Effects of defoliation and cutting in eastern oak forests on Armillaria spp. and a competitor, Megacollybia platyphylla

Gypsy moth (Lymantria dispar L.) and Armillaria root rot interact to cause extensive mortality in eastern oak forests. Defoliation by gypsy moth weakens trees and increases their susceptibility to Armillaria root rot. Partial cutting prior to defoliation has been proposed as a management technique because it may increase tree vigor and the ability to withstand defoliation stress. However, cutting could also increase inoculum potential of Armillaria by providing a resource, the residual stumps. Megacollybia platyphylla (Pers.:Fr.) Kotl. & Pouz. is a native, cord-forming, saprobic fungus that may compete with Armillaria for resources such as stumps, snags and debris. A factorial treatment design with three levels of cutting and three levels of defoliation was used to examine the effects of cutting and defoliation on the two fungi. Among uncut stands, defoliated stands had significantly greater colonization of resource units by Armillaria than nondefoliated stands. However, stands that were cut prior to defoliation had significantly less Armillaria colonization and significantly more M. platyphylla colonization than those that were not cut. Armillaria colonized snags better than stumps and colonized least well in debris, where M. platyphylla showed its best colonizing performance. The data suggest that cutting mitigates the effects of defoliation on colonization by Armillaria and are consistent with the hypothesis that M. platyphylla plays a role in such mitigation.