Location and General Description
This ecoregion is located in southwestern Zambia, in two main portions within White’s (1983) Zambesian Center of Endemism. It extends marginally into Angola, where the grasslands are soon replaced by the Angolan Miombo Woodland ecoregion. The northern and main portion of the ecoregion consists of edaphic grasslands surrounding the patchy Zambezian Cryptosepalum Dry Forest ecoregion. The main factor separating the two ecoregions is the seasonal waterlogging of the soils in the grasslands that prevents tree growth. The Barotse wetlands, which are part of the Zambezian Flooded Grasslands ecoregion lie between the main north and south portions of the Western Zambezian Grasslands. The southern portion of the ecoregion is an area of Kalahari Sands grassland surrounded by Zambezian Baikiaea Woodland.
The ecoregion lies at around 1,000 m elevation and consists of large, flat grassy plains. These are drained by the Zambezi and its tributaries, which form large floodplains in the ecoregion. The area is situated on deep Kalahari sands of aeolian origin (locally known as Barotse sands), which are waterlogged in the rainy season and extremely dry during the rest of the year (Simwinji 1997). The gleysols formed in this environment are nutrient-poor and have a very low clay content.
The ecoregion experiences a tropical savanna climate with three seasons: a hot dry season (August to October), a hot wet season (November to April), and a cool dry season (May to July). Mean annual rainfall ranges from 800 to 1,000 mm. The mean maximum temperature is around 27°C and the mean minimum temperature is between 12° and 15°C.
The vegetation is a short sparse wiry grassland dominated by Loudetia simplex, which is used as a fine thatching grass, and Monocymbium ceresiiforme. These species are often associated with other wiry grasses including species of Andropogon, Eragrostis, Aristida, Elionurus, Rhynchelytrum, and Tristachia. Different sedge species of the family Cyperaceae are common where the soil contains more humus (Werger and Coetzee 1978, White 1983).
Trees are virtually absent and are replaced by rhizomatous geoxylic suffrutices, or woody plants with most of their modified stems underground. They form "underground forests" (White 1983) less than 0.6 m tall. Most of these species are closely related to forest or woodland trees or lianas. They flower precociously before the end of the dry season while grasses are still dormant. This is an evolutionary adaptation to being burned almost annually, which suggests that fires, including fires started by people, have been a part of the ecology of these grassland communities for a very long time (Lock 1998).
This ecoregion falls within the traditional kingdom of Barotseland. The population density of the area is generally low with fewer than 5 people per km2, though this increases considerably around the Barotse Floodplain, which is one of the most densely populated areas, with the largest cattle population, in the Western Province of Zambia (Turpie et al. 1999). The main economic activity in the region is agriculture, and the grasslands in Barotseland are part of a transhumant farming system where people and their livestock move between the floodplain in the dry season and the more wooded uplands in the rainy season. Large numbers of cattle are moved across the grasslands annually, and burning to improve pastures is commonly practised. The sandy soils of the area are unsuitable for permanent cultivation, and various types of shifting cultivation are practised.
Species richness in the ecoregion is moderate, and no animal species are known to be endemic to the area. The grassy plains and surrounding woodland and floodplains provide important habitats for a variety of animal species, and are also an important part of annual migration routes, for wild animals as well as people with their livestock.
The mammalian fauna of the area is representative of that of the southern savannas, and some 140 species are known to occur in the ecoregion. Large numbers of ungulates graze on the extensive plains, and the Liuwa Plain is home to about 30,000 migratory blue wildebeest (Connochaetes taurinus), the largest herd in Zambia. The wildebeest herds start their northeastward migration into Angola in June. The migration takes five months and covers more than 200 km. The animals return to the southern part of Liuwa Plain in October. Approximately 3,000 red lechwe (Kobus leche), move eastwards from Liuwa Plain to the Zambezi floodplain in the dry season (Muleta et al. 1996).
Other ungulate species found in the area include tsessebe (Damaliscus lunatus), oribi (Ourebia ourebi), reedbuck (Redunca arundinum), zebra (Equus burchelli), roan antelope (Hippotragus equinus), sable antelope (H. niger), kudu (Tragelaphus strepsiceros), and Lichtenstein’s hartebeest (Signoceros lichtensteinii). Also present, but more rarely seen ungulates include the following: common duiker (Sylvicapra grimmia), sitatunga (Tragelaphus spekei), buffalo (Syncerus caffer), steenbok (Raphicerus campestris), eland (Taurotragus oryx), and grysbok (Raphicerus sharpei). Large carnivores include lion (Panthera leo), leopard (P. pardis), African wild dog (Lycaon pictus), cheetah (Acinonyx jubatus), and spotted hyena (Crocuta crocuta), though their numbers and conservation status are poorly known and thought to be low. Lions are reported to be largely extinct in Liuwa Plain (Muleta et al. 1996). Hippopotamuses (Hippopotamus amphibius) are common in the rivers.
The ecoregion supports a variety of bird life including small seed-eating passerines, raptors, and many waterbirds. Bird life is particularly abundant in the flood season. The avifauna of the grasslands is partly associated with wetland bird fauna and partly with the avifauna of surrounding woodlands. Many species, including migrants, breed in the grass when floods are receding, starting about June. Two rare birds of special conservation concern occur in the ecoregion: wattled crane (Bugeranus carunculatus) and slaty egret (Egretta vinaceigula). Both are considered vulnerable because they are limited to floodplain habitats and are threatened by disturbance and habitat destruction (BirdLife International 2000). Lechwe are vital for maintaining bird habitat, and associate with wattled crane (Collar and Stuart 1985).
The reptile and amphibian fauna of the ecoregion falls into a broad transition zone between the tropical fauna which has its center in the Moçambique Plain, and the Cape fauna of southwestern South Africa (Poynton and Broadley 1978). Elements of the adjoining ecoregions, as well as more widespread species, are represented here, with a total of 34 reptiles and 14 amphibians native to the ecoregion. No endemic species are known from the ecoregion. Dalophia ellenbergeri, a wedge-snouted worm-lizard, was thought until recently to occur only in a small part of the upper Barotse floodplain, but has since been found more than 300 km away in Angola (Broadley 1997). Crocodiles (Crocodylus niloticus) and water monitors (Varanus niloticus) are found along rivers.
This ecoregion has a long history of human habitation and parts of it have been settled for centuries (Turpie et al. 1999). The vegetation has adapted to some human disturbance, most notably, frequent fires (Lock 1998). In fact, fires and other disturbances aid the expansion of grasslands at the expense of more woody vegetation. However, some degree of fragmentation has occurred as a result of cropping and settlement. Overall, the habitat can be considered relatively intact and continuous, particularly away from the Barotse Plain.
The Liuwa Plain National Park is the only protected area that consists largely of Western Zambezian Grassland. Farther south, the Sioma Ngwezi National Park protects three large grassy plains (Mulonga, Matebele and Siloana) amid the Baikiaea woodland vegetation that is dominant in the park. The large Western Zambezi Game Management Area (GMA) joins and surrounds these two national parks. Although it is mostly Baikiaea and miombo woodland, it contains several areas of Western Zambezian Grassland. The GMA comprises communal lands in which hunting is permitted through a licensing system administered by the national parks. Licences are issued for different categories of hunters, with most being issued to non-residents and safari hunters. Four districts operate under the ADMADE system, and together made a small profit of US$19,800 in 1998 (Turpie et al. 1999).
Liuwa Plain and Sioma Ngwezi National Parks support wildlife representative of the ecoregion, though population numbers have declined and are not known in many cases (Muleta et al. 1996, Simasiku et al. 1996, Turpie et al. 1999). The GMA is now largely devoid of wildlife, except for wildlife migrating through it, due to poaching and lack of management (Muleta et al. 1996).
Wildlife in the Liuwa Plain has been protected as far back as the second half of the nineteenth century, when it was declared a game reserve by King Lewanika of Barotseland. The Litunga (the Paramount Chief of the Lozi people) officially administered this park, as well as Sioma Ngwezi, until 1972 when they were declared national parks and their management was taken over by Zambia’s Department of National Parks and Wildlife Service. The people living in Liuwa Plain were not moved, however, and about 10,000 people with some 10,400 cattle live in 108 villages in the park (Turpie et al. 1999). The villages are concentrated along the eastern and western boundaries, and villagers and their livestock have co-existed with wildlife under a system of conservation regulation for a long time. The wildebeest migration corridor in the northeastern part of the park is not settled. According to local informants, traditional leaders over the years intentionally left this part of the area unsettled for wild animals and it formed part of the traditionally protected wildlife areas (Muleta et al. 1996).
Types and Severity of Threats
The GMA and both national parks experience considerable levels of poaching. This takes the form of subsistence hunting by the local residents and commercial poaching, mostly by outsiders. Birds are hunted and trapped for food as well as for the caged bird trade, and eggs and nestlings are collected. The poaching problem has been worsened by the availability of firearms acquired from freedom fighters in the liberation struggle in Angola and Namibia, while those who cannot afford firearms use wire snares (Muleta et al. 1996, Simasiku et al. 1996). Residents of Liuwa Plain, the GMA, and those who live along rivers receive bags of maize and other forms of payment from poachers based in towns in return for co-operation (Simasiku et al. 1996, Turpie et al. 1999). Migrating animals outside the parks are not protected at all, and pressure from poachers is intense around both national parks.
The grassland plains are used for cattle grazing, and cattle numbers are on the increase, though still considered to be below the carrying capacity of the system (van Gils 1988, Simwinji 1997), mainly because diseases limit cattle numbers. Burning for pasture improvement is common because the wiry grasses, particularly Loudetia simplex, are unpalatable unless burned. While the vegetation is adapted to burning, the increasing frequency of burning is thought to create ecological problems. Early burning disturbs birds nesting in the grass, and a number of bird species are reported to have decreased when burning regulations have been ignored (Turpie et al. 1999). Uncontrolled late burning to provide green forage after grasses start to go dormant is considered to be a major cause of rangeland degradation (Simwinji 1997).
In some parts of the ecoregion, including inside Liuwa Plain National Park, settlements and cultivation have modified and fragmented the grassland vegetation. The extent of the damage to this ecoregion has not been assessed, nor has vegetation recovery on abandoned fields.
While land-use methods such as agriculture have not changed greatly in nature over the long time that the area has been settled, they are intensifying due to population pressures. In addition, people living in the Barotse floodplain area have reported considerable declines in useful plants, fish, and wildlife since the 1960s (Turpie et al. 1999). Hunting and poaching have increased since control over hunting has passed from the Barotse Royal Establishment and its local representatives to central government after independence. The transfer of control and the tendency of central governments to grant hunting licenses and other resource use concessions to outsiders, including foreigners, has led to a lack of interest and involvement in conservation and resource management among local people. This negative change is despite a cultural heritage, which placed great importance of sustainable resource use (Simwinji 1997).
Justification of Ecoregion Delineation
The Western Zambezian Grasslands ecoregion roughly follows White’s (1983) ‘edaphic and secondary grassland on Kalahari Sand’ within the Zambesian Center of Endemism. It is distinguished from the neihboring Zambezian Cryptosepalum Dry Forest by seasonal waterlogging that prevents tree growth in this ecoregion.
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