Under certain conditions, lichen floristic and community analyses can be used in conjunction with measured levels of ambient or depositional pollutants accumulated by lichens to detect effects of changing air quality on vegetation. This information can demonstrate whether air pollutants cause undesirable changes in species composition or presence/absence of lichen species within terrestrial plant communities. It is important that any alternative hypotheses (., drought, grazing, habitat alteration) for changes observed in species condition or composition (in addition to air pollution) are discussed and evaluated when using lichen floristics and community studies in an air pollution context. Lichens exhibit.
