Forest Ecosystem

The standard vegetation classification for Africa, provided by White (1983), uses physiognomic and chorological categories to subdivide African vegetation types into cohesive regions. The three target countries of the TROFCCA include what White classifies as five distinct phytochoric Zones (see Figure 1 below – chosen from many examples as it gives the English and French equivalents):

  1. The Sahara regional transition zone (northern Mali) certain plants characteristic of wadis (e.g. Tamarix) and of shady, rocky, gravelly or saline faces (e.g. Cornulaca, Calligonum, Fagonia
  2. The Sahel regional transition zone (central Mali and northern Burkina) Semi-desert grassland and thorny shrubland (north) to wooded grassland and bushland (south), with Acacia spp., Commiphora africana, Balanites aegyptiaca, Euphorbiaceae, and abundant dryland taxa
  3. The Sudanian regional centre of endemism (southern Mali, all the rest of Burkina and northern Ghana) Woodland and dry forest, with Celtis integrifolia, Hymenocardia acida, Lannea, Prosopis africana, Mytragyna inermis, etc.
  4. The Guineo-Congolian/Sudanian regional transition zone (central & south-eastern Ghana) Mosaic of dry, peripheral, semi-evergreen rainforest and woodland or secondary grassland
  5. The Guineo-Congolian regional centre of endemism (south western Ghana) Lowland rainforest and swamp forest with very diverse endemic flora including Chlorofora, Holoptelea, Uapaca, Musanga and Elaeis guineensis (oil palm); montane rainforest and grassland (above 1000 m altitude) with Olea hochstetteri, Podocarpus and Ilex

The factors that determine the differences in floristic composition of the forest are amount and distribution of rainfall and the differences in soils, physiography and hydrology. Whether in the humid rain forest or the open wood land, the forest ecosystem plays important role in the economies of the region, especially since the severe drought which began in 1968. Besides halting desert enchroachment in the region, the forest provides wood, fuel, charcoal, fruits, nuts and medicine and income for the forest community. The pressure on forest goods and services in an already harsh environmental condition makes the region most vulnerable to climate change impact.

Forest Ecosystems in West Africa have important environmental and ecological linkages. They are linked to the micro and macro climate, water and soil resources, genetic resources of plants and animals, food production and food security, and to energy resources. The effect of rainfall on vegetation is obvious. Vegetation cover generally affects climate via alteration of the physical characteristics of the land surface (like albedo, roughness, water conductivity) and by changing atmospheric gas composition, for example, CO2 and CH4. It is only recently that there seems to be some consensus of the effect of vegetation on regional climate in West Africa although the feedback mechanism remains not clearly understood. There are indications of  positive feedback loops between vegetation clearance and aridity albeit other climate driver in the Sahel. Trials in Burkina Faso demonstrated the extent to which infiltration is affected by drought especially under reduced grass cover and the positive feedback relationship between soil infiltration, edaphic aridity and vegetation cover in maintaining drought conditions over time. Recent work in boreal forests suggests that very significant feedback mechanisms also exist for increasing temperature. Taylor et al also demonstrated the influence of land use change on Sahelian climate and its secondary nature compared to primary drivers linked to SSTs.

Phytochoria of West and Central Africa (Dounias 2000)