The competitive interaction between Acacia karroo and the herbaceous layer and how this is influenced by defoliation.
A study in semi-arid savanna in South Africa of experimentally isolated A. karroo trees (all other trees and shrubs had been cleared from the sites). Three treatments were given in plots of 9 m radius: with a central tree surrounded by grass; with all grass removed; with central tree removed. Grass/foliage was harvested 1, 2 or 3 times a year for 3 yr to simulate grazing and/or browsing. Trees suppressed grass growth up to 9 m away, tall trees more so than short trees, and tree removal also reduced grass growth. Grass growth was reduced when trees were frequently defoliated (attributed to the stimulatory effect of defoliation on competitiveness of A. karroo). Tree production increased in response to sward removal but was unaffected by sward harvesting, except when trees were defoliated frequently, when production of browse increased in response to frequent grass harvesting.