Climatic factors affecting the tree-ring width of Betula ermanii at the timberline on Mount Norikura, central Japan

Tree-ring-width chronology of Betula ermanii was developed at the timberline (2,400 m a.s.l.) on Mount Norikura in central Japan, and climatic factors affecting the tree-ring width of B. ermanii were examined. Three monthly climatic data (mean temperature, insolation duration, and sum of precipitation) were used for the analysis. The tree-ring width of B. ermanii was (n)egatively correlated with the December and January temperatures and with the January precipitation prior to the growth. However, why high temperatures and heavy snow in winter had negative effects on the growth of B. ermanii is unknown. The tree-ring width was positively correlated with Summer temperatures during June-August of the current year. The tree-ring width was also positively correlated with the insolation duration in July of the Current year. fit contrast, the tree-ring width was negatively correlated with summer precipitation during July-September Of the Current year. However, these negative correlations Of Summer precipitation do not seem to be independent of temperature and insolation duration, i.e., substantial precipitation reduces the insolation duration and temperature. Therefore, it is suggested that significant insolation duration and high temperature due to less precipitation in si,,er of the current year increase the radial growth of B. ermanii at the timberline. The results were also compared with those Of Our previous study conducted at the lower altitudinal limit of B. ermanii (approximately 1,600 m a.s.l.) on Mount Norikura. This Study suggests that the climatic factors that increase the radial growth or B. ermanii differ between its Upper and lower altitudinal limits.