Mj. Duncan et Pj. Keane, VEGETATION CHANGES ASSOCIATED WITH PHYTOPHTHORA-CINNAMOMI AND ITS DECLINE UNDER XANTHORRHEA-AUSTRALIS IN KINGLAKE-NATIONAL-PARK, VICTORIA, Australian Journal of Botany, 44(3), 1996, pp. 355-369
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.