In the west of the country is a long line of rounded volcanic mountains and hills stretching from Mt. Cameroon, the highest mountain in west and central Africa, north-eastwards along the former boundary between East and West Cameroon and then along the Nigerian border. Volcanic soils derived from these mountains are more fertile than most others in the country and have permitted much higher rural population densities than elsewhere. Cameroon has a marked south-north gradation of climates, from a seasonal equatorial climate in the south, with two rainy seasons and two moderately dry seasons of unequal length, through southern savannah and savannah climates with one dry and one wet season, to a hotter drier climate of the Sahel type in the far north. Rainfall thus ranges from over 5,000mm in the south-west to around 610mm near Lake Chad. There are large numbers of orchids and ferns.
Mangroves grow along the coasts and the mouths of rivers.
The rain forest gives way to the semi-deciduous forest of the central region, where a number of tree species shed their leaves during the dry season. North of the semi-deciduous forest, the vegetation is composed of wooded savanna with scattered trees 10 to 60 feet high. The density of trees decreases toward the Chad basin, where they are sparse and mainly of Acacia species. Above the forest zone are drier woodland, tall grassland, or patches of mountain bamboo. Above about 7,800 feet in the interior and above about 10,000 feet on Mount Cameroon, short grasses predominate.