Abundance and distribution of rhizomorphs of Armillaria spp. in defoliated mixed oak stands in western Maryland

The abundance and distribution of rhizomorphs of Armillaria spp. in the soil were quantified in undisturbed stands and in stands defoliated 1 and 5 years previously by insects. Although the species of Armillaria was not determined, similar mixed oak forests in south central Pennsylvania contain North American biological species VII (Armillaria bulbosa Baria.). Several analysis techniques were tested for sensitivity to differences in distribution of rhizomorphs. Rhizomorph distribution within the 0.04-ha study plots was uniform in the undisturbed stands, but was significantly greater near dead trees in the defoliated stands. Total rhizomorph abundance was greater on plots defoliated 5 years before sampling than on more recently defoliated plots, and it was least on undefoliated plots. Rhizomorph density near dead trees was highly correlated with overall rhizomorph density. Greater rhizomorph abundance near recently dead trees or stumps may have important implications for management decisions in the presence of gypsy moth (Lymantria dispar L.) infestations.