Effect of intensity of defoliation by goats at different phenophases on leaf and shoot growth of Acacia karroo Hayne.

Abstract

Defoliation by goats (leaves plus shoots) during the growing phenophases resulted in a considerable stimulation of leaf and shoot growth relative to non-defoliated plants. The response differed considerably depending on the intensity and phenophase of defoliation. Plants were most susceptible to defoliation and young shoot removal during the spring flush when carbohydrate levels were at their lowest. During the rest of the growing season carbohydrate levels were high. At these times moderate to heavy (50% to 75% leaf removal) defoliations resulted in the greatest leaf and shoot growth. In contrast, the initial and continuing impact of avian and insect consumption of leaves only reduced leaf and shoot production. The stimulatory effect of defoliation in one season carried through the dormant season to the following growing season. Defoliations during the dormant season did not have any positive or negative impact on plants relative to non-defoliated plants. Leaf and shoot material removed when the plants were growing, was replaced within weeks of defoliation.

Keywords: acacia karroo; alice; carbohydrate; consumption; defoliation; eastern cape; goats; growth; growth stimulation; insect defoliation; leaf growth; leaf mortality; leaf removal; leaves; phenophases; production; shoot growth; shoot production; shoot removal; south africa; university of fort hare