Importance of climate, anthropogenic disturbance and pathogens (Quambalaria coyrecup and Phytophthora spp.) on marri (Corymbia calophylla) tree health in southwest Western Australia

Key message Anthropogenic disturbance and Phytophthora spp., influenced by climate, are resulting in a higher Quambalaria coyrecup infection probability in marri (Corymbia calophylla) and the development of cankers, causing a decline in marri health across the geographical range in southwest Western Australia. Context Since the 1970s, a canker disease caused by the endemic fungal pathogen Quambalaria coyrecup Paap has increasingly affected the health of marri (Corymbia calophylla (Lindl.) K.D. Hill & L.A.S. Johnson), a keystone tree species in southwest Western Australia. Aims In this study, we investigated the distribution and incidence of the canker disease, and the likely predisposing location-specific factors of the disease across the marri range. Methods A systematic landscape-scale survey was undertaken at 62, 100-m radius sites, and canker incidence was related with climate, rainfall and temperature change, proportion non-native vegetation area (i.e. anthropogenic disturbance) and Phytophthora spp. presence using logistic regression. Results On 54 sites, between 2 and 78% of all surveyed trees showed cankers. Eight sites were canker free. Since 1980, all sites experienced a reduction in annual rainfall (2.2-136.1 mm) and increasing temperatures (0.17-0.53 degrees C). Multivariate analyses showed that across the marri range, canker incidence was significantly higher in wetter and cooler areas of the marri distribution, and in areas with high proportions of non-native vegetation area surrounding the studied stands of trees. Presence of pathogenic Phytophthora spp. equally increased canker incidence. Conclusion Our study suggests that anthropogenic disturbance and Phytophthora presence may have reduced the natural defence mechanisms of marri trees, making them more vulnerable to the development of mortality inducing cankers.