Location and General Description
The Angolan Mopane Woodlands ecoregion stretches from southwestern Angola into northern Namibia, between about 15°S and 21°S latitude. It lies inland of the Namib escarpment, but mostly to the west of the Zambezian Baikiaea Woodlands. The large salt pan, the Etosha Pan, falls within this ecoregion but is considered its own ecoregion, the Etosha Pan Halophytics.
Mean annual rainfall in the ecoregion is between 400 mm to 600 mm, increasing inland of the coastal desert areas (Barnard 1998). The rain normally falls in the summer months, between August and April, with most falling in late summer. February usually has the mean maximum rainfall, about 110 mm. The annual rainfall total is unpredictable. In the Etosha National Park, for example, the mean annual rainfall in 1946 was 90 mm, but in 1950 it was 975 mm (Berry 1972). Mean temperatures increase inland, away from the cooling effects of the Benguela Current. Mean maximum temperatures range from around 24°C near the coastal deserts, up to 30°C further inland. The mean minimum temperatures similarly increase inland, from 9°C towards the coast to up to 12°C further inland.
This ecoregion lies on the western edge of the Central African Plateau, at around 1,000 m in elevation. The area is mostly flat, but gains elevation towards the south, where it reaches its highest point in the Waterberg Mountains (1,857 m) (Barnard 1998). The ecoregion is bound to the north, west and southwest by high-elevation, mountainous terrain. To the east and southeast, the topography remains flat. The soils of the ecoregion contain Precambrian basement sediments. They are complex, with a number of major soil units mapped (Barnard 1998). These include halomorphic soils around the Etosha Pan, weakly developed shallow soils of arid origin to the south, and soloetzic and planosolic soils, as well as arenosols, to the north. The halomorphic soils of the Etosha area overlie calcrete and are shallow, alkaline, high in water soluble salts while poor in both phosphates and nitrogen (le Roux 1980).
The Kunene River is the only perennial river flowing through this ecoregion. Its catchment lies to the north of the ecoregion in the Angolan highlands. The Kunene flows south through the ecoregion, and then it heads southwest into the Namibian Savanna Woodland ecoregion where it forms the border between Angola and Namibia. Another important river system is the Cuvelai Drainage Basin in northern Namibia. This is a 7,000 km2 area of ephemeral, shallow, parallel channels or oshanas which fill Lake Oponono when flooded. Lake Oponono is situated about 70 km north of the Etosha Pan and is the largest water body in the Cuvelai Basin (Barnard 1998). It receives floodwaters about twice every three years. The lake is the source of the Ekuma River that flows into the Etosha Pan when the Cuvelai Basin is flooded. Two other ephemeral rivers, the Oshigambo and Omuramba Ovambo, also flow into the pan (Berry et al. 1973). All three rivers flow erratically during the rainy season.
Mopane dominates the vegetation of this ecoregion. Mopane is a single-stemmed tree or shrub with distinctive, butterfly-shaped leaves. It often forms a dense, monospecific stand with a sparse understory. Grass is usually absent under well-developed mopane stands and hence fire damage is minimal, even though the mopane tree itself is resinous and flammable. However, if the canopy is opened up (for example by browsing elephants), grasses invade and the fire frequency is increased. Browsing elephants frequently fell mopane trees, which then coppice from the base. In these situations the mopane woodland is converted to a tall grassland with unusually low (0.3 to 1.6 m), multi-stemmed mopane shrubs. The grass between the individual coppice clumps is generally as tall as the mopane (White 1983).
The mopane in this ecoregion occurs either as a shrub or a tree depending on local conditions. In some areas it forms a dense woodland, whereas in others it grows as a short shrub intermingled with scattered trees (Giess 1971). In Angola, the mopane grows over vast areas in a low, thorny bushveld. It is associated with Acacia kirkii, A. nilotica subsp. subalata, A. hebeclada subsp. tristis, A. erubescens, Balanites angloensis, Combretum apiculatum, Commiphora spp., Dichanthium papillosum, Dichrostachys cinerea, Grewia villosa, Indigofera schimperi, Jatropha campestris, Melanthera marlothiana, Peltophorum africanum, Rhigozum brevispinosum, R. virgatum, Securinega virosa, Spirostachys africana, Terminalia prunoides, T. sericea, Ximenia americana, and X. caffra (Werger 1978 and White 1983). On alluvial soils Acacia kirkii becomes abundant.
In Namibia, the mopane occurs mostly as a 7 m to 10 m high tree and forms a woodland with a shrubby understory (White 1983). Mopane dominates the vegetation of the Etosha National Park, and it has been estimated that about 80 percent of all Etosha’s trees are mopane (Berry 1991). The roots, bark, leaves, and branches of the mopane tree are extensively utilized by the park’s nearly 1,750 elephants (Balfour and Balfour 1992). Over most of the park the mopane grows as a shrub or small tree, but in the Halali area to the south of the park, it becomes a tall, dense woodland interspersed with red bushwillow (Combretum apiculatum subsp. apiculatum), purple-pod terminalia (Terminalia prunioides) and leadwood (Combretum imberbe) (Berry 1991). The mopane is salt-intolerant and does not grow on the brackish soils that fringe the Etosha Pan. Other vegetation types are found within the park. To the west, there are extensive grasslands that attract thousands of ungulates after the summer rains. The grasslands sustain a wide variety of annual and perennial grasses, most of which fall into the "sweetveld" category (Balfour and Balfour 1992). The vegetation to the northeast of the park consists of a mixed tree and shrub savanna. Due to deep Kalahari sands and a higher rainfall, bigger and more varied trees grow here, such as Acacia erioloba, Terminalia prunioides, Lonchocarpus nelsii and tamboti (Spirostachys africana) (White 1983). A major attraction of the Etosha National Park, and a favorite subject for photographers, is the "haunted forest," situated on a vast plain 30 km west of the pan. The forest is made up of several hundred phantom trees (Moringa ovalifolia), from the family Moringaceae. These 6 m to 7 m high trees are contorted by browsing (mainly elephant) and grow into weird shapes. Each tree has many succulent trunks emerging from a swollen base
Levels of endemism are high in the Namibian Savanna Woodland and Kaokoveld Desert ecoregions to the west of the Angolan Mopane Woodlands. These arid ecoregions have evolved a highly specialized fauna and flora that is adapted to their harsh environments. The Angolan Mopane Woodlands has lower levels of endemism, largely a result of its more mesic environment. While the arid ecoregions have high levels of endemism, they have low levels of species richness for birds, mammals and invertebrates. Levels of species richness for these taxa increase towards the more mesic inland ecoregions due to the inclusion of tropical species from central Africa.
The Angolan Mopane Woodlands has a high level of mammalian biodiversity and is home to the charismatic large mammals typical of African savannas. These large mammals occur in vast numbers within the Etosha National Park. During the dry winter months, large numbers of wildlife congregate at the springs and waterholes around the pan. Zebra (Equus burchelli antiquorum), blue wildebeest (Connocheatus taurinus), and springbok (Antidorcas marsupialis) are the most numerous mammals at these waterholes. Other species include elephant (Loxodonta africana) giraffe (Giraffa camelopardus), Hartmann’s zebra (Equus zebra hartmannae), black rhinoceros (Diceros bicornis), gemsbok (Oryx gazella), eland (Taurotragus oryx), kudu (Tragelaphus strepsiceros), roan (Hippotragus equines), steenbok (Raphicerus campestris), Damara dik-dik (Madoqua kirki) and the vulnerable, near-endemic black-faced impala (Aepyceros melampus petersi) (Hilton-Taylor 2000). A small group of white rhino (Ceratotherium simum) has also been recently re-introduced into the park after becoming locally extinct in the early 1900s (Olivier and Olivier 1999). Predators, such as lion (Panthera leo), leopard (Panthera pardus), cheetah (Acinonyx jubatus), spotted hyena (Crocuta crocuta), and brown hyena (Hyaena brunnea) are found close to the wildlife at the waterholes. Smaller predators found at the waterholes include the black-backed jackal (Canis mesomelas) and the bat-eared fox (Otocyon megalotis) (Joubert and Mostert 1975). The spectacular congregations of wildlife at the waterholes around the Etosha Pan have made Etosha National Park one of Africa’s most popular national parks. In the wetter summer months, wildlife migrates away from the waterholes. The major migration is to the west, where the animals utilize the extensive grasslands and their temporary pools (Balfour and Balfour 1992). Etosha’s elephants migrate to the Kavango and the Kaokoveld Desert during the wet season. During the dry months, when water in these regions dry up, they return to the park and its springs. During these months, Etosha’s elephant population often reaches more than 2,000 individuals (Olivier and Olivier 1999).
Four mammals are near-endemic to the Angolan Mopane Woodlands. These are a bush rat, Aethomys thomasi, two white-toothed shrews (Crocidura erica, C. nigricans), and the black-faced impala. Crocidura erica and the black-faced impala are classified as vulnerable in the IUCN red list of threatened animals (Hilton-Taylor 2000).
This ecoregion has a diverse avian fauna, with 375 species recorded, higher than the arid ecoregions to the west and south or the Zambezian Baikiaea Woodlands to the east (Robertson et al. 1998). At least 340 bird species have been recorded in the Etosha National Park (Hall 1994), which has been classified as a globally Important Bird Area (Barnes 1998). The largest numbers of birds are found within the park between October and April, when the summer migrants are present. Etosha supports the only breeding population of the threatened blue crane (Anthropoides paradiseus) outside of South Africa. However, this tiny population has declined over the past 10 years (Simmons et al. 1998b). The park is particularly rich in raptors with 46 species recorded, including all vultures found in Namibia. Nine bird species are near-endemic to the ecoregion, most of which are generally restricted to the mopane vegetation. These species include rockrunner (Achaetops pycnopygius), grey kestrel (Falco ardosiaceus), Carp’s tit (Parus carpi), southern violet woodhoopoe (Phoeniculus damarensis), Bradfield’s hornbill (Tockus bradfieldi), Monteiro’s hornbill (Tockus monteiri), barecheeked babbler (Turdoides gymnogenys), and blackfaced babbler (Turdoides melanops). Only the rufous-tailed palm thrush is not a savanna species, being restricted to the vegetation along the Kunene River (Sinclair and Hockey 1996).
The ecoregion has a large number of reptile species, four strictly endemic species; Afrogecko ansorgii, Coluber zebrina, Ruben's sand lizard (Pedioplanis rubens), and the skaapsteker (Psammophylax ocellatus) a solid-bodied, venemous snake that reaches up to 1 m in length. The African rock python (Python sebae) is also found in this habitat. There is also one strictly endemic amphibian known from the ecoregion, Ptychadena mapacha.
The Angolan Mopane Woodland has the second highest spider diversity in Namibia with 115 species native to the ecoregion, second only to the adjacent Kalahari Acacia-Baikiaea Woodland ecoregion (Griffin 1998). Spider diversity is higher here than in arid ecoregions to the west due to the greater density of trees and large bushes. Seven species are endemic. The ecoregion also has a relatively high number of solifuge and scorpion species, 22 and 21, respectively. Two species of each taxa are endemic to the ecoregion (Griffin 1998).
The Cuvelai Basin is an important freshwater fish habitat in this ecoregion. When rain in Angola floods its tributaries, the basin fills with water and fish that are swept up to 200 km from the permanently watered Angolan areas. During these floods, the basin supports up to 43 crustaceans and 19 fish species (Barnard 1998). The fish are an important natural resource and are extensively utilized by the local people.
Two national parks occur on the Angolan side of the ecoregion. These are Bikuar National Park (7,900 km2) and Mupa National Park (6,600 km2). While these two parks cover a representative area of the Angolan Mopane Woodlands, they do not offer adequate protection, as a result of the 30-year civil war in the country (Dean 2000).
The vast Game Reserve No. 2 originally covered about 80,000 km2 of northern Namibia and was the largest nature reserve in the world. This reserve included the Kaokoveld Desert, the northern portion of the Namib Escarpment and the central area of the Angolan Mopane Woodlands. It stretched from the Kunene River border southward, more than 200 km, to the Hoarusib River. In 1968 the reserve was reduced by 72 percent to become the present Etosha National Park, an area of 22,912 km2. The excised land was re-allocated to communal homelands (Owambo, Kaokoland and Damaraland) for the "sole use and occupation by natives" and was effectively lost to conservation. The allocation of homelands was part of the master plan under South African apartheid and was recommended by the Odendaal Commission of Enquiry into South West Africa Affairs. The commission promoted the ideology of separate development through ethnically partitioned homelands (Barnard et al. 1998).
The remaining area of the Etosha National Park covers a representative portion of the Angolan Mopane Woodlands, which is considered to be reasonably well-protected (du Plessis 1992). A recent assessment of Namibia in terms of taxon richness, endemism and conservation threat did not consider the Angolan Mopane Woodlands ecoregion to be a priority area for conservation action (Barnard et al. 1998).
Other forms of protection, such as conservancies, contribute to the conservation of the ecoregion. A large conservancy in the Angolan Mopane Woodlands has recently been submitted for formal approval (Barnard et al. 1998). It is expected that about 50 percent of the land formally occupied by Game Reserve No. 2 will again be protected, in this case by large communal conservancies. 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 (Barnard et al. 1998).
Private nature reserves and game farms are also found in this ecoregion and game farming is increasing in popularity. Although game farms are sometimes intensively managed to promote selected wildlife species (using fire and chemical control of woody vegetation), their biodiversity conservation value is perceived to be higher than that of livestock farming (Barnard et al. 1998).
Types and Severity of Threats
After Game Reserve No. 2 was dissolved, wildlife in this area was nearly decimated by poaching gangs, colonial officials, contractors and local people armed from Namibia’s war of liberation. The poaching problem has continued and is still a threat to the wildlife of the ecoregion. It is a severe threat to the black rhino population. In an attempt to control poaching, 68 rhinos were translocated to the Etosha National Park between 1967 and 1977 (Hofmeyer et al. 1975) and anti-poaching patrols were set up within the park. More recently, 42 Etosha rhinos have been translocated through a "custodianship program" to well-guarded private farms that meet stringent requirements (Barnard 1998). Rhinos are also being de-horned as a last resort to deter poachers (Berger and Cullingham 1994). A highly successful community game guards program has been set up within the conservancies. This program is funded by donors but controlled by local communities, providing incentives for local people to manage rhinos and other wildlife for long-term benefit (Barnard 1998).
During the first half of the century, severe over-hunting of mammals was a major threat to wildlife outside of Namibia’s protected areas. However, in 1967 legislation shifted the ownership of wildlife from the state to the individual landowner. This significantly reduced the hunting threat to wildlife as landowners began to commercialize wildlife (Griffin 1998). As a result, most mammals in Namibia have not suffered significant reductions in numbers. The Nature Conservation Amendment Act of 1992 has extended similar rights to people living in communal areas with the hope that rural dwellers will realize the value of wildlife and manage it sustainably (through conservancies).
The situation on the Angolan side of the ecoregion is less encouraging. The 30-year civil war in Angola has had a devastating impact on conservation in the area (Dean 2000). Protected areas are open to poachers, timber harvesting, human settlement and agriculture. Few, if any, viable populations of larger mammals have survived and populations of lion, black rhino and giraffe have been reduced to the threshold of local extinction. The situation is similar outside of the protected areas, and over-exploitation of wildlife and other natural resources is commonplace. On the positive side, the Angolan government has recently 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).
On the Namibian side of the ecoregion, most of the land that was once set aside as a homeland by the Odendaal Commission is classified as "communal land" (Moyo et al. 1993). The human impact on the vegetation of these communal lands was assessed by Sullivan and Konstant (1997). The indigenous vegetation fulfils many subsistence needs, providing important sources of food, household medicines, fuel and the raw materials for building, household utensils, and a variety of local industries. The vegetation also provides grazing and browsing for livestock. Sullivan and Kontant (1997) showed that human settlement was having a significant, but small-scale, negative impact on the vegetation. It was concluded however that this effect should not be extrapolated to the communal lands as a whole. It was also noted that Colophospermum mopane has a remarkable coppicing ability and is extremely resilient to these practices on an individual and population level, even though it is sought after for poles and firewood. Land to the south of the ecoregion was formerly classified as "white" and is now held as private farms under a freehold tenure system (Moyo et al. 1993). Farming practices on these farms vary widely. Poor land management through overstocking has led to soil erosion, loss of grass species diversity and bush encroachment on some farms, while other livestock and wildlife farmers practice exemplary land management. This variability in farming practices has stemmed from an uncertainty regarding impending land reform, particularly at the time of independence (in 1990) (Barnard et al. 1998).
The Etosha National Park faces several management challenges. Anthrax has become a significant disease within the park. This infectious bacterial disease affects warm-blooded animals, including humans, causing fatal septicemia (Balfour and Balfour 1992). Anthrax, together with rinderpest, is one of the most dramatic diseases affecting wild animals in Africa (Ebedes 1976). Within Etosha National Park, anthrax has killed a variety of herbivores, from elephants to ostriches. Carnivores such as lion, leopard, hyena and jackal appear to be immune to the disease. The cause of the anthrax epidemic remains unknown. Another disease, feline immune deficiency virus (FIV), is also prevalent. This virus affects cats in the park, particularly cheetah (Simmons et al. 1998b).
Fire control within the park has led to the transition of the vegetation from open savanna to woodland, which has favored the elephant population. Elephant numbers have increased from 100 in 1955 to nearly 2,000 at present. These elephant migrate northwards out of the park during the wet season, creating problems on neighboring farming areas. Lion also migrate out of the Park, become a threat to livestock on the neighboring farms, and are shot by local farmers. The southern and western borders of the park are fenced off with double electric fencing. This fence has disturbed the natural herbivore migration patterns in the area. This disturbance is a particular threat during drought years when the ungulates cannot move away from drought stricken areas (Simmons et al. 1998b).
The oshanas of the Cuvelai Basin are an important source of fish and other wetland resources for rural people in the area. The basin supports more people per unit area than any other non-urban region in Namibia (Barnard 1998). This system is under threat through agriculture, intensive settlement, and overfishing. Another threat to this system is the introduction of alien fish through pipelines. A pipeline carrying water from the Kunene to the Cuvelai Basin has introduced many Kunene species into the basin. Three of these, all cichlids, are now well-established in the oshanas (van der Waal 1991).
Justification of Ecoregion Delineation
The linework for this ecoregion is based on the western portion of White’s (1983) ‘Colophopsermum mopane woodland and scrub woodland. This is distinguished separately from Zambezian and mopane woodlands due to different faunal compositions, ecological processes, and geographic distance (WWF 1998).
This ecoregion is part of larger complex of Caesalpinoid woodland ecoregions that support wet and dry miombo, mopane, thicket, dry forests, Baikiaea woodland, and flooded grassland habitats, among others. The dominance of Caesalpinoid trees is a defining feature of this bioregion (i.e., a complex of biogeographically related ecoregions). Major habitat types (e.g., mopane and miombo) and the geographic separation of populations of large mammals are used to discriminate ecoregions within this larger region. All of these ecoregions contain habitats that differ from their assigned biome or defining habitat type. For example, patches of dry forest occur within larger landscapes of miombo woodlands in several areas. More detailed biogeographic analyses should map the less dominant habitat types that occur within the larger ecoregions.
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Prepared by: Suzanne Vetter
Reviewed by: In progress