Abstract
Bark beetles contributing to ponderosa pine mortality in western North America are ecologically and economically impactful. Future climate patterns are expected to exacerbate these impacts. While reactive management aims to reduce the impact of bark beetle-caused tree mortality after these insects have already entered a forest system, preventative measures can serve to reduce the susceptibility of forested stands to epidemic bark beetle attacks before they occur. It is well documented that stressed trees are more susceptible to beetle attack and subsequent mortality than healthy trees. For this reason, nearly a century of research has been focused on the identification of quantifiable characteristics that serve as proxy variables indicative of tree stress. Dozens of bark beetle susceptibility models exist, though they vary widely in their use of variables, application, predictive capabilities, and region of interest. This review serves to identify bark beetle susceptibility models for ponderosa pine forests in western North America, highlight their limitations, and outline the improvements that can be made in the development of future susceptibility models.