Greater climate change adaptation potential in populations of Quercus macrocarpa at edges of latitudinal gradient.

With current climate trajectories, tree populations will encounter novel selection pressures that risk local extinction if they are unable to acclimate or adapt. Within a reciprocal transplant experiment with Quercus macrocarpa L. established across a latitudinal gradient, we asked: (1) Is there genetic variation within populations? (2) Are there differences in the direction and strength of selection? (3) Do traits within populations differ in adaptation potential in response to future climate conditions? Within each population in each of three gardens (Minnesota, Illinois, and Oklahoma), we estimated genetic variance for nine traits grouped in three realms: physiology, spectral reflectance features, and morphology/growth. We also analyzed selection on these traits and assessed their potential adaptive response to selection. Our results indicate that traits related to morphology and growth have high genetic variance and are under strong directional selection in warmer gardens. The populations that represent extreme ends of the climatic gradient have high potential to adapt to climate change, based on their responses to selection in the warmest garden (Oklahoma). These results inform strategies to improve species resilience by providing seed source information relevant to managers planning assisted migration to promote climate change adaptation.