The Effects of Silvicultural Thinning and &amp;lt;i&amp;gt;Lymantria Dispar&amp;lt;/i&amp;gt; L. Defoliation on Wood Volume Growth of &amp;lt;i&amp;gt;Quercus&amp;lt;/i&amp;gt; spp.

Mary Ann Fajvan,Kurt W Gottschalk

doi:10.4236/ajps.2012.32033

Abstract

Pre- and post-defoliation radial growth rates were used to examine the effects of silvicultural thinning and two consecutive 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 treatment with the lowest residual stocking produced significantly more volume (P = 0.002) after defoliation than the other treatments.

Highlights

The gypsy moth (Lymantria dispar L.) annually defoliates millions of forested acres throughout much of the oak (Quercus spp.) range in the eastern United States
Pre- and post-defoliation radial growth rates were used to examine the effects of silvicultural thinning and two consecutive years of gypsy moth (Lymantria dispar L.) defoliation on Quercus spp. wood volume production
Even though growth was significantly reduced for both species, red oak volume increments were higher than white oak during the defoliation years (P < 0.0001)

Summary

Introduction

The gypsy moth (Lymantria dispar L.) annually defoliates millions of forested acres throughout much of the oak (Quercus spp.) range in the eastern United States. Defoliation is caused by feeding of gypsy moth larvae for about 8 weeks during the spring and early summer, and many environmental factors contribute to annual fluctuations in insect densities [1]. Stands with a high proportion of oaks are susceptible to heavy defoliation, localized higher mortality, growth decline, and reductions in wood quality and yield [1,2,3]. Factors that influence the amount of growth decline or mortality include: the interaction of canopy position and tree vigor before defoliation; the intensity, duration and frequency of defoliation; climatic variables (e.g. drought); and the presence of secondaryaction organisms (e.g. Armillaria spp., Agrilus bilineatus (Weber)) [2,4,5,6,7,8,9,10,11]

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Conclusion