The Impact of Herbivores on Regeneration in Four Trees From Arid Australia.

Abstract

The size distributions of populations of four semi-arid perennial trees were investigated within Kinchega National Park in western NSW. For Acacia ligulata, A, loderi and Alectryon oleifolius, it appears that regeneration has been eliminated or at best severely limited at most sites. Some regeneration has occurred through recruitment of vegetative suckers in Casuarina pauper. Currently these vegetative recruits have high survival rates under both rabbit and kangaroo grazing, although such grazing frequently reduces the height of vegetative suckers back to ground level. Survival of seedlings of Acacia ligulata was very limited, with highest survival when mammals were excluded. There was no survival of seedlings of Casuarina pauper in the presence of rabbits and survival was poor when rabbits were excluded. Many seedlings of both species die through desiccation. The survival data from seedlings and vegetative suckers reinforce the patterns observed in the size distribution of populations. Within Kinchega National Park, control of rabbits is essential to initiate regeneration. A reduction in the total grazing pressure (especially rabbits, sheep, cattle and goats) is necessary in critical dry periods on semi-arid and arid grazing land if regeneration of perennials is to be encouraged.