Effects of rainfall variability and communal and semi-commercial grazing on land cover in southern African rangelands

摘要

ABSTRACT: Semi-arid ecosystems in southern Africa are experiencing change due to natural variability in rainfall and to changes in the type and intensity of land use. This paper applies grazing gradient techniques to vegetation cover dynamics in areas of communal and semi-commercial grazing in the Kalahari rangelands of Botswana to see whether human impact can be separated from that of climate variability. Landsat Thematic Mapper and Multispectral Scanner data were acquired for the Gumare and Hainaveld areas for a number of wet and dry seasons. Vegetation cover was mapped using the PD54 vegetation index. Gradients in both vegetation cover and vegetation response to rainfall were identified under communal use, suggesting both human impact and human-induced degradation. However, patterns were complex because of multiple focal points in the hinterland of larger settlements. Gradients in vegetation response were more effective than gradients in cover as identifiers of human impact in semi-commercial grazing areas. These gradients intensify in dry periods but vegetation partially recovers after good rains. Over time, however, the gradients are intensifying, suggesting that long-term grazing impact is occurring. As gradients intensify and degradation increases, vulnerability of grazing systems to rainfall variability and to drought is likely to intensify.