EFFECTS OF WIDELY SPACED TREES AND LIVESTOCK GRAZING ON UNDERSTORY ENVIRONMENTS IN TROPICAL SAVANNAS

The effects of widely spaced trees of Acacia tortilis and Adansonia digitata on their understory environments were investigated in four savannas located along a gradient of increasing livestock utilization in Tsavo National Park (West), Kenya. Plant species composition and biomass and the physical and chemical properties of soils that occur below tree crowns were compared to open grasslands. The tree-crown zones at lightly and moderately grazed sites had a unique understory flora and higher plant biomass, lower temperatures and bulk densities, and higher levels of P, K, Ca, and mineralizable N than their associated open-grassland zones. In the heavily grazed savanna, few differences between tree-crown and grassland zones were found. The beneficial effects of savanna trees on their understory environments appear to diminish with increasing livestock utilization.