Continuing lichen recolonization in the upper Ohio River valley

lmprovement in the air quality of the upper Ohio River valley has led to lichen recolonization at previously depauperate sites. Between 1973 and 1996 the number of corticolous macrolichen species in the area increased from 6 to 20. During the same time the mean species richness per sire increased from 0.8 to 6.5. An indicator species, Flavoparmelia caperata, was absent from all study sites in 1973, brit present at 27 of 28 study sites in 1996. Lichen studies performed over time provide a good tool to document air quality improvement, but a single study in a changing air quality environment may give problematic results.