The Impact of Man on Semi-Desert Vegetation in the Sudan

Abstract

Problems relating to the influence of man and his animals on vegetation have received the attention of many workers. The effects of burning and grazing by cattle and sheep have been studied by many authors in Britain and other European countries, as well as in North America and Thomas (1945) gave a general account of the influence of human activities in Uganda. In all these studies, the destruction of vegetation by burning or felling was followed by recolonization within a relatively short period. The effect of grazing was mainly to tip the balance in favour of those species which were little relished or totally rejected by animals, or those which, though palatable, could regenerate quickly by vegetative means, thus recovering lost ground. Grazing may favour the growth of some species through curtailing their serious competitors which-would otherwise become tall and overshadow them. The above studies, including those in Uganda, were all carried out under mo-re humid climates than obtain in arid northern Sudan. The amount and distribution of rainfall is such that grazed plants will regenerate naturally, provided, of course, they possess the potential ability to do so. In arid regions on the other hand, the dry climate which prevails throughout the greater part of the year does not allow the regeneration of plants once they are grazed or cut, even though the species in question may be endowed with the power of regeneration under a more humid climate. In thi's region north of Khartoum, man's chief activity is animal grazing and wood and grass cutting, no shifting cultivation or annual burning being practised. In order to study man's influence on semi-desert vegetation, a 2220 acre (898 ha) enclosure belonging to the Sudan Forest Department was chosen, quantitative