Location and General Description
The Kaokoveld Desert stretches along the west coast of southern Africa between about 13° and 21°S 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 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 summer rainfall and a southern area receiving 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 (von Willert et al. 1992). The most important climatic feature of the ecoregion is its very low and highly unpredictable rainfall of less than 100 mm per year. Mean annual rainfall becomes lower and less predictable as you move from east to west across the desert. The low rainfall of the ecoregion has two causes. 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 West Coast of South 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 (von Willert et al. 1992). The cool air does, however, form a stable layer of fog, which is blown inland as far as 50 km. It is controversial whether this fog provides water to higher plants, but it is well known that it is the life-blood for desert-adapted insects and other organisms such as spiders, solifuges, and scorpions (Lovegrove 1993). 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° to 5°C (Barnard 1998). These changes increase inland where they become highly variable, with temperatures reaching extremes of below 0° 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.
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 (White 1983). 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 (von Willert et al. 1992). The soils are made of raw minerals and are sandy and sometimes calcareous 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 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 include arenosol, lithosols, weakly developed shallow soils and halomorphic soils (Barnard 1998).
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 (Barnard 1998).
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 Eragrostis cyperoides (Giess 1971, Werger 1978, White 1983). 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 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 2 m 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 m. Individual Welwitschia plants have been estimated to be upwards of 2,500 years old, have crowns of more than 1 m diameter and leaves up to 3 m long. The leaves, which curl into fantastic shapes along the ground, are the longest-lived leaves of any member of the plant kingdom (White 1983, Armstrong 1990, Lovegrove 1993). Halophytic communities grow on the saline beaches, characterized by Salsola zeyheri, Sesuvium spp., Suaeda fruiticosa, Scirpus littoralis, and Asthenatherum 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 (Giess 1971, Werger 1978, White, 1983).
The Kaokoveld Desert has been arid for at least 55 million years (Barnard 1998). 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 (Armstrong 1990). 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 (Lovegrove 1993). 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 Somali, 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 (Werger 1978).
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.
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 lizard Pedioplania benguellensis is an amazingly fast lizard that can be seen in the heat of the day dashing over the sparsely vegetated sand and gravel flats (Branch 1998). The endemic geckos are distinctive. Palmatogecko vanzeyli, for example, has a medium-sized body and a large head with immense jewel-like eyes. The Kaokoveld Desert has only 9 spider species, possibly due to the lack of vegetation for web-living spiders (Griffin 1998). Two of those spiders are endemic. These species have highly specialized behavior that enables them to survive in the desert sand dunes. The ecoregion has 4 solifuge species and 13 scorpion species. Two of the solifuges and 3 of the scorpions 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 (Griffin 1998).
The Kaokoveld Desert is home at times to ‘desert’ elephants (Loxodonta africana EN), black rhinos (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 (Joubert and Mostert 1975). Although these species are not endemic to the ecoregion, the elephants and black rhinos are globally threatened (Hilton-Taylor 2000). 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 (Berger and Cunningham 1994). Black rhinos and elephants 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 km per day to find adequate food (Lovejoy 1993). Other species found within the ecoregion are Hartmann’s mountain zebras (Equus zebra hartmannae EN), kudu (Tragelaphus strepsiceros LR), springboks (Antidorcas marsupialis LR), gemsboks (Oryx gazella LR), Damara dik-diks (Madoqua kirkii) and black-faced impalas (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 lions (Panthera leo), cheetahs (Acinonyx jubatus VU), bat-eared foxes (Otocyon megalotis), Cape foxes (Vulpes chama), brown hyenas (Hyaena brunnea LR), and black-backed jackals (Canis mesomelas). The brown hyenas and black-backed jackals are found mainly scavenging on the beaches (Griffin 1998). Three mammals that are restricted to the Namib Desert are found in the Kaokoveld: the mongoose Galerella flavescens, Setzer’s hairy-footed gerbil (Gerbillurus setzeri), and the Angola wing-gland bat (Myotis seabrai VU). The bat is classified in the IUCN Red List of Threatened Species (Hilton-Taylor 2000) as vulnerable.
Bird life is abundant in the ecoregion, and 229 species have been recorded to date. Most of these are found along riverbeds. For example, the endemic Cinderella waxbill (Estrilda thomensis, LR) is restricted to 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 Ruppell’s korhaan (Eupodotis ruppelli), which moves into the dunes after rain to take advantage of the flush of vegetation (Sinclair and Hockey 1996). Both of these birds are endemic to the greater Namib Desert area. There is one near-endemic species of bird which has been recently described, Certhilauda benguelensis (Ryan et al. 1999).
A curious feature of the Namib/Kaokoveld Desert is circles on the ground that are accentuated by abrupt changes in the vegetation pattern. These circles, known as "fairy rings" are most noticeable from the air. They occur on the eastern fringes of the 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 (Lovegrove 1993). 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 m in diameter and 1 m 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 (Moll 1994).
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 km along the northern coast of Namibia from the Ugab River to the Kunene River on the Angolan-Namibian Border, a total of 15,800 km2 (Stuart and Stuart 1992). 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 (du Plessis 1992). 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 (4,450 km2) and the Iona National Park (15,150 km2) cover most of the northern portion of the ecoregion (Huntley 1974).
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 km2 and was the largest nature reserve in the world. The reserve stretched from the Kunene River, 200 km south to the Hoarusib River and included the escarpment (ecoregion 110) and the Kaokoveld Desert (Barnard et al. 1998). 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 km2). 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 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 (Barnard et al. 1998).
Types and Severity of Threats
The Namibian side of the Kaokoveld Desert has remained relatively intact 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 (Sullivan and Konstant 1997).
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 (Berger and Cullingham 1994).
The Kaokoveld Desert has recently become a popular destination for off-road enthusiasts. While this may have advantages in bringing tourism’s 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 South African 4x4 enthusiasts were found chasing an old elephant bull up and down the Hoanib Riverbed. The success of the potential 4x4 tourism market will depend on how effectively off-road enthusiasts can be educated about the damage that they can pose to the environment (Lovegrove 1993).
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 3,000 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 (Dean 2000).
Justification of Ecoregion Delineation
Both the Kaokoveld and Namib Desert ecoregions are part of the ‘Namib Desert’ vegetation unit of White (1983) and the ‘Namib’ biogeographical province of Udvardy (1975). 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.
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Prepared by: Amy Spriggs
Reviewed by: In progress