Radial Growth Losses in Preferred and Avoided Tree Species During Gypsy Moth Outbreaks

Abstract

Abstract We investigated the effect of gypsy moth larval density on radial growth of preferred and avoided trees: northern red oak and white ash, respectively. Individual trees were censused for gypsy moth larvae from 1979 to 1992 at a site where several outbreaks occurred. Annual growth rings were measured from 1950 to 1992 on increment cores taken from these same trees, as well as from trees at a nearby site that had not experienced any outbreaks. Regression models of growth at the outbreak site on growth at the nonoutbreak site were developed to isolate the influence of gypsy moth defoliation from other factors such as climate. These were then used to generate expected values for radial growth in the absence of gypsy moth at the outbreak site. During the first year of the first gypsy moth outbreak, there was a mean reduction in radial growth of 46% in red oak, a loss similar to what has been reported in other studies. Growth of white ash was much higher than predicted in 2 yr during and subsequent to the first outbreak. Yearly larval counts from 1979 to 1992 on red oak at the outbreak site were negatively correlated with oak radial growth after correcting for climate, suggesting that nonoutbreak levels of gypsy moth may reduce radial growth more than has previously been thought. Larval counts on ash were uncorrelated with ash growth after correcting for climate. North. J. Appl. For. 16(1):11-18.