Spatial analysis of risks posed by root rot pathogen, 'Phytophthora cinnamomi': Implications for disease management

Phytophthora cinnamomi, a soil-borne pathogen that infects the roots of plants, is listed as a Key Threatening Process under Commonwealth and NSW state biodiversity legislation due to its deleterious effects on native flora. In warm temperate eastern Australia, the disease may cause insidious declines in plant species that have slow rates of population turnover, and thereby threaten their long term persistence. Phytophthora cinnamomi has been known to occur in Royal National Park since the 1970s and systematic surveys for the pathogen were carried out a decade ago. Development of effective management strategies to mitigate the impacts of the disease requires information on the spatial distribution of risks posed by the disease. In this study, we use limited disease survey data to identify areas that are most at risk. We propose and apply a simple risk model in which risks of disease impact are proportional to the product of habitat suitability for the pathogen and abundance of susceptible biota. We modelled habitat suitability of the pathogen from available survey data and found that soil landscapes and topographic variables were the strongest predictors. Susceptible flora were concentrated on sandstone plateaus. Disease risks were greatest on the sandstone plateaus and lowest in the shale gullies with intermediate levels of risk on shale ridges and the coastal sand plain. The outcomes of this spatially explicit risk assessment will help inform the development of management strategies and priorities for the disease in the Park. Our approach lends itself to broader application to conservation planning in other landscapes and to other threats to biodiversity.