Annual variability in acorn production and pre-dispersal damage to acorns of four fagaceous species in two adjacent forest stands with different mixed ratios in western Japan

We investigated the relationships between the annual variation in acorn production and pre-dispersal insect damage to acorns for 6 years in co-occurring fagaceous species (Quercus variabilis, Q. serrata, Q. glauca, and Castanopsis cuspidata) in two adjacent forest stands that had different mixed ratios due to succession: a deciduous broad-leaved forest stand (DB), and an evergreen broad-leaved forest stand (EB). In C. cuspidata, the annual number of sound acorns correlated with that of female flowers. In contrast, for three Quercus species, the annual variability in sound acorn production was not correlated with that in female flowers, but was affected by the annual fluctuation in the percentage of insect damage in both the stands. For the three Quercus species, the dominant types of insect damage were different among the species, but similar between the two stands: damaged by moth larvae in Q. variabilis, and sap suction by adult weevils in Q. serrata and Q. glauca. Key factor analyses showed that the contribution of the dominant type of insect damage was similar between the two stands for the reproductive loss in Q. variabilis, but was different between the stands in Q. serrata and Q. glauca. Different mixed ratios of fagaceous species might affect the annual variability in sound acorn production via changes in the impact of a particular type of insect damage, even between adjacent stands.