Quantifying the roles of climate, host abundance, and spread on forest pest distributions in North America

The distribution of many insect pests and pathogens (hereafter, pests) are driven by a combination of climate and host abundance, and quantifying their relative roles will help inform climate change effects on pests’ future distributions. Here, we develop and implement a framework to predict the contemporary distribution of pest species, that accounts for climate, relative host abundance, and, for non-native species, their spread across the landscape. Using data fusion approaches to integrate disparate sources of pest information, we develop species distribution models to predict the contemporary distributions of 26 forest pest species. We show that pest distributions can primarily be predicted by climatic variables, with relatively minor effects of individual host tree abundances. While individual host trees had only minor effects, the summed total of host abundance had comparatively higher importance – suggesting pest distributions are more strongly impacted by aggregate host abundance in forests compared to individual host-pest associations. Furthermore, non-native pests were strongly impacted by the distance from their discovery location in North America, which we found to interact with climate variables – suggesting most non-native pests are not yet at equilibrium with their climatic niches in North America. This work helps to clarify the generalizable controls on pest distributions, and provides a flexible framework for predicting pest distributions in future climates.