Causal factors for spatial variation in long-term phonological trends in Ginkgo biloba L. in Japan

摘要

Distinct plant phenological changes caused by increasing temperature have been reported in several regions. However, spatial patterns in long-term phenological trends and their causal factors have not been fully examined. Attempts were made to address these issues using a long-term (1961-2000) phenological dataset (budding and leaf fall dates) for Ginkgo biloba L. from 60 meteorological stations in Japan. Although many stations indicated earlier budding and delayed leaf fall, there were large differences among stations. First, the author tried to understand the spatial variation patterns of the long-term phenological trends relative to geography. However, there was no significant relationship between phenological trends and geographical variables: latitude, longitude, and altitude, with the exception of a negative relationship between the trend of leaf fall date and latitude. Second, relationships between phenological trends, long-term trends in air temperature, and phenological sensitivity of Ginkgo to variations in air temperature were investigated as direct causal factors for spatial variations in phenological trends. With respect to the air temperature trend, a negative relationship was found with the budding trend, but there was no obvious relationship with the leaf fall trend. On the other hand, the spatial variability of the phenological sensitivity to temperature was relatively large and displayed a significant linear relationship with trends in budding and leaf fall. Where trees had higher sensitivity to temperature, they showed earlier budding and delayed leaf fall. The results obtained from multiple linear regressions indicated that the spatial variations in phenological trends were dependent more on phenological sensitivity to air temperature than temperature trends.