Environmental History and the Desertification of the Karoo, South Africa

Abstract

This paper reviews the desertification debate in South Africa and emphasizes the methods that have been used to understand the environmental history of the semi–arid rangelands in the eastern Karoo during the last 500 years. These mixed grass/dwarf shrub rangelands, with mean annual rainfall totals typically between 300–400 mm, are described and the main driving variables discussed. A brief historical account of the European settlement of the region is also presented. The desertification debate has focussed on three main issues. Firstly, because arid and semi–arid lands appear to be heavily influenced by climate, the changing climatic regime during the Holocene and particularly during the last two hundred years has been the subject of intensive investigation. While all studies conclude that there is no evidence in the historical record to support the popular perception that rainfall totals have decreased this century, the question of changing rainfall seasonality has not been adequately explored. Although mean annual temperatures over the last 50 years have not changed there have been significant increases in mean monthly maximum temperatures and significant decreases in mean monthly minimum temperatures for some of the stations investigated. The second issue of great interest in the South African desertification literature is that of the nature of pre–colonial environments. A wide variety of archaeological, historical and ecological techniques have been used, including analyses of fossil mammal bones in owl pellets, fossil pollen in hyrax middens, notes from traveller's accounts of the region and stable carbon isotopes in soil as well as fossil mammal bones. While all authors agree that the eastern Karoo was more grassy at some stage in the past there is disagreement as to both the timing and cause of the changes to a more shrubby vegetation. The final issue of great concern to the desertification debate in South Africa concerns the rate of change during the last 100 years. Satellite imagery, matched ground and aerial photography, survey data and an analysis of historical stock records cannot agree as to whether the Karoo is degrading or not. Certainly, the classic view of an annually expanding desert margin has been replaced in recent years by a more realistic understanding of the seasonal dynamics of the vegetation. The recent trend to detailed modelling of the demographic process in key species holds much promise for our understanding of the degradation process. The vibrant community of researchers, employing a range of archaeological, historical and ecological techniques, will make important contributions to South Africa's National Action Plan to Combat Desertification.

Key Words:

• Environmental history
• Desertification
• Karoo
• South Africa