Biodiversity

Kalahari xeric savanna

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Aerial photo of Botswanan Kalahari xeric savanna. Source: C. Michael Hogan

The Kalahari xeric savanna is an ecoregion in southern Africa characterized by a harsh climate, where temperatures may vary by 44°C from night to day, and rainfall is infrequent. Rain appears only during the summer on the reddish-brown Kalahari sands , pelting the savanna with violent, localized storms. Although this area is semi-arid, there is an impressive diversity of migratory birds and large mammals, both herbivorous and carnivorous; in fact, 550 different vertebrates have been observed in the Kalahari xeric savanna. 

This ecoregion is classified within the Deserts and Xeric Shrublands biome. A considerable fraction (approximately 18 percent) of the Kalahari xeric savanna is protected. Where lands are not protected, overgrazing has often severely degraded habitat. Fences are a significant problem because they obstruct the migratory patterns of ungulates, and consequently they pose significant threats to biodiversity in unprotected areas.

Location and general depiction 

caption WWF The Kalahari xeric savanna ecoregion stretches across northwestern South Africa, southern Botswana and southeastern Namibia. Most of this ecoregion lies on the level plains of the Kalahari Basin, interrupted by long, somewhat parallel sand dunes in the south. The Kalahari sands themselves extend from the northern Cape in South Africa to the Democratic Republic of Congo, and there is no consensus regarding their origin of formation. The sands of this ecoregion vary in depth, and are underlain chiefly by calcrete; in fact, this calcrete occurrence is responsible for many of the aircraft landing strips in this remote region. 

In places, native rock below the sands harbors substantial mineral wealth, in the form of diamonds, copper, and coal. The Kalahari sands are generally nutrient poor. A thin layer of iron oxide induces a reddish-brown colour, although water leaching in areas of higher rainfall or near pans commonly causes the colour to fade.

Climate

caption Gemsbok (Oryx gazella), Gemsbok National Park, Namibia. Source: WWF-Canon/ Rick Weyerhaeuser There has been a long term hydrological change in this region, which began with the diversion of a major river flow through the Botswanan portion of the region initiated by a geological rift zone anomaly hundreds of thousands of years ago. This flow alteration eliminated one of the largest permanent lakes in all of Africa, and replaced that depression with a seasonal wetland, the Makgadikgadi Pans. This change affected not only the water table, but also the amount of evaporation and total humidity and precipitation of the region.

Diurnal temperature fluctuations in the Kalahari are extreme. In the southern part of the ecoregion, temperatures on winter nights can plummet to 1°C, while soaring to 30°C during the afternoon. Similarly, a cold summer night may drop to 2°C, whereas the daytime temperature may exceed 46°C. Even the rain, when it falls, arrives most frequently in violent but brief thunderstorms. Rainfall is also remarkably patchy, with great differences occurring between sites only a few kilometers distant. Average annual rainfall is highest in the northeast and lowest in the southwest, ranging between 150 and 500 millimeters. Inter-annual variability in rainfall increases from 25 percent in the east to 40 percent in the west. Latitude, high atmospheric pressure, and the barrier created by the Drakensberg Mountains between the Kalahari and the Indian Ocean are largely responsible for this climate. Topography and elevation are also influential, and although the Kalahari xeric savanna occurs at elevations between 600 meters (m) and 1600 m, most of it lies above 1000 m.

Vegetation

caption Sparse tree cover in the Botswanan xeric savanna.
Source: C.Michael Hogan

In less arid areas, the vegetation is open savanna with grasses (Schmidtia spp., Stipagrostis spp., Aristida spp., and Eragrostis spp.) interrupted by trees such as Camelthorn (Acacia erioloba), Grey camelthorn (A. haematoxylon), Shepherd's tree (Boscia albitrunca), False umbrella-thorn (A. luederitzii), Blackthorn (A. mellifera), and Silver cluster-leaf (Terminalia sericea). Shrubs include Velvet raisin (Grewia flava), Ziziphus spp., Camphor bush (Tarchonanthus camphoratus), Rhigozum spp., Acacia hebeclada, and Lycium spp. In the more arid sectors, large trees typically are found in ancient riverbeds, and the rolling red dunes are sparsely populated by smaller A. erioloba, A. haematoxylon, and B. albitrunca, as well as broom scrub such as Crotalaria spartioides and Dune reed (Stipagrostis amabilis). Creeping Watermelon (Citrullus lanatus), Gemsbok cucumber (Acanthosicyos naudinianus), and Wild cucumber (Cucumis africanus) are vital sources of water and food for both humans and animals.

Plant species richness per unit area in the Kalahari xeric savanna is among the lowest of all the southern African ecoregions, and it is estimated that less than three percent of the plants are endemic. Animal endemism is also low; there are no strictly endemic birds and only three near-endemic birds; furthermore, there is only one near-endemic amphibian, one strictly endemic reptile (Typhlosaurus gariepensis) with nine near-endemic reptiles, and a single near-endemic small mammal, Brants's whistling rat (Parotomys brantsii).

Fauna

caption Gemsbok (Oryx gazella), Kalahari Gemsbok National Park, South Africa. Source: WWF/ Martin Harvey

However, despite the low rates of endemism, the diversity of large mammals at all levels of the food chain is remarkable for such an oligotrophic and arid system. Some flora and fauna are almost synonymous with the region. These include the camelthorn tree, gemsbok (Oryx gazella), sociable weaver (Philetairus socius), and Kalahari lion (Panthera leo).

Mammals

caption Meerkats in the wild in early morning sunning, Kalahari Desert. @ C.Michael Hogan Although not a separate species, the Kalahari lion exhibits behavioral adaptations to surviving in this harsh environment. It lives in small prides, has an expansive home range and hunts smaller prey than lions of more mesic areas; however, large prey, particularly gemsbok, still represents the greatest biomass of food consumed. Its appearance is also different, being taller at the shoulder, slighter in body mass, and with many males exhibiting black manes. The Camelthorn is the sole common large tree in the region. It provides nesting and foraging sites, shade, food, and refuge for a gamut of plants and animals. The animals of the Kalahari xeric savanna evince a range of adaptations to the extremes of this arid ecoregion. Gemsbok are superbly physiologically adapted to the harsh climate and sparse forage.

Apart from the Kalahari lion, the ecoregion boasts an impressive array of other large predators, mainly in protected areas. These include the Cheetah (Acinonyx jubatus VU), Leopard (Panthera pardus), Spotted hyena (Crocuta crocuta LR) and Brown hyena (Hyaena brunnea LR), and Painted hunting dog (Lycaon pictus EN). The representation of smaller vertebrate predators is also remarkable. Among the mammals are the Aardwolf (Proteles cristata), Caracal (Felis caracal), Black-backed jackal (Canis mesomelas), Honey badger (Mellivora capensis), African wildcat (Felis lybica), Black-footed cat (Felis nigripes), Striped polecat (Ictonyx striatus), Small-spotted genet (Genetta genetta), Bat-eared fox and Cape fox (Otocyon megalotis, Vulpes chama), as well as Meerkat (Suricata suricatta) and three species of mongoose: Banded (Mungos mungo), Slender (Herpestes sanguinea), and Yellow (Cynictis penicillata).

Although the Cheetah is the swiftest land predator (capable of reaching speeds of 100 km per hour), its slight build and timid disposition make it subordinate to other carnivores, and it is often robbed of its prey. To avoid this, the cheetah usually hunts during the day, when most of its competitors are inactive. Its main prey are springbok (Antidorcas marsupialis  LR), although when game is scarce, it will also hunt young or weak Hartebeest (Alcelaphus buselaphus  LR), Gemsbok, and Blue Wildebeest (Connochaetes taurinus  LR), as well as Duiker (Sylvicapra grimmia) and Springhare (Pedetes capensis), among others. When antelope numbers are low, Porcupine (Hystrix africaeaustralis) figures prominently in the diet of the Kalahari lion. Numerically, they can represent as much as 32 percent of the annual kill. The porcupine's sharp quills make hunting them hazardous. If the quills cannot be removed from the skin, they can cause severe, and even fatal, infections. In times of scarcity, however, porcupines offer a high fat meal on a limited menu. Kalahari ungulates have evolved reproductive strategies that minimize the risk of predation on the young. Females of wildebeest and springbok herds give birth within a week or two each other. Because the young are very vulnerable for only about the first month of their lives, and most predators are territorial. Thus limited in numbers, eating only until satiated, the chances of survival for each calf or lamb are much greater if births are synchronous than if staggered.

Birdlife

The massive communal nests of the Sociable weaver (up to six metres long and two metres high, weighing as much as 1000 kilograms, and housing up to 300 birds) are so well insulated that they substantially buffer the temperature extremes of the outside air.

Raptors include the Secretary bird (Sagittarius serpentarius), various eagles including the Martial eagle (Polemaetus bellicosus), a gamut of owls, including Giant eagle owl (Bubo lacteus) and an array of falcons, goshawks, kestrels and kites.

Reptiles

caption Namaqua chameleon @ Matt Muir/ iNaturalist Among reptilian predators are the boomslang (Dispholidus typus typus), Cape cobra (Naja nivea), Puff adder (Bitis arietans), and Rock monitor (Varanus exanthematicus albigularis), as well as geckos, lizards, and skinks. As in many arid areas. Other snakes found in the ecoregion are the Angola garter snake (Elapsoidea semiannulata), the Angola python (Python anchietae), the Black-necked spitting cobra (Naja nigricollis) and the Black mamba (Dendroaspis polylepis). Lizards found here include: Karoo girdled lizard (Cordylus polyzonus); African striped mabuya (Trachylepis striata); Anchieta's agama (Agama anchietae); and Blunt-tailed Worm Lizard (Dalophia pistillum). Geckos found here include the Bibron's thick-toed gecko (Chondrodactylus bibronii). The Namaqua chameleon (Chamaeleo namaquensis) is a representative chameleon found in the Kalahari xeric savanna.

Amphibians

As in most arid ecoregions, the  amphibian fauna is not particularly species-rich in the Kalahari, but does include the Giant bullfrog (Pyxicephalus adspersus) that has a omnivorous diet, preying on small birds, rodents, reptiles, and insects. Other anuranAn amphibian that has limbs but no tail (includes all frogs and toads) taxa present here are the African clawed frog (Xenopus laevis); African ornate frog (Hildebrandtia ornata); Boettger's dainty frog (Cacosternum boettgeri); Red-spotted Namibia frog (Phrynomantis annectens); Mababe river frog (Phrynobatrachus mababiensis); Cryptic sand-frog (Tomopterna cryptotis); Kimberley toad (Amietophrynus poweri); Guttural toad (Amietophrynus gutturalis); Knocking sand-frog (Tomopterna krugerensis);

Arthropods

A backbone of the ecoregion are the billions of brine shrimp, which come to life in the Pans with arrival of the seasonal rains. These crustaceans are the fundamental food source for hundreds of thousands of migratory waterfowl, notably flamingos. A number of scorpion species also inhabit the ecoregion, of which the two most important families are the Scorpionidae and Buthidae. Both prey predominantly on insects, and species of the latter often prey on the less venomous members of the former.

Geology

Millions of years ago one of the largest rivers of Africa collected the Zambezi and other rivers rising in the north, flowing through this region of the Kalahari. Geologic uplift around 800,000 years ago blocked this flow from reaching the Orange and Limpopo basins, forming an enormous prehistoric lake at Makgadikgadi. Subsequently tectonic uplift in the extreme north of Botswana diverted the Zambezi and greatly restricted inflow to the Makgadikgadi area; as a result the Makgadikadi Pans are presently strictly a seasonal wetland with the Okavango alluvial fan to the north receiving the residual flow from historic drainages; however the summer wet season finds the Boteti River delivering copious flows here, producing a miracle of emergence of vegetation and wildlife amid the Kalihari Desert. Today's annual flow reaching the Makgadikgadi is less than two percent of the Pleistocene level.

Prehistory

This ecoregion is part of the earliest evolution of man, where significant advances in stone tool technology developed prior to migration northward. Recovery of Early Stone Age tools at the Makgadikgadi shores and lakebed reveals vestiges of prehistoric habitation by Homo sapiens and Homo habilis. Late Stone Age tools are also present, representing more refined designs of recent man. Field reconnaissance in the dry lakebeds (Hogan. 2008) yielded further surficial specimens of early stone tools and later projectile points. Late Stone Age man would have lived here in huts made of sticks and grass in nomadic groups of 15 to 60 individuals .The women would have concentrated on gathering fruits and nuts, while men created snares of twine to catch springhares emerging from their burrows. Springbok and Eland were hunted by spear and arrow, as the Later Stone Age tools had become more sophisticated.

Current status

caption Learning the ways of the San bushmen
Source: C.Michael Hogan
Approximately 18 percent of the ecoregion falls within protected areas, the largest being the Central Kalahari (although not all of this reserve is within the ecoregion) and adjoining Khutse Game Reserves in Botswana. Together they cover 77,800 square kilometers (km2). The Kgalagadi Transfrontier Park (KTP), Africa's first Peace Park, was recently proclaimed and is also large, at 34,390 km2. The KTP is the official union of the former Kalahari Gemsbok National Park (South Africa) and the Gembsok National Park (Botswana). Fortunately, game have always been able to move freely between the two countries, but the establishment of the Peace Park opens the possibility of tourists having the same freedom of movement. Common strategies for both conservation management and tourism development will also be shared across the border.

Types and severity of threats

Fences (farm, veterinary and border) are primarily responsible for the precipitous decline in wild animal populations in the Kalahari since the 1960s. Construction of veterinary fences began in 1954, but continues today. Animals like the blue wildebeest and hartebeest, not truly adapted to aridity, must migrate to obtain food and water. In the urge to migrate, some animals become caught in the fences, while others suffer slow and painful deaths through thirst and starvation. After mining, the cattle industry is Botswana's second largest revenue earner. Botswana's agreement with the European Union in terms of Lomé Convention concessions means it is paid up to 60 percent more for beef than its competitors in the open market, and receives 92 percent of imposed import tariffs back as subsidies. These incentives have encouraged the increase in Botswana's national herd to more than three million animals, twice the number of the human population. The EU's strict import regulations are behind the construction of veterinary fences, through the requirement that cattle be isolated from game, in spite of the fact that conclusive proof that foot-and-mouth disease originates in buffalo or Blue wildebeest is still lacking. Moreover, it is open to question whether the benefit distribution is equitable, because along with cattle smallholders, large-scale farmers and middlemen also profit from the protocol. In some ways, however, the fences may be beneficial to wildlife, in that they also serve to exclude cattle from wildlife areas and reduce conflict with humans. The Botswana government has also shown itself willing to make some concessions. In 1998, it pledged to realign and roll back some fences in the north of the country.

As in other areas where migratory patterns have been disrupted in favor of fences and livestock farming, the change in grazing practices has lead to habitat degradation through alteration of the natural grazing patterns. Thus, although the habitat of the Kalahari Xeric Savanna is not highly fragmented, much has been degraded by heavy livestock grazing. Heavy grazing results in an increase in woody plants and a decrease in grass cover, a phenomenon known as bush encroachment. Not only does this reduce rangeland carrying capacity, but the change in vegetation structure and plant communities also has repercussions for the native fauna. For example, a number of bird species, some of which are listed in the South African Red Data Book, are seriously affected by habitat alteration associated with heavy grazing (e.g. raptors and the Kori bustard). Interestingly, wetland and migratory birds appear indifferent to habitat change brought about by heavy grazing. Attempts to deal with bush encroachment through the application of arboricides leads to further habitat degradation.

Livestock farmers often use poisoned carcasses to kill "problem" animals such as Black-backed jackal (Canis mesomelas) and Caracal (Felis caracal), resulting in the poisoning of nontarget raptors. Some species, like the Martial and Black (Aquila verreauxii) eagles, perceived to prey on domestic livestock and poultry, may be intentionally targeted. Drownings in farm reservoirs are also responsible for a significant number of raptor mortalities in the ecoregion. In South Africa, simple and effective solutions to the problem of reservoir drownings are currently being promoted. Livestock farmers sometimes shoot other predators that wander onto their land, as various cases of lion, Painted hunting dog, and Hyena shootings have illustrated.

The Painted hunting dog is probably the species of most concern in the Xeric Kalahari savanna, listed in the global IUCN and South African Red Data Book as endangered, due to eradication of their prey and shooting by farmers. Efforts to conserve this species are hindered by their large home ranges and tendency to roam vast areas. Other species of special concern in the Southern African context are the African wildcat, Honey badger (Mellivora capensis), Pangolin (Manis temminckii), Aardvark (Orycteropus afer), Kori bustard (Ardeotis kori), Bateleur eagle (Terathopius ecaudatus), Martial eagle, Whiteheaded (Trigonoceps occipitalis), Lappetfaced (Torgos tracheliotus), and Cape (Gyps coprotheres) vultures.

Justification of ecoregion delineation

The boundaries for the Kalahari Xeric Savanna are based on White's (1983) Kalahari deciduous Acacia wooded grassland and bushland and Kalahari/Karoo-Namib transition, with a small transition area of undifferentiated woodland to Acacia deciduous bushland and wooded grassland. A majority of the ecoregion encompasses the plains of the Kalahari Basin, and extends beyond the Kalahari biogeographical province of Udvardy (1975). Despite low levels of endemism, the ecoregion hosts a number of migratory species.

Neighboring ecoregions

Further reading

  • J.P.H. Acocks. 1988. Veld types of South Africa. Memoirs of the botanical survey of South Africa No. 57. Botanical Research Institute, Pretoria, South Africa. ISBN: 062102256X
  • Albertson, A. 1998. Northern Botswana veterinary fences: Critical ecological impacts. Retreived 20/08/2000.
  • M.D. Anderson. 2000. Raptor conservation in the Northern Cape Province, South Africa. Ostrich 71: 25-32.
  • K.N. Barnes, editor. 2000. The Eskom Red Data Book of Birds of South Africa, Lesotho and Swaziland. BirdLife South Africa, Johannesburg, South Africa.
  • G.A. Bartholomew, F.N. White and T.R. Howell. 1976. The thermal significance of the nest of the Sociable Weaver (Philetairus socius): summer observations. Ibis 118: 402-410.
  • Dean, W.R.J., S.J. Milton, and F. Jeltsch. 1999. Large trees, fertile islands, and birds in arid savanna. Journal of Arid Environments 41: 61-78.
  • F.C. Eloff,. 1973. Lion predation in the Kalahari Gemsbok National Park. Journal of South African Wildlife Management 3(2): 59-63.
  • M. Herremans. 1998. Conservation status of birds in Botswana in relation to land use. Biological Conservation 86: 139-160.
  • C. Hilton-Taylor. 2000. The IUCN red list of threatened species. Gland, Switzerland and Cambridge, U.K. ISBN: 2831705649
  • C. Michael Hogan. 2008. Makgadikgadi, The Megalithic Portal, ed. A. Burnham
  • IUCN 1986. Review of the protected areas system in the Afrotropical Realm. In collaboration with the United Nations Environment Programme. IUCN, Cambridge, U.K.
  • R. Keene-Young. 1999. A thin line: Botswana's cattle fences. Africa Environment and Wildlife 7(2): 71-79.
  • M. Knight and P. Joyce. 1997. The Kalahari: survival in a thirstland wilderness. Struik Publishers, Cape Town. ISBN: 1868720195
  • Leistner, O.A. 1967. The plant ecology of the southern Kalahari. Memoirs of the Botanical Survey of South Africa 38: 1-172.
  • Lovegrove, B. 1993. The living deserts of southern Africa. Fernwood Press, Cape Town. ISBN: 0958315477
  • Main, M. 1987. Kalahari: Life's variety in dune and delta. Southern Book Publishers, Johannesburg. ISBN: 033347175X
  • PPF. 2000. Africa's first Peace Park opened: The Kgalagadi Transfrontier Park. Press Release. Peace Parks Foundation News, 12 May 2000. Retrieved from Peace Parks Foundation. August 20, 2000.
  • RAMSAR. 1998. Botswana rolls back fences for wildlife. Retrieved from Ramsar Convention on Wetlands. Retrieved October 7, 2000.
  • Roderigues, J. 1997. Lions of the Kalahari. Custos (January 1997) pp. 19-21.
  • Schmidt, D. 1995. Botswana-EU cooperation: Focus on cattle, copper and conservation. Retrieved on October 7, 2000.
  • Schulze, R.E. 1997. Climate. Pages 21-42 in R.M Cowling, D.M. Richardson, and S.M. Pierce, editors. Vegetation of Southern Africa. Cambridge University Press, Cambridge. ISBN: 0521548012
  • Smithers, R.H.N. 1986. South African Red Data Book : Terrestrial Mammals. South African National Scientific Programmes Report No. 125.
  • Taylor, C.R. 1969. The eland and the oryx. Scientific American 220: 89-95.
  • Udvardy, M.D.F. A classification of the biogeographical provinces of the world. IUCN Occasional Paper No. 18 (International Union of Conservation of Nature and Natural Resources, Morges, Switzerland, 1975).
  • Van der Walt, P., and E. Le Riche. 1999. The Kalahari and its plants. Van der Walt and Le Riche, Pretoria. ISBN: 0620234164
  • Van Rooyen, N. 1999. Kalahari. Pages 10-25 in J. Knobel, editor. The magnificent natural heritage of South Africa. Sunbird Publishing, Cape Town. ISBN: 0624037959
  • White, F. 1983. The vegetation of Africa: a descriptive memoir to accompany the UNESCO/AETFAT/UNSO vegetation map of Africa. UNESCO, Paris, France. ISBN: 9231019554 

Disclaimer: This article  contains information that was originally published by, the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth  have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

 

 

 

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Citation

Hogan, C., & Fund, W. (2014). Kalahari xeric savanna. Retrieved from http://www.eoearth.org/view/article/51cbee467896bb431f6969b3

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