Prioritizing Conservation of Trailing-Edge Populations for Future Climate-Resilient Forests.

Trailing edge tree populations, located at the warm or dry margins of species' ranges, often harbor unique genetic adaptations to marginal environments. These populations face heightened risks from climate change, potentially threatening the persistence of valuable adaptive traits. Here we identify trailing-edge populations for the 100 most common North American tree species using spatially explicit climate and forest inventory data, and prioritize conservation actions based on projected forest cover loss, climate velocity, and species richness. Assisted migration initiatives for these populations could safeguard the long-term persistence of their adaptive traits, ensuring that valuable genotypes are maintained within future forest ecosystems. Trailing-edge populations were geographically concentrated in the Appalachian region, the Midwest, and southern boreal forests. Areas bordering the central plains faced the highest projected forest cover loss and climate velocity, while the Great Lakes basin and eastern Canada emerged as promising recipient regions. Our findings support targeted conservation and assisted migration strategies to maintain genetic diversity and enhance forest resilience under future climates, facilitated by an online tool for climate-informed seed collection and planning (https://tinyurl.com/past-nam).