Weak local adaptation to climate in seedlings of a deciduous conifer suggests limited benefits and risks of assisted gene flow

Intraspecific genetic variation in growth, phenology and cold hardiness was analyzed to test for signals of local adaptation and the effects of selective breeding to better understand the implications for assisted migration and breeding for future climates. We found weak differentiation among populations in all traits, with the proportion of additive genetic variance (QST) values ranging from 0.10 to 0.28. Cold hardiness had the weakest population differentiation and exhibited no clines with geographic or climatic variables.

Selective breeding for faster growth has maintained genetic variation in bud flush phenology and cold hardiness despite delaying bud set. The weak signals of local adaptation we found in western larch seedlings highlights that assisted gene flow among populations is likely to have limited benefits and risks for mitigating maladaptation with climate change. Our findings suggest that assisted migration outside of the range and selective breeding may be important management strategies for western larch for future climates.