Boundaries

The Southern Temperate Highveld ecoregion is situated in the interior of South Africa, with the western boundary formed by the Magaliesberg, Pilanesberg and Waterberg mountain ranges, the northern boundary formed by the Soutpansberg, and the eastern boundary formed by the Drakensberg Mountains (O\'Hagan 1989; Duggan 1990).

Topography

The highveld forms a rolling, grassy plateau 900-1,900m above sea level and gradually slopes down to the coast in the southeastern Cape (Cooke 1964). About 70% of the highveld is comprised of fine sedimentary rocks with significant exposures of dolomite along the northern and western boundaries of some catchments. There is a variety of soil types and most streams originate over Karoo sediments, with some originating over the Witwatersrand system and still others as springs in dolomite (O\'Keeffe et al. 1989).

Freshwater habitats

The Orange River, the largest river system in Africa south of the Zambezi, has two major tributaries, the Caledon and the Vaal, whose basins fall within this ecoregion (Cambray et al. 1986). The Vaal River rises to the north of the Drakensberg Range and flows 900 km across the interior plateau to join the Orange River near Douglas, draining an area of 194,000 km². The catchment slopes gently from elevations on the order of 1,800 m above sea level in the east to about 1,200 m in the west, with some steep areas in the headwaters of the Wilge River, a Vaal tributary on the southeast border of the Upper Orange catchment. The Orange and Vaal rivers are typical of many South African rivers in that they carry very large sediment loads, especially during floods. Rapids and pools are common in the upper reaches before the gradient decreases and the river begins to flow over relatively flat, sandy streambeds with reeds (Kleynhans 1983). Increased flow rates and flooding in all the rivers of the Highveld usually occur during the spring and summer months (September to March) and all indigenous fish species breed during this period.

The ecoregion extends to the coast in the Eastern Cape where the coastal rivers may be divided into three types. The largest systems extend well inland and have tributary headwaters originating on the escarpment (the Gamtoos, Sundays, Great Fish and Kei River systems). The moderate-size rivers extend inland as far as mountains such as the Winterberg or Amatola ranges (Swartkops, Bushmans, Keiskamma, Buffalo and Kowie Rivers). Finally, there are small coastal rivers such as the Coega, Baakens, and Kasuka rivers (Skelton 1980). Riparian zone wetlands (oxbow lakes, pans, high altitude bogs) are unique to the midlands of the northeastern Cape (Forsyth et al. 1997).

Many ephemeral wind-blown pans, which are filled only during times of high summer rainfall (the Lake Chrissie pan complex, for example), dot the landscape of the Highveld (Allanson et al. 1990). Pans and other enclosed drainage basins are particular features of the western part of the ecoregion (Midgley et al. 1994).

Terrestrial habitats

The major vegetation type consists of open, undulating, hygrophilous (living or growing in moist places) Cymbopogon-Themeda grassland with Nama Karoo vegetation towards the west (Midgley et al. 1994; Carruthers 1997; Low & Rebelo 1998) and some bushveld to the north (Stuart et al. 1990; Low & Rebelo 1998). Frosts, fire and grazing maintain the grass dominance and prevent the establishment of trees. The Nama Karoo biome occurs on the central plateau of the western half of South Africa at altitudes between 500 m and 2,000 m, with the majority between 1,000 m and 1,400 m (Low & Rebelo 1998). Trees are mainly found in river valleys further east and in parts of the ecoregion with a high water table (Pritchard 1971). The Vaal River runs through a small part of Kalahari grassland/Acacia wooded steppe (Cooke 1964). The vegetation of mountain ranges like the Pilanesberg is rich floristically, with wiry, sour grassveld in the less rocky parts and a dense, mixed bushveld in the rugged parts (Brett 1989).

Description of endemic fishes

Kneria auriculata is restricted to altitudes between 1,100 m and 1,400 m above sea level and five relict populations are known from tributaries to the Crocodile River (Kleynhans 1986). Varicorhinus nelspruitensis is endemic to the upper Incomati and Pongola systems. Amphilius natalensis lives only in tributaries of the Incomati and Olifants rivers, between 900 and 1,300 m. The rare Incomati rock catlet, Chiloglanis bifurcus, is endemic to the Incomati system and is found only between 900 and 1,200 m. Aplocheilichthys katangae is found in tributaries of the Limpopo and is considered rare in the Transvaal (Kleynhans 1986).

Other noteworthy fishes

Globally threatened fish include the Treur River barb (Barbus treurensis, Upper Blyde River, very restricted distribution), the border barb (Barbus trevelyani, Buffalo and Keiskamma Rivers), the rock catfish (Austroglanis sclateri, Orange-Vaal system, original distribution much reduced), and the Eastern Province rocky (Sandelia bainsii, found in four rivers in the Eastern Cape).

Justification for delineation

The boundaries of this ecoregion follow the ‘Transvaal-Orange Free State’ sub-region of Skelton’s (1993) Highveld aquatic ecoregion(Skelton 1993). The fauna has mixed tropical and temperate affinities and shares many species with both the Limpopo and the Zambezi rivers (Skelton 1990; Skelton et al. 1995). Considerable exchange of the interior drainage (Orange River system) with that of the coastal systems must have occurred along the retreating escarpment (Skelton 1980).

Level of taxonomic exploration

Good. The level of biological and ecological investigation in this ecoregion is high and the threats to ecosystem integrity are known.