Western Zambezian grasslands
Satellite view of the grasslands on the border of Angola and Zambia. (Photograph by National Geographic Society)
The Western Zambezian grasslands ecoregion consists of two principal disjunctive elements situated in western Zambia, to the north and south of the Barotse floodplains. The ecoregion exhibits moderate vertebrate species diversity, with 572 vertebrate taxa having been recorded here. Many ungulates occur in the Western Zambezian grasslands, including Zambia's largest herd of Blue Wildebeest (Connochaetes taurinus), which undertake a spectacular annual migration into Angola. These grasslands have been inhabited by man for centuries, but are adapted to some anthropogenic disturbances such as fires, and have a long history of traditional slash-and-burn agricultural practises.
Location and general depiction
This ecoregion is located in southwestern Zambia, in two main portions within White’s 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.
Source: WWF
The main factor separating the two ecoregions is the seasonal waterlogging of the soils in the grasslands that impedes 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.
Most of the ecoregion is situated at around 1000 metres elevation, and consists of large level grassy plains. These flatlands are drained by the Zambezi River and its tributaries including the Kwando River, which forms extensive floodplains within the ecoregion. The area is located on deep Kalahari sands of aeolian origin (locally known as Barotse sands), which are waterlogged in the rainy season, and extremely desiccatec during the remaining parts of the year. The gleysols formed in this environment are nutrient-poor and have an extremely 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 1000 millimeters (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 Common Russet Grass (Loudetia simplex), which is used as a fine thatching grass, and Oatgrass (Monocymbium ceresiiforme). These species are often associated with other wiry grasses including species of Andropogon, Eragrostis, Aristida, Elionurus, Rhynchelytrum, and Tristachya. Different sedge species of the family Cyperaceae are common where the soil contains more humus.
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" less than 0.6 metres in vertical extent. 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 most grasses are still dormant. This is an evolutionary adaptation to being burned almost annually, which suggests that fires, including fires started by humans, have been a part of the ecology of these grassland communities for a very long time.
This ecoregion falls within the traditional kingdom of Barotseland. The human population density of the area is generally low, with fewer than five people per square kilometer, 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. 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 herds of cattle are moved across the grasslands annually, and burning to improve short term farming productivity of pastures is commonly practised. The sandy soils of the area are unsuitable for permanent cultivation, and various types of shifting cultivation are practised.
Biodiversity
Species richness in the ecoregion is moderate, and no macro-animal species are 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 humans with their livestock.
Mammals
The mammalian fauna of the area is representative of the southern savannas, and around 140 mammalian taxa occur in the ecoregion. Large populations 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 Blue Wildebeests typically begin their northeastward migration into Angola in June. The migration takes five months and covers more than 200 kilometres (km). The animals return to the southern part of Liuwa Plain in October. Approximately 3000 Red Lechwe (Kobus leche) move eastwards from Liuwa Plain to the Zambezi floodplain every dry season.
Other ungulate species found in the area include the Topi (Damaliscus lunatus), Oribi (Ourebia ourebi), Southern Reedbuck (Redunca arundinum), Burchell's Zebra (Equus burchelli), Roan Antelope (Hippotragus equinus), Sable Antelope (H. niger), Greater Kudu (Tragelaphus strepsiceros), and Lichtenstein’s Hartebeest (Signoceros lichtensteinii). Also present, but more rarely seen ungulates include the following: Bush Duiker (Sylvicapra grimmia), Sitatunga (Tragelaphus spekei), Cape Buffalo (Syncerus caffer), Steenbok (Raphicerus campestris), Eland (Taurotragus oryx), and Sharpe's Grysbok (Raphicerus sharpei). Large carnivores include Lion (Panthera leo), Leopard (P. pardis), Painted Hunting Dog (Lycaon pictus), Cheetah (Acinonyx jubatus), and Spotted Hyena (Crocuta crocuta), though the numbers of the last three taxa and their conservation status are poorly known, while thought to be low. Lions are reported to be essentially extirpated from the Liuwa Plain. Hippopotami (Hippopotamus amphibius) are common in the rivers here.
Birdlife
The ecoregion supports a variety of avian species, including small seed-eating passerines, various raptors, and numerous waterfowl. Birdlife is particularly abundant during the flood season. The avifauna of the grasslands is partially 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 often found in the backwater marshes along the Kwando River. Each of these avian species is considered vulnerable, because they are limited to floodplain habitats and are threatened by disturbance and habitat destruction. Lechwe are vital for maintaining bird habitat, and associate with wattled crane.
Reptiles and amphibians
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. Elements of the adjoining ecoregions, as well as more widespread species, are represented here, with a total of 34 reptiles and 28 amphibians (all of them anurans) 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. The Nile Crocodile (Crocodylus niloticus) and the Nile Monitor (Varanus niloticus) are found along rivers.
Senegal Running Frog. @ R.C.Drewes/ African Amphibians Lifedesk Amphibians occurring in the Western Zambezian grasslands are: African Ornate Frog (Hildebrantia ornata); Angola Forest Treefrog (Leptopelis cynnamomeus); Angola Reed Frog (Hyperolius angolensis); Banded Banana Frog (Afrixalus fulvovittatus); Banguella Grassland Frog (Ptychadena anchietae); Spotted Ridged Frog (Ptychadena subpunctata), associated with deeper permanent surface waters such as the Kwando River in the Caprivi Strip of Namibia; Braganca Reed Frog (Hyperolius cinnamomeoventris); Cryptic Sand Frog (Tomopterna cryptotis); Common Reed Frog (Hyperolius viridiflavus); Three-striped Grass Frog (Ptychadena porosissima), an anuran whose eggs are laid in shallow ephemeral grass-choked pools; Kuvanga Running Frog (Kassina kuvangensis), found in dense swamps and vegetation laden lotic waters; Kivu Reed Frog (Hyperolius kivuensis), often found in large swamps and ponds; Guttural Toad (Amietophrynus gutturalis); Long Reed Frog (Hyperolius nasutus), associated with sedges and other pond fringe vegetation; Small Ridged Frog (Ptychadena taenioscelis), who lays eggs in shallow waters and seepages; Mababe River Frog (Phrynobatrachus mababiensis), which breeds in pan edges and lotic waters with emergent vegetaton; Muita Grassland Frog (Ptychadena grandisonae), typically found in flooded grasslands; Muller's Clawed Frog (Xenopus muelleri), found in ponds and lowland rivers; Natal Puddle Frog (Phrynobatrachus natalensis), associated with herbacious vegetation at the margins of marshes and other surface waters; Power's Rainfrog (Breviceps poweri), a fossorial species associated with sandy soils; Spotted Rubber Frog (Phrynomantis affinis); Senegal Running Frog (Kassina senegalensis); South African Snake-necked Frog (Phrynomantis bifasciatus); Transvaal Short-headed Frog (Breviceps adspersus); Upemba Grassland Frog (Ptychadena upembae), found in moist savanna, especially where tussock grasses grow; Uzungwe Grassland Frog (Ptychadena uzungwensis), found in higher elevation grasslands near pools and seeps; Witte's Bannana Frog (Afrixalus wittei); Yellow Swamp Toad (Amietophrynus lemairii), found in swamps and flooded grasslands in the Okavango Delta and Kwando River tributary area.
Ecological status
This ecoregion has a long history of human habitation, and parts have been settled by man for centuries. The vegetation has adapted to some human disturbance, most notably, frequent fires. 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. Licenses 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.
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. The GMA is now largely devoid of wildlife, except for wildlife migrating through it, due to poaching and lack of management.
Wildlife in the Liuwa Plain has had some protection 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. 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.
Ecological threat profile
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. 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. 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, 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. A major cause of rangeland degradation is uncontrolled late burning by indigenous peoples to provide green forage after grasses start to enter dormancy.
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. 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.
Justification of ecoregion delineation
The Western Zambezian Grasslands ecoregion roughly follows White’s ‘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 [[ecoregion]s] 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 [[population]s] 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 are needed to map the less dominant habitat types that occur within larger ecoregions.
References
- BirdLife International. 2000. Threatened birds of the world. Lynx Edicions and BirdLife International, Barcelona and Cambridge, UK. ISBN: 0946888396
- D. G. Broadley. 1997. Geographic distribution: Dalophia ellenbergeri. African Herp News 26:34-35
- N. J. Collar and S.N. Stuart. 1985. Threatened Birds of Africa and related Islands. The ICBP/IUCN Red Data Book, Part 1. 3rd Edition. Cambridge, UK.
- C. Michael Hogan. 2014. Hyperolius cinnamomeoventris. African Amphibians. ed B. Zinkus
- Lock, J.M. 1998. Aspects of fire in tropical African vegetation. C.R. Huxley, J.M. Lock, and D.F. Cutler, editors. Chorology, Taxonomy and Ecology of the Floras of Africa and Madagascar. Royal Botanical Gardens, Kew.
- S. Muleta, P. Simasiku, G. Kalyocha, C. Kasutu, M. Walusiku, and S. Mwiya. 1996. Proposed Terms of Reference for the preparation of the Management Plan for Liuwa Plains National Park. Report prepared for IUCN Upper Zambezi Wetlands and Natural Resources Management Project, Western Province, Zambia.
- J. C. Poynton and D.G. Broadley. 1978. The Herpetofauna. M.J.A.Werger, editor. Biogeography and Ecology of Southern Africa. W. Junk, The Hague. ISBN: 9061930839
- Simasiku, P., K. Chilufya, and S. Mwyia. 1996. Proposed terms of reference for the preparation of the management plan for Sioma Ngwezi National Park. Final Draft for IUCN Upper Zambezi Wetlands and Natural Resources Management project, Western Province.
- Simwinji, N. 1997. Summary of existing relevant socio-economic and ecological information. Report to IUCN on Zambia’s Western Province and Barotseland.
- Turpie, J., B. Smith, L. Emerton, and J. Barnes. 1999. Economic value of the Zambezi Basin Wetlands. Report prepared for IUCN Zambezi Basin Wetlands Conservation and Resource Utilization Project.
- Van Gils, H. 1988. Environmental profile of Western Province, Zambia. ITC report to Provincial Planning Unit, Mongu, Zambia.
- Werger, M.J.A. and B.J. Coetzee. 1978. The Sudano-Zambezian Region. In M.J.A. Werger, editor. Biogeography and Ecology of Southern Africa. W. Junk, The Hague. ISBN: 9061930839
- White, F. 1983. The vegetation of Africa. A descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000). UNESCO, Paris. ISBN: 9231019554
| Disclaimer: This article contains some information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE, or for editing of the original content. |
