Effect of Simulated Insect Herbivore Damage on Survival of Tree Leaves

Abstract

Leaf abscission caused by herbivores is well documented, yet the relationship between abscission and amount of damage required to initiate abscission is poorly known. This relationship was investigated in a southern Appalachian forest by mechanically damaging (0,25,50, and 75% area removed) leaves from red maple, Acer rubrum L., flowering dogwood, Comus florida L., tuliptree, Liriodendron tulipifera L., and chestnut oak, Quercus prinus L., and monitoring leaf survival. Leaf survival was negatively related to percentage leaf area removed in 1985 and 1986. Timing of leaf abscission was not significantly different among tree species in 1985. In 1986, there were, however, significant differences among species, which coincided with a severe drought. Damage by herbivorous insects after treatment was measured in 1986 and differed significantly among treatment levels in tuliptree only. Despite significant effects of treatment damage on leaf survival, abscission of damaged leaves occurred at the beginning of normal autumn senescence and leaf fall (except tuliptree in 1986). These results are interpreted with respect to insect-mediated litterfall and its potential influence on the activities of forest floor decomposer organisms.