Ecoregions

Kaokoveld desert

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Aerial photo of the rugged mountainous core of the Kaokoveld. @ C.Michael Hogan

The Kaokoveld Desert represents the northern area of the vast Namib Desert. It is a harsh, arid landscape of rugged mountains, gravel plains and shifting sand dunes. Surface water is scarce, with only one perennial river flowing through the region, the Kunene River. However, the dry riverbeds transecting the area are the lifelines of the desert. They are well vegetated and are home to large mammals such as African Elephant, Black Rhino and Giraffe. The remainder of the landscape is poorly vegetated and extremely arid. Coastal fogs allow a range of interesting, desert-adapted animal species to survive in this low-rainfall environment. The relict gymnosperm Welwitschia mirabilis, which represents the sole surviving member of its family, is found throughout the ecoregion. The Kaokoveld Desert is well protected in the Skeleton Coast National Park, but outside this park the habitat is under threat. In Namibia, the area is threatened by poaching, and by sometimes unruly off-road enthusiasts. On the Angolan side, threats come from the collapse of infrastructure and of governance during a thirty year civil war, when Soviet financed Cuban mercenaries were sent to Angola in large numbers to destabilise the region.

Location and general description


The Kaokoveld Desert stretches along the west coast of southern Africa between about 13 and 21S latitude. Encompassing the northern Namib Desert, the ecoregion extends from the Uniab River in Namibia northwards into the coastal zone of southern Angola, including the Mossamedes Desert. For most of its length, it is about 100 kilometers (km) wide and extends from the Atlantic Coastline to the foot of the great escarpment, which delimits the interior highlands of southern Africa.

A climatic transition belt that crosses the coastline north of Luderitz in Namibia divides the greater Namib Desert into a northern area receiving austal summer rainfall and a southern area receiving austral winter rain. The Kaokoveld Desert occupies the northern summer rainfall area, with more than 60 percent of its annual rain falling as sporadic thunderstorms between October and March. The most important climatic feature of the ecoregion is its very low and highly unpredictable rainfall of less than 100 millimetres (mm) per year. Mean annual rainfall becomes lower and less predictable as one transitions from east to west across the desert.

There are two chief causes for the low precipitation of the ecoregion. Firstly, the easterly trade winds emerging over the Indian Ocean lose most of their humidity when rising over the eastern escarpment of the Drakensberg Mountains in South Africa. On their way over the continent, they lose further moisture and reach the western escarpment of Namibia warm and dry. These air masses move down onto the low-lying coastal region and produce extremely hot and dry winds. Secondly, the prevailing local southwesterly winds, cooled down by the Benguela Current along the Atlantic coast of southern Africa, provide an inland movement of cold air, which is overlain by the warmer, lighter air. This inversion prevents the convectional rise of the cool, humid air, and thus no clouds are formed. The cool air, however, forms a stable lower atmosphere layer of fog, which is blown inland as far as 50 kilometers (km). This fog is thought to provide water to higher plants, and is well known to be the life-blood for desert-adapted insects and other organisms such as spiders, solifuges, and scorpions.

Air temperatures in the Kaokoveld Desert decrease towards the coast as a result of the cool air coming off the Benguela Current. At the coast, the frequent fogs keep daily and seasonal temperature changes minimal, with daily highs and lows differing by as little as 2°C to 5°C. These changes increase inland where they become highly variable, with temperatures reaching extremes of below 0°C and above 50°C recorded at one location. Greatest fluctuations are over the arid zones where there is little vegetation cover to moderate the temperature.

caption Namibia. (Photograph by WWF/Kate Newman)

The ecoregion is made up of rugged hills, valleys, sand dunes, sand, and gravel plains. A large area of shifting sand dunes occurs in the Iona National Park in southern Angola, between Porto Alexandre and the Kunene River. These dunes are up to 40 km wide in some places. Sand and gravel plains cover much of the ecoregion.

No true soils with well-defined profiles are found because of the low moisture status of the region. The soils are made of raw minerals and are sandy and sometimes calcareousSoils which are high in limestone content or with calcareous crusts, composed of particles in a wide range of sizes. The soil on the gravel plains is cemented into a rock-hard layer by deposition of lime and gypsum, forming a hardpan at a depth of 10 to 50 millimetres (mm). Salt crusts are common on the soil close to the ocean, and the soils are brackish as far as the inland limit of coastal fog. Characteristic soils of the ecoregion are dominated by arenosol, lithosols, weakly developed shallow soils and halomorphic soils.

The Kunene River is the only permanently running river in the Kaokoveld Desert. The other rivers, such as the Hoanib, Hoarusib and Khumib Rivers run intermittently and never reach the ocean, but seep into the sand near the coast.

Biodiversity features

The Kaokoveld Desert has been arid for at least 55 million years. The convergence of the Benguela upwelling and the hot interior has maintained, and perhaps increased, this aridity in recent times, but they did not generate the aridity. The region is considered to be an island of long-term aridity in a sea of climatic change. The arid conditions likely started with the continental split of West Gondwana 130 to 145 million years ago when this area shifted to its present position along the Tropic of Capricorn.

This very long dry period has had a profound influence on the biodiversity; it has remained a relatively stable center for the evolution of desert and dry savanna species, which has resulted in unique assemblages with high levels of endemism and numerous advanced adaptations to arid conditions. In addition, many disjunct distribution patterns are found in both animals and plants between the Kaokoveld and other dry regions of Africa. The most common disjunct pattern is that of taxa occurring in the Karoo-Namib region (which includes the Kaokoveld Desert) and again in the arid areas of Northeast Africa (such as Somalia, Kenya and Ethiopia). The widely accepted explanation is that the present-day disjunctions are a relict situation of a formally continuous arid belt stretching across Africa from Somalia to Botswana, Namibia and South Africa.

Flora characteristics

The Namibian portion of the Kaokoveld Desert consists largely of sand dunes sparsely vegetated by isolated plants of Salsola nollothensis, Ectadium virgatum, Merremia multisecta, and Indigofera cunenensis and the grasses Stipagrostis ramulosa and Cladoraphis cyperoides. Surrounding these dunes are sparse grasslands dominated by desert annuals, mainly Stipagrostis spp. Towards the east, these grassy plains become more luxuriant, and pure stands of Kaokochloa nigrirostris are common. The Angolan portion of the ecoregion is true desert with shifting sand dunes. Here, large areas are completely devoid of vegetation, while elsewhere the Nara Melon (Acanthosicyos horrida) encroaches upon the sand. This spiny, mainly leafless shrub collects wind-blown sand between its branches so that it becomes partially covered, forming a hummock up to two meters high.

Along the coastal stretch are compact gravel deserts devoid of vegetation except for colorful fields of foliose and crustose lichens. Species of Parmelia and Usnea and the orange lichen Teloschistes capensis are common. Further inland, the gravel deserts become less barren, and species like Zygophyllum orbiculatum, Z. simplex, Galenia africana, Sesuvium portulacastrum and Stipagrostis subacaulis are found.

The famous relict gymnosperm Welwitschia mirabilis is also found throughout the ecoregion, and it is often the most conspicuous feature of the vegetation, scattered about the arid plains at intervals of 50 to 100 metres. Individual Welwitschia plants have been estimated to be more than 2500 years old, have crowns of more than one meter diameter and leaves up to three meters long. The leaves, which curl into fantastic shapes along the ground, are the longest-lived leaves of any member of the plant kingdom.

Halophytic communities grow on the saline beaches, characterized by Salsola zeyheri, Sesuvium spp., Suaeda fruticosa, Scirpus littoralis, and Centropodia forskalii. Rocky substrates are found throughout the ecoregion and harbor leaf succulents including Lithops ruschiorum, Sarcocaulon mossamedense, and Othonna lasiocarpa. The dry riverbeds contain a higher diversity of species than found in the adjacent desert.

Dense cushion-like growths of leaf succulents such as Salsola spp., Zygophyllum clavatum and Z. stapffii are common. Towards the east, in the riverbeds on the fringes of the Kaokoveld Desert, Faidherbia albida, Balanites welwitschii, Colophospermum mopane, and Maerua schinzii are found. Small waterholes or wet places can be densely covered by Odyssea paucinervis or a community of Phragmites australis, Thypha latifolia, Scirpus dioicus, S. littoralis and Juncellus laevigatus.

The long arid history, together with the wide range of habitats present in the Kaokoveld Desert, has led to high levels of plant endemism. There are a number of paleoendemics, such as Welwitscha mirabilis and Kaokochloa sp., which indicate the ancient history of the area. There has also been a recent burst of evolution reflected in endemics such as Barleria solitaria, Indigofera cunensis, Merremia multisecta, and Stipagrostis ramulosa.

Fauna characteristics

The high number of endemic animals in the Kaokoveld is made up largely of reptiles. Of the 63 species recorded in the ecoregion, eight are strictly endemic. The endemics include two lizards, three geckos, and three skinks. The endemic Bocage's Sand Lizard (Pedioplania benguellensis) is an amazingly fast-moving lizard that can be seen in the heat of the day, dashing over the sparsely vegetated sand and gravel flats. The endemic geckos are quite distinctive. The Namib Desert Gecko (Palmatogecko vanzeyli),  for example, exhibits a medium-sized body and a large head with immense jewel-like eyes. The Damaraland Pygmy Toad (Poyntonophrynus damaranus) is a restricted range anuranAn amphibian that has limbs but no tail (includes all frogs and toads) that breeds in temporary ponds, and is found only in the Kaokoveld Desert and northern Waterberg region.

The Kaokoveld Desert has only nine arachnid species, possibly due to the lack of vegetation for web-living spiders. Two of those taxa are endemic. These species have highly specialized behavior that enables them to survive in the desert sand dunes. The ecoregion has four solifuge (sun spider) species and 13 scorpion species; moreover, two of the solifuges and three of the scorpion taxa are endemic to this ecoregion. The endemic solifuge Ceroma inerme has adapted the normal solifuge xerophilic behavior to accommodate a nearly marine existence, living just outside the high tide zone and foraging in the intertidal area at low tide.

The Kaokoveld Desert is home at times to Desert Elephant (Loxodonta africana EN), Black Rhino (Diceros bicornis CR) and Giraffes (Giraffa camelopardalis LR), which are found in the riverbeds that the fringe the desert, utilizing trees such as Faidherbia albida. Although these species are not endemic to the ecoregion, the African Eelephant and Black Rhino are globally threatened. The Black Rhino population in this area is the only unfenced population of black rhino in the world and is estimated to number more than 100 individuals. Black Rhino and Desert Elephant are the largest herbivores found in the desert. Both species have adapted to the desert by covering vast distances each day to find sufficient food. Desert Elephants are capable of covering 34 kilometers  per day to find adequate food.

Other species found within the ecoregion include Hartmann's Mountain Zebra (Equus zebra hartmannae EN), Greater Kudu (Tragelaphus strepsiceros LR), Springbok (Antidorcas marsupialis LR), Gemsbok (Oryx gazella LR), Damara Dik-dik (Madoqua kirkii) and Black-faced Impala (Aepyceros melampus petersi VU). These ungulates are restricted to the vegetated riverbeds that transect the ecoregion. The exceptions are the gemsboks, which move out of the riverbeds into the desert for extended periods. Predators include Lion (Panthera leo), Cheetah (Acinonyx jubatus VU), Bat-eared Fox (Otocyon megalotis), Cape Fox (Vulpes chama), Brown Hyena (Hyaena brunnea LR), and Black-backed Jackal (Canis mesomelas). The Brown Hyena and Black-backed Jackal are chiefly found scavenging along the backshores. Three mammal species that are restricted to the Namib Desert are found in the Kaokoveld: the Black Slender Mongoose Galerella flavescens, Setzer's Hairy-footed Gerbil (Gerbillurus setzeri), and the Angola Wing-gland Bat (Myotis seabrai VU). This bat is classified in the IUCN Red List of Threatened Species as Vulnerable.

Avian taxa are abundant in the ecoregion, and 229 bird species have been recorded to date. Most of these are found along the dry riverbeds as well as the two perennial rivers. For example, the endemic Cinderella Waxbill (Estrilda thomensis, LR) is restricted to the lower reaches of the Kunene riverbed. One of the few birds permanently residing within the sand dunes is Gray's lark (Ammomanes grayi). The edges of the desert are occupied by the pale Rüppell's Korhaan (Eupodotis rueppelli), which moves into the dunes after rainfall events to take advantage of the flush of vegetation. Both of these birds are endemic to the greater Namib Desert area. Additionally, there is another near-endemic species of bird which has been recently described, Certhilauda benguelensis.

A curious feature of the Namib/Kaokoveld Desert region is appearance of circles on the ground surface that are defined by abrupt changes in the vegetation pattern. Such a circle, known as a fairy ring is most readily noticed from an aircraft. These rings occur on the eastern fringes of the Kaokoveld Desert from southern Angola to the Orange River, characteristically within the Stipagrostis grassland community. The origin of these circles has generated interest and speculation for centuries. Various hypotheses have been advanced for their formation, from geomorphological phenomena to plants having allelopathic exclusion effects to being animal-derived features.

A similar phenomenon occurs to the south of the Orange River in the form of heuweltjies (originally termitaria) that are about 30 metres in diameter and one metre high. Recent evidence has shown that the harvester termite Microhodotermes viator most likely creates these heuweltjies. It is now thought that the fairy rings of the Namib/Kaokoveld Deserts are created through a similar process by one of three possible termite species: Hodotermes mossambicus, Psammotermes allocerus, or Baucaliotermes hainsei.

Conservation status

A large percentage of this ecoregion falls under formal protection both in Namibia and Angola. The Skeleton Coast National Park covers a narrow portion of the coastal Kaokoveld Desert, stretching 500 kilometres along the northern coast of Namibia from the Ugab River to the Kunene River on the Angolan-Namibian Border, a total of 15,800 square kilometres. The park contains the three main vegetation units found within the Kaokoveld Desert (gravel plains, sand dunes, and dry river beds) and is therefore a good representation of the ecoregion. The northern area of the Park (north of the Unijab River) is a wilderness area and is closed to the public. In Angola, the Mocamedes Partial Reserve (4450 square kilometres) and the Iona National Park (15,150 square kilometres) cover most of the northern portion of the ecoregion.

The only area of the Kaokoveld Desert that is not under formal protection is the southeastern portion, inland from the Skeleton Coast National Park. This area was once under protection in "Game Reserve No. 2," which originally covered 80,000 square kilometres and was the largest nature reserve in the world. The reserve stretched from the Kunene River, 200 kilometres (km) south to the Hoarusib River and included the escarpment (ecoregion 110) and the Kaokoveld Desert. This enormous park allowed for the westward seasonal migration of elephants, lions and other mammals as far as the Atlantic Ocean. In 1963, the Odendaal Commission of Enquiry into South West Africa Affairs removed a large portion of the reserve from protected status for political-ideological reasons. The reserve was reduced by 72 percent to become the present Etosha Pan National Park (with a size of 22,912 square kilometres).

More recently, the portion of the park whose protection was removed in 1963 is becoming increasingly protected through a mosaic of informally protected conservancies that stretch from the Skeleton Coast National Park, across the Kunene River and into Angola. Conservancies are jointly managed for resource conservation by multiple landowners with the financial and other benefits shared between them. They occur on both private and tribal (communal) land. Most aim to enhance habitat for, and numbers of, game species such as ungulates or game birds, and many draw income from tourism. These conservancies provide communities with economic incentives to protect the land that has high conservation value.

Ecoregion threats

The Namibian side of the Kaokoveld Desert has remained relatively intactThe condition of an ecological habitat being an undisturbed or natural environment because of its arid conditions and consequent low population density. To the east, the ecoregion is primarily inhabited by the Ovahimba, who are nomadic pastoralists. Their impact has been local, mainly through the collection of wood and medicinal, edible and culturally important plants. These activities have not had a major impact on the ecoregion. The biggest threat that the Ovahimba pose is through overgrazing the area with their cattle.

The biggest threat on the Namibian side of the Kaokoveld Desert is from wildlife poaching. This started when Game Reserve No. 2 was degazetted in 1963 and administered from afar by the Department of Bantu Affairs in Pretoria. This was a period of corruption and widespread poaching. Poaching of black rhinos is a major problem. Dehorning began in the area in 1991 in an attempt to stop the poaching of these rhinos, which are the last unfenced black rhino population in the world.

The Kaokoveld Desert has recently become a popular destination for off-road enthusiasts. While this may have advantages in bringing tourisms economic benefits into the area, many off-road drivers have been proven to show no regard to the sensitive environments in which they are driving. This behavior is not restricted to driving over fragile landscapes. The September 1998 issue of Getaway magazine reported that southern African four-by-four enthusiasts were found chasing an old elephant bull up and down the Hoanib Riverbed. The success of the potential off-road tourism market will depend on how effectively off-road enthusiasts can be educated about the damage that they can pose to the environment.

The 30-year civil war in Angola has left the Angolan side of the Kaokoveld Desert under-protected. The area is open to poachers, timber harvesting, human settlement and agriculture. There are several hundred Ovahimba pastoralists with more than 3000 head of livestock within the Iona National Park. Few, if any, viable populations of larger wild mammals have survived, and populations of lions, black rhinos and giraffes have been reduced to the threshold of local extinction. On the positive side, in 1992 the Angolan government established a State Secretariat for the Environment and has begun training demobilized soldiers as park wardens. Angola is also a signatory to the Convention on Biological Diversity.

Justification of ecoregion delineation

Both the Kaokoveld and Namib Desert ecoregions are part of the Namib Desert vegetation unit of White and the Namib biogeographical province of Udvardy. The northern Namib, recognized as the Kaokoveld Desert, was separated based on significant geophysical differences. In particular, this northern region receives relatively more rainfall than the Namib Desert, and also follows a summer rainfall pattern versus a winter rainfall pattern in the Namib. The southern boundary of the Kaokoveld ecoregion lies at the Huab River (which also reflects the biogeographic division made by Giess, 1971 - in White). The northern limit reflects that of White's bushy Karoo-Namib shrubland unit. This area is also distinguished as a center of plant diversity, including very old paleoendemics, including monotypic families and genera.

Additional information on this ecoregion

References and further reading

  • Armstrong, S. 1990. Fog, wind and heat: life in the Namib desert. New Scientist. Pages 46-50 in Vol.127 July 14.
  • Barnard, P., editor. 1998. Biological diversity in Namibia. Namibian National Biodiversity Task Force, Directorate of Environmental Affairs, Windhoek.
  • Barnard, P., C.J. Brown, A.M. Jarvis, and A. Robertson. 1998. Extending the Namibian protected areas network to safeguard hotspots of endemism and diversity. Biodiversity and Conservation 7: 531-547.
  • Berger, J., and C. Cullingham. 1994. Active intervention and conservation: Africa's pachyderm problem. Science 263: 1241-1242.
  • Branch, B. 1998. Field guide to the snakes and other reptiles of southern Africa. Struik, Cape Town. ISBN: 0883590425
  • Dean, W.R.J. 2000. The birds of Angola. BOU Checklist No.18. British Ornitologist's Union, Natural History Museum, Tring, UK. ISBN: 0907446221
  • Du Plessis, W. 1992. In situ conservation in Namibia: the role of national parks and nature reserves. Dintera 23: 132-141.
  • Giess, W. 1971. A preliminary vegetation map of South West Africa. Dintera 4: 1-114.
  • Griffin, R.E. 1998. Species richness and biogeography of non-acarine arachnids in Namibia. Biodiversity and Conservation 7: 467-481.
  • Griffin, M. 1998. The species diversity, distribution and conservation of Namibian mammals. Biodiversity and Conservation 7: 483-494.
  • Hilton-Taylor, C. 2000. The IUCN red list of threatened species. Gland, Switzerland and Cambridge, U.K. ISBN: 2831705657
  • Huntley, B.J., and E.M. Matos. 1994. Botanical diversity and its conservation in Angola. B.J.Huntley, editor. Botanical Diversity in Southern Africa. Strelitzia 1: 53-74. National Botanical Institute, Pretoria.
  • Joubert, E., and P.K.N. Mostert. 1975. Distribution patterns and status of mammals in South West Africa. Madoqua 9: 8-22.
  • Lovegrove, B. 1993. The Living Deserts of Southern Africa. Fernwood Press, Vlaeberg. ISBN: 0958315477
  • Moll, E.J. 1994. The origin and distribution of fairy rings in Namibia. Proceedings of the XIIIth Plenery Meeting of AETFAT, Malawi. pp. 1203-1209.
  • Ryan, P.G., I. Hood, P. Bloomer, J. Komen, and T. Crowe 1999. Barlow's Lark: a new species in the Karoo Lark Certhilauda albescens complex. Ibis 140: 605-619.
  • Sinclair, I., and P. Hockey. 1996. The Larger Field Guide to Birds of Southern Africa. Struik, Cape Town. ISBN: 0691096821
  • Stuart, C., and T. Stuart. 1992. Guide to Southern African Game and Nature Reserves. Struik, Cape Town. ISBN: 0844289663
  • Sullivan, S., and T.L. Konstant. 1997. Human impacts on woody vegetation, and multivariate analysis: a case study based on data from Khowarib settlement, Kunene Region. Dintera 25: 87-120.
  • 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)
  • Werger, M.J.A. 1978. Biogeography and Ecology of Southern Africa. Junk, The Hague. ISBN: 9061930839
  • White, F. 1983. The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000). UNESCO, Paris.
  • Von Willert, D.J., B.M. Eller, M.J.A. Werger, E. Brinckmann, and H.D. Ihlenfeldt. 1992. Life Strategies of Succulents in Deserts. Cambridge University Press. ISBN: 0521244684

Disclaimer: This article contains some 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

Fund, W., & Hogan, C. (2014). Kaokoveld desert. Retrieved from http://www.eoearth.org/view/article/153993

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