Ecological genetics and seed transfer guidelines for Pinus albicaulis (Pinaceae)

Whitebark pine (Pinus albicaulis Engelm.) has greatly declined throughout its range as a result of introduced disease, fire suppression, and other factors, and climate change is predicted to accelerate this decline. Restoration is needed; however, no information regarding the degree of local adaptation is available to guide these efforts. A seedling common-garden experiment was employed to assess genetic diversity and geographic differentiation (Q(ST)) of whitebark pine for traits involved in growth and adaptation to cold and to determine climatic variables revealing local adaptation. Seedlings from 48 populations were grown for two years and measured for height increment, biomass, root to shoot ratio, date of needle flush, fall and spring cold injury, and survival. Significant variation was observed among populations for most traits. The Q(ST) was low (0.07-0.14) for growth traits and moderate (0.36-0.47) for cold adaptation related traits, but varied by region. Cold adaptation traits were strongly correlated with mean temperature of the coldest month of population origins, while growth traits were generally correlated with growing season length. We recommend that seed transfer for restoration favor seed movement from milder to colder climates to a maximum of 1.9°C in mean annual temperature in the northern portion of the species range, and 1.0°C in the U. S. Rocky Mountains to avoid maladaptation to current conditions yet facilitate adaptation to future climates.