Angolan mopane woodlands
The Angolan Mopane Woodlands are located in northern Namibia and southern Angola, completely surrounding the Etosha Pan, which is considered a separate ecoregion. Mopane trees (Colophospermum mopane) dominate the vegetation, and are an essential resource for both the people and wildlife of the region. African Bush Elephants (Loxodonta africana) utilize almost every part of the mopane tree, and the region supports other large herbivores, including the critically endangered Black Rhinoceros (Diceros bicornis). Species richness in this ecoregion is high, especially in comparison with the arid deserts to the west. Conservation potential is high in Namibia, due to the vastness of the desolate Namib Desert and the presence of Etosha National Park, and increasing awareness of conservation of natural resources; conversely, conservation in Angola has been severely compromised by the lengthy civil war and residual presence of the Russian funded Cuban mercenary army forces; consequently, and many large mammal species are near local extinction in Angola.
Location and general characteristics
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 millimetres (mm) to 600 mm, increasing inland of the coastal desert areas. 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. 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 1000 metres (m) in elevation. The area is mostly flat, but gains elevation towards the south, where it reaches its highest point in the Waterberg Mountains (1857 m). 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. 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.
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 7000 kilometres squared (km2) area of ephemeral, shallow, parallel channels or oshanas which fill Lake Oponono when flooded. Lake Oponono is situated about 70 kilometres north from Etosha Pan, and is the largest surface water body in the Cuvelai Basin. It receives floodwaters approximately 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, discharge into the pan. All three rivers flow sporadically during the rainy season.The
Mopane trees dominate the canopy 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 thus fire damage is usually 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 metres), multi-stemmed mopane shrubs. The grass between the individual coppice clumps is then typically as high as the mopane.
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. In Angola, the mopane grows over vast areas in a low, thorny bushveld. It is associated with Floodplain Acacia (Acacia kirkii), Kauria babul (A. nilotica subsp. subalata), A. hebeclada subsp. tristis, Blue Thorn (A. erubescens), Melanoides angolensis, Red bushwillow (Combretum apiculatum), Commiphora spp., Medio Bluestem (Dichanthium annulatum var. papillosum), Sicklebush (Dichrostachys cinerea), Mallow-leaved Cross-berry (Grewia villosa), Indigofera schimperi, Jatropha campestris, Melanthera triternata, African Wattle (Peltophorum africanum), Simple-leaved Rhigozum (Rhigozum brevispinosum), R. virgatum, Snowberry Tree (Flueggea virosa), Tamboti (Spirostachys africana), Terminalia prunoides, Silver Cluster-leaf (T. sericea), Hog Plum (Ximenia americana) and Sourplum (X. caffra). On alluvial soils Floodplain Acacia becomes abundant.
In Namibia, the mopane occurs mostly as a seven to ten metre high tree, and forms a woodland with a shrubby understory. 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. The roots, bark, leaves, and branches of the mopane tree are extensively utilized by the park’s nearly 1750 elephants. 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). The mopane is salt-intolerant and will not grow on the brackish soils that fringe the Etosha Pan.
Other vegetation types are found within the park. At the western end, there are extensive grasslands that attract thousands of ungulates subsequent to the austral summer rains. These grasslands sustain a gamut of annual and perennial grasses, most of which fall into the sweetveld category. The vegetation at the northeast of the park consists of a mixed tree and shrub savanna. Due to deep Kalahari sands and more plentiful rainfall, bigger and more varied trees grow in this northeastern extremum, such as Camel Thorn (Acacia erioloba), Purple-pod Cluster-leaf (Terminalia prunioides), Lonchocarpus nelsii and Tamboti (Spirostachys africana). A major draw of the Etosha National Park, and a favourite subject for photographers, known as the haunted forest, situated on a vast plain about 30 km west of the main pan. The forest is made up of several hundred Phantom Trees (Moringa ovalifolia) growing in savanna format, from the family Moringaceae. These six to seven metre high trees are contorted by browsing (chiefly by elephants) and grow into fantastic forms. 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 soil environment. While this arid ecoregion exhibits high endemism, there is a low level of species richness for birds, mammals and invertebrates. The degree species richness for these latter taxa increases 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. burchell's Zebra (Equus burchelli), Blue Wildebeest (Connocheatus taurinus), and Springbok (Antidorcas marsupialis) are the most abundant large mammals at these waterholes. Other mammalian species include;
- African Bush Elephant (Loxodonta africana);
- Giraffe (Giraffa camelopardalis);
- Hartmann’s Mountain Zebra (Equus zebra hartmannae);
- Black Rhinoceros (Diceros bicornis);
- Gemsbok (Oryx gazella);
- Eland (Taurotragus oryx);
- Greater Kudu (Tragelaphus strepsiceros);
- Roan Antilope (Hippotragus equinus);
- Steenbok (Raphicerus campestris);
- Kirk's Dik-dik (Madoqua kirki); and the
- Vulnerable, near-endemic Black-faced Impala (Aepyceros melampus petersi).
A small group of White Rhinoceros (Ceratotherium simum) has also been recently re-introduced into the park after becoming locally extinct in the early 1900s. Predators, such as Lion (Panthera leo), Leopard (Panthera pardus), Cheetah (Acinonyx jubatus), Spotted Hyena (Crocuta crocuta), and Brown Hyena (Hyaena brunnea) are found proximate to the wildlife at the waterholes. Smaller predators found at the waterholes include Black-backed Jackal (Canis mesomelas) and Bat-eared Fox (Otocyon megalotis). The spectacular congregations of wildlife at the waterholes around the Etosha Pan have made Etosha National Park one of Africa’s most engaging national parks. In the wetter austral summer months, wildlife generally migrate farther away from the waterholes. The major migration is to the west, where mammals utilize the extensive grasslands and associated ephemeral pools. Etosha’s elephants generally migrate to the Kavango and the Kaokoveld Desert during the wet season. During the dry months, when water in these deserts disappears entirely, they return to the park and its waterholes. During this arid season, Etosha’s elephant population may attain a level exceeding 2000 individuals.
Four mammals are near-endemic to the Angolan mopane woodlands. These are Thomas's Rock Rat (Aethomys thomasi), Heather Shrew (Crocidura erica), Black White-toothed Shrew (C. nigricans) and the Black-faced Impala. Both the Heather Shrew and the Black-faced Impala are classified as Vulnerable in the IUCN red list of threatened animals.
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. At least 340 bird species have been recorded in the Etosha National Park, which has been classified as a globally Important Bird Area. 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 small population has declined noticeably over the past fifteen years. The park is particularly rich in raptors, with 46 species recorded, including each vulture taxon known to Namibia. Nine bird species are near-endemic to the ecoregion, most of which are generally restricted to the mopane vegetatative community. These species include Rockrunner (Achaetops pycnopygius), Grey Kestrel (Falco ardosiaceus), Carp’s Tit (Parus carpi), southern Violet Wood Hoopoe (Phoeniculus damarensis), Bradfield’s Hornbill (Tockus bradfieldi), Monteiro’s Hornbill (Tockus monteiri), Bare-cheeked Babbler (Turdoides gymnogenys), and Black-faced Babbler (Turdoides melanops). Only the Rufous-tailed Palm Thrush (Cichladusa ruficauda) is not a savanna species, being restricted to the riparian zone vegetation along the Kunene River
The ecoregion has a large number of reptile species, four strictly endemic species; Afrogecko ansorgii, Coluber zebrinus, Ruben's Sand Lizard (Pedioplanis rubens), and the Spotted Skaapsteker (Psammophylax rhombeatus) a sturdy-bodied, venemous snake that reaches up to one metre in length. The African Rock Python (Python sebae) also occurs in this mopane habitat.
There is only one strictly endemic amphibian known from the Angolan mopane woodlands: Ptychadena mapacha. The following additional anuran species occur in this ecoregion: Benguella Reed Frog (Hyperolius benguellensis), found in emergent vegetation at swamp and pond margins; Cinnamon-bellied Reed Frog (Hyperolius cinnamomeoventris), whose breeding sites typically have abundant grassland; Red-spotted Namibian Frog (Phrynomantis annectens), associated with inselbergs and other rocky areas; Cryptic Sandfrog (Tomopterna cryptotis), who prefers sandy soil area of semi-desert or savanna; Common Reed Frog (Hyperolius viridiflavus), often found in emergent vegetation at swamp and river edges; Horseshoe Forest Treefrog (Leptopelis bocagii); and the Khwai River Toad (Poyntonophrynus kavangensis), that breed in seasonally filled pans and other ephemeral pools in sandy soil areas.
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. 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. When rainfall in the Angola mopane woodland basin floods its tributaries, large areas fill with water, and some organisms are swept up to 200 km from the perennial streambeds. During these floods, the basin supports up to 43 crustaceans.
The Cuvelai Basin is an important freshwater fish habitat in this ecoregion. During large scale flood events in the catchment basin, much of the ecoregion fills with water and many fish that are swept up to 200 km distant from the permanent surface waters. During these flood events, the basin supports up to 19 distinct fish taxa. Fish are an important natural resource and are extensively exploited by indigenous people.
Two national parks occur on the Angolan side of the ecoregion. These are Bikuar National Park (7900 km2) and Mupa National Park (6600 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, and the residual occupation by tens of thousands of Cuban mercenary forces, originally funded by the Soviet Union.
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 earlier master plan, 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.
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. 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.
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. 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 more recent policy to return resource management rights to conservancy committees with an approved constitution.
Private nature reserves and game farms are also found in this ecoregion, and awareness is increasing of game farming as a productive economic private enterprise. 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 intrinsically far greater than that of livestock farming.
After Game Reserve No. 2 was dissolved, wildlife in this area was nearly decimated by poaching gangs and local peoples armed from Namibia’s war of liberation. The poaching problem has continued, and remains a threat to the wildlife in the ecoregion. It is a severe threat to the black rhino population. In an attempt to control poaching, 68 rhinoceri were translocated to the Etosha National Park between 1967 and 1977 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. Rhinoceri are also being de-horned, as a last resort in order to deter poachers. A successful community game-guard program has been set up within the conservancies. This program is funded by donors, although controlled by local communities, providing incentives for local people to manage rhinoceri and other wildlife for long-term benefit.
During the first half of the nineteenth 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, since landowners began to commercialise wildlife. As a result, most mammal species 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. 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.
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. The human impact on the vegetation of these communal lands was assessed by Sullivan and Konstant. 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 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. 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.
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. Anthrax, together with rinderpest, is one of the most dramatic diseases affecting wild animals in Africa. 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.
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.
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. 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.
Justification of ecoregion delineation
The linework for this ecoregion is based on the western portion of White’s ‘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.
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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