We used seed traps to examine the flowering and seed production of Japanese beech (Fagus crenata) from 2002 to 2019 at five study sites in Akita prefecture, northern Japan. During the study period, mast-years in which more than 200 healthy seeds per square meter fell at multiple sites were observed four times i.e., in 2005, 2013, 2015, and 2018. The mast-year cycle was approximately five years on an average, ranging from two to eight years. The annual variation in number of flowers tended to be large in the southern sites. According to Spearman’s rank correlation test, the annual variation in the number of flowers was synchronized among four sites excluding the northern site, and the correlation was particularly strong among the three sites along the Ou Mountains. We also examined the correlation between the number of female flowers and seed production in the northern, central, and southern sites in Akita. We found that seed production was primarily affected by the number of flowers in the southern sites, while in the northern and central sites seed production was also affected by the seed predation ratio by insects. The inter-regional synchronization in mast seeding of Japanese beech might be interpreted as a geographic cline along surrounding snow in Akita. The prediction method for seed production of Japanese beech that was developed in Yamagata could be applied to the southern beech forests, while the method developed in Hokkaido could be applied to the central and northern forests in Akita.

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