In Fagus, both flower and leaf primordia develop within the same winter buds in the preceding summer, and full mast seeding years are invariably followed by at least one non-mast year. The amounts of nitrogen (N) contained in seeds are very high. We hypothesized that N limitation is responsible for the poor seed production in years following masting events and tested this hypothesis in F. crenata.

The amount of N and dry mass in flower buds was found to be 1.5-2.2 fold higher than those values in leaf buds, although leaf numbers per current-year shoot developed from the above corresponding buds were not significantly different between reproductive and non-reproductive shoots. These results indicate that 1.5-2.2 folds more of N and carbohydrate is required for the development of a flower bud than a leaf bud. In addition, both leaf number per shoot and annual leaf litter decreased significantly in the mast year. Since both flower and leaf primordia develop within the same winter buds and flower primordia start to differentiate during the month when the amount of N contained in seeds increases rapidly, prioritization of the N supply to seeds in the mast year appeared to reduce the amount of N available for the differentiation of floral primordial, and thus restricted flowering in the following year.