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

Abstract

Key message: Anthropogenic disturbance andPhytophthoraspp., influenced by climate, are resulting in a higherQuambalaria coyrecupinfection 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 °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.