The Effects of Different Forms of Land Use on the Ecology of a Semi-Arid Region in South-Eastern Rhodesia

Abstract

Natural vegetation in the drier parts of Africa probably evolved under light utilization by shifting populations of indigenous herbivores. The pattern and intensity of utilization have changed since the introduction of domestic livestock although, prior to colonization by the white man, utilization remained light because both human and domestic animal populations were small and the African tribesmen were nomadic (Maloiy & Heady 1965). The recent rapid increase in human and livestock populations (Casebeer 1968; Hornby 1968) has led to serious and extensive damage over large tracts of land. In Rhodesia, over-utilization of vegetation began shortly after 1914 and by 1966 some 490% of the Tribal Trust Lands (where there is communal ownership of land) were either overgrazed or had very little herbaceous cover (Cleghorn 1966). Some of the most badly degraded of these areas are in the south-eastern 'lowveld' of Rhodesia. The term 'lowveld' denotes the hot, semi-arid regions of tree/bush savanna, below an altitude of c. 800 m, in which extensive livestock ranching is the main form of land use. The natural vegetation is generally the only source of food for livestock and, by virtue of its cover, it is vital for the conservation of soil and water resources. The area is too dry for planted pastures and improvement of the protective cover and forage value of the range must be achieved by manipulating the natural vegetation. The aim of this study, made in 1970-2, was to determine the composition, trends in composition and primary productivity of an area of lowveld vegetation in which different forms of land use were being applied, and to establish key factors in its ecology. The emphasis has been on overall interrelationships of the vegetation, rather than on detailed studies of particular aspects. In order to reduce inter-site variability, the study was restricted to basalt-derived soils.