Geographical variation in climatic cues for mast seeding of Fagus crenata

Geographical variation in climatic cues for masting of Fagus crenata Blume, which is the most dominant tree species in Japanese temperate forests, was investigated in the northern part of Japan, i.e., the Tohoku district of Honshu Island and the Oshima Peninsula of Hokkaido Island. The data obtained after an 18-year assessment (1989–2006) of 163 stands, covering an area of ca. 200 × 500 km² area, were used in this study. In all stands, mast seeding occurred three times (1995, 2000 and 2005) during the study period and the coefficient of annual variation (CV) in seedfall density was 0.94. Based on cluster analysis, the stands were classified into each of the seven groups, in which the seedfall density was temporally synchronized among the stands and showed higher values of CV (1.04–1.79). These groups were distributed spatially exclusively at the scale of 80–200 km. By selecting the tree model based on AIC values, lower temperature in spring, higher temperature in summer and seedfall density in a year were proved to have a decisive influence on the seedfall density in the subsequent year. The effects of the first two climatic cues overwhelm that of the seedfall density. Lower temperature in spring served as a cue mostly for the population in the Oshima Peninsula, while higher temperature in summer served as a cue for the populations in the Tohoku district. If this suggests a genetic variation in relation to cues, climatic changes (e.g., global warming) will have different impacts on seed production of different F. crenata populations. However, it remains to be tested in future studies whether multiple climatic cues simply reflect regionally variable climatic conditions or not.