Factors Affecting the Population Density of Phytophthora cinnamomi in Native Forests of the Brisbane Ranges, Victoria.

Abstract

Population densities of Phytophthora cinnamomi Rands were measured at 10-day intervals during a period of 13 months at three sites in the Brisbane Ranges. Statistical analyses of results and of simultaneous metereological measurements demonstrated that both low temperatures and dry soils were correlated with a significant decrease in pathogen population. Disease extension occurred uphill on a slope of 4" at 6 . 6 m per year, but only from recent infection. Population densities of older sites were significantly less than that of the new site and no measurable disease extension occurred uphill from them. Disease caused an immediate and continuing reduction in understorey in both the number of species and the ground cover and, in the long term, a reduction in both wood production and the number of trees as the dense dry sclerophyll shrubby forest was changed to an open woodland.