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Changing biomes in South Africa


Increasing temperatures and changing precipitation patterns may deplete species-rich areas in e.g. South Africa. Predictions of the effects of climate change on natural ecosystems in South Africa, over the medium to long term, have included reduced spatial extent of the Grassland biome (Ellery et al. 1991), an increase in the extent of the Desert biome (Macdonald & Midgley 1996), and the occurrence of novel plant communities (Rutherford et al. 1995). The reduction of Grassland biome area may occur as present limits to tree distributions in grassland areas (minimum temperature and fire effects) are relaxed, and trees invade and thicken (Ellery et al. 1991, Midgley et al. 1998).

A recent analysis (Rutherford et al. 1999) based on climatic factors which limit biome distribution, has shown how increasing aridity in the Northern Cape may expose vegetation to stresses not yet experienced by the country’s biomes, thus creating a novel climatic environment. Their findings cast doubt on the potential ability of the current reserve network to retain current plant species richness levels (Rutherford et al. 1999), and have shown that the Augrabies Falls National Park in the Northern Cape stands to lose over a third of its plant species, with little chance of significant species immigration. The Cape Floral Kingdom (fynbos), which occupies only 37,000 km2 at the southern tip of Africa has 7,300 plant species, of which 68% occur nowhere else in the world (Gibbs, 1987). The adjacent Succulent Karoo biome contains an additional 4,000 species, of which 2,500 are endemic (Cowling et al.,1998). These floristic biodiversity hotspots both occur in winter rainfall regions at the southern tip of the continent and are threatened particularly by a shift in rainfall seasonality (for instance, a reduction in winter rainfall amounts or an increase in summer rainfall, which would alter the fire regime that is critical to regeneration in the fynbos).