Boundaries

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.

Freshwater habitats

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).

Terrestrial habitats

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).

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.

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.