The Effects of Silvicultural Thinning and Lymantria dispar L. Defoliation on Wood Volume Growth of Quercus spp.

Pre- and post-defoliation radial growth rates were used to examine the effects of silvicultural thinning and two consecu-tive years of gypsy moth (Lymantria dispar L.) defoliation on Quercus spp. wood volume production. In the first phase of the study, tree rings from 65 dissected stems, were used to develop polynomial models to estimate annual cumulative volume (m3) increment for the entire merchantable stem, as a function of dbh (tree diameter at 1.37 m above the ground). In Phase II of the study, 81 additional trees were sampled using only increment cores. Cumulative diameter increments from the cores were used in the polynomial models to compare tree volume growth changes during and after defoliation among the thinning treatments. Even though there was no significant difference in estimated volume lost during defoliation among treatments, post-defoliation growth was enhanced by thinning. Total volume reduction from defoliation ranged from 28,049 (±17,462) cm3 to 25,993 (±16,251) cm3 per tree. The stand receiving the thinning treat-ment with the lowest residual stocking produced significantly more volume (P = 0.002) after defoliation than the other treatments