Climate change and shoot elongation of alpine dwarf pine (Pinus pumila Regel): Comparisons between six Japanese mountains

In northern to central Japan, alpine dwarf pine (Pinus pumila Regel) is a principal component of vegetation in the alpine life zone above the timberline. In this study, we examined interannual variations in the shoot elongation of P. pumila growing on the summits of six Japanese mountains and analysed the relationships between climatic factors and shoot growth during the period from 1980 to 2003. A significant increment of annual shoot elongation over the last 24 years was detected in three populations studied in central Japan, showing synchronization between the populations. However, such a trend was not found in the populations in northern Japan. In central Japan, interannual increasing trends in summer temperatures during the period were observed at meteorological stations near the populations. In the three populations of northern Japan, however, similar trends were not obvious, but a significant decreasing trend in summer sunshine duration was observed at a meteorological station located near the northernmost population. Summer sunshine duration, as well as summer temperature, was significantly positively correlated with shoot elongation of P. pumila in four out of six populations. We discuss these geographical variations in interannual shoot elongation of P. pumila between the six populations in relation to climate change in Japan.