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 di gitata on their understory environments were investigated in four sava nnas located along a gradient of increasing livestock utilization in T savo National Park (West), Kenya. Plant species composition and biomas s and the physical and chemical properties of soils that occur below t ree crowns were compared to open grasslands. The tree-crown zones at l ightly and moderately grazed sites had a unique understory flora and h igher plant biomass, lower temperatures and bulk densities, and higher levels of P, K, Ca, and mineralizable N than their associated open-gr assland zones. In the heavily grazed savanna, few differences between tree-crown and grassland zones were found. The beneficial effects of s avanna trees on their understory environments appear to diminish with increasing livestock utilization.