Temporal and spatial variations in budding and leaf coloring dates of Ginkgo biloba in Japan

Abstract

　In the present study, we analyzed temporal variations in both budding and leaf coloring dates of Ginkgo biloba from 1977 to 2007, as well as their degrees of similarity in the variations and geographical differences, using statistical methods. The data on the budding and leaf coloring dates were recorded by the Japan Meteorological Agency at 45 and 29 meteorological stations, respectively. Mean regression slopes between the phenological dates and the year indicated that budding in spring, on average, advanced by 1.3 days per decade, and that the leaf coloring in autumn was delayed by 3.9 days per decade. This more significant trend of the later autumn as compared with the earlier spring was supported by the results of comparisons between the mean phenological dates in the 2000s and those in the two subintervals (the 1980s and 1990s) and the comparison of temporal changes in the first principal component (PC) scores. The first PCs of the trends in the budding and the leaf coloring dates accounted for 50 % and 45 % of variations in the phenological dates, respectively. Therefore, temporal trends at approximately half of the total stations were similar. An apparent latitudinal pattern of temporal trends in the budding was indicated by the geographical distribution of the factor loadings of the second PC. The budding advanced significantly at several stations in northern Japan, which were located in cold regions. Conversely, the trends at the stations located in low latitudes and warm areas showed no clear signal. On the other hand, there was no apparent geographical pattern of temporal trends in the leaf coloring.