McCune, Bruce. 2000. Lichen communities as indicators of forest health. The Bryologist. 103(2): 353-356.
Forest health: what is it? "Health" is an inherently fuzzy concept, even when applied to our-selves. And forests (and other ecosystems) are fuzzier than organisms, being weakly bounded and loosely organized. So the concept of "forest health" can seem hopelessly vague. Nevertheless,in extreme cases anyone can spot a "sick" forest. Despite forest health being a fuzzy concept, people want healthy forests and expect resource management agencies to monitor them.
The concept of ecosystem health is contentious not only because it is fuzzy, but also because item bodies societal values and preferences (Lackey1998). The more that people disagree on these values, the more contentious the concept of ecosystem health.
One way ecologists make progress on inherently fuzzy concepts is to make them practical with operational definitions (Peters 1992). For example, we could define a person's health by a combination of their internal temperature, blood pressure, and cholesterol levels. These are indicators of health, not acomprehensive examination. Nor do the indicators in themselves usually allow the diagnosis of a specific problem. Rather, these indicators tell us when we need to examine a problem more closely. These data are easy to obtain, yet tell us a lot.
Similarly we want to identify indicators of forest health. The indicators should point to ecosystems where a problem exists or is emerging. They should also tell us when and where forest health is improving. Lichen communities have the honor of being included as indicators of forest health by the U.S. Forest Service and other government agencies.