Sabkha Regions of Tropical East Africa

Abstract

Sabkhat in the region of tropical East Africa (treated here as Uganda, Kenya and Tanzania) are comparatively small in area and limited mostly to lake basins in the Eastern Rift and a few coastal areas. A relatively large inland sabkha lies in North Kenya, west of Lake Turkana, associated with the Chalbi Desert (a former lake). The chief plants of saline flats that surround the saline lakes in Kenya and Uganda include Cyperus laevigatus, Sporobolus spicatus and Dactyloctenium spp. The coastal sabkhat, flooded only at spring tides, are occupied by monospecific stands of stunted Avicennia marina. At the more open parts of the Avicennia fringe Arthrocnemum indicum, Paspalum vaginatum, Sesuvium portulacastrum, Sporobolus virginicus, S. spicatus, S. kentrophyllus, Pedalium murex and Suaeda monoica form the main associates. In the inland sabkhat low rainfall and high potential evaporation have resulted in an arid and saline landscape dominated by grasses Aristida adscensionis, A. mutabilis, Drake-Brockmania somalensis, Sporobolus consimilis, S. virginicus and Psilolemma jaegeri, and the subshrubs Duosperma eremophilum and Indigofera spinosa. Lagenantha nogalensis occurs on gypsophilous soils and Dasysphaera prostrata on saline soils at the edges of Lake Turkana and the Chalbi Desert. Stunted woody vegetation is dominated by Acacia reficiens and in drainage channels by Salvadora persica. Floristically the coastal sabkhat of tropical East Africa fall in the Zanzibar-Inhambane regional mosaic and the inland sabkhat in the Somalia-Masai regional centre of endemism. There are no endemic genera in the coastal sabkhat, but all of the nine East African mangrove species occur in Kenya, Tanzania and Mozambique. In the inland sabkhat, the Somalia-Masai regional centre of endemism includes the endemic genera Drake-Brockmania and Dasysphaera. There is no arid-zone agriculture in the inland sabkhat region and nomadic pastoralists, depending on their livestock for subsistence, are the main occupants; Duosperma and Indigofera are amongst some of the important food plants of livestock (camels). Salt deposits are harvested from the extensive flats surrounding the saline and soda lakes, and the mangrove is an important economic resource as a nursery for fish and crustaceans, as well as a source of poles, timber and firewood. Over-harvesting of wood and conversion to saltpans and aquaculture, housing and industry is a threat to many parts of the mangrove area. There are no strict nature reserves in the inland sabkhat of tropical East Africa designated for the protection of arid landscapes and its flora; however the Mount Kulal Biosphere Reserve in northern Kenya covers the salt desert and lake ecosystems; Lake Manyara and Amboseli Biosphere Reserves also partly cover the saline and alkaline ecosystems. Mangrove areas are included in Watamu Marine National Park, Kiunga National Marine Reserve and Ras Tenewi Marine National Park in Kenya, and in Mafia Island Marine Park, Jozani National Park and Sadaani Game Reserve in Tanzania. Other areas of East African mangrove are included in forest reserves, with varying degrees of protection.