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# of Endemic Species
555: Zambezian Headwaters
Major Habitat Type:
tropical and subtropical upland rivers
Scott, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa
Paul Skelton, South African Institute for Aquatic Biodiversity, Grahamstown, South Africa
The fast-flowing Zambezian headwater streams contribute to two major sub-Saharan rivers, the Zambezi and the Okavango. The ecoregion extends from the Okavango catchment in the west to the headwaters of the Kafue River in the east, and includes the headwaters of the Upper Zambezi River. The majority of the rivers drain the interior of Angola, but parts of the upper Zambezi and the upper Kafue flow through northern Zambia. The headwaters of the Zambezi share a common watershed divide with the Congo River Basin to the northeast, and with the headwaters of the Cuanza and other westward draining rivers of Angola to the northwest.
Main rivers or other water bodies:
The major Upper Zambezi tributaries in the ecoregion are the Lungwebungu, the Luanginga, the Cuando, the Luena, the Dongwe, and the Kabompo Rivers (Bell-Cross 1972). The major tributary of the Kafue is the Lunga River. The Okavango tributaries, the Cubango and the Cuito, arise on the plateau of central Angola, and the Cunene River (1,200 km long) arises in west-central Angola. The Cunene’s flow is disrupted by a series of rapids and by the 122-m high Ruacana falls, located at the divide between the rim of the continental plateau and the Atlantic coastal slope (Roberts 1975).
Mean annual rainfall is varied across the region, declining sharply from east to west, from an annual average of 1,400 mm in the upper catchment of the Kafue River, to 50 mm at the mouth of the Cunene (Hughes 1997). Seasonality is marked, with maximum rainfall falling throughout the region from October to March. Air temperatures average 20-25°C, with little variation in the humid east (Davies 1986; Barnard 1998).
The rivers of this ecoregion are permanent and characterized by steep gradients in places. However, these rivers are unlike many mountain headwaters in that high gradient zones are discontinuous (Allanson et al. 1990).
The vegetation is predominantly miombo (Brachystegia, Julbernardia spp.) woodland, containing an extensive network of grassy dambos along drainage lines, with dense gallery forests along major watercourses and a few dense patches of evergreen forest. Dambos are seasonally waterlogged regions set into the landscape through the weathering action of the lateral flow of groundwater (Desanker et al. 1997). Nutrients in water flowing into the dambos are adsorbed by clay particles or assimilated by organisms in the soil, and thus dambos are regions of intense biological activity. The woodland is interspersed with cultivated land and urban and industrial areas associated with mining. A region of mopane (Colophospermum mopane) and thorn scrub savanna (Acacia / Sclerocarya) is found to the southwest. It includes stretches of dense dry Baikiaea plurijuga forest Pterocarpus woodland savanna, and semi-arid grassland (Stuart et al. 1990; Hughes 1997).
Shales, sandstones, dolomites, and quartzites of the Katanga system underlie the tributaries of the Upper Zambezi and Kafue. The associated soils are deep (1.8m) and friable, varying from clays to sandy clay loams with clay content increasing with depth (Hughes 1997). The soil is ferralitic, and mineral reserves are generally low in the Zambezian headwaters (Davies 1986). The predominant upland soils in woodland areas are infertile, consisting of alfisols, oxysols, and altisols. Lithosols on ridge crests in drier areas are well drained, but give way to poorly drained vertisols in the dambos (Desanker et al. 1997).
The upland tropical rivers of the Zambezian Headwaters ecoregion support a fauna that is well adapted to its clear, fast flowing rivers. Kneria polli, Amphilius uranoscopus, and Parakneria fortuita are typical of these waters, where they live among rocky substrata and feed on larval Chironomidae, Trichoptera, and Odonata. Schilbe yangambianus, otherwise known from the western Congo basin, further substantiates links between the Congo and Zambian systems (Jackson 1986).
Description of endemic fishes:
Five species of fish, Paramormyrops jacksoni, Parakneria fortuita, Hypsopanchax jubbi, Barbus bellcrossi, and Schilbe yangambianus, are endemic to the headwaters of these rivers.
Other noteworthy aquatic biotic elements:
Two rare dragonfly species, Aciagrion rarum and Monardithemis flava, are near-endemics to this ecoregion. The Nile crocodile (Crocodylus niloticus) occurs here, and populations are considered to be of reasonable size but nonetheless vulnerable (Stuart et al. 1990).
Justification for delineation:
This ecoregion is defined by the headwaters of the upper Zambezi River, as well as the headwaters of the Okavango, Kafue, and Cunene rivers. The Okavango, Upper Zambezi, and Kafue Rivers have a very similar aquatic ichthyofauna, which is closely related to that of the upper Cunene. According to Skelton (1994), the early Tertiary drainage of the confluent Cunene, Okavango, Upper Zambezi, and Kafue Rivers flowed in a south-westerly direction, draining to the ocean in the vicinity of the present-day Orange River mouth. This, together with drainage capture along the Zambezian/Congolian headwater divide, accounts for much of the similarity in the fauna of the Zambezian headwaters. Presently the Zambezian headwaters share a number of species with the southern tributaries of the Congo River; hence, some of the most upstream portions of these Congo headwaters have been included in the Upper Zambezian Headwaters ecoregion (Bell-Cross 1972; Skelton 1994). The capture of the Upper Zambezi and Kafue by the Middle Zambezi in the Plio-Pleistocene had little effect on the nature of the fauna of this ecoregion, as Kafue Gorge and Victoria Falls presented impassable barriers to the upstream migration of fish (Skelton 1994).
Level of taxonomic exploration:
Poor. The level of biological investigation in this ecoregion is low. Angola is very poorly known biologically, and a substantial amount of further investigation is needed in this ecoregion before an adequate evaluation of biological distinctiveness can be made.
Allanson, B. R., Hart, R. C., et al. (1990)"Inland waters of southern Africa: An ecological perspective" In Dumont, H.J.;Werger, M.J.A. (Ed.). Monographiae Biologicae 64. The Netherlands: Kluwer Academic Publishers.
Barnard, P. (1998). "Biological diversity in Namibia" Windhoek, Namibia: Namibian National Biodiversity Task Force.
Bell-Cross, G. (1972). "The fish fauna of the Zambezi River system" Arnoldia (Rhodesia) 5(29) 1-19.
Davies, B. R. (1986)"The Zambezi River system" In Davies, B.R.;Walker, K.F. (Ed.). The ecology of river systems. (pp. 225-267) Dordrecht, The Netherlands: Dr W. Junk Publishers.
Desanker, P. V., Frost, P. G. H., et al. (1997) "The Miombo Network: Framework for a terrestrial transect study of land-use and land-cover change in the Miombo ecosystems of Central Africa. IGBP Report 41". Stockholm, Sweden. The International Geosphere-Biosphere Programme (IGBP).
Hughes, D. A. (1997) "Southern African "FRIEND" - The application of rainfall-runoff models in the SADC region. Report 3/97". Grahamstown, South Africa. Institute for Water Research.
Jackson, P. B. N. (1986)"Fish of the Zambezi sytsem" In Davies, B.R.;Walker, K.F. (Ed.). The ecology of river systems. (pp. 269-288) Dordrecht, The Netherlands: Dr W. Junk Publishers.
Roberts, T. R. (1975). "Geographical distribution of African freshwater fishes" Zool. J. Linn. Soc. 57 249-319.
Skelton, P. H. (1994). "Diversity and distribution of freshwater fishes in East and Southern Africa" Annals of the Royal Central Africa Museum (Zoology) 275 95-131.
Stuart, S. N., Adams, R. J., et al. (1990) Biodiversity in Sub-Saharan Africa and its islands: Conservation, management and sustainable use, Occasional Papers of the IUCN Species Survival Commission No. 6. Gland, Switzerland: IUCN.