Takahashi et al. 2Tree-ring width chronology of Betula ermanii was developed at the timberline (2400 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 were used for the analysis (i.e., mean temperature, insolation duration, and sum of precipitation). The tree-ring width of B. ermanii was negatively correlated with December and January temperatures and with January precipitation prior to the growth. However, why high temperatures and much 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 to August of the current year. The tree-ring width was also positively correlated with the insolation duration in July of the current year. On the contrary, the tree-ring width was negatively correlated with summer precipitation during July to 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., much precipitation reduced the insolation duration and temperature. Therefore, it is suggested that much insolation duration and high temperature due to less precipitation in summer 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 in the lower altitudinal limit of B. ermanii (approximately 1600 m a.s.l.) on Mount Norikura. This study suggests that climatic factors increasing the radial growth of B. ermanii differ between its upper and lower altitudinal limits.Key words: Betula ermanii; climatic conditions; dendrochronology; Mount Norikura; timberline; tree-ring width chronology. Takahashi et al. 3 INTRODUCTIONTimberlines are the most severe climatic conditions such as low temperature, strong winds and short growing season for plants along altitudinal gradients, and therefore, the regeneration of trees at the timberlines is supposed to be sensitive to climatic changes (e.g., Briffa & Osborn 1999;Kusnierczyk & Ettl 2002;Lloyd & Fastie 2002;Chapin et al. 2004;Daniels & Veblen 2004;Dullinger et al. 2004). For example, some researchers have discussed that frequent seedling establishment occurred in warmer and/or more mesic years near the timberlines (Kullman 1986;Taylor 1995;Kajimoto et al. 1998;Camarero & Gutiérrez 1999;Gervais & MacDonald 2000). In addition, many dendrochronological studies have revealed that radial growth of trees near the timberlines increased in ameliorated years with higher temperatures than the average (Ettl & Peterson 1995;Gostev et al. 1996;Buckley et al. 1997;Peterson & Peterson 2001;Wilson & Hopfmueller 2001). Trees may respond to climatic conditions more quickly in growth rather than seedling establishment. Thus, the growth is a useful indicator to examine how climatic conditions affect regeneration of trees at the timberlines. Although many researchers investigated the effects of climat...

This study examined the effects of climate on tree-ring widths and maximum latewood densities of Abies veitchii and Abies mariesii at the upper and lower distribution limits in central Japan. A. veitchii and A. mariesii dominated at the lower and upper parts of the subalpine zone, respectively. Residual chronologies of tree-ring width and maximum latewood density were developed for the two Abies species at the upper and lower distribution limits, and were compared with monthly mean temperatures and monthly sums of precipitation. Tree-ring widths of the two Abies species at the upper and lower distribution limits positively correlated with temperatures during the beginning of the dormant season and during the growing season of the current year, except for A. veitchii at the lower distribution limit, which showed no positive correlation with temperature. Maximum latewood densities of the two Abies species at the upper and lower distribution limits positively and negatively correlated with temperatures and precipitation, respectively, during the growing season of the current year. Therefore, tree-ring widths and maximum latewood densities of the two Abies species were sensitive to low temperature, except for the tree-ring width of A. veitchii at the lower distribution limit with the warmest thermal conditions along the altitude. Global warming is suggested to affect maximum latewood densities and tree-ring widths of the two Abies species along the altitude.