Defoliation by gypsy moths negatively affects the production of acorns by two Japanese oak species

Abstract

This study showed the negative effects of insect defoliation on the reproduction of canopy trees, where defoliation was not artificially manipulated but rather observed in a natural setting. The gypsy moth (Lymantria diapar) is a serious defoliator with the ability to completely defoliate forest canopies. Although the negative effects of defoliation on tree reproduction have been revealed in studies with artificially manipulated defoliation, few studies have examined the effect of insect defoliation on the reproduction of canopy trees under natural condition. In this study, visual surveys were used to clarify the effect of gypsy moth defoliation on the production of acorns by oaks (Quercus spp.). Surveys were conducted in an outbreak year at 22 sites in central Japan (13 sites with Quercus crispula and nine sites with Q. serrata). Five of the Q. crispula sites were severely defoliated (mean defoliation ranged from 67 to 88 %), while the remainder of the Q. crispula sites and all of the Q. serrata sites were lightly defoliated (0–20 %). A negative effect of gypsy moth defoliation on acorn production was detected for Q. crispula. However, there was a synchronous decrease in acorn production from the previous year and crop levels were low at all sites regardless of the defoliation severity. The consistent low crop levels were likely the result of weather-related factors. Defoliation also negatively affected the production of acorns for Q. serrata; however, severe defoliation was not present at any Q. serrata sites. This study suggests that insect defoliation can affect forest ecosystem processes, such as the regeneration of host trees and the behavior of wildlife that depend on seed production, by reducing the reproductive potential of host trees.