Abstract: An extensive sensitivity analysis of a model for the Simulation of Production and Utilization on Rangelands (SPUR) was conducted. A perturb and observe approach was employed in a series of fractional factorial experiments. State variables selected as sensitivity indicator variables included: peak standing crop, maximum plant nitrogen to carbon ratio, integrated year-long mineralization of soil nitrogen, integrated season-long plant death, integrated season-long carbon assimilation, integrated effect of soil moisture on net photosynthesis, integrated season-long forage intake by steers and cummulative season-long change in steer weight. The 1st of three stages of the analysis showed dynamics which affect simulated warm and cool-season grasses, warm and cool-season forbs and shrubs were similar in the absence of grazing. Therefore, one plant functional group (warm-season grasses) was used in subsequent stages, allowing a greater number of plant species specific parameters to be examined. In the 2nd stage, also without grazing, optimum, minimum and maximum temperatures for plant activity, the day senescence ends and their joint effects had the largest impacts on the plant component. Characteristics of the soil and soil-water relationships had only minor effects on plant-related indicators. Grazing caused many of the interactions which previously affected plant-related indicators to become less important. Effects associated with day senescence ends were greatly reduced in both magnitude and importance. Steer forage intake and weight change were sensitive to stocking rate and the parameter which converts the percent nitrogen of the forage into total digestible nutrients. Plant parameters which affected the relative quantities of carbon and nitrogen in plant biomass, tended to mediate the effects of livestock-related parameters.
Abstract: A methodology is described for the analysis of Holocene charcoals excavated from a rock shelter in the Lubombo Mountains of northeast Swaziland. Scanning electron microscopy was used to compare these with modern reference woods. Of the ancient material 96·6% could be identified, in some cases at specific level. It is in such a subtropical area, where the woody flora is so rich, that assemblages of local taxa can be used in palaeoclimatic reconstructions. The changing taxa indicated by the charcoal fragments from the rock shelter clearly reflect minor shifts in Holocene climate, from moist to dry and back to moist in recent times. This is of relevance to the fluctuations in Stone Age populations in southern Africa. The wider use of such evidence to complement other palaeoenvironmental and archaeological data is advocated.
Abstract: Directional reflectance factors that spanned the entire exitance hemisphere were collected on the ground throughout the morning period for common cover types in Tunisia, Africa. NOAA 7/8 AVHRR bands 1 (0.58-0.68 [mu]m) and 2 (0.73-1.1 [mu]m) were used in data collection. The cover types reported were a plowed field, annual grassland, steppe grassland, hard wheat, salt plain, and irrigated wheat. Several of these cover types had geometric structures that are extreme as compared to those reported in the literature. Comparisons were made between the dynamics of the observed reflectance distributions and those reported in the literature. It was found that the dynamics of the measured data could be explained by a combination of soil and vegetation scattering components. The data and analysis further validated physical principles that cause the reflectance distribution dynamics as proposed by field and simulation studies in the literature. Finally, the normalized difference transformation [(Band 2 - Band 1)/(Band 1 + Band 2)], which is useful in monitoring vegetation cover, generally decreased the variation in signal with changing view angle. However, several exceptions were noted.
Abstract: Three methods for measuring the benefits of commercial and subsistence livestock production in Africa are discussed. Firstly, biological measures of herd performance are illusstrated with material from Botswana. Secondly, the profitability of the herding operation can be measured economically, a technique which requires the ascription of cash values to in-kind produce. An improved method for imputing these values is presented. Finally, one can compare the nutritional status of human populations engaged in commercial and non-commercial livestock production. Each of these three techniques provides a limited description of the total environment which conditions farmer decision-making. As a general rule, therefore, we should favor a combination of techniques and exercise considerable skepticism in evaluating the results of any undimensional comparison.
Abstract: Some features of the central area of the Australian continent visible with Geostationary Meteorological Satellite (GMS) imagery are mapped. It is believed that this is the first detailed map of a significant fraction of the Australian Continent prepared from a single satellite image frame. Some of these features are not readily identified on other imagery systems and include both sharp- and diffuse-edged boundaries of obvious ecological significance. This paper covers mapping of static geographical features only, using the visible channel, with two purposes in mind: first to identify visible features that are apparent at this scale and second to provide a geographical base for subsequent study of more dynamic but less easily recognized hydrological features that appear on the coincident thermal imagery.
Abstract: The effects of cultivation and erosion on organic matter transformations were studied by systematically sampling slope positions on three paired rangeland and cropland toposequences. The toposequences were on differing parent materials, sandstone, siltstone and shale in southwestern North Dakota. Soils weathered from the three parent materials were all Haploborolls or Argiborolls but differed in texture and solum depth. Carbon, nitrogen, phosphorus and soil loss have been previously measured. Microbial biomass C and N by chloroform fumigation, mineralizable C and N during 10, 20 and 60 day incubations, and organic C and N content were measured. Decreases in the above soil properties occurred in cropland soils, but the proportion of organic N mineralized increased. Biomass and mineralizable C and N concentrations were correlated with organic C and N concentrations, rather than with total accumulation in the profile. Total accumulation and proportion of N mineralized were correlated with clay content. Changes in respiration:mineralization, mineralization:biomass and microbial C:N ratios suggested differences in substrate and microbial population composition between rangeland and cropland. Microbial biomass and mineralization rates did not vary with slope position, but parent material had significant effects. The siltstone site which had the highest soil losses began with the highest microbial biomass and mineralizable C and N concentrations and had the highest losses. The sandstone site suffered high soil but low OM constituent losses whereas the shale site suffered low soil and OM constituent losses. The sites can be classified in terms of their response to perturbation using concepts of "resistance" and "resilience" from ecosystem theory. The sandstone and shale sites may both be considered "resistant" with respect to agricultural perturbation, whereas the siltstone site was not.
Abstract: Nine plant growth models for grassland ecosystems were examined. Model objectives, complexity and inclusiveness were compared. A large degree of diversity in model complexity and structure exists in grassland models. The models examined during this comparison consisted primarily of linear and nonlinear difference/differential equations. Though grassland models use many of the same concepts of other plant growth models, grassland models tend to be more concerned with moisture and nutrient status then their cropland counterparts. The system level models require large amounts of data to use, yet these data are often unavailable and parameters are hard to establish. These models seem best suited to merely approximate system behavior, but it will become extremely useful as more understanding of the grassland ecosystem is gained. Grassland models which combine plant growth with animal grazing tend to include spatial heterogeneity of vegetation, thereby allowing these models to simulate multiple landscape points and patchy grazing by herbivores.
Abstract: The trend of change in the cation exchange capacity of ferrallitic soils under bush fallow in south-western Nigeria was examined during the first 10 years following the cessation of cropping. The general trend is that the soil cation exchange capacity increases over time but this increase is largely restricted to the 0-10 cm layer of the soils. Three years of fallowing in the study area was generally inadequate to maintain soil cation exchange capacity at a level that would ensure continued high fertility. It is suggested that a short fallow of 3 years should be accompanied by the application of organic manures and inorganic fertilizers to increase the supply of plant nutrients. Soil percentage base saturation decreased with increasing length of the fallow period, presumably due to nutrient uptake from the soil by fallow vegetation. It is suggested that soils should be limed after a long fallow of 62;10 years in order to increase soil percentage base saturation and nutrient availability. Organic matter appears to be the main factor influencing the cation exchange capacity of soils under bush fallow in the study area. The effects of fallow vegetation on organic build-up in fallow soil and their implications for managing soil fertility during cropping are discussed.
Abstract: A mathematical model is presented of the regional cattle herd within a subsistence pastoral system, in a semi-arid region, where empirical data on herd production are restricted to a few basic properties under average conditions. The model was developed to estimate the potential market offtake for a region in Kwazulu (Republic of South Africa). Currently, this region is overstocked and low production levels are prevalent. The model was used to simulate various offtake strategies and it was found than an approximate threefold increase in sustainable annual revenue can be achieved while simultaneously reducing grazing pressure.
Abstract: Simultaneous measurements of Aitken nuclei, cloud condensation nuclei and aerosol particles sizes larger than 0.3 [mu]m in the Guinean savannah during the dry season show an aerosol of very exceptional physical properties: numerous cloud condensation nuclei (2000-3000 per cm3) active at low supersaturation (or slight [`]undersaturation'), absence of very small Aitken nuclei active at 180% of supersaturation and concentrations of large aerosol particles (D > 0.3 [mu]m) between 30 and 60 per cm3. The analysis of the aerosol behavior during a [`]typical' 24-hr period of the dry season and during a fog situation indicates that (1) the aerosol is a very homogeneous and aged one; (2) the active nuclei might be of a mixed nature or nuclei on the surface of which the capillary condensation plays an important role.
Abstract: Dwarf goats and sheep are ubiquitous in the humid zone of West Africa, although only as a supplement to cash and food crop production. This paper presents estimates of the returns obtained from these small ruminants under traditional production systems. Returns are, on average, high, but variable, especially in view of disease risks. Apart from disease control measures to reduce mortality, improved nutrition is needed for intensifying production. At current levels of management neither pasture production nor housing and hand-feeding are likely to yield increased returns. Alley farming, a system of intercropping with shrub species and the feeding of shrub trimmings to small ruminants, seems a promising alternative.
Abstract: NOAA-6 and NOAA-7 1-km and 4-km advanced very high resolution radiometer data were obtained at frequent intervals during the 1980, 1981, 1982, 1983, and 1984 rainy or growing seasons in the Sahel zone of northern Senegal. Above-ground herbaceous biomass clippings, visual estimates, and hand-held radiometer measurements of herbaceous vegetation were made during and at the conclusion of the rainy seasons for 4 of the 5 years. The satellite data were compared to sampled above-ground biomass data and the integral of the satellite data over time was compared to end-of-growing-season above-ground total dry biomass. A strong correlation between the integrated NOAA-7 satellite data and end-of-season above-ground dry biomass was found for ground samples collected over a 3-year period. The satellite data documented the highly variable precipitation regime in the Senegalese Sahel both within years and among years and suggest a direct method of monitoring Sahelian total herbaceous biomass production in areas where the percentage cover of woody species is less than 10%. Predicted average total dry biomass production was 1093 kg/ha for 1981, 536 kg/ha for 1982, 178 kg/ha in 1983, and 55 kg/ha in 1984 for the ~ 30,000 km2 study area.
Abstract: Computer-based aids have been used extensively to support surveys of threatened plants in Southern Africa. The surveys have shown that by far the highest concentration of threatened plants occurs in the relatively small area of the Cape Floristic Kingdom, a region with many local endemics that are easily put in hazard by impacts such as agriculture, invasive exotics and over-frequent fires. Of the estimated 20 000 vascular plants in Southern Africa, 2373 appear to be critically rare, threatened or recently extinct. Sixty-eight per cent of the plants in hazard occur in the Cape Floristic Kingdom. Obstacles to conservation, particularly a lack of nature reserves in critical areas, are discussed.
Abstract: The Mfolozi and Hluhluwe Valleys of southeastern Africa are representative of a sub-tropical biome and have archaeological evidence for farming settlement spanning more than 1500 years. By collecting information on soils and plant communities within the same sample frame as archaeological data, the relative importance of environmental and anthropomorphic influences can be assessed. It is argued that, although climate and soils have determined the overall distribution of plant communities, human land use has had a considerable effect on the composition of both woodland and grassland. The nature of this interaction between man and environment provides inferential data on prehistoric economies and also aids the formulation of conservation policies in protected areas.
Abstract: A versatile computerised overlay technique to analyse the capability of relatively constant and objectively measured land characteristics to sustain any defined land use was developed in FORTRAN. The mapped form of each land characteristic is stored in a data base system for subsequent use and overlay by a grid of selected cell size. Existing information is used to derive a capability value for each land characteristic, whose influence upon the overall capability is included by user-defined weighting values. The overall capability of each grid cell. is the weighted mean of the individual capability values of each land characteristic analysed. A foreclosure of options in land use is also performed. A trial run of the procedure illustrated the influence of the selected grid cell size and the weighting value. The value of a versatile capability analysis tool, able to analyse any defined land use for an area of unrestricted size, using weighting values and capability values related to existing, up-to-date information, was seen.
Abstract: Since 1978 the U.S. Agency for International Development (USAID) has funded a regional remote sensing project for East and Southern Africa. The project, hosted by the Regional Centre for Services in Surveying Mapping and Remote Sensing, has provided a programme of training courses, user services and project support. This included the equipping and establishment of a photo-laboratory complex for processing Landsat images and the provision of advice and support for agencies undertaking natural resources analysis. Response to the training programme has been very good. Courses are usually over subscribed and there is a continued demand for training. Assessments of the courses by participants are highly positive and the courses have featured consultants of international calibre. Requests for follow-up courses, and for specialist group training indicate a strong response to this training activity. User services are active, consultations with staff, use of the browse file and interpretation equipment and the purchase of data for project work all produce an average demand of 12 active enquiries per working week. The photo-laboratory is particularly active and demand for products exceeds available capacity. Project work is now being supported but limited resources restrict the range and amount of project activity. Response to the opportunities offered for projects has been favourable and this activity is ripe for expansion. The difficulty in expanding to meet the expressed demand is primarily financial. The east and southern Africa region is not economically strong and has a great need for natural resources data for development work and planning. The responses to satellite remote sensing opportunities will be limited by these financial constraints which effectively means by the level of international aid directed to this activity. For such aid to be effective it must be coordinated and firmly attached to the region. Such coordinated aid programmes would avoid fragmentation of distribution and applications work. Fragmentation could seriously disrupt the present growth in natural resources activity based on remote sensing data from satellites. The lack of financing for a regional ground receiving station is also a significant limiting factor.
Abstract: This paper presents the results of a two-year study commissioned by the Department of Interior to examine the costs and benefits of a remote data acquisition system for natural resource management. Because earlier experience with a number of experimental programs had been so favorable, it was felt that a full analysis should be undertaken. Subsequently, five areas were selected for detailed investigation: agriculture, land use, forestry, water resources, and rangeland. In each instance, the modeling was performed within the framework of a case study. Net benefits were derived from two sources: (1) cost savings at the data acquisition level; and (2) increased economic efficiencies at the operational level. Calculations were done parametrically to account for technological diffusion, uncertainties in implementation, and various assumptions concerning discount rates and cloud cover impacts. The results have shown that a two-satellite system will more than likely pay for itself over the program's planned ten year life.
Abstract: The Plio-Pleistocene sediments of Olduvai Gorge, Tanzania, are well known for their records of both hominid evolution and the paleoenvironments where these early hominids lived. This paper investigates the paleohabitat reconstructions of Bed I and Lower Bed II of Olduvai and provides an analysis using bovid tribes as habitat indicators. The habitat inferences based upon the bovids are compared with paleoenvironmental reconstructions from studies of the micromammals, pollen profiles, isotope geochemistry, and geology. These various habitat indicators are shown to corroborate each other closely with regard to both the kind of habitat present and the timing of inferred habitat change. The general agreement on habitat types appears to present especially strong support for the paleoecological reconstructions of Bed I and Lower Bed II. Paleohabitats ranged from closed woodland or forest to a mixture of open woodland and grassland to open grassland. The pattern of paleohabitats through time supports the idea of a climatic trend towards greater aridity, but with intermittent shifts to more humid conditions. The Plio-Pleistocene climatic history of the Olduvai basin may prove useful in understanding the evolution of East Africa climates.
Abstract: A model of kleingrass (Panicum coloratum L.) growth and utilization by steers is presented. The model included stochastic inputs of climatological characteristics, water retention at different soil depths, rainfall runoff, potential evapotranspiration, forage growth, forage intake and steer performance. The model was used in a 2 × 3 × 4 factorial experiment where the factors were energy systems (ARC, 1965 versus NRC, 1976), stocking rates (2·47 head per hectare, 4·32 head per hectare and 6·18 head per hectare), and four management options. Individual steer weights by months were not significantly affected by the use of either energy system. Steer weights at the end of the grazing season were affected (F = 0·06) by energy system, the NRC system predicting 7·2 kg per head more liveweight gain than the ARC system. The light stocking rate had greater (P = 0·01-0·13) daily gains over months than the heavier stocking rates. The heavy stocking rate resulted, however, in greater (P < 0·05) production per hectare per year than the lighter stocking rates. Season-long production per hectare favored (P < 0·1) management options that removed steers immediately after forage was consumed rather than anticipating rainfall and new forage growth. The light stocking rate had the least mean seasonal production per hectare (P < 0.·05) but also had the least year-to-year variability. The heavy stocking rater yielded the greater (P < 0·05) mean seasonal production per hectare but the year-to-year variation was much greater. It was emphasized that the use of such probabilities of production could aid the grazier in making stocking rate and related decisions.
Abstract: The oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water. The carbon isotopic cycle for CO2 in soils can be described in terms of the proportion of biomass using the C4 photosynthetic pathway and the CO2 respiration rate of the soil; at low soil respiration rates significant atmospheric CO2 mixing can occur. In general, the carbon isotopic composition of soil carbonate is related to the proportion of C4 biomass present in soil, but soils that freeze to the depth of carbonate formation often have a significant atmospheric component. This suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation. Because of these relationships, the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred.
Abstract: ILCA's overall aim is to improve human welfare and food supplies in Africa. Increased livestock production provides the cash income so essential for increases in food grain production in a part of the world where adequate credit mechanisms are rarely available. ILCA's approach, to increase farm income through low cost increases in livestock production, is seen as the most cost-effective means of reversing the current decline in food availability in Africa.
Abstract: The responses of East African grasses to defoliation at specific heights and frequencies were simulated mathematically over a single optimal growing season. The simulation model used morphological and physiological features of graminoid growth that are known to affect responses to defoliation. Water and nutrient limitations were not considered. Except under the most severe defoliation regimes, the model simulated greater aboveground and belowground productivities in grazed plants than ungrazed plants. This simulation of productivity was maximal at moderate grazing intensities, declining at both high and low grazing intensities. Short, mid, and tall-grasses exhibited different responses to defoliation. Short-grasses gave greater yields with greater frequencies of defoliation than mid and tall-grasses. Since mid and tall-grasses maximized their production through increased shoot sizes, greater intervals between grazing events were necessary. Short-grasses maximized production through increased shoot numbers, hence maximum yields could be obtained with greater grazing frequencies. At greater frequencies and lower heights of defoliation the proportions of blade tissue increased, stems decreased, nitrogen contents increased and a dense, leafy concentration of live shoot biomass was induced by enhanced tillering, removal of culm meristems and prevention of senescence. The most important factors responsible for grazing stimulation were: stimulation of tillering through decreased self shading, continued activity of non-elevated tiller meristems which had escaped grazing removal, release from apical dominance and subsequent stimulation of tillering, and the presence of a high maximum photosynthetic rate which rapidly replenishes carbohydrate reserves used for the early regrowth. The three essential properties a plant must have in order to compensate for herbivory are: (a) the ability to protect and regenerate apical meristems; (b) the ability to store carbohydrates that can supply activity of these meristems following substantial leaf area reduction; and (c) a photosynthetic rate great enough to support continued shoot and root growth, and to replenish carbohydrate reserves. Stimulation of photosynthetic rate by defoliation contributes greatly to the latter requirement.
Abstract: Summary Following the severe droughts in the Sahel and Ethiopia in the late 1960s and early 1970s, which focused the world's attention on drought and desertification, the United Nations system organized and held the UN Conference on Desertification (UNCOD) in Nairobi in 1977. The principal outcome of the Conference was a Plan of Action to Combat Desertification (PACD), containing 28 major recommendations. The follow-up and coordination of implementation of the PACD was entrusted to UNEP, which created a Desertification Branch in 1978 to undertake the task. The PACD recommended that a first General Assessment of Progress in its implementation be conducted for the seven year period 1978-1984. UNEP has finished the General Assessment, a two year endeavor, and the results will be presented by the Executive Director, Dr Mostafa Tolba, at the twelfth session of the UNEP Governing Council in May of this year. The Governing Council will devote a special two day session to consideration of the report, after which a set of recommendations for future action will be adopted. The General Assessment concludes that the global desertification situation has deteriorated since 1977 and that at present some 34 750 000 sq km of the world's drylands, which make up 75 percent of the productive area, are affected by desertification. If land continues to be lost at the current rate, it will become a global catastrophe by the year 2000. The Executive Director's report recommends that affected nations establish National Plans of Action to Combat Desertification and that institutions be created to coordinate the Plans. Ten years ago the world's newspapers and magazines were full of stories about the terrible effects of drought in the Sahel and Ethiopia. Great numbers of people and millions of livestock animals died due to drought-related causes, and many more people were impoverished. What experts had known for a long time suddenly came to the attention of Governments and the man-in-the-street: land in many parts of the world was degrading into desert, and deserts do not produce food. The serious droughts of the late 1960s and early 1970s in Africa aroused the international community and triggered the United Nations Conference on Desertification (UNCOD), where 94 countries and many international bodies deliberated on the problem in Nairobi in 1977. At that time it was thought that the Sahelian drought of 1968-1973 was over. Today we know that the near-normal rains which fell in 1974 and 1975 were only a temporary respite. Like a spectre come back to haunt us, the same kinds of stories that we read are reappearing in the world's news media--but now it is the great drought of 1968-1983, and it may not be over yet. In fact, it looks like the drought conditions are spreading. The period 1982-1983 was one of the worst in recorded history for worldwide drought, threatening more people than ever before. Many parts of Africa, North America, Australia, South America, Europe and Asia all suffered somewhere from severe dry spells. Experts are increasingly investigating the possibility of a relationship between changes in the environment, which are man-induced, and climatic change. Drought is a temporary problem, desertification is not. Man can do little or nothing to prevent drought, he can halt desertification, which in the long run is a much more serious problem. Realizing this, UNCOD formulated a comprehensive Plan of Action to Combat Desertification (PACD) which contained a number of recommendations on action to take at the national, regional and international levels to halt and even reverse the desertification process. The Conference gave UNEP the job of following up and coordinating the implementation of the Plan of Action. The PACD called for a first General Assessment of Progress in its implementation after the seven year period 1978-1984. UNEP has been involved in this activity for over two years and a summary of the findings will be presented in a report by the Executive Director, Dr Mostafa Tolba, to the twelfth session of the UNEP Governing Council in May of this year. Two special days will be devoted to a consideration of the assessment results by the 58 Member States, 30 or so observer States, and UN and other international bodies attending. In his report, Dr Tolba will be presenting a fresh set of recommendations for action over the next 15 years. After a consideration of the report, the Governing Council will then adopt recommendations which will guide the actions of UNEP and other concerned organizations, agencies and Governments in future efforts to combat desertification. The main findings of UNEP's global assessment are: (1) The scale and urgency of the problem of desertification as presented to UNCOD have been confirmed. The goal set by UNCOD to arrest the advance of desertification by the year 2000 is no longer feasible. (2) Desertification threatens 35 percent of the earth's land surface (45 million sq km) and 19 percent of its population, some 850 million people. Seventy-five percent of this area and 60 percent of the population are already affected. (3) Of the world's drylands (defined by UNEP as including arid, semi-arid and sub-humid areas), 60 percent are already affected by desertification, with between a quarter and a half severely so. (4) In the seven years since UNCOD, desertification has extended and intensified in all its forms as follows: (a) Land lost--i.e., reduced to desert-like conditions--continues at 60 000 sq km annually, the rate reported in 1977; (b) Land reduced to zero or negative net economic productivity is showing an increase at 210 000 sq km a year; (c) Areas affected: -- rangelands 31 million sq km (80 percent of the total) -- rainfed croplands 3.35 million sq km (60 percent) -- irrigated lands 400 000 sq km (30 percent of the total) (5) The total desertified area of 34 750 000 sq km makes up 75 percent of the productive area in the world's drylands and 40 percent of the entire world's productive area. (6) The direct cost of desertification in the form of a loss in agricultural production stands at $26 billion annually, not counting the serious social costs. These staggering findings serve to reinforce the view at UNEP that desertification is one of the major problems facing mankind today. If the march of desertification continues, by the year 2000 the situation will have become a global catastrophe, according to the conclusions of the assessment. In a recent interview with a Nairobi-based journalist, Dr Tolba said that [`]patching exercises' were not enough to thwart the crisis. "Either you control desertification by a full, integrated programme to stop it, or you try to stop it by bits and pieces and nothing will stop. We said in 1977 that the recommendations (of the PACD) were not to be taken in isolation. You might implement them at varying rates, but they have to be implemented together. ...We said this loud and clear and the desertification conference approved it, the General Assembly approved it, and here we are just where we were in 1977." Why has so little been done since 1977 to implement the 28 recommendations contained in the PACD? An expert study group estimated that it would cost about $4.5 billion per year over a 20 year period, or $90 billion in all, to put into effect the main components of the PACD. This sounds like a lot of money, but when compared to the cost of lost agricultural production over the same period--$520 billion--it seems like a very sensible investment. A Special Account for financing anti-desertification projects was established six years ago. Less than $50 000 has been contributed, none of it from developed countries. That is part of the problem in implementing the PACD. Developed nations prefer to give assistance through bilateral aid agreements. In this way they reap secondary benefits from their own largesse--contracts, employment, political influence, etc. Several hundred million dollars have been spent since UNCOD on desertification-related projects in affected countries, but because the efforts were not well coordinated the results have had minimal impact in stopping desertification. Donor countries and international financing organizations need to put more trust into UNEP's ability to utilize funds effectively, and they must learn to put less emphasis on their own immediate self interest. In the long run, it is in everyone's self interest to halt desertification. Loss in agricultural production due to desertification leads to hunger and poverty in the affected countries. A large poor population leads to political instability and economic stagnation, neither of which are good for international trade or the professed goals of development. Another problem involves policies within the affected countries. Desertification is not usually accorded a priority position in development planning. In most countries there is no effective internal governmental [`]lobby' to negotiate for anit-desertification funds. National leaders like to have quick visual evidence of their actions, and environmental programmes do not yield immediate returns. When government ministries request foreign aid, therefore, they are most often for structures such as roads, bridges, factories and dams. The donor countries are very happy to fund such projects as they, too, like to see the concrete results from their assistance. To mount an effective campaign to stop desertification national priorities in affected countries have to be realigned. Government leaders must understand that desertification is not drought, which goes away when the rains return, but that it is a steady process that is robbing their lands of productive capabilities, rendering their economies ever more dependent on outside sources of support. One of the first steps to take to ameliorate the situation, as recommended in the PACD and reemphasized in the Executive Director's report, is to establish a national machinery and institutional support to coordinate national action. This involves developing a National Plan of Action to Combat Desertification, in which a detailed assessment is made of a country's desertification problems, priority projects are identified to address the most serious of them, and the institutional support to organize and coordinate the National Plan is at least outlined. A lack of national Plans of Action or of specific institutions to deal with desertification has been a great hindrance to the implementation of the PACD at both the national and global levels. UNEP is prepared to give assistance to any developing country in the development of National Plans of Action and in the formulation of priority anti-desertification projects. UNEP first needs an invitation from the Government, however, and these have been very few in coming. Since the Desertification Branch was established in 1978 in UNEP only three countries have been assisted in this way--Tanzania, Burundi and Uruguay. UNEP has also sent exploratory missions to Bangladesh, Nepal, Yemen Arab Republic, Yemen People's Republic, Benin, Botswana and Lesotho, and others are currently being planned. The UN Sudano-Sahelian Office (UNSO) undertakes the coordination and follow-up of the PACD in the nineteen Sudano-Sahelian countries on behalf of UNEP and National Plans are in preparation in several countries in the region. The world's leaders, in developed and developing countries alike, must understand the menace that desertification poses for the future and, in cooperation with the United Nations system and other international organizations and NGOs, come to realize that now is the time for action.
Abstract: Recognition of (late) Tertiary shorelines on continental coasts is becoming increasingly common. It is argued that the elevations of such features are central to their approximate dating and the demonstration of contemporaneity with similar features elsewhere. South Atlantic coasts have not had a long history of investigation, yet there exist many diffuse observations, in both time and space, which are here drawn together into a preliminary synthesis and the case for widespread occurrences of late Tertiary shorelines in the region reviewed. This allows comparison with other areas from which Tertiary shorelines are known, the Atlantic seaboards of the Southeastern United States and Northwest Europe, for example. The coasts of oceanic islands are probably the best places to examine the legacy of late Cenozoic sea-level changes. It is suggested that, since many of the cliffed shores of these islands appear to be the result of a rapid emergence, coastal features predating this event might be preserved on the cliff-tops. Possible late Tertiary shorelines from South Atlantic islands are described, as are those which have been positively dated to this period, in the Eastern Canary Islands, for instance. Sedimentary and morphological indicators of Tertiary high sea-levels are described from Antarctic coasts. South American and African Atlantic continental margins. Evidence from the latter two areas is most suspect, owing to their generally more complex Quaternary tectonic histories. A summary of the evidence for Tertiary shorelines on South Atlantic coasts is tabulated. Methods which have been or could be used to date late Tertiary shorelines are described. Minimum age can be deduced from that of deposits resting on an erosional surface, maximum age from that of the youngest formation across which a surface is cut. More precise age can be estimated where a marine surface is sandwiched between datable non-marine formations or where periods of tectonic activity (responsible for differential surface deformation) can be dated. Elevations of surfaces can be used to estimate ages. Problems in both recognising and dating Tertiary shorelines are discussed. Recognition of their origin is made more difficult by their degraded state and, if they occur within a Quaternary erosional sequence, their antiquity may not be realised. It is suggested that fluctuations in the Antarctic ice sheet during the late Tertiary induced substantial glacio-eustatic changes of sea-level which may have been most marked in adjacent areas. This is considered to be the mechanism through which late Tertiary shorelines in the area were formed yet, considering the paucity of the morphological and sedimentary data, these should not be used as the basis for a eustatic chronology.
Abstract: Evidence is presented here to show that the upland soils of central northern Nigeria are formed in aeolian mantles deposited by two aeolian processes: aeolian suspension (or dust) deposition and aeolian saltation (or dune sand) deposition. The soils to the south and west of Kano are largely the product of Harmattan dust deposition, whereas the northern soils appear to originate from dune sand migration from the Quaternary dune fields to the east of the study area. The spatial pattern of particle-size populations (or quanta) and quartz grain roundness characteristics, within the mantles and dune sands, indicates that considerable mixing of dune sands and dust has occurred in the formation of these mantles.
Abstract: Surface soil moisture content is a state variable that is either simulated or required as input for many hydrologic models. In distributed hydrologic modeling, the watershed system is subdivided into spatial elements that should be as homogeneous in hydrologic response as possible. In this study, the variation of surface soil moisture was examined because soil moisture is a major factor in determining hydrologic response. The influence of variations in land cover, soil properties and topography on surface soil moisture was investigated. Statistical analysis showed that topography was the most important factor controlling the distribution of soil moisture within the small agricultural watersheds at Chickasha, Oklahoma. The presence of vegetation tends to diminish the soil moisture variations caused by topography, while the effects of minor variations in soil type were usually insignificant. Comparison of variograms developed for nearly flat cropland water-sheds and more sloping rangeland watersheds indicated that a much denser network of sampling points would be required to develop soil moisture maps of a given accuracy on the rangeland watersheds. For many modeling purposes, the subdivision of low-slope cropland watersheds into spatial units of homogeneous hydrologic response can be based on topography alone.
Abstract: Arguing that increased attention to the problems of women farmers in Africa can help solve both urban and rural food supply problems, this paper builds its case on a close examination of the extensive farming system of the Beti peoples of southern Cameroon and the intensive farming practices of the Haya of northwestern Tanzania. The first part of the paper addresses technological and socio-economic problems constraining the expansion of food production and marketing; the second describes two situations in which the removál of specific constraints allowed women farmers to demonstrate their capacity and willingness to expand their output and improve their welfare.
Abstract: Recent advances in communications and satellite technology now make it possible to provide large, synoptic imagery of the earth's surface at relatively low cost. This paper reports on acase study that was designed to estimate the benefits that might be realized by rangeland managers from an Earth Resources Survey system. Information needs and current practices are first discussed and then related to available remote sensing and data distribution techniques. The analysis showed that cost savings from an applications system would be broadly evident in the areas of resource re-allocation, range productivity, and livestock management. Depending upon the assumptions concerning the discount rate and factors affecting technological diffusion, total benefits were estimated to range from $38.7 million to $115.4 million over 10-year operational period.
Abstract: A simulation model which estimates the net primary production of the ground-storey component of the extensively grazed Acacia aneaura rangelands of semi-arid Queensland, Australia, was applied to the assessment of grazing capacity. The method described represents an alternative approach to the traditional method used by land administrators. Historic climatic records for a continuous period of 25 years were analyzed for one centre. Annual live herbage biomass production fluctuated widely in relation to both climate and grund-storey condition class. Herbage biomass carryover from year to year decreased significantly as the level of herbage utilization through animal consumption increased. At a conservative level of use, herbage biomass carryover provided an important reserve to supplement the smaller amount of live biomass produced in low rainfall years. Consequently, grazing capacity was related to the total herbage biomass available to the grazing animal at the end of each summer growing period. There were only small changes in the mean value of end-of-summer peak herbage biomass crop and sheep carrying capacity over the excellent to good ground-storey condition classes. However, there was a pronounced decline in these values as condition class decreased from moderate to poor. The implications of this method assessing grazing capacity for semi-arid rangeland management and administration are discussed.
Abstract: There is a continous overlap of interests within the Kainji Lake Basin, Nigeria, resulting in conflicts between land users such as the nomadic Fulanis, peasant farmers and wildlife/forestry conservation authorities. The basin is a major agricultural crop producing area of Nigeria. It is also a main traditional source of dry season supply of pasture and water for the migratory livestock from the Sudan and Sahelian vegetation zones in the north. Within the basin is the Kainji Lake National Park which is fast becoming a big-game tourist centre of international standard. Between Yelwa and Jebba, and within a distance of approximately 50 km around the lake and the River Niger, about 200 000 cattle, 100 000 sheep, 25 000 other livestock (goats, horses, donkeys and dogs), as well as 10 000 wildlife comprised of 14 species are estimated. The physical developments and proposals for agricultural improvement by the Niger River Basin Development Authority are reported upon. Recommendations (with national implications) are advanced ffor eliminating conflicts in the utilization of rangeland within the basin.
Abstract: Soil-feeding termites ingest humified, organic-rich soil. The soil faeces are used for nest construction and mounds of two species of Cubitermes contained more soil, clay, exchangeable Ca and Mg, available P, total N and organic C than adjacent topsoil. Available P increased by 1.4-6.0 times. Mounds of a plant-debris feeding termite, Trinervitermes, contained significantly more of these fractions, with the exception of available P, than adjacent topsoil. The modification of Trinervitermes mounds by Cubitermes resulted in a 2-fold increase in available P, whereas organic C remained the same and N increased by 1.5-times. The relatively large increase in available P resulting from soil feeding termites could be attributed to the high pH regime in their hind-guts.
Abstract: Empirical evidence indicates that the magnitude of global warming to be expected from the relase of CO2 into the atmosphere by the burning of fossil fuels has been greatly overestimated by scientists employing general circulation models of the atmosphere. Indeed, real-world data suggest that increasing levels of atmospheric CO2 are actually to be desired, as they have no significant climatic ramifications but tend to promote greater water use efficiency and productivity in the world's natural and managed forests, crops and rangelands.
Abstract: Use of Landsat vegetation indices (combinations of spectral bands) to measure standing crop biomass production in rangelands is addressed. The theoretical basis for vegetation indices is briefly reviewed for ratios, differences and normalizations. Both optical and digital indices are discussed. The reliability of indices as indicators of rangeland primary production is evaluated in relation to drought impact. Seasonal green-up and senescence cycles are shown to be important factors when using indices as stress or drought indicators. Experimental results for the short grass prairies of Colorado show the onset and recovery from drought from 1973 to 1978. The use of vegetation indices to monitor the changing quantity and condition of the vegetative cover of the earth's surface is one of the most promising applications of Landsat data. This application appears to be reliable and inexpensive and uses the attributes of multispectral information, rather than suffering from the loss of spatial information. By responding to the primary productive functioning of plants, the indices provide a measure that is difficult to make in any other way. Rather than being a substitute for more conventional measurements, the vegetation index provides a unique measure of vegetation that will be of value to many users for many applications, including the monitoring of drought impact.
Abstract: During the past ten years, the number of goats has slowly decreased because of limitation policies in some countries and the greater difficulty in managing this species than sheep or cattle, but opposite trends are now occurring in countries such as France and Greece. Many local breeds, or populations with very different production characteristics, exist in the Mediterranean basin because of various climatic conditions and systems of production. Goats do not have any problems with the Mediterranean vegetation because they select what they graze and eat large portions of bushes and trees when there is very little grass. The goat is more harmful to woody vegetation than other ruminants because it browses. It has been shown that the goat alone is not able to destroy natural vegetation without human help. In the Mediterranean area, the proper management of goats can be used to control bush encroachment by clearing the undergrowth which will reduce the risk of forest fires. Among the production systems used in the Mediterranean area, two systems are mentioned: one using ranges only, or supplemented with cultivated forages, and the other using intensive systems where the range vegetation only meets a small proportion of the needs. The former systems generally produce meat, hair and milk, while the latter are mainly intended for milk and cheese production. Systems based essentially on ranges are very precarious and their maintenance requires specific techniques and administrative assistance. Intensive systems may also be precarious because they generally depend on high milk prices.
Abstract: Hand-held MARK-II radiometric measurements were used to estimate biomass yields and nitrogen (N) content of Alicia grass (Cynodon spp.) plots having five levels of nitrogen fertilization. The radiometric RED (630- to 690-nm) and NIR (760- to 900-nm) measurements obtained from the plots were converted to reflectance factors and to perpendicular (PVI) and ratio (RVI = NIR/RED) vegetation indices and then correlated with grass biomass yield and N content. The coefficients of determination (r2) in estimating biomass yield for the RED and NIR reflectance factors were 0.04 and 0.73,1 respectively, and for PVI and RVI they were 0.681 and 0.61,1 respectively. The correlations for N content were 0.02, 0.71,1 0.69,1 and 0.60,1 respectively. Since beef cattle protein needs are related to grass N content these results may be useful to operational rangeland remote sensing programs for estimating animal carrying capacity using satellite data.
Abstract: Nine years of infiltration measurements were made over a 12-yr. period on a big sagebrush (Artemisia tridentata) site in southern Idaho that was plowed and seeded in the fall of 1968. Results of the study thus far indicate that plowing caused an initial significant decline in infiltration rates. Grazing, started in 1970, did not further reduce infiltration but seasonal trends were eliminated and there was no recovery of infiltration. Exclosures indicate it would take at least six years for complete recovery of infiltration rates, assuming no grazing. Suggestions are given for the use of deterministic models in predicting infiltration rates based on grazing intensity.
Abstract: A model of litter decomposition in a South African savanna is described. Decomposing material is divided into a number of particle classes, distinguishing material of different ages, origins and size. Each particle class is further divided into a number of chemical constituents. Processes modelled include ageing, physical disintegration, consumption by termites and decay. Sources of fresh litter include tree and grass leaves. Results from a standard run of the model and a number of runs with changed parameter values to test the model's sensitivity to these are presented and discussed. From exercise of the model it appears that the most important processes relate to soil-feeding termites, with decay and physical breakdown being the background against which termites operate.
Abstract: The growth and species structure of vegetation in relation to the proximity of termite (M. michaelseni) mounds was studied in a semi-arid savannah ecosystem during 1978-1980. The dry matter yield in the termite-modified area at 1-10 m distance from mounds was significantly greater (P 60; 0.01) than that in the area beyond 22 m which is relatively unaffected by the termites. Themeda triandra and Digitaria scalarum, dominant grass species of the area, were totally absent in the 1-10 m zone around the mound. The major species in the immediate vicinity of the mound were Pennisetum stramineum and Cynodon dactylon, the latter was a dominant species (over 90%) within the 0-10 m zone and entirely absent beyond 15 m from the mound. The number of grass species increased from 2-3 species around the mound to 6-7 species in the area apparently beyond the influence of the mound. High concentration of nutrients and favourable water availability, together with good drainage, appeared to be the major causes of increased biomass and different species composition of vegetation around the mound.
Abstract: This paper reviews the application of Landsat to transformation monitoring and a selection of current Australian research projects on land transformation processes. The projects reviewed include forest, rangeland, agriculture, urbanization and wetland monitoring.
Abstract: The rangelands of the world are declining in productivity in spite of the introduction of programmes designed to modernise these traditional pastoral systems of livestock production. This paper suggests that, in designing the modern systems, planners have failed to appreciate the factors influencing success in the traditional systems and that disadvantages have resulted from the introduction of modern systems which reflect only [`]western' conditions. The maintenance of animal mobility and the common use of range pastures, together with a proper appreciation of critical resources and feedback information in traditional systems, should be the constituents of plans to improve productivity.
Abstract: Pollen analyses of rare spring deposits in the Transvaal, South Africa, ranging back to roughly 35 000 B.P., were carried out. A photographic record of 140 types of palynomorphs was made. Indicators such as various arboreal pollen types of the bushveld savanna and also non-arboreal types are briefly discussed in terms of the modern distribution of their parent plants and their importance in surface and sediment samples. Some of especially the NAP were more abundant during the coldest phase of the Late Pleistocene when trees were reduced. Pollen types of the local vegetation associated with the aquatic habitat and the damp surroundings of the spring sites are also listed. The information compiled on the different pollen and spore types helps to assess their value in palaeoecological interpretations.
Abstract: Data for all of the landmass of Canada has been received and archived since the launch of LANDSAT-1 in July 1972. This data has been used in a number of mapping and monitoring programs such as: revising topographic maps, mapping forest fire burns, mapping the variability of water levels in shallow prairie lakes and sloughs, evaluating rangeland conditions, mapping sedimentation levels due to natural phenomena or human activities, monitoring the environmental effects of major hydro electric projects.
Abstract: It was thought for a long time that equatorial regions had remained virtually unchanged at least since the Tertiary period -- it is only from the Late Tertiary that we can talk of the present disposition of land and sea about the equator. Our teaching has supposed that these regions were the hearth from which general spread to the remainder of the planet's surface by gradual adaptation and speciation. This warm, humid zone has been seen as a refuge for species unable to maintain temperature ranges in the face of stresses and fluctuations to north and south. The diversity of species in rain forest environments was assumed to reflect their essential stability. So indeed it may, but not in quite the manner supposed originally by ecologists. The variety of species present in the various regions of rain forest are greatly different, with African exhibiting a relatively poor list compared with South America. This, as it turns out, may well be a function of disturbance. During the last 25 years and gathering momentum within the last decade a variety of studies have demonstrated that the concept of equatorial biological stasis is no longer tenable. Evidence for equatorial environmental changes is derived from theoretical as well as empirical studies. Regarding the former, various attempts have been made to model the earth's atmosphere at different periods of the Pleistocene and there is now fairly good agreement about the consequences for equatorial regions of a general global cooling, namely a critical drying at lower elevations. The empirical evidence is derived on the one hand from stratigraphic studies of peats and lake muds and also the analysis of ocean cores. It is also derived from studies of the geographical ranges of plant and animal species.
Abstract: Landsat data have been employed to study and map agricultural developments in three regions of China: 1) Pearl River delta; 2) Nen River basin; and 3) Xinjiang Autonomous Region. Manual interpretation procedures used in conjunction with multi-date Landsat images and collateral information permitted rice yields to be estimated for the Pearl River delta in 1978. A combination of manual and computer-assisted analyses of Landsat data of Northeast China revealed that more than 15,000 km2 of agricultural land in a 184,500 km2 study area had been reclaimed from rangeland and marshland. These analyses also indicated a shift in cropping practices, with the foodcrops wheat and corn replacing cash crops such as soybeans. In the arid west, Landsat image data provided valuable input to a geographic information system (GIS). It appears the GIS approach will prove useful for evaluating agricultural land potential in the remote areas of China.
Abstract: A major problem for many decision-makers is the lack of reliable information on which to base decisions. This is particularly true for the extent and location of as well as changes in such natural resources as forests, rangeland, agricultural fields and water bodies. A very useful data source in providing such information is the Landsat orbiting satellites. These satellites have been repetitively collecting images of essentially the entire earth's surface since 1972. These images are readily available, inexpensive, useable and can provide exceptional resource information. Examples are presented on the use of this data for a variety of resource analyses.
Abstract: Pollen spectra from cores of organic spring deposits from the Transvaal provide evidence for the climatic evolution of the province during the last 35,000 yr B.P. or more. The past climatic phases are derived from palynological reconstructions of past vegetation types by comparison of fossil pollen data with modern surface pollen spectra from various localities. Evidence is provided for an early moist, cool phase with relatively mesic bushveld and expanded montane forest in the central Transvaal, followed by a drier period with drier bushveld which probably lasted until approximately 25,000 yr B.P. During the next phase, which at the latest ended about 11,000 yr B.P., the temperatures were probably 5°-6°C cooler than at present. At that time bushveld vegetation in the central Transvaal was replaced by open grassland with macchia elements. Climatic amelioration came and semiarid savanna returned to the plains, at first gradually and then developing into a warm Kalahari thornveld-type vegetation. After 6000 yr B.P. it apparently became slightly wetter and a more broad-leafed bushveld developed. About 4000 yr B.P. it again became cooler and slightly wetter and the bushveld vegetation on the central and northern plains was comparable to present open upland types. After 2000 yr B.P. conditions gradually became warner until about 1000 yr B.P., when the modern climate of the central Transvaal bushveld originated.
Abstract: Carbon isotopic ratios in tooth apatite of Pliocene fossil mammals from Omo, Ethiopia, dated at 2.0 m.y. ago reported here are consistent with dietary predictions based on modern herbivores of the African savannah. The results indicate the applicability of the technique in reconstructing dietary patterns of fossil animals including hominids.
Abstract: Extensive systems of fixed linear dunes occur in the Kalahari region of southern Africa, from 28°S to 16°30'S. They provide evidence for large-scale expansion of arid climates in the subcontinent during the Quaternary. On the basis of differing dune morphologies and alignments, three periods of Upper Pleistocene aridity are recognised. Patterns of dune alignments reflect paleosand flow regimes and permit deduction of past winds and circulation patterns, leading to the conclusion that arid episodes were associated with, and probably caused by, greater strength and persistence of the South African anticyclone. A tentative chronology of the arid periods tends to support the hypothesis that subtropical aridity was contemporaneous with glacial conditions in high latitudes.
Abstract: Radar backscatter measurements were made of experimental prairie on Campus West of the University of Kansas, Lawrence, Kansas, during the period from July to November 1978. Experiments were performed with a surface-based FM--CW scatterometer that swept from 8.5-17.5 GHz. Natural grass field and mowed grass fields were observed. Results indicate that the plant moisture content has somewhat close correlation with the differential cross-section of [sigma]° of VV polarization, and plant biomass might be able to be estimated from [sigma]° of HH polarization. Also, [sigma]°dB was found to have an almost linearly decreasing angular response.
Abstract: Forest and grassland clearing by means of prescribed fires in tropical areas of the world may be responsible for large inputs of fine particulates to the global atmosphere besides being a major source of trace gases. The major continents on which extensive biomass burning takes place are Africa and South America. Such agricultural practices of burning have been employed throughout man's existence, but the importance and significance of such burning relative to anthropogenic industrial emissions to the atmosphere has not until extremely recently been seriously studied. In August-September 1979 project "Brushfire 1979" took place based in BrasÃlia, Brazil. The Air Quality Division of the National Center for Atmospheric Research made ground level and aircraft measurements of trace gases (e.g. CO2, CO, CH4, N2O, H2, CH3Cl, COS, NO, NO2, O3) and Florida State University sampled ground level aerosol emissions from grass and forest burnings. Aerosols were sampled using plastic 7-stage single orifice cascade impactors and FSU type linear and circular "streakers". Long term sampling was made of regional background for total particulates (<15 [mu]mad) with 2 h resolution using streakers and with impactors for 24 h resolution of 7 particle size fractions (<0.25 to >8 [mu]mad). Short term sampling within grass or forest fires was made using impactors incorporated into portable kits containing 4 miniature 12-18 V dc Brailsford pumps and a disposable dry cell power pack. Sampling times of 5-15 min were found optimal under these conditions. Grass fires were sampled in the savannah area northeast of BrasÃlia and forest fires in the state of Mato Grosso on the southern edge of the dryland forest of the Amazon basin. Residual ash samples were collected. All of the samples were analyzed at Florida State University using PIXE for 15-20 elements including Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Pb and Sr. Computer reduction of the X-ray spectra was made using the "HEXB" program. One of the prominent features found was the large flux of small particles (<2.0 [mu]m) from both fire types. P, S and Cl were mostly small particle, Mg, Al, Si and K showed a bimodal distribution biased towards the small particle range, while Ca, Ti and Fe (crustal elements) predominated in the large particle mode. As Cl was found to be exclusively small particle, a formation mechanism in which HCl gas neutralizes small organic particles containing P and S may be hypothesized. A much more extensive field program for the summer of 1980 is planned to take place in the central Amazon basin using ground and airborne aerosol samplers, to capitalize on the work pioneered in this study.
Abstract: To provide information on the nature of the plant food diet probably available to Australopithecus africanus in the Makapansgat area, under climatic conditions similar to those at present, wild plant foods were collected during the 1980-81 dry and wet seasons. The structural toughness of the food items was estimated from force deformation during compression loading with the standard Instron Universal Testing Machine and a specially designed field apparatus. During the late wet season, in contrast with the dry season, there is relative abundance and a variety of wild plant foods available. Moreover, the most important potential plant food staples include very tough dry berries, beans and nuts, which require an average of 50-250 kg of compressive force to crack and crush them. Comparisons of food toughness measures, previously reported data on human maximum bite forces (91-158 kg), and maximum bite force values hypothesized for Australopithecus africanus (150-200+kg), suggest that although these fossil hominids would have been able to prepare orally many of the tough food species, it also appears likely that they would have had to process artifactually (with simple stone tools) the toughest of these food items to assure their survival in this environment.
Abstract: The importance of the water balance in determining cropping patterns in West Africa is examined. Crops in each country were ranked in order of area occupied. Crop diversity is reduced when the period of water surplus is very short or very long. The fraction of the cropped area occupied by a particular crop is related to the length of the period of water surplus. Four basic cropping patterns are identified.
Abstract: The effects of variation in rainfall on yields of millet, sorghum, groundnuts and rice in seasonally arid West Africa were examined by multiple regression. Satisfactory relationships were established for some countries but not for others. Yields were usually positively related to total rainfall, or to rainfall in specific months, but in some cases were negatively related to August rainfall.
Abstract: The sagebrush (Artemisia)/grasslands of western North America are a tremendous grazing resource that currently is producing forage at only about one-half of its potential. The history of degradation of this environment is traced from the late 19th century, when livestock were introduced to the sagebrush rangelands. The dominant species of sagebrush that characterize the landscape are not preferred by domestic livestock. Continuous excessive grazing greatly reduced the perennial grass cover and allowed shrubs to increase. Phenoxy herbicides proved to be very valuable and economically feasible tools for improving grass and other forage production on shrub-dominated rangelands. Second-generation herbicides were used in controlling alien annual weeds to permit the seeding of degraded sagebrush rangelands. These techniques for control of herbaceous weeds were vertically integrated with brush control and seeding techniques for total range improvement. Environmental and economic constraints brought improvement of sagebrush range to a virtual standstill during the nineteen-seventies.
Abstract: A forage model and a cattle production model were interfaced and adapted for tropical production conditions in East Africa. The objectives of the modelling were to structure and conceptualise a complex system for better comprehension, thereby determining constraints on a traditional African grazing system. The model was designed to simulate the physical linkages between the scarce resource of forage and the outputs of cattle, meat and milk. The effects of improved management practices were examined for a traditional village livestock grazing system. Verification and validation for the baseline village herd were carried out using several different sources of data. A combination of a restricted breeding season, supplemental feeding during the dry season and a seasonal sales policy resulted in a 40% increase in net revenue to village producers above the baseline for a ten-year period.
Abstract: Natural groundwater recharge characteristics were evaluated, using precipitation data, soil depth, soil water and groundwater observations, for a semi-arid rangeland environment of southwest Idaho. Recharge in these study was area occurs via three separate mechanisms -- by infiltration through low-relief rubbly basalt outcrops; infiltration through shallow soils; and by transmission through bedrock channels during runoff and channel flow. To initiate recharge, rainfall in excess of 20-30 mm over 24 hr., or higher-intensity cloud-burst storms are required. Time to peak, the time from the end of a precipitation event to the peak of groundwater hydrograph, was found to be independent of season, depending only on soil depth. Regression analysis of time to peak vs. soil depth produced a correlation coefficient of 0.941. The rate of groundwater recharge for the study area was computed at ~4.6·10-4 cm/min.
Abstract: Greywing and redwing francolins are members of a fire climax grassland. From previous observation the immediate effect of fire depresses densities of these birds, as does the long-term exclusion of fire. Since the birds are of localised habit it was hypothesised that developing a fine-scale fire mosaic would maintain high densities of the birds. The hypothesis was tested in several ways in a field experiment in the Natal Drakensberg. The outcome of one test was equivocal, but the other tests did not refute the hypothesis. Densities declined markedly when large areas of veld were burnt cleanly. The rate of population recovery apparently varied locally. On large areas burnt cleanly biennially in spring, spring and autumn densities were always lower in the first than in the second year after fire. The birds preferred unburnt rather than burnt areas shortly after the application of fire in spring, but this preference was reversed in autumn six months later.
Notes: 6 microfiches (543 fr.) : ill. ; 11 x 15 cm.
Ann Arbor, Mich. : University Microfilms International, 1983.
Facsim. ed. originally published: (Fort Collins, Colo.)
