The distribution of Phytophthora cinnamomi in the Brisbane Ranges National Park of Victoria was mapped and related to vegetation susceptibility, disease severity and past distribution. P. cinnamomi extended its distribution from 1% of the park in 1970 to 31% in 1980-81. The dispersal of the pathogen has occurred through roadworks and subsequent drainage of water-borne zoospores. In 1980-81, 50% of 1191 grids (250 x 250 m) occurred in susceptible vegetation (sclerophyllous forest/woodland). Of these, 45% (266 grids) were moderately diseased and 16% (95) severely diseased. Stands of dead trees occurred in 29 severely diseased grids which were in shallow gullies with impeded drainage. The 39% (231) of susceptible vegetation which remained unaffected occurred mainly on ridges and hilltops. P. cinnamomi was isolated from 3% of apparently resistant vegetation (graminoid forest/woodland). Restriction of access is recommended to the remaining areas of susceptible unaffected vegetation.

The distribution, population density and regeneration of some prominent spp. of understorey and overstorey (dominant Eucalyptus spp.) were monitored over a period of 20 yr in seasonally well drained dry sclerophyll forest. Changes varied with susceptibility to the pathogen and to fire. Changes in spp. composition and crown density of the overstorey were attributed to fire. Population density, basal area and crown cover of the Eucalyptus spp. which were associated with the pathogen, also declined in 1962-82. Both distribution and population density of Xanthorrhoea australis and Isopogon ceratophyllus declined markedly following the spread of infestation, whereas those of Hakea sericea and Lepidosperma semiteres increased. Regeneration of X. australis but not of I. Ceratophyllus was observed in certain areas of the infested plots 12-20 years after infection. This is the first record of such regeneration. It is postulated that a bush fire in 1967 both stimulated X. australis seed production and reduced further an already declining pathogen inoculum density.

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