Lichens

Because they are capable of colonizing bare rocks and other mineral substrates, lichens are important in soil formation during some ecological successions. For example, lichens are among the first organisms to colonize sites as they are released from glacial ice. In such situations lichens can be important in the initial stages of nitrogen accumulation and soil development during post-glacial primary succession.

Lichens are an important forage for some species of animals. The best known example of this relationship involves the northern species of deer known as caribou or reindeer (Rangifer tarandus) and the so-called reindeer lichens (Cladina spp.) that are one of their most important foods, especially during winter.

Some species of lichens are very sensitive to air pollutants. Consequently, urban environments are often highly impoverished in lichen species. Some ecologists have developed schemes by which the intensity of air pollution can be reliably assayed or monitored using the biological responses of lichens in their communities. Monitoring of air quality using lichens can be based on the health and productivity of these organisms in places variously stressed by toxic pollution. Alternatively, the chemical composition of lichens may be assayed, because their tissues can effectively take up and retain sulfur and metals from the atmosphere.

Some lichens are useful as a source of natural dyes. Pigments of some of the more colorful lichens, especially the orange, red, and brown ones, can be extracted by boiling and used to dye wool and other fibers. Other chemicals extracted from lichens include litmus, which was a commonly used acid-base indicator prior to the invention of the pH meter.

Some of the reindeer lichens, especially Cladina alpestris, are shaped like miniature shrubs and trees. Consequently, these plants are sometimes collected, dried, and dyed, and are used in "landscaping" the layouts for miniature railroads and architectural models.

In addition, lichens add significantly to the aesthetics of the ecosystems in which they occur. The lovely orange and yellow colors of Caloplaca and Xanthoria lichens add much to the ambience of rocky seashores and tundras. And the intricate webs of filamentous Usnea lichens hanging in profusion from tree branches give a mysterious aspect to humid forests. These and other, less charismatic lichens are integral components of their natural ecosystems. These lichens are intrinsically important for this reason, as well as for the relatively minor benefits that they provide to humans.