Ecological Studies on the Rain Forest of Southern Nigeria: I. The Structure and Floristic Composition of the Primary Forest

Abstract

The Rain Forest of south-western Nigeria was examined with the chief object of comparing it with Rain Forest in British Guiana and Sarawak. The Rain Forest of the whole of south-western Nigeria is situated near its climatic limits. The annual rainfall varies from over 2600 mm. to just over 1600 mm., but the dry season is strongly marked, 2-5 consecutive months have less than 50 mm. Where the annual rainfall falls below 1600 mm., the Rain Forest gives place to Mixed Deciduous Forest, but the annual rainfall is not believed to be the factor directly responsible for the boundary between the two. Only 2 types of primary Rain Forest were met with, the Mixed Rain Forest and the Fresh-water Swamp Forest. The former is considered to be the climatic climax of the region and the latter an edaphic climax conditioned by a high-water table. A number of soil profiles in primary Mixed Rain Forest are described these soils belong to the Tropical Red Earth or Yellow Earth types. The stratification of the Mixed Forest is described with the help of profile diagrams. There are 3 fairly well-defined stories of trees at 120-150 ft. (37-46 m.), 50-120 ft. (15-37 m.) and up to 50 ft. respectively. Beneath the tree stories there are ill-defined shrub and herb strata. The herb stratum is composed of synusiae of shade-loving and shade-tolerating species: the latter are analogous to the "wood marginal" spp. of temperate woodlands. The synusiae of climbers and epiphytes are described. The epiphytic vegetation of the region is remarkably poor in species. The floristic composition of the Mixed Forest was studied by enumerating according to their vernacular names all trees of 4 in. (10 cm.) diam. and over on three sample plots each 160,000 sq. ft. (1.49 ha.) in area.