The influence of an<i>Acacia karroo</i>tree on grass production in its vicinity

Abstract

Abstract The investigation was concerned with the impact of an Acacia karroo tree on the productivity of the surrounding herbaceous layer. It was established that a consistent pattern of grass production occurs around isolated A. karroo trees. This is characterized by high yields under and immediately south of the tree canopy, and low yields immediately to the north of the canopy. The former is attributed to favourable influences by the tree (e.g. shade and tree leaf litter), whereas the latter is probably a result of reduced water input associated with physical redistribution of rainfall by the tree and competition from the tree for soil water. It is argued that the net effect of the favourable or unfavourable influences of A. karroo on grass production is dependent on tree density. This explains why grass production is greater where there are a few A. karoo trees than where there are no trees and why grass production declines as tree density increases beyond a critical level.