标题：Effects of Climatic Conditions on Shoot Elongation of Alpine Dwarf Pine ( Pinus pumila ) at Its Upper and Lower Altitudinal Limits in Central Japan
其他标题：Effects of Climatic Conditions on Shoot Elongation of Alpine Dwarf Pine ( Pinus pumila ) at Its Upper and Lower Altitudinal Limits in Central Japan
摘要：The effects of climatic conditions on the shoot elongation of alpine dwarf pine ( Pinus pumila ) were examined at its lower and upper altitudinal limits on Mt. Norikura (2500 and 2840 m a.s.l.) and Mt. Shogigashira (2640 and 2675 m a.s.l.) in central Japan. Altitudinal forest-structural changes were also described. Shoot elongation and stem height of P. pumila increased with decreasing altitude, but its abundance was markedly decreased at the altitudinal ecotone between the upper P. pumila zone and the lower Betula ermanii zone because of the suppression by tall B. ermanii . Thus, the lower altitudinal limit of P. pumila was probably determined by the competition with B. ermanii . The interannual variation in the shoot elongation of P. pumila was related to climatic conditions; long shoot length was associated with high summer temperatures of the previous year at both the upper and lower altitudinal limits on the two mountains. In addition, rates of the increase of shoot elongation in response to the increase of air temperature were not different between the upper and lower altitudinal limits. Thus, the increase of summer temperatures would enhance the growth of P. pumila from its upper to lower altitudinal limits. However, it is harder to predict the altitudinal distribution shift of P. pumila due to environmental change because its lower altitudinal limit is largely affected by competition with B. ermanii . Therefore, this study concluded that long-term monitoring of the population dynamics at the P. pumila – B. ermanii ecotone is necessary to predict the distribution shift of P. pumila .
