Climate-related variation in leaf size and phenology of <i>Betula ermanii</i> in multiple common gardens

Leaf phenology and properties are the vital traits of productivity and fitness of individual trees. Understanding the climatic conditions associated with the trait variation is essential for evaluation of the tree species’ capacity to face and adapt to environmental change. This study focused on the habits of the tree species in the alpine forests where they are experiencing some of the highest rates of warming under recent climate change. Thus, we examined the climate-related variation in leaf area, specific leaf area (SLA) and the timing of bud break in common gardens of Betula ermanii across a wide latitudinal range, as well as their height that was strongly correlated with leaf traits. Based on analysis of variance, all recorded traits were found to be genetically controlled, and leaf area was most strongly affected by genetic factors. Traits of saplings from higher latitudinal populations included taller height, larger leaf area, larger SLA and earlier bud break. Leaf area of B. ermanii saplings was strongly correlated with the height of the saplings, as taller saplings exhibited larger leaves. Saplings derived from regions with fewer precipitation in summer showed taller height and larger leaves. In contrast, we could not observe significant associations between SLA and timing of bud break, and any climatic variable for two experimental years. Increasing earliness of bud break of B. ermanii with increases in latitude was likely to associate with the gradients of photoperiod. Climate gradients between populations seemed to contribute to the geographic variation in the height, leaf and phenological traits of B. ermanii.