Boundaries

Intermittent rivers and scattered seasonal pans occur in the arid landscape of this ecoregion, covered nearly in its entirety by a mantle of sand between 3.5 and 35 m thick (Parris 1984; Van Wyk & Le Riche 1984; Skelton 1993). Spanning the northern border of the Northern Cape Province in South Africa, and parts of southern Botswana and Namibia, the Southern Kalahari ecoregion includes the Kalahari Gemsbok National Park (South Africa) and the adjacent Gemsbok National Park (Botswana). 

Freshwater habitats

River water tends to be alkaline and turbid, but the rivers flow only briefly after rainfall and rapid infiltration into the sandy Kalahari soil means that floods, although they do at times occur, are rare, and river flow ceases quickly (Parris 1984; Skelton 1993). Indeed, flood discharges from the Auob and Nossob rivers only reach the Molopo system after periods of exceptional rainfall (e.g. 1933, 1974) (Lancaster 1989). The pans within this area tend to be endorheic. Calc-pans, the most common form of pans, are underlain by lime with varying quantities of clay, and retain standing water for short periods of time. Other kinds of pans include rarer rock pans, dune pans, and salt pans.

The rivers of this ecoregion, referred to as fossil rivers (Parris 1984), are relicts of a wetter epoch during the early Quaternary (Lancaster 1989). Although their vertical erosion was stopped by the onset of desert conditions, their present-day geomorphology reflects this wetter past. The Nossob River, for example, once received enough water to flow as a mature river, with meanders and oxbow lake formations, while vertical erosion led to the formation of terraces (Malherbe 1984). Similarly, the proliferation of pans in this area also reflects a history of climatic change. As flow in rivers such as the Nossob decreased, the river was no longer able to erode wind-deposited sand fast enough, with the result that minor tributaries dammed against the higher base level of the Nossob, and formed pans (Malherbe 1984). Other pans, further away from the riverbeds, were formed by deflation following periods of higher groundwater levels, and deepened by wind action and the effect of trampling by animals (Lancaster 1989). The only permanently inundated pan, Barberspan, is a relict ephemeral pan in the fossil bed of the Palaeo-Harts River (Barnes 1998). Earlier this century, the channel connecting this pan to the upper reaches of the Harts River was widened, changing the river into a perennial system (Noble & Hemens 1978). This has resulted in the wetland providing aquatic habitat to birds, amphibians, and invertebrate fauna throughout the year, and today Barberspan is noted as a refuge for waterbirds, including flamingoes (Noble & Hemens 1978). 

Terrestrial habitats

The Southern Kalahari landscape is dominated by a 100-200 km wide belt of linear dunes (Lancaster 1989). The terrestrial vegetation is largely Kalahari thornveld, comprising an extremely open shrub or tree savanna. Riparian plant communities are characterized by Acacia erioloba trees, while the pans support mainly a shrub veld of Rhigozum trichotomum and grasses (Van Rooyen 1984). During the dry season, vegetation in the pans tends to be short and sparse, and the soils dry and heavily trampled. 

Other noteworthy fishes

Accorded national monument status in 1992, the “eye of Kuruman” is a dolomite spring in which the southern mouthbrooder (Pseudocrenilabrus philander) has been found to breed.

Justification for delineation

This ecoregion is delineated based on the distribution of the relict river systems in the Kalahari that flowed into the Orange River basin. The few aquatic species retain affinities with both the southern temperate and Zambezian faunas (Skelton et al. 1995).

Level of taxonomic exploration

Poor. Hall-Martin (Hall-Martin 1984) recognised the dearth of existing knowledge on ecosystem processes in the Southern Kalahari. The role of the ephemeral rivers in the maintenance and functioning of the broader ecosystem, for example, is largely unknown (Parris 1984 corroborated by personal comments (LD) with Kalahari Gemsbok Park’s officials, 2001). Even basic species check-list information is limited for many taxonomic groups, with invertebrates being particularly poorly studied.