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Few studies have analyzed pollen and seed movements at local scale, and genetic differentiation among populations covering the geographic distribution range of a species. We carried out such a study on Cercidiphyllum japonicum; a dioecious broad-leaved tree of cool-temperate riparian forest in Japan. We made direct measurement of pollen and seed movements in a site, genetic structure at the local scale, and genetic differentiation between populations covering the Japanese Archipelago. Parentage analysis of seedlings within a 20-ha study site indicated that at least 28.8% of seedlings were fertilized by pollen from trees outside the study site. The average pollination distance within the study site was 129 m, with a maximum of 666 m. The genotypes of 30% of seedlings were incompatible with those of the nearest female tree, and the maximum seed dispersal distance within the study site was over 300 m. Thus, long-distance gene dispersal is common in this species. The correlation between genetic relatedness and spatial distance among adult trees within the population was not significant, indicating an absence of fine-scale genetic structure perhaps caused by high levels of pollen flow and overlapping seed shadows. Six populations sampled throughout the distribution of C. japonicum in Japan showed significant isolation-by-distance but low levels of genetic differentiation (F ST ¼ 0.043), also indicating long-distance gene flow in C. japonicum. Longdistance gene flow had a strong influence on the genetic structure at different spatial scales, and contributes to the maintenance of genetic diversity in C. japonicum. Heredity (2006) 96, 79-84.

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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)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) of 163 stands, covering an area of ca. 200 9 500 km 2 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.