The Future of Forest Pathology in North America

Forests provide key ecosystem services globally, with economic values ranging from $125 to $145 trillion per year (Costanza et al., 2014). Forests are important not only for carbon sequestration goals and global biodiversity (Bonello et al., 2020a; Di Sacco et al., 2021; Palmer, 2021), but also for the economic (e.g., timber), environmental (e.g., water purification), and social (e.g., recreational activities) benefits (Trumbore et al., 2015) they provide (Bastin et al., 2019, 2020). Increasingly, forests are viewed as directly important to human health (Donovan et al., 2013); indeed, urban green environments are now considered essential in city planning (Nowak et al., 2006; Donovan and Butry, 2009; Donovan et al., 2013; Ideno et al., 2017).

The health of forests impacts their value and ability to deliver these ecosystem services. However, the definition of a healthy forest is actually quite complex and has long been debated (Raffa et al., 2009). In the absence of significant exogenous disturbances, forest ecosystems are ecologically dynamic, yet holistically stable and resilient. A healthy forest is not disease-free, but rather one that can self-perpetuate in a state of dynamic equilibrium, equivalent to a forest on its way to, or at, the climax state. A healthy forest, therefore, “encompasses a mosaic of successional patches representing all stages of the natural range of disturbance and recovery” (Trumbore et al., 2015). Indeed, a healthy forest supports pathogens and other disturbance agents that are essential for natural forest regeneration and nutrient cycling and, ultimately, increased resilience. Unfortunately, in the Anthropocene, forests have become increasingly threatened by human-mediated intensification of natural stressors, e.g., higher temperatures and lower water availability due to global warming, which make trees maladapted to their current habitats and thus more susceptible to insect pest and/or pathogen attacks (Sherwood et al., 2015).