With more than 3600 species in the United States and Canada, lichens are a major component of biological diversity. Lichens, though, are extremely vulnerable to habitat alteration, so it comes as no surprise that the habitats with the highest lichen species diversity are the remnants of ancient forests and other undisturbed ecosystems. Pseudocyphellaria rainierensis, for instance, grows in the old-growth coniferous forests of the Pacific Northwest. Lichens are like little sponges that take up everything that comes their way, including air pollution. In a baseline air-quality study, lichen specimens from the Tongass National Forest in Alaska were chemically analysed to see what toxics were in the air.
Most lichens are extremely vulnerable to air pollution.
When lichens disappear, they give early warning of harmful conditions. Scientists using lichens to monitor air quality often compare current lichen inventories with past records. Ecological costs of livestock grazing in western North America.