Distribution and environmental correlates of fungal infection and host tree health in the endangered American chestnut in Canada

Restoration of plants endangered by introduced pathogens relies in part on the ability to predict geographic variation in the incidence of disease and its impact on tree health. Environmental factors can influence plant-pathogen interactions but large scale, multifactorial analyses of environmental determinants are often lacking. Here we use a multi-year survey of the endangered American chestnut in southern Canada and geospatial data on climatic, edaphic, and landscape characteristics to test for spatial heterogeneity in, and environmental associations with, blight occurrence (current incidence of chestnut blight, infection of healthy individuals over 13 years) and tree health (presence of healing/healed cankers, tree mortality). We detected geographic hotspots for all measures of blight occurrence and tree health, suggesting tree-pathogen interactions are moderated by local conditions. Individual measures of blight occurrence were correlated with nine climatic, edaphic and landscape variables and were consistently related to precipitation, surficial geology and elevation. Measures of tree health were consistently affected by mean annual temperature, and individually correlated with five climatic and landscape variables but no edaphic variables. Overall, environmental variables explained 9–22% of variation in blight and tree health, reflecting the complex processes underlying host -pathogen interactions in a system in which blight persists throughout the range. Nevertheless, environmental correlates are sufficient to guide further research on mechanisms of tolerance and aid conservation priorities and action in this species