Vertical distribution of grass and tree roots in arid ecosystems of Southern Africa: niche differentiation or competition?

A distinguishing, co-dominance feature of trees and grasses in Savannas was prominently explained by Walter. He hypothesized that water is the limiting factor and grasses are superior competitors for water in the upper soil, while trees have exclusive access at deeper layers. However, a new field evidence from the Kalahari, where the water table is too low for the tree roots' tapping, revealed-that both plant types invest the bulk of their roots in the surface horizons. Further investigation should consider focusing on determining the co-dominance mechanism of both plant types without the displacement of the less-efficient. species. (C) 2003 Elsevier Science Ltd.