Michael E. Meadows

A record of rapid Holocene climate change preserved in hyrax middens from southwestern Africa

The discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central Namib Desert, Africa, is providing unprecedented insight into the region’s environmental history. High-resolution stable carbon and nitrogen isotope records spanning 0–11,700 cal (calibrated) yr B.P. indicate phases of relatively humid conditions from 8700–7500, 6900–6700, 5600–4900, and 4200–3500 cal yr B.P., with a period of marked aridity occurring from 3500 until ca. 300 cal yr B.P. Transitions between these phases appear to have occurred very rapidly, often within <200 years. Of particular importance are: (1) the observed relationship between regional aridifi cation and the decline in Northern Hemisphere insolation across the Holocene, and (2) the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing. Together, these elements call for a fundamental reexamination of the role of orbital forcing on tropical African systems, and a reconsideration of what factors drive climate change in the region. The quality and resolution of these data far surpass any other evidence available from the region, and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern Africa.

Desertification in the semi-arid Karoo, South Africa: review and reassessment*

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

Late Quaternary Palaeoenvironments of the southwestern Cape, South Africa: a regional synthesis

The contemporary uniqueness of the southwestern Cape environemnt suggests that its response to the environmental perturbations of the late Quaternary may have been correspondingly distinctive. Despite the wide variety of palaeoenvironmental evidence which has accumulated from within the region, a coherent picture of the evolution and development of its environments has remained elusive. Since the publication of several regional reviews over the last decade or so, a considerable body of palynological and other palaeoecological evidence has emerged which prompts a fresh synthesis as to the nature of late Quaternary environmental changes in the southwestern Cape’s fynbos biome. Although there are few sediments which date to the appropriate period, the last glacial maximum, in contrast to the situation evident in the summer rainfall region, is suggested to be a period characterised by considerably cooler and wetter conditions in certain parts of the biome. The first half of the Holocene appears to have been somewhat drier than much of the second half and the warmer temperatures of the Holocene hypsithermal are associated with reduced moisture availability. Intra-regional contrasts are evident in the response to late Quaternary environmental changes. Furthermore, it transpires that, for much of the later Quaternary and for large areas of the region, precipitation may have fluctuated out of phase with changes in the interior of the subcontinent, a situation which has great relevance to the prediction of future environmental changes and their impacts in the southwestern Cape.

Late glacial interhemispheric climate dynamics revealed in South African hyrax middens

Our ability to identify the timing and extent of past major climate fluctuations is central to understanding changes in the global climate system. Of the events that have occurred in recent geological time, the Younger Dryas (YD, 13–11.5 ka), an abrupt return to near-glacial conditions during the last glacial–interglacial transition (ca. 18–11.5 ka), is one of the most widely reported. While this event is apparent throughout the Northern Hemisphere ([Peteet, 1995][1]), evidence for its occurrence in the Southern Hemisphere remains equivocal due to a lack of well-dated terrestrial records. Here we report high-resolution stable carbon and nitrogen isotope records obtained from a rock hyrax midden, revealing the first unequivocal terrestrial manifestation of the YD from the southern African subtropics. These results provide key evidence for the relative influence of the YD, and suggest that a subtropical-temperate transition zone existed along the oceanic Subtropical Front (∼41°S) across the Southern Hemisphere, with the Northern Hemisphere exerting a strong influence on all but the higher latitudes of the Southern Hemisphere after the Heinrich Stadial 1 (15 ka). [1]: #ref-22

The nature, extent and causes of land degradation in South Africa: legacy of the past, lessons for the future?

The aim of this paper is to reassess the land degradation and desertification problem in South Africa. The country has a wide range of interrelated environmental and development challenges existing in a socio-political context recently subject to substantial change. The paper outlines the fundamental environmental constraints and opportunities that underlie degradation phenomena and illustrates the nature, extent and geographical distribution of the major forms of soil and vegetation degradation in the country. The principal causes of degradation are identified and some important land use and land tenure questions that need to be addressed in the near future are posited.

Land degradation and climate change in South Africa

This paper considers the potential impact of future climate change on the nature and extent of land degradation in South Africa. The basis of the assessment is the comprehensive review published by the Department of Environmental Affairs and Tourism (DEA&T) as a contribution to the South African effort in respect of the United Nations Convention to Combat Desertification. The DEA&T report is founded on information collated from 34 workshops, one in each of the agricultural regions of South Africa, involving some 453 participants consisting mainly of agricultural extension officers and soil conservation technicians. This analysis reveals that land degradation is underpinned by poverty and its structural roots in colonial and apartheid political planning. Nevertheless, future climate change represents a key challenge to the developing economies of countries like South Africa. Regionally downscaled models predicting the nature and degree of rainfall changes in the future are used to assess the possible impact of future change on the South African land degradation situation. It is concluded that the most severely degraded areas of the country, including large areas of the former ‘homeland’ states, are likely to become even more susceptible under predicted climate change scenarios.

Soil erosion in the Swartland, Western Cape Province, South Africa: implications of past and present policy and practice

Abstract The Western Cape Province of South Africa has a long history of human occupation and utilisation; the impact of colonial settlement (late 17th century onwards) on agriculture has been especially prominent. The Mediterranean-type climate of the Western Cape results in landscapes which are potentially susceptible to land degradation, perhaps even desertification. The Swartland is a gently undulating inland plateau underlain largely by fine-grained and nutrient-rich shales of the pre-Cambrian Malmesbury group. Agriculture is the dominant land use to the extent of wholesale landscape transformation. The area has been subject to significant levels of land degradation in the past, manifesting itself as widespread gully erosion. During the 1940s, the region was described as on the verge of economic collapse due to the severity of soil erosion, but concerted soil conservation and education efforts under the political dispensation of the time appear to have averted that scenario. The region now faces the combined challenges of potentially rapid climate change under a considerably altered socio-economic and political order. Downscaled climate change scenarios facilitate a regional assessment of changes in the parameters affecting soil erosion susceptibility in the Swartland and leads to a consideration of the implications of such scenarios for the continuation of contemporary land use practices.

Late Holocene environments at verlorenvlei, Western Cape Province, South Africa

Abstract Evidence on late Quaternary palaeoenvironments of the western and southwestern Cape of South Africa has facilitated detailed reconstructions mainly for the mountains, where organic sediment accumulation has been favoured by relatively humid climates. On the lowlands, particularly those of the west coast region, the search for sites traditionally regarded as suitable for the accumulation of sediments containing preserved fossil pollen has commenced only more recently. This area of the Western Cape Province has, however, provided Quaternary scientists with a rich archaeological record that has yet to be tested against independent lines of palaeoecological evidence. A sequence of sediments which have accumulated in what is today a large freshwater coastal lake, Verlorenvlei, has been sampled at Grootdrift, 15 km inland of the coast. A series of seven sediment cores was extracted during 1991 and three of these have now been sub-sampled, radiocarbon dated and subjected to a range of palaeoenvironmental techniques, in particular pollen analysis, sedimentology and geochemistry. Three pollen diagrams are presented which reveal the vegetation history of both the immediate Grootdrift environment and the wider catchment during several periods over the last 5500 years. A mid-Holocene higher sea-level is evident in two of the cores which were examined for pollen throughout their length. The surrounding area appears at this time to have been somewhat more arid than today. Following a hiatus in sedimentation some time after 4300 BP, the marine conditions at the site disappear and are replaced by fresh water as the dominant hydrological and ecological influence. Around the time of colonial occupation of the region, some 300 years ago, lacustrine conditions prevailed at Grootdrift and greater moisture availability is indicated in the catchment. During the last 300 years, the picture revealed by high resolution palynology of the third core is one of progressive levels of human disturbance both in and around the Verlorenvlei. Evidence from a textural and geochemical analysis of the sediments is consistent with the interpretation based on fossil pollen. The implications of this information are examined against the archaeology and palaeoecology of several cave sites in the vicinity of the vlei. The consistency apparent in the range of types of evidence suggests that some reliance can be placed on the mid-late Holocene palaeoenvironmental reconstruction at Verlorenvlei. The paper thus provides insight into the nature of the complex interactions between late Holocene climate change, sea-level fluctuation, vegetation change, vlei hydrology and human activity in the Western Cape coastal region.

The history of mediterranean-type environments: climate, culture and landscape

This editorial introduction highlights four of the principal themes in late-Quaternary research on summer-dry, mediterranean-type environments: first, issues of historical biogeography, such as convergent evolution; second, the synchroneity of past climate change between and within different regions; third, how far mediterranean-type environments represent cultural constructs or pristine habitats; and, fourth, the environmental future of mediterranean-type regions - for example, whether past records can help inform our understanding of how their distinctive biotas and often fragile landscapes will respond to predicted climate change. These issues are illustrated from three of the worlds five mediterranean-type regions: the Western Cape Region of South Africa. South and Western Australia, and the Mediterranean Basin.

Holocene vegetation history and palaeoenvironments at Klaarfontein Springs, Western Cape, South Africa:

Several sedimenit cores ai-ounid the coastal lake of Verlorenvlei, Westem Cape, have thus far revealed important details of the development of this semi-arid winter-rainfall environment during the late Quatemary. Complex interplay between climate change, sea-level fluctuation and human activities have characterized the Verlorenvlei record and suggests that these environments have been subject to high degrees of disturbance over time. However, due to the discontiniuous nature of the sedimentary record, the Holocene record has remained fragmentary. Investigation of a 6 in vibracore sequence at Klaarfontein (32δ25′26″S; 18δ29′40″E). an artesian spring site some 18 km inland of Elands Bay. facilitates a more complete Holocene palaeoenivironmental reconstruction. Pollen concentrations in 37 spectra distributed through the 6 m core vary with organic content, but at all depths are stufficient to facilitate interpretation of vegetation history and reveal a high degree of dynamism in the local and regional environments. The lower sediments are characterized by elements strongly indicative of more xeric conditions and the catchment appears to have been dominated by drought-resisting woody shrubs. Local vegetation in the mid-Holocene is consistent with the occurrence of two sealevel transgressions resulting in each case in the development of a salt marsh at the site. The uppermost pollen spectra are all relatively modern (post 200 BP). Grass pollen declines from 1900 BP, possibly as a result of the occupation of the area by pastoralists, although climate change cannot be ruled out. A decline in pollen diversity towards the surface is associated with a further reduction in grass pollen and ani increase in the proportion of succulents, hence offerinig support for the hypothesis of significant colonial and post-colonial disturbance of the vegetation. The evaluation of the pollen sequence at Klaarfontein supports previous palaeoenvironmental reconstructions and at once reveals new insights regarding the complex Holocene limnology, hydrology and geomorphology of the Verlorenvlei system.