What is a lichen?
It is an obligate mutualistic association between a fungus and a photosynthetic partner (either green algae, cyanobacteria, or both).
Functional Roles -- Click here to see some functional groups of lichens along with the roles they play in forest ecosystems.
What is not a lichen? Moss, Spanish moss, dodder, mistletoe, for example (see photos).
Do they harm the trees? There is no evidence that lichens and bryophytes as epiphytes substantially harm their supporting trees and shrubs. These epiphytes derive no nutrients or water directly from the host plant. Some shading of trees with photosynthetic bark (e.g. aspen) may occur (Solhaug et al. 1995). Some horticulturalists believe that heavy epiphyte loads may increase the likelihood of wind damage. Apart from these exceptional cases lichens and bryophytes are unlikely to have negative effects on their trees.
Concern about lichens and bryophytes harming trees is a common inquiry to extension agents in the Pacific Northwest. Click here to read a sample Q/A from Oregon.
Indicator Value. Lichens are great indicators of air quality. They are being used for this by the U.S. Forest Service in the National Lichens and Air Quality Database and Clearinghouse and the Forest Health Monitoring (FHM) Program (now part of Forest Inventory and Analysis, FIA).
Aesthetic value. Epiphytes are inherently beautiful and interesting in their own right. They add diversity, interest, color, and intricacy to a forest.
Contribution to Biodiversity. Epiphytes are a major component of the diversity in forests of the Pacific Northwest (e.g., Lesica et al. 1991, McCune et al. 2000, Rhoades 1995, Nadkarni et al. 2001). The number of species of epiphytic bryophytes and macrolichens is typically 40-75 species in a 1-acre (0.4 hectare) plot. This often exceeds the number of flowering plant species in the same forest. An additional 20-50 species of crustose lichens are usually present as well.
Economic Uses. Epiphytic lichens have many economic uses; for example, as antibiotics, decorations, dyes, natural remedies, and stabilizers for perfumes. For more information see www.lichen.com and Purvis (2000).