Namibian savanna woodlands
The Namibian savanna woodlands ecoregion covers the Great Escarpment that delimits the interior of southern Africa from both the Kaokoveld Desert and Namib desert. This broken and deeply dissected escarpment is an area of high endemism for plants, invertebrates, amphibians, reptiles, mammals and birds. The northern area of the ecoregion, the Kaoko escarpment, is an endemism "hotspot" (area of extremely high species richness and endemism). The Namibian savanna woodlands comprise a land area of approximately 87,100 square miles.
This northern area is poorly protected and is under threat from poaching, off-road driving, and to a lesser extent from farming, and resultant habitat fragmentation; much of this destabilisation in the Angolan portion of the ecoregion stems from the Cuban mercenaries aided with USSR funding, that invaded the region in the 1970s; this militarisation of the Angolan portion of the ecoregion has led to significant decline of environmental protection and reduction of ability of scientific monitoring of the northern part of the ecoregion. The formal conservation status of the southern portion of the ecoregion is also not sound. Other forms of protection, such as conservancies, private nature reserves and game farms do, however, promote conservation of the Namibian portion of the ecoregion. If these areas can be effectively managed through collaboration with local communities, some progress may be made in the ecological conservation crisis within the ecoregion. The Namibian savanna woodlands are classified within the Deserts and Xeric Shrublands biome, as an element of the Afrotropic Realm.
Location and general description
The Namibian savanna woodlands (Namaland) ecoregion covers the narrow escarpment belt that lies inland of the Namib and Kaokoveld Deserts and broadens gradually towards the south, where it comprises extensive areas on the plateau south of Windhoek. The ecoregion extends from near the town of Sumbe in western Angola southward through Namibia, with the southern boundary located immediately north of Groot Karas Berg.
Precipitation in this ecoregion is scant, annually ranging from 60 millimetres (mm) in the west to 200 mm in the east. Most of the rain falls as thundershowers in the summer months, from October to March; however, here is great variation between years, with the driest years having the least predictable rainfall. The predictability of the rainfall increases towards the east. The low humidity of the area, without the cooling effect of the Benguela Current, results in extreme temperatures. Mean minimum monthly temperatures drop to -9°C in places, and extrema readings are even lower. Winter frosts are common in the ecoregion. The mean maximum monthly air temperature can exceed 40°C.
The ecoregion is a transition zone between the low-lying desert and the central highland plateau. The escarpment that rises from the deserts is narrow, broken and deeply dissected. It includes the Brandberg, Namibia’s highest mountain at 2038 metres (m). Other mountains such as the Baynes (2038 m), Erongo (2319 m), Naukluft (1974 m), Spitzkoppe (1759 m) and the Gamsberg (2347 m) also lie along the escarpment edge. Towards the south, the ecoregion broadens to include more land area from the rocky central plateau. This plateau lies above and east of the escarpment, between about 1000 m and 2000 m. The landscape stony and almost level in places, and it is dramatically mountainous in others. To the west of the town of Windhoek, it includes the Hochland Plateau that varies from rugged in the north (with broad valleys and inselbergs) to a flat and stony plateau dissected by deep valleys in the south. Finally, the Kalahari sandveld stretches southeast from the central plateau, with deep sands overlaying the bedrock. In contrast to the rugged and stony land to the northwest, most of the sandveld topography is relatively level.
Soils differ markedly within the ecoregion, with litholithic and sandy loams on the escarpment and the southwestern part of the plateau, and deep, red or pale, sandy (and to some extent calcareousSoils which are high in limestone content and silty) soils in the southern Kalahari.
Most of the rivers in Namibia have their major watersheds in this highland. The Kunene River that runs along the Angola-Namibia border is the only perennial river within the ecoregion. Other important rivers are the Swakop, Kuiseb, and Fish Rivers. The Swakop and Kuiseb Rivers flow infrequently and are usually dry riverbeds. The Fish River, one of Namibia’s longest rivers, begins in the Naukluft Mountains southwest of Windhoek and winds its way south for 800 kilometres (km) before flowing into the Orange River.
The vegetation of the Namibian savanna woodlands is varied in structure, physiognomy and species distribution. This reflects diverse topographic factors and related soil and microclimate characteristics. According to the Geiss vegetation map of Namibia, the ecoregion contains three vegetation types: mopane savanna, semi-desert and savanna transition, and dwarf shrub savanna. The mopane savanna lies to the north of the ecoregion and is characterized by Colophospermum mopane. This species occurs as a tree or shrub, depending on local conditions. In some areas, it forms dense woodland, whereas in others it grows as a short-stemmed shrub intermingled with scattered trees. In the western part, towards the Kaokoveld Desert, the mopane is confined to depressions and riverbeds where it often grows together with the Desert Date (Balanites welwitschii). Other components of the mopane savanna are two species of Sesamothamnus. S. benguellensis occurs along the Kunene River, and S. guerichii is well-distributed over the mopane savanna. Ceraria longipedunculata is typical of the [[mountain]ous] areas to the west of the mopane savanna.
The mopane savanna extends as far south as the vicinity of the Brandberg; it then grades into the semi-desert and savanna transition zone. This zone is characterized by a great variety of species, many of which are endemic. Typical of the area is Euphorbia guerichiana, a shrub or small tree with conspicuous, shiny, brownish-yellow, papery bark growing to a height of 5 m. Also common are Cyphostemma spp. with succulent stems, Adenolobus spp., the Quiver tree (Aloe dichotoma), and the Phantom tree (Moringa ovalifolia). Two species of Acacia are confined to this vegetation type; these are the Brandberg acacia (Acacia montis-ustii) and A. robynsiana. Senegal gum (Acacia senegal) and Umbrella thorn (A. tortilis) are also found, mainly in the alluvial sands and silts along ephemeral rivers in the ecoregion.
High diversity of the genus Commiphora is particularly characteristic of both the mopane savanna to the north and the semi-desert and savanna transition zone. To the south, the vegetation becomes more open, is dominated by karoo shrubs and grasses, and is classified as dwarf shrub savanna. This vegetation type extends eastwards into the Kalahari Xeric Savanna ecoregion. Rhigozum trichotomum is a very characteristic shrub of this vegetation type. Parkinsonia africana, Acacia nebrownii, Boscia foetida, B. albitrunca, and Catophractes alexandri as well as smaller karoo bushes such as Pentzia spp. and Eriocephalus spp. are also typical. Tufted grasses, mainly Stipagrostis spp., are found scattered among the woody plants.
On rocky ridges, the conspicuous Quiver tree becomes abundant. Near Keetmanshoop there is a small Quiver tree woodland of about 300 trees. This forest is a national monument. Trees such as Acacia giraffe, A. karroo, Tamarix usneoides, Euclea pseudebenus, and Rhus lancea are found along the riverbeds throughout the ecoregion.
Namibia has two distinct biodiversity hotspots, defined as areas of high endemism and high species richness. One is the Sperregebiet region, located in the southwest of the country in the Succulent Karoo ecoregion, and the second is the Kaoko Escarpment in the far northwest. The northern area of this ecoregion encompasses the Kaoko Escarpment and is therefore rich in species and endemics. Most of the endemics are clustered around the Brandberg Mountain and around the Khomas highlands north of Windhoek. The Brandberg Mountains support 90 of Namibia’s endemic plants and eight plants that are only found there. The high altitude of this isolated relict inselberg and the cool, moist conditions at its summit could explain the high level of endemism found in this region. Two of the most striking plants of the Brandberg Mountain are the Brandberg acacia (Acacia montis-usti) and the Brandberg euphorbia (Euphorbia monteiroi subsp. brandbergensis).
The Khomas region contains Namibia’s second highest mountain, the Auasberg, at 2479 metres, and it is in a transitional arid region, representing ideal conditions for speciation of desert plants. There are 68 endemic plants in this region. Other endemics and near-endemics found within the ecoregion as a whole are Panicum arbusculum, Stachys burchelliana, Schotia afra, Berkheya chamaepeuce, Barleria lichtensteiniana, Euphorbia gariepina, E. gregaria, E. avasmontana, Zygophyllum dregeanum, and Z. microcarpum. The ecoregion has many interesting, well-defined species that are taxonomically isolated, for example, the monotypic genera Phlyctidocarpa and Kaokochloa (Poaceae). Other well-defined species include Acacia robynsiana, Balanites welwitschii, and Petalidium spp. Intense recent speciation has occurred within the Petalidium genus.
According to Maggs et al. more than 25 of the species recorded by Nordenstam for the Brandberg Mountain are likely the descendent remains of an old arid flora, and have disjunct distributions among the arid areas of the Karoo-Namib region and the Saharan area of the Sudano-Zambezian region. The most widely accepted explanation for these present-day disjunct distributions is that they are relicts from a previously continuous arid belt stretching across Africa from Somalia to Botswana, Namibia and South Africa.
The Namibian savanna woodlands ecoregion is also a center of high faunal endemism and species richness. The ecoregion has a significantly larger number of Namibian endemic invertebrates, amphibians, reptiles, mammals and birds than adjacent ecoregions. This distribution suggests relict populations isolated, perhaps, by low desert temperatures and mobile sands on the coastal plains, isolating rocky habitats and promoting speciation. Further inland, oscillating patterns of regional rainfall and global temperature may have isolated species on rocky islands and inselbergs. There are a total of 529 vertebrate taxa present in the ecoregion.
Endemic and near-endemic mammals are chiefly comprised of bats, rodents and small carnivores. The Namaqua slender mongoose (Galerella sanguinea swalius) and the Shortridge's rock mouse (Petromyscus shortridgei) are restricted to the Namaland escarpment. A further six species of small mammal and bat are also near-endemic to the ecoregion, including the Angola wing-gland bat (Myotis seabrai, VU) and the bat Laephotis namibensis, EN. The only large mammal endemic to this region is the mountain zebra (Equus zebra hartmannae, EN), which is near-endemic to the ecoregion, and is the only large mammal endemic to Namibia.
Among the larger mammals the ecoregion is well-known for its desert-dwelling populations of elephant (Loxodonta africana, EN) and black rhinoceros (Diceros bicornis, CR). The black rhino population in this area is one of the few unfenced populations of black rhinos in the world, and it is estimated to number more than 100 individuals. Other large mammal species found within the ecoregion are kudu (Tragelaphus strepsiceros LR), springbok (Antidorcas marsupialis LR), gemsbok (Oryx gazella LR), Damara dik-diks (Madoqua kirkii), and black-faced impala (Aepyceros melampus petersi VU). Predators include lion (Panthera leo), leopard (Panthera pardus), cheetah (Acinonyx jubatus VU), bat-eared fox, (Otocyon megalotis) and Cape fox (Vulpes chama).
There are a number of anuranAn amphibian that has limbs but no tail (includes all frogs and toads) taxa present in the ecoregion, a complete list being the African ornate frog (Hildebrandtia ornata); Angola river frog (Amietia angolensis); Boettger's dainty frog (Cacosternum boettgeri); Cape river frog (Amietia fuscigula); Mossamedes toad (Poyntonophrynus grandisonae); Okahandja toad (Poyntonophrynus hoeschi); Senegal running frog (Kassina senegalensis); and the widespread African clawed frog (Xenopus laevis). These anurans are the sole amphibians found in the Namibian savanna woodlands.
Seven reptile taxa are strictly endemic to the ecoregion. Albert’s burrowing skink (Sepsina alberti) is an interesting pale green skink with a bright blue tail that is restricted to the northern portion of the ecoregion. In total, four lizard taxa, a gecko, a skink and a tortoise are reptilian specialists within this habitat: Husaben sand lizard (Pedioplanis husabensis), Namaqua spinytail lizard (Cordylus namaquensis), Campbell's spinytail lizard (Cordylus campbelli), Herero girdled lizard (Cordylus pustulatus), Brandberg thick-toed gecko, Albert's skink, and Nama padloper (Homopus sp. nov). Around fifty reptile species are either endemic or near-endemic reptiles in the ecoregion. Of these, 83 percent occur on and around the Brandberg, suggesting relict populations. For example, the Brandberg thick-toed gecko (Pachydactylus gaiasensis) is restricted to the Brandberg. Only two amphibians are considered endemic to the ecoregion, the Okahandja toad (Bufo hoeschi) and the Mossamedes toad (Poyntonophrynus grandisonae).
The Kaoko Escarpment that makes up this ecoregion has the highest level of avian diversity in Namibia, with 297 bird species recorded to date. Most of the avifauna is restricted to the rocky habitats of the ecoregion and is found at elevations of between 600 m and 1,200 m. Five birds are endemic or near-endemic to this ecoregion: including the Karoo chat (Cercomela schlegelii), tractrac chat (Cercomela tractrac), greybacked cisticola (Cisticola subruficapillus), and the herero chat (Namibornis herero). All the near-endemic species except the Cinderella waxbill (Estrilda thomensis) are restricted to rocky habitats. The Cinderella waxbill is found in the wetter area of southern Angola, entering the ecoregion down the Kunene River.
Namibia’s recent biodiversity assessment identified priority conservation areas in the country. The Kaoko Escarpment in the northern part of this ecoregion is an endemism hotspot, and it also has immense value in both cultural and scenic wilderness terms. It represents one of the most significant gaps in habitat protection within Namibia, and it is a top-priority area for urgent biodiversity protection measures. Presently there are only two small protected areas: the Damaraland Wilderness Reserve (1,600 km2) and the Brandberg National Monument. The area was once part of "Game Reserve No. 2," which originally covered 80,000 square kilometres (km2) and was the largest nature reserve in the world. It stretched from the Kunene River, 200 km south to the Hoarusib River and included this escarpment and the coastal plain. 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 Southwest Africa Affairs re-allocated land to ethnically partitioned homelands to promote the ideology of separate development. Game Reserve No. 2 was reduced by 72 percent to become the present Etosha Pan National Park (with a size of 22,912 km2).
The south of this ecoregion is also poorly protected. A small portion of the Namib-Naukluft National Park extends into the ecoregion to include the Naukluft Mountains (southwest of Windhoek).
Other forms of protection, such as conservancies, private nature reserves and game farms add largely to the current protection of the area. Conservancies are jointly managed for resource conservation by multiple landowners with financial and other benefits shared among them. They occur on private and communal (tribal) land. Most aim to enhance habitat for, and numbers of, game species, such as ungulates and game birds to draw income from tourism ventures. A large communal conservancy was submitted for formal gazetting in 1997. It stretches along the eastern boundary of the Skeleton Coast National Park, in the area previously occupied by Game Reserve No. 2. The proximity of the Skeleton Coast Park and Etosha Park offers considerable benefits to rural communities, making ecotourism and conservancy management an attractive land-use option. The formation of conservancies has been stimulated by the government’s recent policy to return resource management rights to conservancy committees with an approved constitution. There are some private nature reserves and game farms in the area. Game farming is increasing in popularity, partly because much of the area is only marginally suitable for livestock. Although game farms are sometimes intensively managed to promote selected game species, using fire and chemical control of woody vegetation, their biodiversity conservation value is perceived to be higher than that of livestock farming.
On an ecoregion scale, many species such as springboks, leopards and gemsboks have not suffered significant range reductions, and the distributions of smaller mammals have changed little during recorded history. A few species, like the Greater kudu and the Damara dik-dik have even benefited from bush encroachment. The establishment of artificial water sources and reduced predator numbers has increased distributions of these species. While bush encroachment has benefited these species, it leads to a reduction in diversity and is therefore not seen as positive for conservation within the ecoregion.
Severe overhunting of game mammals on private land was a major threat to wildlife for the first half of the century, but this was significantly reversed in 1967 when legislation shifted the ownership of game from the state to the individual landowner. This allowed landowners to commercialize game rather than incur losses through competition of game with livestock. The Nature Conservation Amendment Act of 1992 extends similar fundamental rights to people living in communal areas, with the hope that rural dwellers will realize the value of wildlife and manage it sustainably. The conservation status of all Namibian mammals is now under review and, as an interim measure, a list of species with provisional conservation status rankings has been produced. Many of the species do not have sufficient data to evaluate them and place them into categories. Thus, the interim status confers a high level of protection until the species can be confidently assessed.
After the deproclaimation of Game Reserve No. 2 in 1963, the northern areas of Namaland were administered from afar by the Department of Bantu Affairs in Pretoria. This was a period of corruption and widespread poaching. This poaching problem has continued and is a present-day threat to the wildlife of the ecoregion, especially to the unfenced black rhino population. In an attempt to control poaching, these rhinos are being de-horned and have also been previously translocated to the Etosha Pan National Park.
Plant poaching by collectors of succulent species is impacting the flora of the ecoregion. Illegal trade in spectacular succulent species is believed to be considerable.
Farming practices in Namibia vary widely in their environmental impact. Poor land management through overgrazing has led to soil erosion, loss of grass species diversity, and bush encroachment. Numerous livestock and game farmers in Namibia, however, practice exemplary land management. However, this is expensive and such practices have been jeopardized by uncertainty about impending land reform, particularly at the time of independence in 1990. A study by Sullivan and Konstant carried out in the Kunene region to the north of this ecoregion shows that communal farming has a negative effect on the vegetation through overgrazing, browsing and cutting for firewood. They conclude, however, that this effect is on a local scale and should not be extrapolated to the ecoregion as a whole. They also note that Colophospemum mopane has remarkable coppicing ability and that it is extremely resilient to these practices on an individual and population level, even though it is sought after for poles and firewood.
Lastly, the Namaland escarpment has recently become a popular destination for off-road enthusiasts. While this may have advantages in bringing tourism into the area, many off-road drivers have proven to show no regard to the sensitive environments in which they are driving.
Justification of ecoregion delineation
This ecoregion is largely based on the ‘bushy Karoo-Namib shrubland’ of White and also includes a small transition area of ‘Colophospermum mopane scrub woodland to Karoo-Namib shrubland.’ This woodland ecoregion stops about 50 km from the coast compared to White’s vegetation unit, although the northern limit is the same. The southern limit stops north of Groot Karasberg, near Keetmanshoop roughly around the 900 m contour. This ecoregion is characterized by faunal and floristic elements of both the Namib and Kalahari. The Namibian savanna woodlands is accorded the ecocode AT1316 by the World Wildlife Fund.
The following ecoregions have tangency to the Namibian savanna woodlands:
- Kalahari xeric savanna, to the southeast
- Nama Karoo, to the south
- Namib Desert, at the southwest
- Kaokoveld Desert, at the northwest
- Angolan Miombo woodlands, at the northeast
- Angolan mopane woodlands, to the east
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