Spatio-temporal variation in invasion of woodlands and forest by Phytophthora cinnamomi

This study determined spatio-temporal invasion dynamics of Phytophthora cinnamomi, examined differences between disease centres and inferred mechanisms of invasion. Patch disease extension was measured from aerial photographs of three Banksia woodland areas infested with P. cinnamomi. Disease extension was also determined from the fronts of six disease centres in Banksia woodland biomes and a disease front in Eucalyptus marginata forest. A localised, salient, disjunct pattern of spatial variation in upslope disease extension that occurred in all disease centres between years was probably due to growth of P. cinnamomi in major lateral roots and infection of plants by root to root contact. The square root of the area invaded was significantly related to year after first assessment (R 2 = 0.59–0.97). Linear rates of disease extension from baselines with years after first assessment ranged from 0.1 ± 0.07 and 1.46 ± 0.39 m/year. Differences in P. cinnamomi isolation frequency, community structure and measured variables in different soils did not indicate reasons for the variation in rate of invasion between Banksia woodland disease centres. Management options to limit invasion will depend on whether disease extension is the result of unrestricted movement of infectious propagules in overland and subsurface flows, or relatively restricted growth through roots and root to root contact. The hierarchy of factors affecting the invasive success of P. cinnamomi is discussed.