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

Armillaria root disease is a contributing factor to oak decline in the Ozar k Mountains of central USA. We have identified Armillaria gallica, Armillar ia mellea, and Armillaria tabescens in Quercus-Carya-Pinus forests of the r egion. Presence/absence patterns of each Aumillaria species as well as ail possible Aumillaria species combinations were analysed by contingency table s and/or stepwise logistic multiple regressions with principal characterist ics of the studied sites and forest stands, both quantitative and qualitati ve: geographic land-type association, bedrock type, landform position, slop e direction (aspect), soil type and soil surface stone cover, down woody de bris, 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 mos t sensitive to Armillaria infection. Site characteristics related to the di stributions of Aumillaria species and decline mortality were also related t o the preponderance of Q. coccinea and Q. velutina, regional vegetation his tory (i.e. conversion of Pinus echinata stands to hardwoods), and the diffe rent strategies of territory acquisition and spread of the Armillaria speci es involved. The presence of A. gallica may reduce the activity of more vir ulent Armillaria species.