Understanding the relationship between masting and stored carbohydrate resources in trees by a radioactive carbon analysis method

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Many tree species undergo a large fluctuation from year to year in seed production, a phenomenon known as masting. The resource budget model, based on the assumption that abundant seeding in a masting year depends on abundant resources stored over several years, is a key hypothesis in explaining the mechanism of masting. But do masting species really need such a long-term storage in order to produce a large seed crop? To test this hypothesis, we studied relation between carbon accumulation periods for seed production, estimated by radiocarbon (^<14>C) analyses, and reproductive intervals in 10 canopy-tree species in a temperate deciduous forest and 17 dipterocarp species in a tropical rain forest. These species differ widely in their reproductive intervals. In all the species studied, the accumulation period toward seed maturation was less than 1.4 years. Moreover, regardless of species or reproductive intervals, there was no significant correlation between the carbon accumulation period and the fluctuation of annual seed production. Our results suggest that temperate and tropical canopy trees used the photosynthates produced in the current and/or the previous year for seed production regardless of reproductive intervals. It might therefore be necessary to reconsider the importance of stored carbohydrate resources for masting.