Secondary Vegetation and the Transition to Savanna Near Ibadan, Nigeria

Abstract

Ibadan lies in the Lowland Rain Forest zone, and its vegetation consists of a patchwork of food crops (chiefly cassava, yams and maize), cacao, oil palm and bush fallow in plots seldom exceeding 0.1 acres (0.05 ha) in size. There is a correlation between soil, topography, land use and vegetation, and 3 main vegetation complexes can be recognized; (1) on clayey spils, (2) on sandy soils, and (3) on poorly drained and swampy soils. Within each of these major units 3 trends of succession may be observed: (a) The normal rotation of cultivation: thicket, secondary forest, and recultiva-tion. (b) Degeneration in the nature of the fallow as a result of frequently repeated cultivation. Eventually grass is admitted and, with the advent of annual burning, savanna species become dominant. (c) Decline of cacao plantations as the canopy becomes opened by "die-back" and intercultivation commences. It is concluded that the forest-savanna boundary, now about 30 miles (48 km) north of Ibadan, is slowly moving southwards, particularly on sandy soils under heavy cultivation.