Climate, Host Abundance and Spread: Unravelling the Drivers of Forest Pest Distributions in North America

Aim Forest pathogens, insect pests and parasitic plants are among the most important disturbance agents in forested ecosystems. Understanding where pests occur and where they might occur in the future will be important for understanding their impacts on host trees, and planning for future pest outbreaks. Location North America. Taxon Insect pests, pathogens and parasitic plants of forest trees. Methods Here, we develop and implement a framework to predict the contemporary distributions of 26 pest species that accounts for climate, host abundance and, for non‐native species, their spread on the landscape. Results We show that pest distributions can be predicted primarily by climatic variables. The abundance of individual host trees had only minor explanatory power, but the summed total of host abundance frequently had greater importance—suggesting forest composition and the relative frequency of hosts and non‐hosts place strong limits on pest distributions. Non‐native pests were strongly impacted by the distance from their original discovery location in North America, which tended to interact with climate variables—suggesting most non‐native pests are not yet at equilibrium with their potential climatic ranges in North America. Main Conclusions This work helps to clarify the generalised controls on pest distributions and provide a framework for predicting pest distributions in future climates.