Local Adaptation for Seasonal Cold Tolerance in a High‐Elevation Conifer Species, Subalpine Larch ( <i>Larix lyallii</i> Parl.)

Subalpine larch (<i>Larix lyallii</i> Parl.) is a deciduous conifer that only grows at treeline in the Cascade Range and Rocky Mountains of western North America. This habitat is shrinking due to climate change but subalpine larch is unlikely to migrate or adapt in situ and is therefore at risk of maladaptation and eventual extirpation. Future conservation efforts should be informed by an understanding of local adaptation in key traits. In this study, cold tolerance was assessed for 18 populations of subalpine larch from the Canadian portion of the species range that are grafted <i>ex situ</i> at the Kalamalka Forestry Centre in Vernon, BC. Electrolyte leakage was measured after stem tissue was subjected to artificial freezing tests at a range of subzero temperatures (-10°C to -40°C) over 2 years and three seasons (winter, spring, and autumn). Adaptive clines in cold tolerance were observed, providing the first evidence of local adaptation in this species. Temperature-associated climate variables such as the length of the frost-free period (FFP), the Julian date for the end of the frost-free period, and mean coldest month temperature were significant predictors of cold injury at -40°C in all three seasons. Populations from colder sites with a shorter FFP were found to have significantly higher cold tolerance in all three seasons, with the biggest differences observed in spring and autumn. Future management strategies should prioritize the conservation of adaptive variation in cold tolerance.