| This study investigates geographic patterns of genetic variation in aspen spring phenology to understanding how tree population adapts to climatically risk environments. These finding suggest rules to guide seed transfer between regions. I use a classical common garden experiment to reveal genetic differences among populations from western Canada and Minnesota, and present a novel method to seamlessly map the heatsum required for remotely sensed green-up. Both approaches reveal two major geographic patterns: northern and high elevation aspen populations break bud earlier than sources from the boreal plains, and late budbreak is strongly associated with the driest winter and spring environments. This suggests selection pressures for late budbreak due to both frost and drought risks in early spring, and we therefore caution against transfer of seed to drought-prone regions of the boreal plains. Although such transfers have been shown to increase plantation productivity in short-term tests, non-local planting material may be susceptible to exceptional spring droughts. |
