Habitats
The tropical environment is rich in terms of bio-diversity. Tropical African forest is 18 per cent of the world total and covers over 3.6 million square kilometers of land in West, East and Central Africa. This total area can be subdivided to 2.69 million square kilometers (74%) in Central Africa, 680,000 square kilometers (19%) in West Africa, and 250,000 square kilometers (7%) in East Africa. In West Africa, a chain of rain forests up to 350 km long extends from the eastern border of Sierra Leone all the way to Ghana. In Ghana the forest zone gradually dispels near the Volta river, following a 300 km stretch of Dahomey savanna gap. The rain forest of West Africa continues from east of Benin through southern Nigeria and officially ends at the border of Cameroon along the Sanaga river.
Semi-deciduous rainforests in West Africa began at the fringed coastline of Guinea Bissau (via Guinea) and run all the way through the coasts of Sierra Leone, Liberia, Ivory Coast, Ghana, continuing through Togo, Benin, Nigeria and Cameroon, and ending at the Congo Basin. Rain forests such as these are the richest, oldest, most prolific, and most complex systems on earth, are dying, and in turn are upsetting the delicate ecological balance. This may disturb global hydrological cycles, release vast amounts of green house gases into the atmosphere, and lessen the planet's ability to store excess carbon.
The rain forest vegetation of the Guinea-Congolian transition area, extending from Senegal to western Uganda are constituted of two main types: The semi-deciduous rain forest characterized by a large amount of trees whose leaves are left during dry season. It appears in areas where the dry period (rainfall below about 100 mm) reach three months. Then, the evergreen or the semi-evergreen rain forest, climatically adapted to somewhat more humid conditions than the semi-deciduous type and is usually there in areas where the dry period is shorter than two months. This forest is usually richer in legumes and variety of species and its maximum development is around the Baie of Biafra, from East Nigeria to Gabon, and with some large patches leaning to the west from Ghana to Liberia and to the east of Zaïre-Congo basin.
Judging against rain forest areas in other continents, most of the African rainforest is rather dry and receives between 1600 and 2000 mm of rainfall per year. Areas receiving more rain than this mainly are in coastal areas. The circulation of rainfall throughout the year remains less than other rain forest regions in the world. The average monthly rainfall in nearly the whole region remains under 100 mm throughout the year. The variety of the African rain forest flora is also less than the other rain forests. This lack of flora has been credited to several reasons such as the gradual infertility since the Miocene, severe dry periods during Quaternary, or the refuge theory of the cool and dry climate of tropical Africa during the last severe ice age of about 18000 years ago.
A recent vegetation map of Africa published by UNESCO and the main vegetation features of Central African rain forest divides the area into the following categories: . This type of forest shows no substantial seasonal behavior. At the border of the central basin is the mesophilous semi-deciduous forest that is mixed with deciduous and evergreen trees in the upper-stratum, unusual age distribution, continuous shrub stratum at the lower canopy, and a more marked seasonality.
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