干旱区生态环境知识资源中心

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.