In western Canada, both interior spruce (Picea glauca, Picea engelmannii, and their hybrids) and lodgepole pine (Pinus contorta) are important commercial forest tree species. However, a changing climate may lead to mal-adaptation and thereby decrease forest productivity and threaten forest health. Assessing the adaptive characteristics of populations within these species is important for the development of forest management strategies to match reforestation stocks with predicted future climates. This research, conducted as part of the AdapTree project, investigates phenotypic variation of lodgepole pine and interior spruce at the landscape level. Seeds were collected in British Columbia and Alberta from over 250 locations, germinated and grown in environmental chambers with four different temperature and moisture regimes. Phenotypic traits (i.e. height, diameter, budbreak, budset and cold hardiness) were measured to investigate variation among sampled populations. Central objectives in the analysis are to: 1) assess phenotype-climate correlations and 2) examine geographic patterns of phenotypic variation to then 3) determine groups of populations having similar phenotypes as the basis for seedzone delineations. Phenotypic traits will also be used in future genome-wide association studies to determine the genomic basis of local adaptation to climate.
Individual climate variables could explain between 5 and 25% of the variance in measured growth and adaptive traits. Variables such as mean warmest month temperature and growing degree-days best explained variance in growth, whereas variables related to winter temperatures correlated best with cold hardiness. Geographic distribution of phenotypic variation in interior spruce indicated a separation of cold hardy populations east of the Rocky Mountains from susceptible populations in the west. The most rapid growth was observed for seedlings originating from the interior valleys of British Columbia. High elevation interior spruce populations were distinguished by late budbreak and early budset. Lodgepole pine showed similar patterns with the exception of a few frost hardy and simultaneously well growing populations from Alberta. Provenances from Pinus contorta ssp. contorta the BC coast stood out from interior ssp. Iatifolia with late budbreak and high susceptibility to frost. Multivariate partitioning of genetic variation using a regression tree approach suggests 11 seed zones for interior spruce and 9 seedzones for lodgepole pine that account for 18% and 14% of the total observed phenotypic variation, respectively.