Lichens are useful bioindicators of environmental quality. Lichen mapping, one of the oldest biomonitoring techniques, examines the distribution and abundance of lichens. Lichen mapping provides a direct measure of lichen health and an indirect measure of air quality within ecosystems. In environments with poor air quality, pollution intolerant species become depauperate, extinct, or replaced with pollution tolerant species. Lichen diversity, abundance, and external health (based on "normal" thallus morphology, color, and lichen prevalence) have been monitored in permanent study quadrats on the boles of red spruce, Picea rubens, at one inland (University of Maine Experimental Forest) and three coastal sites (Small Point, Isle au Haut, Roque Island) in Maine every two years since 1988. Baseline (1988) measurements demonstrated intra- and intersite differences in presence, abundance, and external health and suggested that lichens were less healthy at Small Point and the inland site and more healthy at Isle au Haut and Roque Island. Hypogymnia physodes was the most prevalent species at all sites. Overall, 27 macrolichen species have been found in study quadrats. Red spruce at Roque Island has had the greatest diversity: 23 lichen species in 1988, but only 16 species in 1998. Over the 10-year biomonitoring period, local extirpations of pollution intolerant species outnumbered new recruits except at the inland site. By 1998, Small Point, the site closest to the northeast urban-industrial corridor, had the greatest relative negative change in lichen diversity, abundance, and external health. In contrast, only the inland site showed relative positive change. The trends manifested after the initial baseline measurements demonstrate the value of long-term biomonitoring for better understanding the distribution and abundance patterns of lichens.

Key words: Hypogymnia physodes , Picea rubens , biomonitoring, diversity, lichens, pollution