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. Hypogymnia physodes was the most prevalent species at all sites. 23 lichen species in 1988, but only 16 species in 1998.