Determination of intraspecific variation in seed weight, leaf functional traits, and sapling size of Betula ermanii using a common garden experiment

Habitat loss of forest tree species distributed in cold temperate and alpine zones is a serious issue in the context of global warming. Considering that intraspecific variation is essential for adaptation to changing environments, intraspecific variation in seed weight, leaf traits, and sapling size of a sub-alpine broad-leaved tree species, Betula ermanii, was examined in this study using seeds collected from 11 populations across its natural distribution. Seeds were sown in seed beds, and containerized seedlings were grown in a greenhouse with a uniform environment (a common garden experiment). The effects of four climate variables, i.e. warmth index (WI), minimum temperature of the coldest month (TMC), summer precipitation (PRS), and maximum snow depth (MSD) were evaluated on seed weight, leaf functional traits, and sapling size using a generalized linear mixed model (GLMM). Positive latitudinal clines were detected for seed weight, whereas negative clines were detected for both specific leaf area and leaf nitrogen. These clines were not consistent with the general trends observed in previous studies. The reasons might be partly explained by geographic variation in climatic variables and nutrient availability. The findings obtained from this study should be useful for conservation of mountainous forest ecosystems in the age of climate change.