IMPACTS OF PASTORALISTS ON WOODLANDS IN SOUTH TURKANA, KENYA - LIVESTOCK-MEDIATED TREE RECRUITMENT

Since the turn of the century, African pastoralists have been held res ponsible for overuse of woody plants and for the degradation and deser tification of many arid and semiarid lands. We analyzed the impacts of pastoral nomads and their livestock on the recruitment (establishment to first reproduction) of Acacia tortilis, a dominant tree in the dry woodlands of South Turkana, Kenya, where Acacia seedpods make up an i mportant part of livestock diets. Seed density averaged over 85 times higher in bush-fenced livestock corrals than in the surrounding enviro nment. The survival and growth of 14 cohorts of trees ranging in age f rom 1 to 39 yr were investigated comparing tree stands originating ins ide livestock corrals with those originating outside. Corral soils con tained nine times more C, three times more N, and six times more P tha n adjacent noncorral soils immediately following corral abandonment. C orral soils also retained more moisture than noncorral soils after rai nfall. These soil conditions accelerated seedling emergence in corrals , and enhanced survival and growth of Ist-yr seedlings. Survival of ol der trees in corral stands was not significantly different from those established outside corrals during this study. However, comparison of tree densities over time suggests that corral stands thin more rapidly than noncorral stands, probably because of crowding. The early surviv al and growth advantages of the corral environment appear to stabilize the reproductive patterns of A. tortilis in this arid ecosystem, wher e successful recruitment in noncorral sites may be restricted to the f ew years with high rainfall. Contrary to the conventional wisdom, past oralists may be improving rangelands in South Turkana by enhancing rec ruitment reliability in this important tree species.