Tropical moist forest occurs in humid tropical areas, usually with 1,500 mm (60 in) or more of precipitation and a dry season (or seasons) of three to four months or less. West of the highlands of East Africa and centered in the basin of the Congo River is a great tropical moist forest extending some 600 km (400 mi) north of the equator and a similar distance south of the equator. On the west, the forest extends to the Atlantic coast in the Congo, Gabon, and Cameroon, and stretches in an interrupted belt along the West African coast to Sierra Leone. Tropical moist forest also occurs along the eastern side of Madagascar.
Scientists recognize two major subtypes of tropical forest: tropical rain forest and tropical wetland forest. Tropical rain forests are characterized by a dense mass of evergreens, oil palms, and numerous species of tropical hardwood trees divided vertically into strata, or layers. The upper canopy of treetops forms a dense cover over the middle layer of treetops and the surface layer of shrubs, ferns, and mosses below. Rising above the canopy are scattered tall trees, known as emergents. In dense forest environments, the shrub layer tends to be quite sparse, except along streams, because the canopy limits the amount of light that penetrates to the forest floor. Tropical rain forests are extremely diverse in species; pure stands of a single tree species are rare.
Tropical wetland forests include both freshwater and saltwater subtypes. Freshwater swamp forests cover large parts of the Middle Congo River Basin. Saltwater swamp forests occur in many areas between Senegal and Angola on the Atlantic coast and between South Africa and the Red Sea on the coast of East Africa. Mangrove species, with their characteristic tall, arched roots, are highly adapted to the fluctuating water levels and brackish water found in estuaries and other tidal environments. Mangrove forests are tangles of roots, tree trunks, and branches reaching 8 to 23 m (25 to 75 ft) high. Significant areas of mangrove forest have been lost in order to clear land for rice cultivation, particularly in West Africa. All of the countries above fall within the tropical moist forest.