VEGETATION CHANGES ASSOCIATED WITH PHYTOPHTHORA-CINNAMOMI AND ITS DECLINE UNDER XANTHORRHEA-AUSTRALIS IN KINGLAKE-NATIONAL-PARK, VICTORIA

Changes in the species composition associated with the presence of Phy tophthora cinnamomi Rands and changes in the potential activity of the fungus were measured at a dry sclerophyll forest site in Kinglake Nat ional Park. In soil infested with P. cinnamomi, both the percentage co ver and density of the major overstorey species (Eucalyptus dives Scha uer in Walp. and E. macrorhyncha F.Muell.) and major understorey speci es (Xanthorrhoea australis R.Br., Daviesia ulicifolia Andrews and Dill wynia phylicoides Cunn.) were significantly reduced, while both the co ver and density of the sedge species (Gahnia sieberiana Kunth., Lepido sperma laterale R.Br. and L. semiteres F.Muell.) increased significant ly. The density of the major grass species, Chionochloa pallida (R.Br. ) S.W.L.Jacobs, did not change. Species that were susceptible to P. ci nnamomi showed varying patterns of decline. Xanthorrhoea australis was the most sensitive to the presence of P. cinnamomi, showing an immedi ate and large decline in both percentage cover and density, while Davi esia ulicifolia was the least sensitive, showing a decline only at lat er stages of disease development in the vegetation. Lepidosperma later ale and L. semiteres were the major colonisers of the diseased vegetat ion at this site, and were succeeded by Gahnia sieberiana, which becam e the dominant sedge species in the diseased zone after the dead plant s of X. australis had collapsed. A seasonal survey (1992-1994) of P. c innamomi found the pathogen to be potentially active all year round at this site, with summer and winter maxima. A decline was measured in t he potential activity of P. cinnamomi underneath diseased and dead pla nts of X. australis after a disease outbreak. The potential activity o f P. cinnamomi was greatest in soil collected from the base of dying p lants of X. australis and zero in soil from under dead and collapsed i ndividuals of that species. A similar pattern of decline in the potent ial pathogen activity was measured for the same host species at diseas e sites in the Brisbane Ranges National Park and Angahook State Park. A similar consistent pattern of decline in the disease potential of P. cinnamomi in soil from under diseased and dead plants of X. australis was observed in a pot bioassay. This decline in disease potential was overcome by the addition of Eucalyptus sieberi L.A.S.Johnson seedling s and P. cinnamomi inoculum to the soil.