The Vegetation of the Sese Islands, Uganda: An Illustration of Edaphic Factors in Tropical Ecology

Abstract

The vegetation of the Sese Is., a small group in L. Victoria, is described; the islands are remarkable on account of the sharp division between belts of tropical evergreen forest and short sparse grassland. Particulars are given of the climate and of the soils; on account of the heavy well-distributed rainfall and the equable temp. it would be expected that the islands would be covered with forest. When the islands were evacuated of men and stock for over 10 yrs. the farms quickly reverted to secondary forest, yet the trees spread very slowly into the grassland. None of the Sese soils is rich in plant nutrients, but when samples in close proximity are taken from the grassland and from the forest, the supply of bases in the forest soils is greater than that in the grassland soils which contain a very small proportion of available plant nutrients; the differences in composition of the soil are the factors controlling the distribution of vegetation. The influence of soil poverty on the agriculture of Sese and of Bukoba (where similar conditions obtain) is discussed and it is suggested that insufficient importance has been attached to edaphic factors in tropical ecology, especially in its relation to agric. problems.