Geographic variation and adaptation to current and future climates of Callitropsis nootkatensis populations

Abstract

Forty-one range-wide Callitropsis nootkatensis (D. Don) Orsted (syn. Chamaecyparis nootkatensis (D. Don) Spach) populations were tested at 12 geographically and ecologically diverse sites throughout British Columbia, Canada. There were significant region and population within region effects for 15-year height at most sites but not for adaptability, a binary trait combining survival and cold hardiness. Across-site analysis revealed significant site by population within region interaction for both traits. These interactions were less pronounced when just the core sites were analysed and without two southern disjunct populations. Based on a productivity index that combined height, survival, and cold hardiness, populations were adapted to broad temperature gradients compared with most temperate tree species and were relatively insensitive to moisture. Only the northern California population from the extreme southernmost part of the species’ range had consistent and significant adaptive differentiation, showing maladaptation characterized by severe cold damage and mortality at all test sites. Northern populations grew slowly but survived well. Productivity of this montane species is likely to increase in situ with projected warming across the range of tested sites. Transfer to sites warmer than the population origin increases productivity. Currently and in the long term, populations from the core of the species’ range can be widely transferred for reforestation with minimal risk of maladaptation, provided highly inbred sources from isolated, small populations and sites at risk for yellow cypress decline are avoided.