5 - Historical background of invasions in the mediterranean region of southern Africa

Summary

The area of mediterranean-type climate sensu stricto at the south–western tip of the African continent is restricted and is centred on Cape Town (Aschmann, 1973). Northwards along the western coast and inland from Cape Town, precipitation decreases sharply over the ranges of the Cape fold mountains. Eastwards towards Port Elizabeth rainfall tends to be bi-seasonal with equinoxial maxima and thus the climate is not strictly mediterranean, although there may be a deficit in summer precipitation.

The physiographic character of the region has a pronounced effect on precipitation, with both the width of the coastal platform and the strike of the bordering ranges of the mountains being of particular importance. It is noteworthy that the syntaxis of the north–south and east–west trending ranges is the Cape Town–Caledon mediterranean-type climate area which has the highest terrain diversity and is the most prominent centre of species richness (Deacon, 1983a).

The Capensis floral region as defined by Taylor (1978) corresponds to the Cape fold mountains and the attendant coastal platform. Typical montane and coastal fynbos vegetation is associated with quartz arenite substrates that are poor in bases. Afromontane forest inliers occur in restricted favourable localities on equally nutrient-poor substrates whilst renosterveld shrublands and thicket are found on more base-rich substrates. Phytogeographers have been impressed by the complexity of the vegetation associations in the Capensis region, in their distributions, diversity and the degree of endemism found.