Two-year cycles of synchronous acorn and leaf production in biennial-fruiting evergreen oaks of subgenus Cyclobalanopsis (Quercus, Fagaceae)

Many masting species switch resources between vegetative growth and reproduction in mast and non-mast years. Although masting of oak species is well known, there have been few investigations of the relationship between vegetative growth and reproduction based on long-term monitoring data, especially in evergreen oaks of subgenus Cyclobalanopsis. We investigated annual variations over 13 years in acorn and leaf production of three evergreen oak species in subgenus Cyclobalanopsis, genus Quercus (Fagaceae)—Q. acuta, Q. salicina and Q. sessilifolia—in western Japan. In these species, the maturation of acorns occurs in the second autumn after flowering, which is known as a biennial-fruiting habit. We found a pattern of acorn production and masting in alternate years that was synchronized in all three species. Masting was not correlated with temperature and precipitation. Annual leaf-fall also showed 2-year cycle in the three oak species; peak years were synchronized between species and peak leaf-fall alternated with acorn production in all three species. Furthermore, there was a significant negative correlation between acorn and leaf production in all three species. Data showing 2-year cycles of acorn and leaf production and the negative correlation between them supports the hypothesis of resource switching between vegetative growth and reproduction. The 2-year cycle might be the basic, intrinsic rhythm of resource allocation in biennial-fruiting Cyclobalanopsis species.