Alpine and subalpine forests are sensitive to climatic changes because of the sever environments, such as low temperature, drought, deep snow cover, wind exposure. In such forests, previous studies showed the positive effect of high temperature on radial growth of trees, and suggested tree line will advance to higher altitudes. By contrast, our data indicated the larger negative effect of high temperature in summer on tree-ring width at higher altitude in a cool-temperate, subalpine forest. Based on this result, one can hypothesise that temperature-induced drought in summer possibly repress radial growth of trees. To test this hypothesis, we examined the relationships among tree-ring width, climatic factors and carbon isotope ratio in tree rings as an index of water stress, and compared the relationships along altitudes in Mt. Oakan and Mt. Nishikumaneshiri. In this seminar, I will present the negative effect of temperature-induced drought on tree-ring width near tree line in Mt. Oakan; in contrast, the positive effect of high temperature in Mt. Nishikumaneshiri.