Impact of liming on the abundance and vigor of Armillaria rhizomorphs in Allegheny hardwoods stands

Abstract

Abundance of rhizomorphs of Armillaria was characterized in 1995-1996 in 32 plots located in sugar maple (Acer saccharum Marsh.) stands in the Susquehannock State Forest (Pennsylvania, U.S.A.). All of the plots were thinned, and half of the plots were limed in 1985 when the plots were established. Frequency and abundance of Armillaria rhizomorphs in soil samples, on dead wood food bases (stumps, snags, fallen logs), and on the root collar of living sugar maples were determined in each plot. Rhizomorph vigor was evaluated by measuring their ability to colonize fresh striped maple (Acer pennsylvanicum L.) stem sections in the soil, or potato tubers in the laboratory. Isolates of Armillaria were obtained from rhizomorphs in the soil samples and species were determined by somatic incompatibility tests. Armillaria calvescens Bérubé & Dessureault was the major species present, representing about 66% of the isolates. Armillaria gemina Bérubé & Dessureault and Armillaria mellea (Vahl:Fr.) Kummer were also identified in the plots. Frequency of rhizomorphs in the soil, on food bases, abundance of rhizomorphs on root collars, as well as the proportion of rhizomorphs per plot that regenerated and (or) colonized fresh substrates were all correlated. However, abundance of ectotrophic rhizomorphs on the root collar was only weakly correlated with the other components of rhizomorph abundance and vigor. Frequency of the rhizomorphs as well as their ability to colonize fresh substrates were greater in plots either limed or with a high proportion of the basal area in sugar maple prior to thinning. By contrast, abundance of ectotrophic rhizomorphs on root collars was not affected by these factors.