IMPACT AND DISEASE CENTER CHARACTERISTICS OF PHYTOPHTHORA-CINNAMOMI INFESTATIONS OF BANKSIA WOODLANDS ON THE SWAN COASTAL-PLAIN, WESTERN-AUSTRALIA

Phytophthora cinnamomi Rands was isolated from either dead plants or s oil at 46 disease centres in Banksia woodland at national parks and re serves on the Swan Coastal Plain. Phytophthora cryptogea Pethybridge & Lafferty was also isolated from roots of dead Acacia pulchella R.Br. in one disease centre infected with P. cinnamomi. Dead plants were inf ected with Armillaria luteobubalina Watling & Kile in four disease cen tres on the Spearwood Dune System, and these centres were excluded fro m further analysis. Phytophthora cinnamomi diseased areas ranged from 0.01 to 30 ha in size (mean 1.6 +/- s.e. 0.7 ha). The total area infes ted for the 46 disease centres was 71.5 ha. Impact of P. cinnamomi was high in 17% of disease centres and low in 11% of disease centres. Age of plant death was a mixture of old and recent in 85% of disease cent res. Mainly old deaths occurred in only 4% of disease centres. The pro portion of species dying in infested areas varied between 10-64% (mean 28 +/- s.e. 2%) and was positively correlated with impact type. It wa s found that infestation decreased species number; on average, there w ere seven fewer species in infested compared to non-infested areas. Fo ur plant species associated with moist sandy sites tended to occur mor e frequently in centres of high impact than by chance alone. Occurrenc e of P. cinnamomi was related to soil association with soils of 60% of the disease centres belonging to the Bassendean or Southern River ass ociations of the Bassendean Dune System. Sixteen percent of disease ce ntres occurred in the Cannington, Guildford and Serpentine River assoc iations of the Pinjarra Plain. No disease centres of P. cinnamomi were found on soils of the Spearwood and Quindalup Dune Systems. A water t able was found within 3 m of the soil surface in 48% of the centres. D isturbance was associated with all disease centres. Firebreaks were as sociated with 72% of disease centres. Banksia woodland remnants on the Bassendean Dune System and the Pinjarra Plain are highly vulnerable t o infection by P. cinnamomi and their conservation requires control of existing infestations and protection from introduction of the pathoge n.