Distribution of <i>Armillaria</i> species in upland Ozark Mountain forests with respect to site, overstory species composition and oak decline

Summary Armillaria root disease is a contributing factor to oak decline in the Ozark Mountains of central USA. We have identified Armillaria gallica , Armillaria mellea , and Armillaria tabescens in Quercus‐Carya‐Pinus forests of the region. Presence/absence patterns of each Armillaria species as well as all possible Armillaria species combinations were analysed by contingency tables and/or stepwise logistic multiple regressions with principal characteristics of the studied sites and forest stands, both quantitative and qualitative: geographic land‐type association, bedrock type, landform position, slope direction (aspect), soil type and soil surface stone cover, down woody debris, abundance and basal area of woody vegetation and decline mortality by species. Most decline mortality consisted of two red oak species (section Erythrobalanus , Quercus coccinea and Quercus velutina ), which also were most sensitive to Armillaria infection. Site characteristics related to the distributions of Armillaria species and decline mortality were also related to the preponderance of Q. coccinea and Q. velutina , regional vegetation history (i.e. conversion of Pinus echinata stands to hardwoods), and the different strategies of territory acquisition and spread of the Armillaria species involved. The presence of A. gallica may reduce the activity of more virulent Armillaria species.