ABSTRACT
Herbivores, particularly introduced ones such as sheep and rabbits, have reduced the levels of regeneration of a number of species of native trees and shrubs in the arid rangelands of southern Australia since European settlement. These reduced levels of regeneration mean that populations of some species are declining while others, less palatable to herbivores, are being maintained, hence gradually altering the composition and/or overall cover of vegetation. Based on the Leslie growth model, we construct a stage-structured model of the dynamics of Myoporum platycarpum (sugarwood), under grazing pressure and external stochastic factors. The effect of grazing is incorporated into the model based upon data primarily collected from the T.G.B. Osborn Koonamore Vegetation Reserve, 400 km north of Adelaide in South Australia within and without the exclosure. The results suggest that only with higher than average rainfall for extended periods will the species of interest, M. platycarpum, survive under grazing. We can use the Vandermeer–Moloney algorithm to determine the optimal size of stage classes of the species under study when the data is collected according to physical dimensions.
