Location and General Description
The Eastern Miombo Woodland ecoregion consists of a relatively unbroken area covering the interior regions of southeastern Tanzania and the northern half of Mozambique, with a few patches extending into southeastern Malawi. The Central Zambezian Miombo Woodland ecoregion lies beyond Lake Malawi to the west, while north, the ecoregion is bordered by Acacia-Commiphora Bushland and Thicket belonging to the Somali-Masai phytochorion (White 1983). The East African coastal mosaic of White’s (1983) Zanzibar-Inhambane Regional Center of Endemism lines the shore. The Zambezian and Mopane Woodland ecoregion lies to the south.
Unlike the other miombo woodland ecoregions (Angolan, Central Zambezian, and Southern), which are found on the Central African Plateau, this ecoregion is mostly confined to lower elevations of the East African Plateau (Bridges 1990), ranging from 200 m along the eastern coastal regions to 800 to 900 m in the interior. Several rivers traverse this area in a predominantly west-east direction; these include the Rufiji River in Tanzania and the Rio Ruvuma and Rio Lurio in northern Mozambique. The Zambezi River is found beyond the southern border of the ecoregion. Moderately undulating ridges mixed with shallow flat-bottomed valleys, or dambos, that are often seasonally waterlogged characterize the landscape. Inselbergs are common, especially in northern Mozambique, rising noticeably above the uniform woodlands. The underlying geology of the Eastern Miombo Woodland consists mainly of metamorphosed upper-Precambrian schists and gneisses, interspersed with intrusive granites (Bridges 1990). The combination of the crystalline nature of these 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, nutrient-poor, and acidic with low organic matter. Oxisols and alfisols are most common in the south and central regions of the ecoregion, while a higher percentage of ultisols are found to the north.
The ecoregion experiences a seasonal tropical climate with most rainfall concentrated in the hot summer months from November through March. This is followed by an intense winter drought that can last up to 6 months (Werger and Coetzee 1978). Mean annual rainfall ranges between 800 and 1,200 mm, although peaks up to 1,400 mm per annum are found along the western margins. Mean maximum temperatures range between 21°C and 30°C depending on elevation, with the hottest temperatures experienced in the lowland areas. The ecoregion’s mean minimum temperatures are between 15°C and 21°C, and the area is virtually frost-free.
Miombo woodlands form the dense forest woodland that bisects Africa directly south of the Congo Basin and East African savannas. It stretches all the way from Angola in the west to Tanzania in the east. These woodlands are dominated by trees of the subfamily Caesalpinioideae, particularly species belonging to the Brachystegia, Julbernardia and Isoberlinia genera, which seldom occur outside miombo (Campbell et al.1996). Much of the area covered by this ecoregion overlaps with White’s (1983) floristically impoverished drier Zambezian miombo woodland. Dominant tree species include Brachystegia spiciformis, B. boehmii, B. allenii, and Julbernardia globiflora. In areas of higher rainfall, a transition to wetter Zambezian miombo occurs (White 1983). Here, miombo trees are usually 12 to 18 m tall, with a broadleaf shrub and grass understory beneath. This vegetation supports greater floral richness and includes almost all the miombo dominants, such as Brachystegia floribunda, B. glaberrima, B. taxifolia, B. wangermeeana, B. utilis, Marquesia macroura, Julbernadia globiflora, J. paniculata, and Isoberlinia angolensis. Deciduous riparian forest lines the numerous rivers in the area, while dry forest and thicket associations are also found in the ecoregion, especially in rocky places.
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). However, in addition to being naturally fire-prone, miombo is frequently burned by people to clear land for cultivation, to maintain pastures for livestock, or to drive game animals to positions where they can be easily hunted.
Human populations in this ecoregion are generally low, with some areas being virtually unpopulated (Moyo et al.1993). The 1997 population densities for Mozambique and Tanzania were 23 and 36 persons per km2 respectively (Federal Statistical Office Germany 2001), although the areas covered by the Eastern Miombo Woodland ecoregion are generally much more sparsely populated (Moyo et al.1993). This is largely due to the nutrient-poor soils that limit agricultural potential, the widespread presence of tsetse fly (Glossina spp.), and vectors of trypanosomiasis, which affects humans as well as domestic livestock. Historically, the threat of this disease prevented people from bringing cattle into many areas (Matzke 1996). The armed conflict in Mozambique, which ended in 1995, has also contributed to low population densities, because most people migrated to urban centers or along major transport routes which offered safer living conditions.
The overall faunal diversity of this ecoregion is moderate, and generally lower than its neighboring miombo ecoregions. However, these figures may reflect insufficient surveys, especially in northern Mozambique. True species richness could be significantly higher than presently estimated.
This ecoregion supports typical miombo fauna, and most large mammal species also utilize surrounding miombo and savanna ecoregions. Long winter droughts and poor soils result in vegetation of low nutritional value. This greatly reduces the ecoregion’s faunal carrying capacity, and large-bodied herbivores generally occur only in fairly low densities. Typical mammals include elephant (Loxidonta africana), Lichtenstein’s hartebeest (Signoceros lichtensteinii), eland (Taurotragus oryx), black rhinoceros (Diceros bicornis, CR), and waterbuck (Kobus ellipsiprymnus). Elephant (Loxidonta africana) and Lichtenstein’s hartebeest (Signoceros lichtensteinii) are both found in high numbers in the Selous Game Reserve in southern Tanzania. According to a 1994 census, more than 30,000 elephants (Barnes et al 1998, WCMC 1998) and more than 20,000 hartebeests (East 1998) are known from this protected area.
Due to annual droughts and frequent fires, many species are at least seasonally dependent on non-miombo vegetation within or adjacent to the ecoregion to provide food, water, or shelter. These refuges provide a greater variety of habitats, resulting in higher richness in ecotonal areas, such as near inselbergs or rivers, than in areas of uniform miombo woodland (Rodgers et al. 1996; Rodgers 1996). For example, sable antelope (Hippotragus niger), are largely confined to the miombo belt but move onto more open grassy areas during the dry season (Kindgon 1997). Other species of ungulates found in the ecoregion are limited to areas of permanent water. These include African buffalo (Syncerus caffer), greater kudu (Tragelaphus strepsiceros) and Burchell’s zebra (Equus burchelli). Wildebeest (Connochaetes taurinus) are mostly found in areas of short grass close to permanent waters, while Bohor’s reedbuck (Redunca redunca) and oribi (Ourebia ourebi) prefer unstable grasslands that are maintained by flooding, fires, drought or heavy grazing. Sharpe’s grysbok (Raphicerus sharpei) is mainly restricted to low thicket and secondary growth around rocky outcrops. Southern reedbuck (Redunca arundinum) inhabits grass valleys within miombo woodland. Hippos (Hippopotamus amphibius) are fairly common in several rivers of the ecoregion. Smaller antelope of the ecoregion include bushbuck (Tragelaphus scriptus), blue duiker (Cephalophus monticola), and impala (Aepyceros melampus).
Large carnivores characteristic to the region include lion (Panthera leo), leopard (P. pardis), cheetah (Acinonyx jubatus), spotted hyena (Crocuta crocuta), side-striped jackal (Canis adustus) and the endangered African wild dog (Lycaon pictus). Smaller predators include caracal (Felis caracal), serval (F. serval), miombo genet (Genetta angolensis), Selous’s mongoose (Paracynictis selousi), and bushy-tailed mongoose (Bdeogale crassicauda), a species restricted to southeast Africa, but widespread throughout the region.
While bird life in the ecoregion is prolific, with more than 450 birds recorded in the Selous Game Reserve alone, only Stierling’s woodpecker (Dendropicos stierlingi) qualifies as a near-endemic. Several globally threatened species are also known to occur in the area. These include wattled crane (Grus carunculatus, VU), corncrake (Crex crex, VU), and lesser kestrel (Falco naumanni, VU) (BirdLife International 2000).
Reptiles are the only vertebrate group with any level of endemism, with only three of these being strict endemics (the chameleon Chamaeleo tornieri, and the lizards Playsaurus lineicauda and P. maculatus). The Nile crocodile (Crocodylus niloticus) is widely distributed in the ecoregion, but is mainly found in protected areas such as Selous Game Reserve. The Masiliwa shovelsnout frog (Hemisus brachydactylus) is the only near-endemic amphibian of the ecoregion, and is restricted to central Tanzania (American Museum of Natural History 1999).
Poor soil quality and the presence of tsetse fly in the ecoregion have historically resulted in very low human population densities with low levels of agriculture and other human activities. In 1989, most of the Tanzanian section of the ecoregion was virtually free of cattle (Moyo et al. 1993). Over the last few decades, the armed conflict in Mozambique caused the mass exodus of people from rural areas in northern Mozambique to coastal or urban areas or along major transport routes where access to food and increased security were sought. These factors in combination have resulted in large stretches of habitat that are presently relatively unaffected by human settlement and activities. The floral biodiversity is thus relatively well-preserved compared to miombo woodland areas in other ecoregions where human pressures have had far greater impact.
Four internationally recognized protected areas are found in the ecoregion, of which the Selous Game Reserve is most important. Covering an area of roughly 50,000 km2, this is the second largest World Heritage Site in Africa (WCMC 1998). Predominantly miombo woodland, the reserve hosts several large populations of characteristic savanna animals. Although numbers have declined drastically, it still supports one of the highest concentrations of elephants in Africa, with 31,735 individuals recorded in 1994 (Said et al. 1995), as well as one of the most impressive populations of Nile crocodile on the continent (Games and Severre 1999). High numbers of buffalo, wildebeest, sable, Lichtenstein’s hartebeest and hippo also occur in the area. In addition, the park supports possibly the largest population of endangered African wild dogs in Africa (GTZ/Selous Management Plan 1995). Other threatened species found in the park include the black rhino and cheetah. The only national park of the ecoregion, the 3,230 km2 Mikumi National Park, is adjacent to Selous. The park is characterized by the grassland and wooded savanna of the extensive Mkata River floodplain, and is surrounded by hilly country. Brachystegia and Combretum-Terminalia woodland are most common between the hills and floodplain. Noteworthy mammals include lion, leopard, sable antelope, eland and Lichtenstein’s hartebeest. More than 360 bird species have been recorded in the park. Mikumi and Selous form a block of habitat that joins with the Kilombero Valley Game Controlled Area. Collectively, these areas provide the largest single conservation unit in the African savanna-woodland habitats.
Niassa, a large game reserve 15,000 km2 in extent, is located in Mozambique, with its northern boundary on the Tanzanian border. Dominated by miombo and Baikiaea woodland, the reserve is intersected by numerous rivers and dambos. As many as 8,700 elephants are found in the area (Barnes et al. 1998). Other characteristic mammals include lion, buffalo, zebra, wildebeest, Lichtenstein’s hartebeest, eland, sable, oribi, black rhino, and hippo. Gile Game Reserve, the smallest of the ecoregion’s protected areas (2,100 km2), consists mainly of miombo woodland and associated dambos. The endemic cycad (Encephalartos turneri) is found on some of the surrounding inselbergs (IUCN 1987, Goode and Comrie-Greig 1989). Wildlife is similar to Niassa.
Types and Severity of Threats
The low human population densities for most of this ecoregion have ensured that the vegetation of the Eastern Miombo Woodland has remained relatively intact. Furthermore, forced abandonment of large areas of the ecoregion because of the civil war in Mozambique and the Ujamaa villagization programme in Tanzania has resulted in the regeneration of vegetation in many areas. However, this ecoregion still experiences a range of threats, including deforestation, poaching and mining. While most of the deforestation in Mozambique and Tanzania presently occurs outside this ecoregion (World Bank 1988 cited in Moyo et al.1993), up to 40 percent of the wooded area in Mozambique had been degraded towards scrub by the mid-1980s. In Tanzania, woodlands and forests, which cover 40-50 percent of the country, were being consumed at a rate of 3,000 to 4,000 km2 per year in the early 1990s. This is a rate that was at least 10 times greater than the combined forest regeneration capacity and tree planting initiatives at the time. In addition, more than 90 percent of the total energy consumed nationally in Tanzania is in the form of fuelwood. Finally, while charcoal plays only a small part in fuel supplies in Mozambique, as much as 70 percent of Tanzania’s urban population rely on this form of fuel (Moyo et al 1993). Clearing of woodland is therefore a problem, especially along the eastern coastal border where population densities are much higher. The area between Dar-es-Salaam and Morogoro was highlighted by Moyo et al (1993) as having been seriously degraded by fuelwood collection and charcoal production.
Although commercial logging does not pose a large threat in general, African blackwood (Dalbergia melanoxylon), a prized commercial tree, is mostly contained within the boundaries of the Eastern Miombo Woodland ecoregion. It is used for the production of musical instruments, such as clarinets and piano keys, as well as for traditional and tourist-trade carvings. Generally, only large trees with straight poles are logged. With such consistent selective felling, there is growing concern that the genetic strain of this species is becoming inferior, because seeds from prime specimens are increasingly less available. Furthermore, evidence suggests that the occurrence of the species is decreasing and becoming more scattered. Although it is protected in Tanzania, exploited on a license system, the country lacks the resources to enforce the laws limiting its use (African Blackwood Project).
Deforestation for cultivation and livestock pastures are problematic in much of the ecoregion, except in the south and northeast, where higher population densities and better agricultural potential have resulted in the cultivation of staple and cash crops such as maize, cassava, sorghum, cashew nuts, and tobacco (Moyo et al 1993). Overgrazing from cattle is a threat only in the northwest margins of the ecoregion. At present, the only way to eradicate the tsetse fly is to clear woodland, which provides an incentive to clear thickly wooded habitat bordering populated areas.
Poaching and illegal hunting for bushmeat pose serious threats to wildlife throughout the ecoregion (Stuart et al. 1990, TRAFFIC 2000). Elephant and rhino poaching have been extremely severe due to insufficient management within protected areas as well as the civil war in Mozambique (Stuart et al. 1990; Moyo et al 1993). In the Selous Game Reserve alone, the elephant population has been reduced from 100,000 in 1981 (Campbell 1991) to roughly 31,000 in 1994 (Said et al 1995) as a direct result of poaching. Black rhinos, numbering 3,000 in 1981, declined to fewer than 100 five years later (WCMC 1998). Trafficking in hides of leopards, lions and crocodiles is a further problem. In addition, the live animal trade in Tanzania is one of the biggest in Africa, especially in birds and tortoises. This activity could severely affect local wildlife populations (Stuart et al. 1990).
While both Mozambique and Tanzania have a wealth of mineral deposits, mining activities have been fairly limited in the ecoregion. However, where mineral exploration, extraction and processing are underway, negative impacts are evident. These include water and air pollution, infertility, land subsidence, and devastation of woodlands (Moyo et al 1993).
Justification of Ecoregion Delineation
This ecoregion is separated from other miombo ecoregions in that it is mostly confined to lower elevations of the East African Plateau, and is dominated by the floristically impoverished ‘drier Zambezian miombo woodland’ outlined by White (1983). Dominant tree species include Brachystegia spiciformis, B. boehmii, B. allenii, and Julbernardia globiflora. In areas of higher rainfall, a transition to wetter miombo occurs (White 1983). This ecoregion is separated from adjacent ecoregions to the west by Lake Malawi and the Shire River, running south from Mount Mulanje. In the north it is separated from the Central Zambezian Miombo Woodland ecoregion by the Eastern Arc and Southern Rift Montane areas.
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: Karen Goldberg
Reviewed by: In progress