Kalahari Of Botswana Research Articles

Groundwater flow regime, recharge and regional-scale solute transport in the semi-arid Kalahari of Botswana derived from isotope hydrology and hydrochemistry

Summary A synthesis of isotope hydrological (2H, 3H, 18O, 13C, 14C, 3He, 4He) and hydrogeochemical tools was used to analyze flow regimes and their time scales, to determine recharge conditions, and to describe the regional-scale hydrogeochemical evolution of groundwater from the Triassic Ntane Sandstone Aquifer between Serowe and Orapa in the Kalahari of Botswana. This location is taken as an example of a complex hydrodynamic setting relating to semi-arid climatic conditions, low recharge amounts, thick unsaturated zones (up to 100 m) and long groundwater residence time scales. Capabilities and limits of the individual methods are discussed, and relations to solute transport are demonstrated for nitrate. Chemical classification allows the distinction of six different groundwater types. This characterization is reflected in the isotopic composition and in part can be attributed to different age ranges (up to greater than 20 ka). We show that the regional-scale groundwater flow regime in the aquifer is only slow, and that groundwater is recharged in Serowe and Orapa. However in both investigated regions, mixing between over- and underlying aquifers is evident which limits a clear derivation of one regional flow regime. The challenges imposed on the identification of the regional groundwater flow regime by resulting mixing processes and for groundwater dating are discussed and evaluated.

Anticipating Vulnerability to Climate Change in Dryland Pastoral Systems: Using Dynamic Systems Models for the Kalahari

It is vitally important to identify agroecosystems that may cease functioning because of changing climate or land degradation. However, identifying such systems is confounded on both conceptual and methodological grounds, especially in systems that are moving toward thresholds, a common trait of dryland environments. This study explores these challenges by analyzing how a range of external pressures affect the vulnerability of dryland pastoral systems in the Kalahari. This is achieved by employing dynamic systems modeling approaches to understand the pathways by which communities became vulnerable to drought. Specifically, we evaluate how external pressures have changed: (1) different agroecosystems' abilities to tolerate drought, i.e., ecosystem resilience; (2) rural communities’ abilities to adapt to drought, mediated via their access to assets; and (3) the ability of institutions and policy interventions to play a role in mediating drought-related crises, i.e., socio-political governance. This is done by reanalyzing ecological and participatory research findings along with farm-scale livestock offtake data from across the Kalahari in Botswana. An iterative process was followed to establish narratives exploring how external drivers led to changes in agroecosystem resilience, access to assets, and the institutional capacity to buffer the system. We use “causal loop diagrams” and statistical dynamic system models to express key quantitative relationships and establish future scenarios to help define where uncertainties lie by showing where the system is most sensitive to change. We highlight how that greater sharing of land management knowledge and practices between private and communal land managers can provide ‘win-win-win’ benefits of reducing system vulnerability, increasing economic income, and building social capital. We use future scenario analyses to identify key areas for future studies of climate change adaptation across the Kalahari.

Comparison of ground TEM and VTEM responses over kimberlites in the Kalahari of Botswana

Kalahari cover greater than 60 m thick precludes indicator sampling from identifying individual kimberlite intrusions in the Kokong kimberlite field of Botswana. Employing concurrent multidisciplinary geophysical surveying methods is the exploration technique for the discovery of kimberlites. Time Domain Electromagnetic (TEM) surveying is an effective technique for the prioritization of aeromagnetic and gravity signatures. Diagnostic discrete conductive TEM signatures are usually returned from kimberlites overlain by up to 120 m of Kalahari cover. Following the success of kimberlite identification by ground TEM, a VTEM helicopter time domain survey was flown over the Kokong field to increase the TEM coverage in this prospective kimberlite terrain. A comparison of responses over covered kimberlites traversed by both TEM survey methods and their comparative effectiveness for kimberlite identification is presented.

Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition

Trace elements together with some O and C isotope analysis were undertaken on duricrust strandline deposits in the palaeo-Makgadikgadi sub-basin (PMSB) to provide insight into palaeo-climatic conditions through the interpretation of calcrete, silcrete–calcrete intergrade and silcrete deposits. Trace element content and relative abundance suggest that the duricrust origins are associated with the long-term weathering of the Karoo Large Igneous Province which underlies the PMSB. This work shows that duricrust origins are related to Ca 2+ and Si (and associated trace elements) being transported mainly through the groundwater and then subsequently precipitated at different strandline elevations over time. Local groundwater feeding in towards the pan margin and accumulating in near-neutral pan-marginal pools, appears to facilitate Si concentration and permeation of pre-existing calcretes. The silica precipitates as the pH drops when renewed freshwater enters the pools. Hence the inferred palaeo-climatic regime for silcretisation may be similar to that occurring in Botswana at present being dry semi-arid with low seasonal rainfall. In contrast the extensive calcrete precipitation in the strandlines results from abundant Ca 2+ in adjacent waters which appear to be derived from both local and regional sources. The arrival of Ca 2+ from regional sources (shown by trace element evidence) infers heavy rainfall in the upper catchment suggesting a major humid event followed by regional drying. Palaeo-climatic inferences suggest the juxtaposition of major humid events interspersed with more normal semi-arid palaeo-climates with an exception obtained from isotope data, of drier and cooler conditions than usual for the region around 80–90 000 years ago. Whereas trace element data can greatly assist in the interpretation of complex deposits such as duricrusts, care should be taken over the use of particular ratios (such as Yb/Gd ratio) which may produce spurious results.

Comparison of ground TEM and VTEM responses over kimberlites in the Kalahari of Botswana

One hundred meter square in-loop ground TEM soundings were an effective way to screen aeromagnetic, ground gravity, and Falcon gravity gradiometer signatures caused by kimberlite intrusions overlain by 40-120 meters of transported Kalahari sedimentary cover in the Kokong kimberlite field of Botswana. Ground TEM?s effectiveness in identifying kimberlite pipes led to the flying of the VTEM aeroTEM system over selected areas at Kokong. Ten kimberlites previously covered by ground TEM surveys were over flown by the VTEM survey. A comparison of the ground TEM and VTEM responses show that the VTEM effectively drill-screened nine out of the ten kimberlite magnetic or gravity signatures, whereas the ground TEM systems effectively screened all 10 kimberlite signatures. KS40, the largest kimberlite at Kokong and the one kimberlite less well mapped by the VTEM was, at 10-30 msec, a later-time conductor that best responded after the VTEM?s last channel 27 at 7.5 msec. KS40?s kimberlite crater was mapped as a good late-time conductor (later than 7.5 msec) by both ground TEM systems. The ground TEM systems employed were a Geonics TEM57 transmitter and PROTEM receiver, and two Zonge ZT-30 transmitters and GDP32 receivers.

Impact of recharge variations on water quality as indicated by excess air in groundwater of the Kalahari, Botswana

Groundwater is an important and often exclusive water resource in arid and semi-arid regions. The aim of the present paper was to gain insight into the processes and conditions that control the deterioration of groundwater quality in the semi-arid Kalahari of Botswana. Measurements of 3He, 4He, 20Ne, 22Ne, and of 14C of dissolved inorganic carbon (DIC) were combined with existing isotopic and hydrochemical data to investigate groundwater from the Ntane Sandstone Aquifer, which is affected by high nitrate concentrations of non-anthropogenic origin. All groundwater samples revealed neon concentrations in excess to air-saturated water, which we attributed to the addition of excess air during recharge. Neon concentrations ranged from values close to air saturation for 14C DIC rich samples (up to 80.5%MC) up to values of 90% in excess to air-saturated water for lower 14C DIC contents (2.6–61.3%MC). A strong linear correlation of excess Ne with nitrate concentrations suggests an intimate connection between groundwater quality and the processes and conditions during groundwater recharge. Low groundwater recharge rates under present-day semi-arid conditions are associated with low amounts of excess Ne and elevated nitrate concentrations. In contrast to this, higher excess Ne values in groundwater of lower 14C DIC and nitrate contents indicate that the high quality groundwater end-member presumably is related to higher groundwater table fluctuations during wetter climatic conditions in the past. We attribute the decline in groundwater quality with respect to nitrate to a decreasing rate and temporal variability of groundwater recharge, and to concurrent changes in biogeochemical activities following a transition to a drier climate during the Holocene. Under such conditions, a much stronger decrease in groundwater recharge compared to the release of nitrate from soil organic matter may result in elevated nitrate concentrations in the vadose zone and groundwater. This implies a strong impact of climate change on the transport of solutes like nitrate through the vadose zone which needs to be considered in predictions of future groundwater quality.

Understanding the origin and fate of nitrate in groundwater of semi-arid environments

Though nitrate enrichment in groundwater is a worldwide phenomenon and mainly related to human impact, processes leading to nitrate enrichment in scarcely inhabited semi-arid regions are not yet well understood. In those regions, elevated nitrate concentrations put additional pressure on the scarce water resources, as they pose a serious health risk. This study applies a multidisciplinary approach (hydrogeology, isotope hydrology, and geochemistry) to understand the origin and fate of nitrate in groundwater of the semi-arid Kalahari of Botswana. Our investigations suggest that nitrate in groundwater of the study area is of natural origin, leached from a pool in the unsaturated zone that was actively involved in the soil nitrogen cycle. The presence of active (minor) recharge was found, showing that nitrate may be transported into the groundwater under the present conditions. Yet, slow travel times of replenishing water and the low recharge amounts render the thick unsaturated zone into a long-term reservoir for nitrate. Being only little influenced by reactive processes, nitrate has a high persistency in the observed groundwater system. Concentration increases induced by the present land-use do not yet appear to affect the groundwater quality but may within decades.

Carbon dioxide fluxes from cyanobacteria crusted soils in the Kalahari

The surface of dryland soils is frequently characterised by a biological crust comprising of various combinations of cyanobacteria, algae, moss and lichens. In the Kalahari of Botswana, soil crusts are predominantly made up of cyanobacteria, which when moist, are capable of fixing N and C. Many cyanobacteria also produce extracellular polymeric substances (EPS) which bind soil particles together and decrease erodibility. The physical integrity and metabolic activity of soil crusts is thus critical to ecological productivity, erodibility and CO 2 fluxes in dryland regions. There are, however, few studies of the magnitude and controlling factors of soil CO 2 flux within these systems. Our aim was to quantify in situ soil CO 2 flux during contrasting antecedent moisture conditions in the south west Kalahari of Botswana. We have designed a gas exchange chamber for field deployment coupled to a portable gas chromatograph, control and data logging instrumentation. The optical and active thermal control specifications of the chamber have been designed to permit photosynthesis and cope with the temperature extremes of the Kalahari whilst minimizing disturbance to the cyanobacteria soil crust. This approach has enabled CO 2 fluxes to be monitored in situ with a high degree of precision for extended periods. In August 2005, when the surface and subsoils were dry, the ambient CO 2 efflux was negative and low during the daytime (−6.15 mg C m 2 h −1). When 8 mm rainfall equivalent of water was added to the surface there was an immediate uptake of CO 2 during the daytime at rates up to 75 mg C m 2 h −1 demonstrating that rates of net photosynthesis are greatly enhanced by available moisture. In contrast, in May 2006 following a prolonged wet period when the subsoil was moist, there was a net positive efflux of CO 2 from the soil at rates of up to 60 mg C m 2 h −1 irrespective of whether the surface soil was moist or not. This is consistent with subsoil heterotrophic bacterial respiration becoming an important contributor to soil efflux.

Archaeological excavations at Bosutswe, Botswana: cultural chronology, paleo-ecology and economy

Excavations at the site of Bosutswe on the eastern edge of the Kalahari Desert in Botswana have uncovered over 4 m of deposit ranging in age from CE 700 to 1700. Our research has produced quantitative and qualitative measures of the material and ecological dimensions that structured the everyday actions and behaviors through which social identities were constituted, maintained, and transformed during the period when the polities of Toutswe, Mapungubwe, Great Zimbabwe and Khami rose to power. By examining the material dimensions that underlay shifting relations of production, exchange, and social stratification we are able to contextualize the social judgments that ascribed value to material goods and food ways, while specifying the ways these were used to create and naturalize social relationships and power differentials. Stable isotope analyses, combined with evidence of vitrified dung, further enable us to suggest changes in herd management strategies used by the inhabitants of the site to compensate for ecological changes brought about by long-term occupation, while at the same time enabling them to economically tie subordinates to them as social divisions became more rigidly defined after CE 1300. The cultural and economic changes that took place at Bosutswe thus directly impact our understanding of the social transformations that immediately preceded contemporary configurations of ethnicity in Botswana.

A phenological study of dominant acacia tree species in areas with different rainfall regimes in the Kalahari of Botswana

The phenology of three dominant and economically important tree species; Acacia erioloba, Acacia luederitzii and Acacia mellifera, all widespread in the Kalahari in Botswana, was studied at Tsabong (25°56.65′S, 22°27.72′E) and Maun (20°09.60′S, 23°46.63′E) receiving 300 and 463 mm annual rainfall, respectively. The main aims were to investigate how possible environmental cues influence timing and development of phenophases and whether different tree species have different seasonal responses to these cues. Likely effects of climatic changes on phenological development patterns were also considered. All three species studied had generally comparable seasonal responses irrespective of the mean annual rainfall at each site, but differed in the timing of certain phenophases. Both A. erioloba and A. mellifera flowered at the end of the cool dry season. Acacia erioloba produced new leaves simultaneous with flowers while A. mellifera produced fully developed fruits before leaves. On the other hand, A. luederitzii produced leaves and flowered after rain and well into the growing season, with leaves appearing before the flowers. For A. erioloba and A. mellifera, temperature and daylength appeared to be the most probable phenological cues, while in the case of A. luederitzii, it was rainfall. All species produced lower amounts of certain litter components during the year of lower rainfall at the Tsabong site, affecting fodder availability. Livestock was observed feeding on newly emerged flowers, leaves and new twigs, relieved from scratching the ground for dry grass, fallen leaves and pods. Other studies have also observed new growth to provide valuable fodder in the dry season and drought periods, making phenological timing economically crucial. Any shift in climatic factors that affect this timing may have detrimental consequences. Drought is the best-known example of an extreme shift. There is need for more information on the likely extent of other shifts and possible effects in vulnerable areas such as the Kalahari in the face of changing environmental and climatic conditions.

Effects of drought on birds in the Kalahari, Botswana

Results are presented from point-counts at six sites in the Kalahari in Botswana. Counts were repeated three times: during a dry season following good rains (1991), during the next wet season when rains were far below average, and the following dry season (1992) when the area became drought-stricken. Compared to the wet season, bird numbers decreased during the drought by 37–81% and species by 8–52%; compared to the previous dry season, birds decreased by 5–71% and species by 2–47%. Bird diversity (relative to numbers) tended to increase during the wet season but was little affected by drought, except in the northern Kalahari, where a greater proportion of birds moved out in response to drought. This gave the northern Kalahari the most distinct bird community during a wet cycle, but it became again typically Kalahari during the drought. Thus, the typical Kalahari bird communities expanded their range during drought into the moister periphery. Changes in numbers, most probably resulting from (local) movements were found in many species. Most confirmed earlier reports on their nomadic nature but some, like Red-crested Lophotis ruficrista and Northern Black Afrotis afraoides Korhaan, Chestnut-vented Tit-Babbler Parisoma subcaeruleum, Ant-eating Chat Myrmecocichla formicivora, Tinkling Cisticola Cisticola rufilatus, Black-chested Prinia Prinia flavicans, Marico Flycatcher Bradornis mariquensis and Brown-crowned Tchagra Tchagra australis have not been or are not widely recognised as mobile species.

A reconnaissance laser Raman and Fourier transform infrared survey of silcretes from the Kalahari Desert, Botswana

AbstractThis paper documents the first application of laser Raman and Fourier transform infrared vibrational spectroscopic techniques (Raman/FT‐IR) to the analysis of silcrete. Analyses are undertaken at a reconnaissance level on bulk silcrete samples of varying ages, drawn from a range of geomorphological settings across the Kalahari Desert of Botswana. Results suggest that Raman/FT‐IR, combined with inspection of petrographic thin‐sections, provides an effective tool for establishing the range and type of silica polymorphs present within samples. Analyses of Raman and mid‐infrared spectra indicate that the majority of silcretes are dominated by α‐quartz with subordinate moganite. There is, however, considerable inter‐sample variability, ranging from silcretes consisting of almost pure quartz to those containing complex admixtures of disordered microcrystalline or non‐crystalline silica in association with quartz and clays. Taken as a whole, the results are supportive of a similar environment of formation for all samples, with development taking place under broadly semi‐arid conditions. Raman/FT‐IR is also shown to have a number of benefits over other conventional techniques for silcrete analysis, such as X‐ray diffraction. Firstly, inspection of the OH region of the infrared spectrum of bulk samples is shown to have potential for establishing the provenance of quartz clasts within silcrete host sediments, through the identification of high‐temperature conditions of crystal growth in detrital quartz grains. Raman and mid‐infrared analyses also permit clay identification within silcrete samples where such minerals are not readily resolvable in thin‐section. The technique further allows the relative maturity of silcrete cements to be established, particularly for recently formed silcretes. These are found typically to contain less mature silica polymorphs and incorporate larger quantities of molecular water than α‐quartz dominated silcretes. Comparisons of the range of silica polymorphs identified using Raman/FT‐IR with those established by petrographic investigation can also reveal evidence of silica paragenesis. This is the case in two stratigraphically older samples from the Kalahari margin in which less stable silica polymorphs appear to have transformed over time to chalcedony and microquartz. Whilst the ‘whole‐rock’ approach used in this survey generates some problems of interpretation, the overall results suggest that the use of micro‐Raman and micro‐FT‐IR techniques should allow even more precise information about the environments of formation and developmental histories of silcrete profiles to be produced in the future. Copyright © 2004 John Wiley & Sons, Ltd.

Climate variability in the Botswana Kalahari from the late Pleistocene to the present day

Noble gas concentrations and oxygen isotopes in groundwaters from the Kalahari Desert in Botswana contain a ∼45 ka paleotemperature record indicating that mean annual temperatures during the period from 24 ka BP to 45 ka BP were 5.2 ± 1.5°C cooler than from ∼16 ka to the present day. In addition to enrichments in oxygen‐18, groundwaters recharged after 16 ka BP also contain higher concentrations of excess‐air (entrained air bubbles). Taken together, the noble gas, oxygen isotope, and excess‐air based paleoclimate archives provide evidence that the high interior desert of southern Africa was both cooler and dryer prior to the Last Glacial Maximum (LGM). Cool, dry conditions also suggest a weaker hydrological cycle in southern Africa. This is contrary to the predicted enhancement of monsoon strength by increased summer insolation in the southern tropics induced by orbital precession during the LGM.

Prospects for subsistence livelihood and environmental sustainability along the Kalahari Transect: The case of Matsheng in Botswana's Kalahari rangelands

Botswana's Kalahari rangelands have historically supported a diversity of wildlife and a number of subsistence livelihood activities, such as agropastoralism, hunting and gathering. Recently, however, concerns about environmental and livelihood sustainability in the Kalahari have been raised. This paper demonstrates the validity of these concerns using data from research undertaken in the Matsheng area of southwest Botswana. It is illustrated that: (a) Matsheng soils are too infertile to sustain productive arable farming, (b) herbaceous vegetation cover decreases in a reversed decay function towards settlements, (c) the herbaceous vegetation cover trend is inversely reflected by woody-thorny vegetation, (d) despite being a major rangeland activity, livestock production benefits only a minority of inhabitants, and (e) rangelands are no longer the major source of livelihood for the majority.

Vegetation cover trends along the Botswana Kalahari transect

Vegetative response aspects of climate change studies include the determination of vegetation cover changes across climatic gradients. Vegetation characteristics and soil moisture measurements were obtained from four locations with decreasing rainfall along the Botswana Kalahari transect. These are referred to as Pandamatenga, (698 mm year −1), Maun (460 mm year −1), Okwa (407 mm year −1) and Tshane (365 mm year −1). Trends in major vegetative cover and soil components included species types and richness assessments which reflected certain changes southward but also showed interesting degrees of variability. This occurred despite the apparent homogeneity of the Kalahari sands and predominantly semi-arid savanna shrub–woodland vegetation cover. Despite linear decreases, both in rainfall and soil moisture content, results indicated high soil moisture variability at the Okwa location which relates to unique climatic and geological factors. Also many species are unique to specific locations for instance Pandametanga is characterized by Zambesian species while the Maun location is characterized by Colophosphermum mopane. This changes southwards as Acacias become more dominant and significantly co-occur with Grewia flava. While the average total numbers of plants decreased, total numbers of different species varied little from the wetter to the drier end of the moisture gradient. The association between rainfall and woody cover is negative implying that canopy cover extents (in terms of vegetation density) increase along the gradient due to increases in bush encroachment in drier areas. Therefore, while representing a continuum in terms of species numbers, in other respects (e.g. species types and ground cover components) vegetation zones in the Kalahari may be regarded as discontinuous units. Differences between mapped vegetation zones may be accounted for in terms of relatively unique ecosystem factors which function partly in response to geological conditions and partly in response to local (as opposed to regional) climatic factors. This appears to have led to ecosystem adaptive measures (in terms of species responses) rarely mirrored elsewhere along the gradient. Hence adaptability in terms of species migrations in response to relatively rapid climate changes may not readily take place over the Kalahari in Botswana.

Isotope hydrology and its impact in the developing world

Ground water has increasingly taken its place in the provision of safe, potable supply in the developing world. Large investments have been made in infrastructural development for rural ground water supply schemes, but far too little attention has been given to assess the sustainability of these supplies. Overexploitation of aquifers, evident in failing boreholes and deteriorating water quality, has become a world-wide concern. Developments in physics half a century ago established the basis of isotope hydrology. Radioactive isotopes give information on ground water dynamics and recharge rates whilst non-radioactive - or stable - isotopes indicate origins of ground water and delineate ground water bodies. Environmental isotope hydrology is increasingly seen as a powerful discipline in assessing ground water systems. This is particularly important in developing environments, where historical data is rarely available. Brief examples are presented of isotope applications to collaborative ground water studies conducted at the University of the Witwatersrand. Recharge estimates based on isotope ‘snapshot’ data conform well with results from subsequent long-term water level observations in the Kalahari of Botswana. The importance is demonstrated of irrigation return flow and pollution hazard to the Lomagundi dolomite of Zimbabwe. Isotopes suggest the source of high nitrate concentrations to an important ground water supply in Tanzania. Mechanisms of the release of arsenic into millions of tube wells in Bangladesh are put into perspective. Isotope hydrology as appropriate technology is highlighted in terms of its cost-effectiveness and the investigative empowerment of local investigators.

The nature of calcareous deposits along pan margins in eastern central Namibia

AbstractIn a region along the western margin of the Kalahari in eastern Namibia and western Botswana, many pan basins have mainly calcareous deposits along part of their margins. These are typically lined by low vertical scarps. In Namibia, these pans are mainly located in dry river beds. The petrographical study of these deposits demonstrates that they consist of lacustrine sediments that have to a varying extent been affected by early‐diagenetic processes and by the formation of late‐diagenetic features.The original composition of the deposits ranges from highly calcareous sediments, typically with ostracod, diatom and charophyte remains, to entirely non‐calcareous diatomites. The deposits generally show an upward increase in total carbonate content, which is mainly a synsedimentary feature. The early‐diagenetic processes that affected the deposits include the formation of orthic siliceous nodules. At a later stage, secondary calcite enrichment occurred, leaving only the silica‐impregnated sections unaffected. This enrichment partly accounts for the upward increase in total carbonate content in some profiles and often resulted in the development of a highly calcareous surface horizon. Sepiolite and amorphous silica that are part of the groundmass of the deposits may also partly have formed at this stage. Late‐diagenetic features include various forms of secondary calcite and silica.This study of pan basins in eastern central Namibia indicates that a lacustrine rather than purely pedogenic origin should also be considered for calcareous deposits that commonly occur along pan margins in other parts of southern Africa. Copyright © 2002 John Wiley & Sons, Ltd.

Outcomes of Social and Environmental Change in the Kalahari of Botswana: The Role of Migration

Migration now features prominently both in poverty-reduction discourses, as a 'tool' for reconciling rural populations with available resources, and in sustainable livelihoods debates, as a 'coping strategy' employed in times of livelihood stress. This paper assesses the contemporary significance of migration as populations are affected by the dual impacts of natural environmental variability and structural land-use change in the Kalahari of Botswana. Three study areas, located across the arid to dry-sub-humid climatic gradient, were investigated. These had been redesignated as commercial ranching areas under the Tribal Grazing Lands Policy of 1975. Under this policy, pre-existing populations were to be resettled in specially designated Service Centres that were expected to reduce poverty and improve livelihood opportunities and household food security. The findings of this study reveal that the policy was accompanied by extensive population displacement rather than migration per se as ranch owners exercised their exclusive rights to the land. While some ranch populations moved to Service Centres, lack of infrastructure and alternative livelihood opportunities forced many of them back into ranch areas where many now live as squatters dependent on the goodwill of ranch owners. Thus the policy has not resulted in envisaged sedentarisation but instead has produced a population of transients involved in a number of highly localised moves. The mobility patterns of absent householders provided some evidence to suggest that, despite rapid urbanisation, rural to urban migration from the study areas was limited, as were associated remittance flows, suggesting that TGLP areas may not be currently integrated within a national migration system. There were significant differences in the implementation of the policy between study areas and these differences have had a considerable bearing on the population's ability to respond to environmental variability. In one of the Study Areas (Ncojane), severe drought has resulted in a more flexible implementation of ranches: fences had been taken down, and people and cattle were able to move between ranches in search of water and veld products. Population mobility here was thus a significant coping strategy, ironically where commercial ranch owners had reverted back to the old cattle-post system which emphasises circulation and reciprocity.

Outcomes of Social and Environmental Change in the Kalahari of Botswana: the Role of Migration

Migration now features prominently both in poverty-reduction discourses, as a ‘tool’ for reconciling rural populations with available resources, and in sustainable livelihoods debates, as a ‘coping strategy’ employed in times of livelihood stress. This paper assesses the contemporary significance of migration as populations are affected by the dual impacts of natural environmental variability and structural land-use change in the Kalahari of Botswana. Three study areas, located across the arid to dry-sub-humid climatic gradient, were investigated. These had been redesignated as commercial ranching areas under the Tribal Grazing Lands Policy of 1975. Under this policy, pre-existing populations were to be resettled in specially designated Service Centres that were expected to reduce poverty and improve livelihood opportunities and household food security. The findings of this study reveal that the policy was accompanied by extensive population displacement rather than migration per se as ranch owners exercised their exclusive rights to the land. While some ranch populations moved to Service Centres, lack of infrastructure and alternative livelihood opportunities forced many of them back into ranch areas where many now live as squatters dependent on the goodwill of ranch owners. Thus the policy has not resulted in envisaged sedentarisation but instead has produced a population of transients involved in a number of highly localised moves. The mobility patterns of absent householders provided some evidence to suggest that, despite rapid urbanisation, rural to urban migration from the study areas was limited, as were associated remittance ows, suggesting that TGLP areas may not be currently integrated within a national migration system. There were significant differences in the implementation of the policy between study areas and these differences have had a considerable bearing on the population’s ability to respond to environmental variability. In one of the Study Areas (Ncojane), severe drought has resulted in a more flexible implementation of ranches: fences had been taken down, and people and cattle were able to move between ranches in search of water and veld products. Population mobility here was thus a significant coping strategy, ironically where commercial ranch owners had reverted back to the old cattle-post system which emphasises circulation and reciprocity.

Environmental Change in the Kalahari: Integrated Land Degradation Studies for Nonequilibrium Dryland Environments

Recent decades have seen major intensification of cattle-based agricultural production in semiarid savanna ecosystems. In the Kalahari of Botswana, cattle production now occurs on privatized and fenced ranches. Patterns of ecological change, notably increased bush dominance, have been linked to increased cattle-grazing intensity, but it remains contentious whether these changes represent land degradation. Uncertainty in ecological understanding stems from the dynamic, “nonequilibrium” functioning of semiarid ecosystems. Given the inherent ecological variability of drylands, we argue that degradation assessments should be based, not on ecological observations alone, but on the study of long-term changes in pastoral production figures and on changes in the ecologically determining factors of soil water and soil nutrient availability. Provided here is a framework incorporating soil and ecological changes at a range of scales that can enable us to distinguish drought-induced fluctuations from long-term ecological-state changes. The results demonstrate that increased cattle use and associated ecological changes have not been caused by, nor are they associated with, changes in soil water and nutrient availability. We present a model of ecosystem dynamics that does not display bush encroachment as a definite form of land degradation. Encroachment may also be curtailed by resilience mechanisms found in protected ecological niches and by the resilience of the nutrient-poor sandy soils.