Climatic factors influencing the tree-ring growth of Alnus japonica in Kiritapp Mire, northern Japan

Alnus japonica in Kiritapp Mire, eastern Hokkaido, northern Japan was studi ed to determine the effects of temperature, precipitation, and sunshine upo n radial growth. Alnus japonica grows in wetlands, and the distribution in Kiritapp Mire is at the latitudinal limit of the species. Wood samples (n = 101) were collected from a well-developed A. japonica wetland forest, and standardized tree-ring-width indices were developed using a third-order pol ynomial equation and high-frequency-pass filter. A significant positive cor relation was found between tree-ring-width indices and corresponding annual mean temperatures and between both mean temperature and cumulative sunshin e period during the growing season (June-October). Precipitation during the period of generally lowest redox potential (September) showed a significan t positive correlation with tree growth. June sunshine of the ring-formatio n year and August sunshine during the previous growth year also showed sign ificant positive correlations.