1 Forest species in West Africa show clear distribution patterns in relation to the principal rainfall gradient and associated soil fertility gradient in the region. The distribution of each species presumably reflects environmental limitation of seedling establishment, but the segregation of seasonal drought or soil conditions as controlling factors is obscured because soil nutrient availability and rainfall strongly covary. 2 Frequency of occurrence of individual species in four categories based on rainfall and a composite fertility variable are compared with the distribution of all samples. Four possible groups of species are identified, each showing a bias to one of the four site categories: dry-fertile, wet-fertile, dry-infertile and wet-infertile. A fifth group of species include those whose distribution is not significantly different from that of all sample sites. 3 Apart from the indifferent species, the wet-infertile group includes the majority of the tree species tested, including two ectomycorrhizal legumes; the wet and dry fertile groups are notable for the inclusion of deciduous Sterculiaceae. No species were found to be significantly biased to the inhospitable dry-infertile forests, which are composed principally of species with widespread distribution. 4 Experiments are proposed to test the drought tolerance and soil nutrient sensitivity of species implied by these results.
SWAINE, M.D. Rainfall and soil fertility as factors limiting forest species distributions in Ghana. Journal of Ecology (1996) 84. (3). pp. 419-428.