Tree mortality following defoliation by the European gypsy moth (Lymantria dispar L.) in the United States: A review

This review presents information related to defoliation by the European gypsy moth (Lymantria dispar L.) and subsequent tree mortality in the eastern United States, The literature describing defoliation-induced tree mortality is extensive, yet questions sti II remain concerning (1) the association between initial stand composition and subsequent tree mortality, (2) the influence of site quality on tree mortality, and (3) observed differences between mortality rates in initial and subsequent outbreaks. Our review and analysis of the available literature indicates that initial species composition affects subsequent defoliation, Stands with predominantly susceptible host species have higher levels of species-specific and total mortality than mixed stands of susceptible, resistant, and immune host species. Differences in mortality on sites of varying productivity do not appear to be a direct result of site quality; rather, site quality indirectly influences mortality rates through its effect on species composition and therefore defoliation, Differences between initial and subsequent outbreaks appear to be due primarily to losses of vulnerable oaks and lower canopy species during the initial outbreak; oak mortality in initial outbreaks was found to be significantly greater (P = 0.0727) than oak mortality in subsequent outbreaks.