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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

571: Southern Kalahari

Major Habitat Type:

xeric freshwaters and endorheic (closed) basins

Author:

Liz Day, The Freshwater Consulting Group, Cape Town, South Africa

Reviewers:

Paul Skelton, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa

Countries:

Botswana; Namibia; South Africa

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). 

Main rivers or other water bodies:

In the north an ancient watershed, the Bakalahari Schwelle, forms the divide between the Okwa River in the north and the Nossob and Molopo rivers in the south (Parris 1984). The Nossob is joined by the Auob River in its southerly reaches, and flows from here in a southeasterly direction from Namibia. It joins the Molopo River on the South African / Botswana border near Ashkam. Historically, the Molopo would flow into the Orange River, upstream of Augrabies Falls; however, the link-up between Molopo and Orange River is not functional at present due to dune blockage (Moore 1999).

Two particularly important pans included in this ecoregion are the Hakskeenpan complex and Barberspan, both in the Northern Cape Province of South Africa. Unlike most of the pans, Barberspan is a permanent, shallow water body, fed by the natural diversion of the Harts River into Barberspan’s fossil channel. The Hakskeenpan complex is one of four extensive pan systems in southern Africa, namely: Etosha, Makgadikgadi, Hakskeenpan and the Grootvloer-Verneukpan system (Lloyd & Le Roux 1985). 

Climate:

The climate within the Southern Kalahari ecoregion is semi-arid (Van Rooyen 1984). Temperatures fluctuate greatly, on both a seasonal and a daily basis, with mean January and July maximum and minimum temperatures of 35.7°C and 19.5°C, and 22.2°C and 1.2°C, respectively. Rainfall is unreliable and irregular, falling primarily during short-duration, high-intensity thunderstorms between November and April. Before the rainy season begins, strong northwesterly winds blow between September and November, producing dust storms. Mean annual precipitation varies from approximately 223 mm in the south, increasing gradually in the north to the order of 250 mm. Humidity is low, and evaporation high (Parris 1984), the latter resulting in the characteristic large deficit in the annual water budget (Van Rooyen 1984).

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. 

Fish Fauna:

As well as its ephemeral rivers, this ecoregion also contains some of the largest concentrations of pans in southern Africa (Lancaster 1989). Water availability in the Southern Kalahari is, however, severely limited (Barnes & Anderson 1998) and species richness as a whole is low in the ecoregion, with no endemic obligate-aquatic fauna believed to occur here - fish species, for example, tend to be hardy species or relicts (Skelton 1993). 

Only a few widespread species of fish are known to frequent the intermittent waterways of the Southern Kalahari. The southern mouthbrooder (Pseudocrenilabrus philander) lives in a few permanent and isolated springs and sinkholes in this ecoregion (e.g. Kuruman Eye, Wondergat sinkhole). During rare flood events the sharptooth catfish (Clarias gariepinus) washes down the rivers from farm dams in their upper catchments and forms a briefly abundant food resource to human and animal populations (Haacke 1984). The presence of an accessory air-breathing organ enables this species to breathe air and survive in extreme conditions (Bruton 1979).

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.

Other noteworthy aquatic biotic elements:

The amphibian fauna are limited to hardy, opportunistic species, able to breed at virtually any time of year when water is available, and to aestivate, often over long periods of time (Harrison et al. 2001). Species of giant bullfrog (Pyxicephalus spp.), for example, aestivate through the dry season in holes in the ground. Buried, they are protected from desiccation by a waxy cuticle, formed from mucus and layers of shed skin. In addition, the frogs store water in bladder-like outgrowths of their digestive tract, while their metabolic rate drops to less than one quarter of its normal resting level (Lovegrove 1993).

Both the pans and ephemeral rivers of the southern Kalahari form focal points for the large herbivores of the ecoregion, providing minerals to animals throughout the year and water during the rainy season (Barnes & Anderson 1998). The pans are also used by the Kalahari fauna variously for burrowing, grazing, saltlicks, and seasonal waterholes (Parris 1984). In addition, the trees associated with the riverbeds provide locally rare nesting and roosting habitat to birds. In the Kalahari Gemsbok National Park these birds include globally and nationally threatened raptors (Cape vulture (Gyps coprotheres) and whiteheaded vulture (Trigonoceps occipitalis); and the whitebacked vulture (Gyps africanus)and lappet-faced vulture (Torgos tracheliotus), respectively) (Barnes & Anderson 1998). 

Within a region where open water bodies are scarce, Barberspan is vitally important for regionally nomadic waterfowl and as a stopover site for Palearctic migrant waders (Barnes 1998). Waterbirds congregate here in numbers exceeding 20,000 individuals during the dry season (May – October), when the smaller wetlands in the surrounding area have dried up (Barnes et al. 2001). Most of these birds disperse with the rainy season, moving to the temporary pans to breed. Depth of water in the pan is a critical determinant of the species utilizing the pan at any one time. When water levels are low, waders such as ruff (Philomachus pugnax), lesser flamingoes (Phoenicopterus minor) and greater flamingoes (P. ruber) are usually present, with greatest abundance during dry years. In wet years, inundated grassland along the shoreline provides nesting habitat for herons, egrets and great crested grebes (Podiceps cristatus) (Barnes 1998). As well as being of international importance in terms of its bird habitats, Barberspan is also an example of a rare grass pan (Barnes 1998). 

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.

References/sources:

Barnes, K. N. (1998)"Important Bird Areas of the North-west Province" In Barnes, K.N. (Ed.). The Important Bird Areas of southern Africa. (pp. 93-101) Johannesburg, South Africa: BirdLife International.

Barnes, K. N., Johnson, D. J., et al. (2001)"South Africa" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 793-876) Newbury and Cambridge, UK: Pisces Publications and BirdLife International (Birdlife Conservation Series No. 11).

Barnes, K. N.,Anderson, M. D. (1998)"Important Bird Areas of the Northern Cape" In Barnes, K.N. (Ed.). The important bird areas of southern Africa. (pp. 103-122) Johannesburg, South Africa: BirdLife International.

Bruton, M. N. (1979). "The survival of habitat desiccation by air breathing clariid catfishes" Environmental Biology of Fishes 4 273-280.

Haacke, W. (1984). "The herpetology of the southern Kalahari domain" Supplement to Koedoe 1984 171-186.

Harrison, J., Burger, M., et al. (2001) "Conservation assessment and management plan for southern African frogs. First Draft. January 2001. Southern African Frog Atlas Project". Cape Town, South Africa. Avian Demographic Unit, University of Cape Town.

Lancaster, N. (1989). "Late quaternary palaeoenvironments in the southwestern Kalahari" Palaeogeography, Palaeoclimatology, Palaeoecology 70 367-376.

Lloyd, J. W.,Le Roux, A. (1985) "A conservation assessment of the Verneukpan-Copperton area". Cape Town, South Africa. Department of Nature and Environmental conservation.

Lloyd, J. W.,Le Roux, A. (1985) "A conservation assessment of the Verneukpan-Copperton area". Cape Town, South Africa. Department of Nature and Environmental conservation.

Lovegrove, B. (1993). "The living deserts of Southern Africa" Vlaeberg, South Africa: Fernwood Press.

Malherbe, S. (1984). "The geology of the Kalahari Gemsbok National Park" Supplement to Koedoe 1984 33-44.

Moore, A. E. (1999). "A reappraisal of epeirogenic flexure axes in southern Africa" South African Journal of Geology 102 363-376.

Noble, R. G.,Hemens, J. (1978) "Inland water ecosystems in South Africa: A review of research needs. South African National Scientific Programmes Report No. 34". Pretoria, South Africa. CSIR.

Parris, R. (1984). "Pans, rivers and artificial waterholes in the protected areas of the south-western Kalahari" Supplement to Koedoe 1984 63-82.

Skelton, P. H. (1993) A complete guide to the freshwater fishes of Southern Africa. South Africa: Southern Book Publishers, Halfway House.

Skelton, P. H., Cambray, J. A., et al. (1995). "Patterns of distribution and conservation status of freshwater fishes in South Africa" South African Journal of Zoology 30(3) 71-81.

Van Rooyen, T. (1984). "The soils of the Kalahari Gemsbok National Park" Supplement to Koedoe 1984 45-61.

Van Wyk, P.,Le Riche, E. (1984). "The Kalahari Gemsbok National Park: 1931-1981" Supplement to Koedoe 1984 21-31.

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