Determination of the Ecological and Geographic Distributions of Armillaria Species in Missouri Ozark Forest Ecosystems

Armillaria root rot contributes to oak decline in the Ozarks. Three Armillaria species were detected in Ecological Landtypes (ELT's) representing south- to west-facing side slopes (ELT 17), north- to east-facing side slopes (ELT 18), and ridge tops (ELT 11). Armillaria mellea was detected in 91 percent of 180 study plots; was detected with equal frequency in all three ELT's; and was ubiquitous in block 3. Armillaria gallica was detected in 64 percent of the study plots; was detected least frequently in block 3; and was detected least frequently on ELT 17 in block 3. The distribution of A. tabescens remains incompletely resolved; it is the least abundant species and the most difficult to survey. Armillaria mellea was much more frequently associated with oak mortality than were A. gallica or A. tabescens, based on isolations from dying or recently killed trees. If these three species compete for substrate, oak decline levels may be influenced by landscape patterns of Armillaria species co-occurrence. We hypothesize that oak decline will be most severe in block 3, and especially on ELT 17, where A. mellea most often occurs in the absence of A. gallica.