The Origin and Distribution of Valley Grasslands in East Africa

Abstract

Vegetation studies are often based on the conception of a more or less static climax and all other vegetation is regarded as secondary, and resulting from man-induced changes. In the present survey, the plant catena is considered to have developed during the functioning of the erosion cycle and therefore to be a natural bioclimatic phenomenon. Modifications to the catena have resulted from biotic and other pressures, and these to some extent can be assessed. This dynamic view of the vegetation enables the status of the different formations and associations to be analysed, and for conclusions to be reached by which the various types of grasslands can be classified. An attempt is made to present an integrated appraisal of some problems related to the probable origin, subsequent history and present status of valley grasslands in relation to topography and other types of vegetation. The work was undertaken in order to elucidate significant features of the environment occupied by the red locust (Nomadacris septemfasciata Forsk.). It has been continued as a background study to the ecology of other grassland-inhabiting animals. The effects of flood and drought, resulting from the markedly seasonal climate in this part of Africa, are discussed. It is assumed that the climate of the past has been both wetter and drier, and it is shown that cyclic variations still occur. All such changes influence the ecology of the valley grasslands and an account of some of the changes observed is given. Resulting from these extremes, the valley grasslands have remained largely unexploited by man, because development has been hindered by the uncertainty of the rainfall and flooding. Nevertheless valley grasslands are extensively used by animals that are adapted to the environmental hazards. Therefore wild life conservation could be a profitable form of land utilization in this habitat.