Location and General Description
This ecoregion comprises moist, deciduous broadleaf savannas and woodlands interspersed with areas of edaphic and secondary grassland. It forms the westernmost part of the large miombo woodland belt that is the dominant type of savanna woodland in the Zambezian Center of Endemism (White 1983). To the north and northeast lie the Southern and Western Congolian Forest-Savanna Mosaic vegetation, while the drier Zambezian Baikiaea Woodland is found on Kalahari sands to the south. The high peaks of the western highlands and the escarpment form the western boundary of the ecoregion where the miombo gives way to the Angolan Scarp Savanna and Woodlands and, at the highest elevations, to the Angolan Montane Forest-Grassland Mosaic. To the east lie the floristically distinct Central Zambezian Miombo Woodlands and the Zambezian Cryptosepalum Dry Forests and the Western Zambezian Grasslands.
Most of the Angolan Miombo Woodland is found at elevations between 1,000 and 1,500 m above sea level. The ecoregion lies mainly in the Cubango-Zambezi Basin, which is an extensive area of gently undulating hills drained by rivers that flow eastwards into the Zambezi River. It is also drained by the endorheic Cuando-Cubango system and the Cunene River. The northern portion of the ecoregion is part of the Congo Basin, while in the west, it extends onto the Old Plateau which includes the highlands of Huíla, Huambo, and Bié (Huntley 1974).
The geology of the area comprises a mixture of gritty sandstones of the Karoo sediments, deep aeolian sands of the Pleistocene Kalahari system and gneisses, gneissic granites and metamorphosed sediments of the Precambrian basement complex (Huntley 1974). The combination of the crystalline nature of many of the rocks, low relief, moist climate and warm temperatures has produced highly weathered soils that are commonly more than 3 m deep (Frost 1996). The soils are typically well-drained, highly leached and nutrient-poor and tend to be acid with low organic matter. In some areas, drainage is restricted by shallow depth, low relief, clay subsoils or indurated laterite, and this may result in seasonal waterlogging.
The area experiences a tropical climate with rainfall strongly concentrated in the summer months. Rainfall increases, and temperatures decrease, with decreasing latitude and increasing elevation. Mean annual rainfall in the ecoregion ranges from less than 800 mm in the south to about 1,400 mm in the north and west (Huntley 1974). Mean maximum temperatures are around 30° C in the south, falling to about 27° C over most of the area, and declining to about 24° C at the higher elevations. Minimum temperatures range from 15° to 18° C in the low-lying areas to 9° C over much of the higher elevation areas in the western and central parts of the ecoregion.
The vegetation comprises extensive woodlands with a canopy height from 5 to10 m, little or no shrub layer and grassy ground cover. These are interspersed with grassy plains and drainage lines, as well as patches of denser forest. The physiognomy and floristic composition varies considerably across the ecoregion (Huntley 1974).
Miombo woodland is distinguished from other African savanna, woodland and forest formations by the dominance of tree species in the family Fabaceae, subfamily Caesalpinioideae, particularly in the genera Brachystegia, Julbernardia, and Isoberlinia which are seldom found outside miombo (Campbell et al. 1996). The more widespread large tree species in the Angolan miombo ecoregion are Brachystegia spiciformis, Julbernardia paniculata, and Copaifera baumiana, while Brachystegia floribunda, B. boehmii, B. gossweilerii, B. wangermeeana, B. longifolia, B. bakerana, Guibourtea coleosperma, and Isoberlinia angolensis are locally dominant (Werger and Coetzee 1978, Huntley 1994, Dean 2000). The grass layer is up to 2 m tall and several species of Loudetia, Hyparrhenia, Tristachya, and Monocymbium ceresiiforme predominate. Most of the miombo tree and shrub species shed their leaves in the late dry season, and the miombo vegetation is bare for a short time, usually less than three months. A few weeks to a month before the onset of the rains, the trees flush again and color the countryside with their predominantly bright reddish new foliage. Brilliant green young foliage is also found in some species (Werger and Coetzee 1978). Most of the miombo trees and shrubs also flower in the same period immediately before the rains.
On seasonally waterlogged soils along drainage lines, especially on Kalahari sands, the woodland gives way to grasslands dominated by Loudetia, Andropogon, Trachypogon, and Tristachya species (Huntley 1974). Open woodlands with scattered Uapaca, Piliostigma, Annona, Entadopsis, and Erythrine species often develop on the ecotone between the woodland edge and drainage lines (Dean 2000). In some parts in the center and the northeast of the ecoregion, extensive gallery forests occur along rivers flowing into the Congo River Basin. These represent part of a transition with the Guineo-Congolian Center of Endemism to the north (White 1983, Huntley 1994). Several extensive grassy plains covered with the shrub Landolphia parviflora are found in the Congo River Basin, and a very large seasonally inundated grassy plain dominated by Loudetia simplex is found to the south of the Congo-Zambezi divide. Small areas of Marquesia acuminata, Guibourtia coleosperma, and Cryptosepalum exfoliatum evergreen dry woodland are scattered throughout the northeast of the ecoregion. Transitions to Colophospermum mopane and Baikiaea plurijuga communities occur in the drier southern parts of the ecoregion.
Fire is an important ecological factor in miombo woodland. The strong seasonality in precipitation leaves the vegetation dry for several months of the year, and thunderstorms at the start of the rainy season can easily set the vegetation alight (Werger and Coetzee 1978). In addition to being naturally fire-prone, the vegetation has been regularly set alight by humans for agriculture, hunting, and to improve pastures. Humans have probably burned the vegetation for millennia (Frost 1996). Late dry season fires are particularly destructive to trees, as their great intensity coincides with trees breaking their dormancy. Where they occur regularly, they result in more open savanna with scattered fire-tolerant trees.
Human populations in miombo woodland areas are generally low, due to the nutrient-poor soils that limit agricultural potential, as well as the widespread presence of tsetse fly (Glossina spp.). Tsetse flies are vectors of trypanosomiasis that affects humans as well as domestic livestock. In most of Angola, human population density is less than five people per km2 (Huntley and Matos 1994) although the human population is not evenly distributed throughout the ecoregion. Population density increases in the higher elevation areas in the southwest, but population densities are lowest in the southeast, and large areas are nearly uninhabited.
Overall species richness of the ecoregion’s flora is high, though the diversity of canopy tree species is relatively low. Miombo is notable among dry tropical woodlands for the dominance of tree species with ectomycorrhizal rather than vesicular-arbuscular mycorrhizal associations (Frost 1996). These may enable them to exploit porous, infertile soils more efficiently than groups lacking ectomycorrhizae. Many of the fungal species involved in these associations produce mushrooms, some of which are edible. This has resulted in a culture of mushroom-gathering among indigenous people that is widespread in miombo, but largely absent in other tropical African woodlands.
Faunal richness is moderate, with birds being better represented than other vertebrate taxa. The ecoregion is part of the large miombo woodland belt, the most extensive tropical seasonal woodland and dry forest formation in Africa, covering an estimated 2.7 million km2 (Campbell et al. 1996). Many of the plant and animal species found in the ecoregion are widespread throughout the savanna and woodland areas in southern Africa. While there are many species specialized and endemic to miombo vegetation, relatively few are confined to this ecoregion. Because little biological research has been carried out in Angola over the last 25 years due to the ongoing civil war, species richness estimates are likely to be an under-representation. Some of the species reported as endemic are poorly studied and collected, and their ranges may, in fact, be larger than is currently known.
More than 170 mammal species are known to occur in the ecoregion, including five endemic small mammal species, one of which, Dendromus vernayi (CR), is restricted to this ecoregion. The mammal fauna of miombo woodlands is poorer in both species and animal numbers than in the savanna communities of the Southwest arid biome to the south or the Guineo-Congolian forests to the north (Huntley 1974). Because miombo vegetation grows in nutrient-poor soils, it has a low nutrient content. This, together with the harsh dry season and long droughts, limits the density and biomass of large herbivores as well as biasing their composition towards larger bodied species such as elephants (Loxodonta africana) and buffaloes (Syncerus caffer), which can bulk feed on low-quality forage. Large-bodied antelope species such as sable antelope (Hippotragus niger), roan antelope (H. equinus) and Lichtenstein’s hartebeest (Signoceros lichtensteinii) are specialized feeders able to select high-quality growing shoots of tall grass. Specialized ungulate browsers are rare because of a shortage of browse in the dry season, the low quality of leaf matter, and the high, inaccessible canopies of most trees (Frost 1996).
Within the miombo vegetation, "islands" of other vegetation types, such as eutrophic savanna on richer soils, river terraces and floodplains, provide superior forage. This raises the ungulate carrying-capacity and variety in these areas compared to extensive areas of pure miombo (Frost 1996). Giraffe (Giraffa camelopardalis) is rarely found in miombo woodland, but occurs in the southern parts of the ecoregion on floodplains or more eutrophic savanna vegetation which provides high-quality browse. Bushbuck (Tragelaphus scriptus), blue duiker (Cephalophus monticola) and yellow-backed duiker (C. silvicultor) prefer more densely wooded areas, while sitatunga (Tragelaphus spekei) and waterbuck (Kobus ellipsiprymnus) are found in wetlands and marshes. Tsessebe (Damaliscus lunatus) prefer open, grassy, and often seasonally flooded habitat.
Other large mammals found in the ecoregion include hippopotamus (Hippopotamus amphibius), zebra (Equus burchellii) in the south and in the east of the ecoregion, and several large predator species such as lion (Panthera leo), leopard (P. pardus), cheetah (Acinonyx jubatus), African wild dog (Lycaon pictus), side-striped jackal (Canis adustus) and spotted hyaena (Crocuta crocuta). Smaller carnivores include wild cat (Felis sylvestris), serval cat (F. serval), caracal (F. caracal), and the miombo genet (Genetta angolensis), which has a wide distribution but is endemic to the miombo woodland belt. Large insectivores such as ground pangolin (Smutsia temminckii) and aardvark (Orycteropus afer) feed on the numerous ants and termites found in the miombo. Many of the large mammals are thought to be rare or even extinct in the ecoregion today, due to large-scale uncontrolled hunting and lack of wildlife management. Of special interest and concern is the giant sable antelope (Hippotragus niger variani), a subspecies endemic to the ecoregion which is critically endangered due to poaching.
While the avifauna of the Angolan miombo region is relatively rich, endemism levels are low with only the black-tailed cisticola (Cisticola melanura) considered near-endemic to the ecoregion. The Brachystegia-restricted avifauna in the ecoregion is similar to that of western Zambia and southern Democratic Republic of Congo (Benson and Irwin 1966a in Dean 2000). Miombo woodlands in the Zambezi River drainage basin generally share more species with western Zambia, while those of the Congo basin tend to share species with southern Democratic Republic of Congo. (Dean 2000). Typical miombo species include miombo grey tit (Parus griseiventris), miombo rock-thrush (Monticola angolensis), red-capped crombec (Sylvietta ruficapilla) and Böhm’s flycatcher (Muscicapa boehmi). Birds breeding in miombo woodlands generally have relatively short breeding seasons and start nesting before or during the early rains. Others, such as the bronze-winged cursor (Cursorius chalcopterus), Senegal plover (Vanellus lugubris), fiery-necked nightjar (Caprimulgus pectoralis), and pennant-winged nightjar (Macrodipteryx vexillaria) rely on fires to provide breeding habitat. They nest in early spring following late winter and early spring fires (Dean 2000).
Many seasonally or permanently flooded areas are found throughout the ecoregion, and their aquatic vegetation supports a variety of water birds. These include greater swamp-warbler (Acrocephalus rufescens), African yellow warbler (Chloropeta natalensis), chirping cisticola (Cisticola pipiens), Bocage’s weaver (Ploceus temporalis), saddle-billed stork (Ephippiorhynchus senegalensis) Marabou Stork (Leptoptilos crumeniferus), Goliath heron (Ardea goliath), and wattled crane (Bugeranus carunculatus).
The herpetofauna of the ecoregion is only moderately species rich, with two strict-endemic frog species, the Angola ornate frog (Hildbrandtia ornatissima) and the Huila forest tree frog (Leptopeltis anchietae), and one other near-endemic frog, the Luita River reed frog (Hyperolius vilenai). Among the reptiles, there are strictly endemic species, including Bocage’s horned adder (Bitis heraldica). According to Poynton and Broadley (1978), the upland areas of Angola such as the Bié Plateau, which form the heart of the ecoregion, do not appear to be notable centers of reptile or amphibian endemism. Most of the herpetofauna is shared with the broader miombo region.
Invertebrates (termites and caterpillars in particular) are important ecological agents in miombo woodlands and probably remove more biomass than large mammals. While termite consumption is continuous throughout the year, caterpillars feed in spectacular outbreaks that can remove considerable proportions of leaf biomass of their preferred forage species (Frost 1996). Termites are widespread and produce enormous mounds throughout the miombo region. These mounds change soil properties and produce patches rich in nutrients and organic matter within an otherwise nutrient-poor landscape. They support vegetation markedly different in structure and composition from the rest of the ecoregion. The Angolan termite mound flora has been poorly studied compared to that of many other areas, but general trends apply, such as an increased incidence of woody plants with small or sclerophyllous leaves, prickles or thorns, and animal-dispersed seeds. The fauna of termite mounds is also distinctive as the mounds provide shelter, lookout points and food such as fruit and insects. Characteristic food webs develop on active and deserted termite mounds (Malaisse 1978, Frost 1996).
Since 1974, Angola has experienced an almost continuous, intense civil war which has affected every town and inhabitant of the country at some point or another in all but the most remote rural areas. The conflict escalated after the 1992 elections and an estimated 1,000 people a day were then dying from direct conflict or through hunger and disease, most of whom were civilians. About two million people (nearly one fifth of the total population) are displaced within the country (Huntley and Matos 1994). Large areas of the country are inaccessible due to land mines. This has had numerous consequences for the conservation status of the ecoregion’s ecosystems, fauna and flora.
Due to the low population densities and the movement of many rural people to cities where security is better, large stretches of habitat are presently unaffected by human settlement and activities. The floral biodiversity is thus relatively well preserved, compared to miombo woodland areas in other countries where human pressures have had greater impact.
A number of protected areas fall within the ecoregion, all of them in Angola. Luando National Park and the nearby Kangandala Integral Nature Reserve were both formed to protect the giant sable antelope and are the only known areas where populations of this species still exist. Proposals have been made to join these two parks, but these plans have not been implemented (Stuart et al. 1990). The vegetation in these two protected areas is typical miombo woodland and also includes several permanent streams and marshes (Huntley 1974). Kameia National Park is an enormous, seasonally inundated grassy plain drained by three permanent rivers. Three lakes are also found in this park, providing habitat for a variety of waterbirds as well as antelope species with a preference for marshy or open, grassy habitat such as sitatunga, oribi (Ourebia ourebi), waterbuck, tsessebe and lechwe (Kobus leche). The status of Mavinga and Bufalo Partial Reserves is unclear; neither Texeira (1968), Huntley (1974), Huntley and Matos (1994) or Dean (2000) list them among Angolan protected areas, and their contribution to conservation is unclear. Also, though Bufalo Partial Reserve just falls within the ecoregion, its vegetation is more typical of Colophospermum mopane and Acacia savanna. In addition to the areas which fall entirely into the ecoregion, the Bikuar and Mupa National Parks fall into the transition zone between Baikiaea woodlands of the southwest arid biome and the miombo woodland belt (Huntley 1974). About one-third of the total area of these reserves is covered by miombo woodlands contained in Zambezian Baikiaea Woodlands. The total area officially protected amounts to roughly 34,700 km2, or 6.3 percent of the ecoregion, and the different habitat types are well represented.
As a result of the long civil war, the protected areas have been effectively abandoned for various periods of time, as park wardens were forced to leave due to economic or security reasons. Also, conservation and protected area management under these conditions have had little or no priority, and the protected areas became open to poachers, human settlement and cultivation (Huntley and Matos 1994). The three most important protected areas in the ecoregion, Kangandala, Kameia, and Luando, all have substantial human settlements (Huntley 1974, Huntley and Matos 1994). The impact of the war on the fauna has been catastrophic throughout Angola, and Huntley and Matos (1992) concluded that few, if any, viable populations of several large mammal species have survived in the country. These species include lion, cheetah, elephant, black rhinoceros, giraffe and giant sable. Research, including surveys of the conservation status quo, is hindered by the tenuous security, including the risks posed by land mines.
Types and Severity of Threats
The ongoing civil war has led to poor security, mass displacement of people and a depressed economy. As a result, conservation is a low priority of government, non-governmental organizations and the general public.
Hunting for subsistence and for valuable body parts of some species, much of it illegal, is the most serious threat to the wildlife in Angola. Wildlife had already been decimated outside protected areas prior to independence (Huntley 1974), and the civil war, shortage of food in many areas, and lack of security hinder measures to control poaching and manage protected areas.
Most of the ecoregion is sparsely settled at present. Thus, habitat fragmentation and modification through settlement and agriculture, woodcutting and livestock impacts are minimal in much of the Angolan miombo woodlands. Around cities and towards the southwestern highlands, however, human population pressure is more intense and Huntley (1974) described the vegetation and soils in these areas as degraded. The present extent and severity of degradation are not documented.
The breakdown in the distribution of fuel supplies has forced more and more people to cut trees for firewood and charcoal manufacture (Huntley and Matos 1994). Charcoal manufacture in miombo woodlands has resulted in large cleared areas that are slow to recover (Dean 2000). The impact of this is, again, highest around cities.
Illegal strip-mining is increasing in parts of Lunda Norte and Lunda Sul Provinces, and this is irreversibly modifying large areas of woodland and grassland by altering soil structure and drainage patterns, as well as resulting in soil erosion (Dean 2000).
Justification of Ecoregion Delineation
The Angolan Miombo Woodland ecoregion falls within the Zambezian Regional Center of Endemism outlined by White (1993). Bordered on the east by the Zambezi River, it forms the western portion of ‘wetter Zambezian miombo woodland,’ and includes ‘mosaic of Brachystegia bakerana thicket and edaphic grassland,’ which shares similar faunal patterns.
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