and the efficiency with which small versus large ruminants ingest different plant parts and life forms may be different. Teh likelihood that domestic ruminants learn to forage presents both problems and opportunities for livestock and rangeland managers. On the one hand, learning may result in inefficient foragers when animals are moved to new environments. On the other, through the manipulation of past dietary experience, a manager may create a foraging group that better fits specific management goals.

Abstract: Many areas of East Africa show signs of misuse of natural resources by man. An improved use of these resources can be made if land use is integrated within the boundaries of a natural ecosystem, taking into account the long-term effects of exploitation, the potential of the land for different economic activities, and nature protection. In this paper the Masai Ecosystem of northern Tanzania is used as such a functional unit in which land use can be integrated. For this purpose this Ecosystem is described and its boundaries are defined. The potential (agricultural) land use for different areas within the boundaries are highlighted, and a review of the importance of the National Parks and Conservation Area for Tanzania's national economy is given. It is concluded that tourism can play an important role in the development of the country but within the Ecosystem the flow of tourists should be re-adjusted. Some of the Parks are more profitable than others but the most profitable appears to be over-utilised by tourists, while the least profitable is under-utilised. An alternative tourist circuit is proposed, and a number of recommendations are given to make better and safer use of the land with the new Agricultural Policy of the Government of Tanzania in mind. It is concluded that land use and nature conservation are tightly interlinked and that people and wildlife can both benefit from improvements aimed at integrated land use, agricultural development and higher economic returns.

Abstract: The spectral behavior of an arid, Lehmann lovegrass (Eragrostis lehmanniana), range canopy with varying quantities of live, green grass, senesced, yellow grass, weathered, gray litter, and different soil backgrounds was analyzed with a ground based radiometer. The analysis included rangeland field plots and artificial mixtures of live and dead grass. Senesced grass and weathered litter were found to significantly alter the spectral response of the range canopy in the first four Thematic Mapper wavebands (0.45-0.52; 0.52-0.60; 0.63-0.69; 0.76-0.90 [mu]m). These influences seriously hampered the utility of spectral vegetation indices in assessing green phytomass levels. Gray litter lowered the response of the green vegetation index (GVI) and perpendicular vegetation index (PVI) while minimally influencing the ratio vegetation index (RVI) and the normalized difference vegetation index (NDVI). Yellow, senesced grass increased the greenness response of plots without green vegetation and decreased the greenness response of plots with green vegetation. Higher reflecting soils increased the GVI and PVI response and decreased the RVI and NDVI response of comparable range canopy mixtures. Small amounts of 30 cm tall, green grass (750 kg/ha) could not be detected within a 75 cm tall, senesced grass stand (5000 kg/ha). The results of this study show spectral vegetation indices to be unreliable measures of green phytomass in arid rangelands. A mixture model employing principal component analysis was used to extract a green vegetation signal, but green phytomass detection was not improved. Apparently, the green vegetation signal emerging from range canopies is diminished by the scattering influences of the vertically oriented elements of the senesced grass phytomass.

Abstract: NOAA-6 and NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) global-area coverage (4 km ground resolution) data were obtained at three-day intervals throughout each of the four-month periods covering the 1980, 1983 and 1984 growing seasons, between latitudes 10° and 22° North in the Democratic Republic of Sudan. Daily rainfall data for twelve meteorological stations spanning the Savanna Zone were analyzed. Rainfall in Sudan during 1980 was below normal, but in 1983 and 1984 there were moderate and severe droughts. The satellite data were used to calculate normalized difference vegetation index (NDVI) values from the visible and near-infrared bands of the satellite data. These were processed into ten-day composite data sets using the AVHRR thermal-infrared channel as a cloud screen and a temporal compositing procedure that reduces cloud contamination and selects viewing angles closest to nadir. The ten-day composite NDVI values and integrals of NDVI for each growing season were found to be closely correlated with rainfall. The constants of regressions between NDVI and rainfall were lower in 1983 and 1984 than in 1980, which suggests there was reduced water-use efficiency by the rangeland vegetation in drought years. It was found that July and August NDVI values were closely related to the integrated NDVI values; hence early- and mid-season NDVI data could be used to predict annual primary production. The precision of the relationship between rainfall and the vegetation indices for the meteorological stations encourages the view that NOAA AVHRR GAC composite NDVI values can be used to monitor effective rainfall in the Savanna Zone of the Democratic Republic of Sudan.

Abstract: Pasture production not only depends on precipitation amount and distribution patterns, but also on soil type and evaporative demand. The simulation model of Rose et al., developed using improved pastures, is one that accounts for these factors and also takes into account the effect of fertilizer levels on production. From this a simplified model is proposed for Mozambique using as inputs annual precipitation, annual potential evapotranspiration and soil moisture storage capacity. The model is applicable only under negligible soil slope and no bush or tree cover, but can be adapted to varying phosphate fertilizer levels. Estimates from this proposed model show close agreement with experimental data from cleared natural pastures in Zimbabwe and with improved pastures of Townsville stylo in Australia under high phosphate fertilizer levels.

Abstract: Considering an arid area in the High Atlas mountains of Morocco, the assessment of vegetation cover is carried out from ground spectral measurements and analysis of satellite imagery. Ground measurements have been made with SPOT simulation radiometer; results are related to reflectance-vegetation coverage relationships and to spectral responses obtained at a local level (120m transects). Analysis of Thematic Mapper and SPOT data includes visual interpretation of color composite imagery for geomorphological units delineation, principal component analysis and examination of bispectral scatter plots.

Abstract: The use of manure on crop land and the grazing of crop residues and fallow lands are important interactions between cropping and cattle husbandry in seasonally dry West Africa. In central Nigeria, cattle spent 50% of their dry-season grazing time on sorghum (S. bicolor), millet (P. typhoides), rice (O. glaberrima), and soybean (G. max.) residues and weeds remaining in fields after grain harvest. This resulted in N and P removals of approximately 25 and 4 kg ha-1 respectively. The manure N and P return to crop land during this grazing period was 1·7 and 0·3 kg ha-1 respectively. Herds camped on crop land for two to three consecutive nights deposited 41-104 kg of N per hectare and 10-15 kg P per hectare, depending on the season of confinement. Approximately 18% and 33% of the manure N and P was assimilated by a maize (Z. mays) crop; the remainder was taken up by weeds. As a dry season supplement, fallow lands sown to stylo (Stylosanthes spp.) provided a high protein diet supplement to cattle during the dry season. These fodder banks were more effective than natural fallow in restoring soil productivity. Maize grown after stylo produced up to 1·4 t ha-1 more grain than in areas of natural fallow, giving a net benefit of up to 80 kg N per hectare.

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Abstract: A unique pollen/spore flora from a lacustrine deposit overlying an 8 myr old basalt flow on the Northwestern Ethiopian highlands is described. A total of 126 pollen taxa is recorded. The pollen flora presents strong characteristics of a lowland rainforest and lacks the diagnostic elements of upland forests, the gymnosperms Podocarpus and Juniperus in East Africa. The commonest savanna element that characterizes the pollen diagrams from East Africa, the Gramineae, is very weakly represented. The pollen/spore diagram, which is constructed from 20 selected taxa, shows six distinct developments of the palaeovegetation during the deposition of the lake-beds. Semi-quantitative evaluation of the distribution of three diagnostic clay minerals shows developments parallel to that of the microflora. Kaolinite and illite are dominant in the humid pollen zone and an increase of smectite towards the end of the sedimentation period seems to agree with the observed general aridity trends in the clay mineral assemblages of equatorial zones towards the end of the Miocene. The flora most probably predates the Late Cenozoic global cooling and the Mediterranean desiccation. The northerly presence of lowland rainforest-type vegetation, as suggested by the composition of the Chilga palaeoflora, as recent as the latest Miocene is of great interest for the phytogeographic evolution of the continent.

Abstract: The stagnation and mixing of various air masses at the level of the ITCZ in the dry season, together with the absence of rain, favor, in the Guinean savannah, the formation of a well-aged and homogeneous aerosol made up of very active mixed nuclei. When the drought increases, the aerosol always remains an aged one, i.e. absence of particles with radius r 60; 0.02 [mu]m, no nucleation mode. However, different properties show a younger and less homogeneous aerosol, i.e. very high counts in all the categories of particles (the concentration of nuclei activated at the supersaturation S [reverse similar, equals] 0.32% reaches 9960 cm-3), poor correlations between the concentrations of various groups of particles and no fog. When the fires are frequent and spread all over the savannah, a permanent addition of new particles to the local background aerosol (due to a complicated circulation) prevents the ageing of the aerosol that is observed during the usual drought with a moderate extension of bushfires.

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Abstract: This paper examines the various sources of radiological land contamination; its extent; its impacts on man, agriculture, and the environment; countermeasures for mitigating exposures; radiological standards; alternatives for achieving land decontamination and cleanup; and possible alternatives for utilizing the land. The major potential sources of extensive long-term land contamination with radionuclides, in order of decreasing extent, are nuclear war, detonation of a single nuclear weapon (e.g. terrorist act), serious reactor accidents, and nonfission nuclear weapons accidents that disperse the nuclear fuels (termed) "broken arrows"). Over the long term, external radiation doses are dominated primarily by 137Cs and internal radiation doses primarily by 90Sr. Plutonium and the transuranic elements are also important, primarily because of their long half-lives and relatively high inhalation doses. Costs for cleanup of contaminated land are very high. For example, cleanup of the broken arrow in Palomares, Spain, was approximately $33,600 per hectare. If cleanup of agricultural land is impractical, alternative land uses might include production of fiber crops, seed-stock crops, or plant biomass for alcohol fuels, or diversion of the land from crop production. Conversion of cropland to pasture or rangeland takes benefit from the generally lower accumulation of radionuclides into animals products compared with plant products. Another alternative is to fence off the land and use it for production of timber. This alternative would allow for 25-100 y or more of radiological decay before recovery of the timber.

Abstract: Temporal variation in earth-atmosphere system reflectance in the 0.5-1.1 [mu]m wavehand was determined from Landsat MSS data for an area of and rangeland in south-central New Mexico. Data were extracted from eight MSS scenes for the period 1973-1983, with four scenes from 1976. Maximum potential change between the extremes of rangeland degradation status was estimated to provide a benchmark for assessing the significance of the observed variations. Reflectance standardized for differences in sensor radiometric response by ERIM coefficients increased significantly from 1973 to 1983, but standardization by Landsat Data Users Handbook coefficients resulted in little long-term change. Short-term ( > 1 year) variation was significant relative to maximum potential change. A sequence of three Landsat-2 scenes within one year showed a decrease in reflectance with increasing solar zenith angle. The effect of zenith angle on shading of the soil surface by plants (" protrusions effect" of Otterman) was estimated and found to be about the same magnitude as the observed within-year variation in reflectance with solar zenith angle.

Abstract: Airborne video imagery was evaluated for assessing phytomass production within grass plots fertilized with five rates of nitrogen. Video imagery was taken with two black-and-white video cameras--one visible light and the other visible/near-infrared light sensitive. Red (0.644-0.656-[mu]m) and infrared (0.815-0.827-[mu]m) narrowband filters were used with the visible and visible/near-infrared light sensitive cameras, respectively. Hand-held red and infrared radiometric reflectance and phytomass measurements were made on the day that imagery was obtained. Red and infrared digital video data were obtained from the plots using an image processor. The plots were studied on two dates: 15 April and 22 May 1985. On 15 April, three phytomass levels could be distinguished within the infrared video image. Moreover, a infrared/red ratio video composite produced on an image processor enhanced differences among nitrogen treatments to the extent that generally four levels of phytomass could be identified. Coefficients of determination (r2), obtained by regressing red, infrared, and infrared/red reflectance, and red, infrared, and infrared/red digital video data on phytomass measurements were significant statistically. Imagery acquired on 22 May, however, showed few differences among treatments. This may have been caused by plant phenological and canopy architectural differences among the grass species. Nevertheless, video imagery should be a useful tool to assess phytomass production on rangelands when grasses are actively growing.

Abstract: Gross energy and crude protein balances of cattle in traditional systems and ranching in eastern Botswana have been estimated. The calculations show that ranching is more productive on a per animal basis while traditional systems are more productive on a per hectare basis. Ranching appears to be more efficient than traditional systems in terms of animal gross energy produced per unit of gross energy used for maintenance. Traditional systems, on the other hand, appear to be more efficient in terms of animal gross energy produced per unit of plant energy produced, and in terms of food chain efficiency. The same conclusions were drawn when crude protein balances were considered. The risk of pasture degradation might be greater at the higher stocking rates found in traditional systems, and feed shortages might occur more often, but lower stocking rates and ranch-type changes in product allocation in these systems would most probably lead to lower productivity per hectare. Consequently, this would lead to lower food production and less employment on a national scale. A socio-economic analysis at a national level is urgently needed to be able to weigh the advantages and disadvantages of the development of ranching at the cost of traditional systems.

Abstract: This paper presents, develops and applies an exploratory linear model of an expert 039;s judgments of medium-term prospects for pastoral enterprises in Australia 039;s rangelands. Viability prospects are first modelled for a simple set of rangeland locations in terms of management factors (costs, returns, stock numbers). To allow extrapolation to a comprehensive set of rangeland locations, each management factor is further modelled in terms of readily available bio-physical attributes of locations (soils, vegetation, climate, accessibility). Whilst the model cannot be tested in any strict sense, it gives results in conformity with current pastoral practice. Its major appeal is that it allows application of a single evaluation procedure to the diversity of Australia 039;s extensive rangelands. Possibilities for the further development and use of such models in land use policy analysis are noted.

Abstract: South Coast Renosterveld is a small-leaved shrubland confined to the semi-arid and sub-humid coastal forelands of the southern and south-eastern Cape, South Africa. The flora of this vegetation type is biogeographically complex and includes numerous local endemics, many of which are geophytes. Much of the renosterveld is being converted to cereals and artificial pastures; conservation status is critical. There is evidence that the renosterveld has been derived in historical times from a Themeda triandra-dominated grassland. It is suggested that the reestablishment of a vigorous grassy sward would be the most effective long-term conservation strategy since utilisation would be compatible with conservation. Management models to improve the grazing status of South Coast Renosterveld should consider the biological attributes of key species. On the basis of phenological and other life history data on the dominant undesirable shrub (Elytropappus rhinocerotis, Metalasia muricata) and desirable grass (Themeda triandra) species, autumn is considered the optimum season of burn for the re-establishment of grassland.

Abstract: With high and accelerating population growth and with low and declining efficiency in the use of resources, Africa is currently facing a long-term declining trend. Since agriculture accounted for 41% of the GDP of Africa in 1982, formulation and implementation of efficient land use policies are prerequisites if the long-term adverse trend is to be reversed.

Abstract: In a series of three experiments, the effect of offering conserved forage indoors to grazing dairy cows was examined. In Experiment 1, hay was offered ad libitum for 45 min after morning milking. In Experiments 2 (early season) and 3 (late season), silage was offered ad libitum either after morning milking or overnight. All experiments included a control grazing treatment that received no supplementary forage. Grazing time was reduced by offering forage, particularly at the high levels of forage intake when cows were housed overnight. The bite size and rate of herbage DM intake were reduced for cows eating large quantities of silage, but the rate of biting was not affected. As the grazing season advanced there was a small increase in the rate of biting and grazing time in all treatments, but a large reduction in bite size and the rate of herbage intake. Heifers had a 25% smaller bite size, 5% faster rate of biting and similar grazing times to cows. Spring-calving cows had higher grazing times than autumn-calving cows, with little difference in biting rate. Forage was consumed at a rate between 2 and 4 times that of grazed herbage. Offering forage increased rumination times, particularly when it was eaten in large quantities. Rumination time was reduced for cows on spring grass and when total intakes were low.

Abstract: In spite of good rains in 1985, much of Africa is still dependent on food aid and millions of people remain displaced from their homes. The reasons for this situation are not climatically related. Although drought exacerbates the situation, the main causes of insufficient food production are related to land degradation-disertification-and high population growth rates. Human growth rates in Africa show no signs of abating in the near future, thus to ameliorate the overall situation, disertification must be halted. To halt disertification policy makers and planners need to devote more resources to programmes and projects that are environmentally related. To facilitate this goal, a new way of analysing the economics of land degradation and rehabilitation needs to be devised and implemented.

Abstract: The potential impacts on vegetation and watersheds in the western U.S. by feral horses are discussed. Feral horses select open habitats with relatively large amounts of grass. Horse dietsare largely grasses but shrubs are used in some areas. Utilization levels are proportional to animal numbers but equivalent numbers of horses may consume more than cattle because of differing digestive physiology. Predicted vegetation changes under heavy feral horses use may result in range dominated by unpalatable shrubs. Watershed conditions would probably not change except underheavy use by horses when soil compaction, soil disturbance and fouling of water holes could result.

Abstract: This article looks at desertification -- both on a global scale and as it relates to Africa. Desertification is defined here as the diminution or destruction of the biological potential of the land, and is caused basically by overuse of inherently fragile productive systems. After distinguishing between desertification and drought (two closely related ecological hazards), the author goes on to outline the terrible effects of desertification and the impact it has on the world population's ability to feed itself. Finally, recommendations to halt and reverse desertification are looked at together with attempts to mobilize the resources needed to face this global problem.

Abstract: The design of improved technology or production policies depends upon evaluation of alternative options in terms of their efficiency. Measurement of the efficiency of a pastoral livestock system may be based on the food energy output per livestock unit, while rangeland carrying capacity is assessed in terms of livestock units per square kilometre. On this basis we conclude that, for the Sidamo Borana and probably other pastoral societies: (i) rangeland carrying capacity is limited by the existing density of dry-season waterpoints rather than the primary productivity of the rangeland, with the implication that research in hydrology and design of water supplies may be more beneficial than studies aimed at increasing primary productivity of the rangeland; (ii) that pastoralists have a comparative advantage in milk production and, up to a point, human consumption is a more efficient use of milk than feeding it to calves; (iii) the trade of livestock products for grain is essential for survival.

Abstract: The stagnation and mixing of various air masses at the level of the ITCZ in the dry season, together with the absence of rain, favor, in the Guinean savannah, the formation of a well-aged and homogeneous aerosol made up of very active mixed nuclei. When the drought increases, the aerosol always remains an aged one, i.e. absence of particles with radius r < 0.02 [mu]m, no nucleation mode. However, different properties show a younger and less homogeneous aerosol, i.e. very high counts in all the categories of particles (the concentration of nuclei activated at the supersaturation S [reverse similar, equals] 0.32% reaches 9960 cm-3), poor correlations between the concentrations of various groups of particles and no fog. When the fires are frequent and spread all over the savannah, a permanent addition of new particles to the local background aerosol (due to a complicated circulation) prevents the ageing of the aerosol that is observed during the usual drought with a moderate extension of bushfires.

Abstract: Gross energy and crude protein balances of cattle in traditional systems and ranching in eastern Botswana have been estimated. The calculations show that ranching is more productive on a per animal basis while traditional systems are more productive on a per hectare basis. Ranching appears to be more efficient than traditional systems in terms of animal gross energy produced per unit of gross energy used for maintenance. Traditional systems, on the other hand, appear to be more efficient in terms of animal gross energy produced per unit of plant energy produced, and in terms of food chain efficiency. The same conclusions were drawn when crude protein balances were considered. The risk of pasture degradation might be greater at the higher stocking rates found in traditional systems, and feed shortages might occur more often, but lower stocking rates and ranch-type changes in product allocation in these systems would most probably lead to lower productivity per hectare. Consequently, this would lead to lower food production and less employment on a national scale. A socio-economic analysis at a national level is urgently needed to be able to weigh the advantages and disadvantages of the development of ranching at the cost of traditional systems.

Abstract: This paper analyses the ecological status of the Barbary macaque in the Djebala region of North Morocco. Results are presented of vegetation surveys and of preliminary studies on resource availability, diet and habitat use of the Barbary macaque in the four main habitat types where the species occurs. Factors affecting the distribution and abundance of the monkeys are considered and data on the past and present distribution in the Djebala habitats are discussed in relation to the influence of man. An assessment is made of whether current monkey populations reflect real differences in the suitability of habitats (i.e. habitat quality and productivity) or whether they are restricted purely by human interference. The latter term is defined both as direct predation and indirect action through modification of habitats via grazing of domestic stock, burning and tree-felling.

Abstract: Situated in a tectonically active foreland basin, the Magdalena River consists of vertically accreting, levee-confined channels and adjacent extensive wetlands, which are interpreted as an anastomosing river sedimentary system. Equivalent rates of basin filling and subsidence average 3.8 mm yr-1 based on 18 14C dates from five bore holes drilled to depths of 55 m and sediment transport budgets from 35 years of measurement. Located in a savanna-tropical climate, anastomosing river deposits of the Magdalena are remarkably similar to the anastomosing deposits of the upper Columbia River in a temperate-cold climate in western Canada, suggesting that climate is not a controlling factor of anastomosis. The geometry of anastomosing channel-fills in the Magdalena consists of stratigraphically non-uniform, low sinuous, narrow stringers of sand up to 30 m thick by 600 m wide, a width-depth ratio of 20. Thin (1-2 m) off-channel crevasse-splay sand sheets extend laterally up to 10 km distance. When buried, both sand deposits become encased by lacustrine or marsh mud to form stratigraphic traps. While there are few modern anastomosing river systems as compared to braiding and meandering, there may be a disproportionately large number of ancient anastomosed fluvial rock sequences due to the rapid rate of vertical accretion. Such a different depositional style and geometry of sand bodies have considerable significance in the interpretation of some ancient fluvial rock sequences because it provides an alternative to the meandered and braided-river deposition models.

Abstract: This paper describes a method of identifying the crucial soil properties influencing yields of crops, using the example of maize in south-western Nigeria. The method involves first, the examination of the relationship between soil properties and the maize parameters using the simple bivariate correlation analysis and the multiple regression model. It also involves, in part, the computation of an index of soil variable contribution to maize prediction in order to identify the crucial soil properties influencing the yield of the crop. In the current study, the multiple regression model reduces the 20 soil properties analysed to the 14 that have made significant contributions to the crop's prediction. The 14 variables were later reduced to two using the maize-prediction index. The index has the merits of being very simple to compute and the ability to reduce the numerous variables to few significant ones as far as the crop under investigation is concerned.

Abstract: The Transvaal Threatened Plants Programme was initiated during 1976. After the publication of the first Threatened Plants Report for Southern Africa during 1980 (Hall et al., 1980) considerable progress has been made with the programme. The progress made with the taxonomic, practical, analytical phases and conservation of threatened plants is discussed. Although certain objectives were not achieved during the survey, sufficient data have been accumulated to recommend 43 conservation category changes. A total of 23 species were eliminated from the list of 216 threatened species of the Transvaal based on the findings of the distribution surveys. An updated checklist of 246 threatened plants, which includes 53 new threatened species, is presented for the Transvaal.

Abstract: Landsat data were simulated for a three-component rangeland scene consisting of grass, brush, and soil to evaluate the effect of soil background reflectance on the sensitivity of ratio and orthogonal spectral indices to vegetation density. The simulations were done using soils with low, intermediate, and high reflectances for conditions representing periods of active growth in which brush and grass are green, and summer dormancy in which brush is green and grass is dormant. When soil reflectance was low, the sensitivities of the ratio vegetation index and the normalized difference decreased as the density of green vegetation increased. When soil reflectance was high, the sensitivity of these same indices increased as vegetation density increased. The sensitivity of greenness, calculated from published coefficients, was greater when soil reflectance was low, and differences due to soil reflectance decreased as canopy cover increased. The sensitivity of soil-specific greenness, calculated from coefficients derived from the simulated data, was greater when soil reflectance was high, and differences due to soil reflectance increased as canopy cover increased. Soil reflectance also affected the sensitivity of the indices to the density of dormant grass. The results suggest that discrimination of brush and vegetation may not be possible during active growth when both are green, but may succeed during summer dormancy when the grass is dormant. The results further suggest that even if soil-specific calibrations and soil lines are used, the accuracy of any estimates of rangeland vegetation density derived from the indices may vary with the soil background.

Abstract: Young animals face unique constraints in foraging on rangelands. They are at an inherent disadvantage to older animals because they have higher nutritional requirements and they lack foraging experience. Comparisons were made in diet selection, foraging time and weight changes for adult (does) and juvenile (kids) goats foraging at two stocking rates (heavy vs. light) during the winter of 1979 on rangeland dominated by blackbrush (Coleogyne ramosissima). The previous experiences of adult and juvenile goats differed because does had browsed blackbrush during the winter of 1978, while kids were raised from birth until 6 months of age on alfalfa hay. Does and kids in the heavily stocked pasture consumed diets that were similar in percentage blackbrush (95 vs. 94), blackbrush leaf:stem ratios (0.44 vs. 0.45), crude protein (7.2 vs. 6.9%) and in vitro digestible organic matter (39.3 vs. 39.2%). Does and kids in the lightly stocked pasture consumed diets that were similar in blackbrush leaf:stem ratios (0.41 vs. 0.42) and crude protein (6.6 vs. 6.6%), but does consumed diets that were slightly higher (P = 0.039) in percentage blackbrush (94 vs. 88), but lower (P = 0.028) in in vitro digestible organic matter (36.0 vs. 39.5%). Kids spent considerably more time foraging than did does (P < 0.0000) in both the heavily (59 vs. 41%) and the lightly (65 vs. 47%) stocked pastures. Kids also lost a greater percentage of body weight (P = 0.02) than did does (22 vs. 17).

Abstract: A fundamental issue in many LDCs is the degree to which natural resource mismanagement is caused by common property arrangements. This view has led to widespread attempts to "privatize" forests, rangelands and water resources. Many of these efforts have failed to stop overuse, and have contributed to inequality in resource distribution. This paper seriously questions this approach, and describes a number of reasons why common property may continue to be both efficient and equitable, complementing and combining with private rights in a way consistent with the resource endowments of village economies. A theoretical approach is outlined, showing that the "Tragedy of the Commons" is an unsatisfactory model of common property. An alternative model is presented, together with a call for research into institutional alternatives in resource management.

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Abstract: Seasonal averaged ground level concentrations for ozone have been calculated for the Netherlands by means of a lagrangian long-range transport model. The calculations indicate that the influence of European anthropogenic emissions of nitrogen oxides (NOx) and volatile organic compounds (VOC) on the growing season, day-time averaged (may to September, 10-17h) ozone concentrations in the Netherlands is small. A European VOC emission reduction will lead to a reduction in growing season averaged ozone and oxidant (sum of O, and NOx) concentrations. A reduction of European NO emissions leads to a reduction of oxidant concentrations, but in areas with a high NO concentration such as the Netherlands, an increase in ground level ozone concentrations is predicted due to a shift in the photostationary equilibrium. When VOC emission reductions are combined with NO emission reductions a slightly decreased groundlevel ozone concentration is expected.

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Abstract: Seasonal averaged ground level concentrations for ozone have been calculated for the Netherlands by means of a lagrangian long-range transport model. The calculations indicate that the influence of European anthropogenic emissions of nitrogen oxides (NOx) and volatile organic compounds (VOC) on the growing season, day-time averaged (may to September, 10-17h) ozone concentrations in the Netherlands is small. A European VOC emission reduction will lead to a reduction in growing season averaged ozone and oxidant (sum of O, and NOx) concentrations. A reduction of European NO emissions leads to a reduction of oxidant concentrations, but in areas with a high NO concentration such as the Netherlands, an increase in ground level ozone concentrations is predicted due to a shift in the photostationary equilibrium. When VOC emission reductions are combined with NO emission reductions a slightly decreased groundlevel ozone concentration is expected.

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