This BioProvince (as defined by Armen Takhtajan) includes the Great Karoo (or Nama Karoo) east of the Western Cape BioProvince in South Africa and lying at the centre of the South African plateau (or meseta). It also extends over the Orange River into Namibia in the northwest. The Great Escarpment, which runs parallel to the coast 100 km to 200 km inland divides it into two parts: one between 550 m to 900 m in elevation, the other between 900 and 1300 m. The climate is harsh. Droughts are common and there are considerable seasonal and daily temperatures fluctuates. Temperature extremes range from -5°C in winter to 43°C in summer and variations of up to 25°C between day and night are common. Rainfall is highly seasonal, peaking between December and March with an annual range of 100-500 mm. This is a summer rainfall area whereas the succulent karoo receives most of its rainfall in winter. Shallow, weakly developed lime-rich soils cover much of the region which is largely underlain by sediments of the Dwyka Formation. Dolerite dykes and sills being more resistant to weathering than the surrounding sandstones and shales produce to flat-topped hills (mesas) typical of the Karoo terrain. These were formed over a time span ranging from the Carboniferous period (some 345 million years ago) to the Jurassic period (some 141 million years ago). Examples include the Falminkskop, Buffelskop and Talfelberg meses in the northeastern areas. The vegetation on parts of these meses has remained largely free of domestic grazing and can be regarded as near natural. Other landscape features include koppies (buttes) and dongas (erosion trenches). Most of the regional drainage is through the Orange River Basin but many of the associated river systems are seasonal. Nevertheless, the Fish River canyon is second in size only to the Grand Canyon of America with a depth of 550 m in places. The Fish River normally only flows in the wet season, but residual pools remain throughout the year. One of the most comprehensive accounts of the vegetation describes the vegetation in terms of veld types. These are defined as units of vegetation whose range of variation is sufficiently small to have the same farming potential. Little of the remaining karoo vegetation is thought to be in its original condition but some veld types (described as false veld) have been radically altered by grazing pressure. In the case of false arid karoo, for example, it probably would have been something like grass-veld until excessive grazing eliminated all the palatable species allowing arid karoo species to either invade or become more conspicuous. Some of these areas are now little different from natural arid karoo.
The following accounts for this BioProvince have been written or will be written with particular reference to endemic and locally important species. Accounts available are displayed in green or yellow. Those displayed in red are either in the pipeline or awaiting expert contributions.
|Vascular Plant Flora|