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

Abstract

The semi-desert round Omdurman, Sudan supports a scrub of Acacia spp., perennial grasses (Panicum turgidum) and annual grasses, mainly Aristida spp. The daily mean minimum temperature is 15.6[degree]C in Jan. while the daily mean maximum is 41.8[degree]C in May. Rainfall is extremely erratic and inconsistent. The total annual varies from 26 mm to 328 mm (average for 18 years 157 mm), most of which falls during July, August and Sept. The soil is predominantly a red brown sand with some gravel desert. The vegetation is subject to intensive human interference. Shrubs and perennial grasses are cut for fuel and thatching. Annual grasses are grazed by cattle, sheep, goats and camels. The latter two also browse the twigs and pods of acacias. A 2220 acre (898 ha) goat-proof enclosure furnished the background of this study. Effective protection of the vegetation inside the enclosure started only in 1957 Quantitative estimates were made of the vegetation inside and outside the enclosure after a prolonged drought period of about 12 months. They included shrub density and performance, perennial grass frequency and tussock height, annual grass frequency, cover and height. Data were treated statistically. The data indicate that shrubs outside the enclosure away from villages are subject to felling by wood thieves from far away, and to browsing by animals. Those outside the enclosure near the villages are subject mainly to browsing (no felling). Perennial grass is very sparse everywhere but tussocks are significantly shorter outside the enclosure. Annual grasses are completely wiped out outside the enclosure near the villages while beaten down remnants occur away from villages. The effect of human interference on vegetation and soil conservation is discussed.