Genetic variation and adaptation of white birch populations across Canada

Abstract

Trees adapt to local climates, however growing concern surrounding climate change has generated predictions suggesting mass extinction or redistribution of taxa across the landscape. A lack of redistribution will result in species inhabiting suboptimal conditions for growth and survival. Current reforestation efforts are to understand how species will respond to different climates. Seed representing twenty-one white birch (Betula papyrifera Marsh.) populations were collected, grown and planted in a common garden study. Populations were observed for height, root collar diameter (RCD) and survival percentage. There was a significant effect of population on each growth variable. Survival had a positive correlation with height and RCD growth (May to September) (Pearson’s r = 0.828 and 0.660 respectively). Summer temperature had a strong relationship to each measured trait (r2 = 0.326 to 0.682 respectively). The second set of observations was bud flush, bud cessation and leaf yellowing. Bud flush observations began in early May and categorized bud development into six stages from dormant to fully flush. Bud cessation commenced in the first week of September every four days until bud set requirements were met. Leaf yellowing was observed simultaneously with bud cessation until 50% leaf yellowing was achieved. These traits represent phenological responses to temperature and photoperiod. There was a significant effect of population on each variable. Bud flush had a strong negative relationship with height growth, RCD growth and survival (r = -0.735, -0.693 and -0.539 respectively). Bud set influenced season length (Julian days), which had a positive correlation to height growth, RCD growth and survival (r = 0.568, 0.407 and 0.537 respectively). Leaf yellowing also showed a positive correlation to height growth and survival (r = 0.443 and .590 respectively). Principal component analysis was utilized to summarize the 21 white birch populations in regards to their growth and phenological responses to the common garden study. Principal component analysis produced two components, which represented 24.2% and 16.61% of the variation respectively. No definitive titles were given to each principal component. Temperature was a main predictor of growth and phonological responses during the study. Summer and winter temperatures, along with growing degree days (a function of temperature), were influential in predicting both growth and phenological responses.