Future climate change promotes novel gene-climate associations in balsam poplar (Populus balsamifera L.), a forest tree species

A central challenge to predicting climate change effects on biodiversity is integrating information on intraspecific variation, specifically population-level local adaptation to climate. Assessing how climate change could disrupt local adaptation to climate can provide a new way of understanding population risk and vulnerability to climate change. For the wide-ranging boreal tree species, balsam poplar (Populus balsamifera L.), we used models of existing population-level genetic differentiation to estimate three key components of populations vulnerability to climate change: (1) predicted shifts in genetic composition with and without migration, (2) the potential for future novel gene-climate associations, and (3) the distance populations would need to migrate to minimize future maladaptation. When assessed across the range of balsam poplar, these three metrics suggest that vulnerability to climate change is greatest in the eastern portion of balsam poplars range, where future maladaptation peaked, migration distances to sites that minimized maladaptation were greatest, and the emergence of novel gene-climate associations were highest. Our results further suggest greater maladaptation to climate when migration distances were limited - consistent with the possibility of migration to lessen maladaptation to future climate. Our work provides a comprehensive evaluation of populations vulnerability to climate change by simultaneously assessing population maladaptation to future climate and the distances populations would need to migrate to minimize maladaptation, in a way that goes beyond species-level bioclimatic modelling. In doing so, our work helps advance towards the long-held goal of incorporating genomic information in models of species responses to climate change.