Regional variation in branch morphological and mechanical traits in Abies sachalinensis associated with winter climatic conditions in variable snowfall environments

In boreal forests, regional variation in overwintering strategies including snow adaptation can be expected in branches of conifer trees. The geographical pattern of morphological variation associated with snow conditions may provide cues to the selection of traits associated with winter adaptation, while few transplanting trials have quantified specific functional traits to date. This study explored the candidate traits for snow damage resistance from the morphology and mechanic of the branches of Sakhalin fir ( Abies sachalinensis ) as a representative species of boreal conifers with local adaptation. A comparing 12 morphological and nine mechanical traits among eight provenances with climatic gradients revealed that 13 traits showed regional variation. Based on the association with provenance environments, the eight functional traits among 13 showing regional variation were selected as candidates for snow damage resistance, including the estimated quadratic flat areas of the main branch, the relative number and mean angle of lateral branches, and the rigidity of the raw and frozen main branch. Correlations among these traits showed that a larger number of lateral branches, lower the rigidity of a main branch. These trade-off between the lateral and main branches were associated with winter environments. Contrary to our expectations, positive correlations among candidate traits and total monthly daylight hour in winter were observed, indicating that the branches that allocates resource on the lateral branches rather than the main branch may be associated with the adaptation to winter ambient conditions such as intense light and extremely low temperature in regions with less snowfall.