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.

Uittreksel

Ontblaring deur bokke gedurende die groeiende fenofases, het tot gevolg gehad dat blaar‐ en lootgroei aansienlik gestimuleer is, relatief tot onbenutte plante. Die reaksie het beduidend verskil, afhangende van die intensiteit en fenofase van ontblaring. Hierdie plante was die meeste gevoelig vir ontblaring gedurende die lente, wanneer hulle uitloop en wanneer die koolhidraatvlakke die laagste is. Gedurende die res van die seisoen was die koolhidraatvlakke hoog. Gedurende hierdie tye het ‘n matige tot hoë (50 % tot 75 % blaarverwydering) ontblaring die hoogste blaar‐ en lootgroei tot gevolg gehad. Die stimulerende effek van ontblaring gedurende een seisoen is oorgedra, deur die dormante periode, na die opeenvolgende groeiseisoen.

In kontras hiermee, het die aanvanklike en aanhoudende aanslag van voël‐ en insekverbruik die blaar‐ en lootproduksie ver‐minder. Ontblaring gedurende die dormante periode het nie enige positiewe of negatiewe uitwerking op die plante gehad relatief tot onbenutte plante nie. Blaar‐ en lootmateriaal wat verwyder is terwyl die plante aan die groei was, is vervang binne weke na ontblaring.

Additional index words:

• Growth stimulation
• leaf and shoot removal
• insect defoliation
• leaf mortality

Notes

Present address: Division of Wildlife and Ecology, CSIRO, PO Box 84, Lyneham, ACT 2602, Australia.