I can still recall a school field trip as a child when we were looking at lichen on a rock. Lichen can tell us how healthy the quality of air is since they get the food they need to survive directly from it. In the U.S., scientists in the Forest Service and Park Service use lichen to assess the quality of the air. When the air has too many pollutants, like sulphur, heavy metals, or nitrogen, it can be deadly to lichen.
Lichen are made up of three layers. The outer layer is fungus, the middle layer is algae, and the lower layer helps it stick to surfaces. When it comes to surfaces that lichen adhere to, it can attach to nearly any surface, including rocks, trees, soil, and even glass and metal. Lichens can grow in extreme conditions where most other life forms cannot. The algae layer produces food using photosynthesis, the outer layer protects it from too much sun, and filters water down for the algae layer to thrive. They are quite self-sufficient and can survive without water for a long time; this feature is important in extreme or barren habitats. They can reproduce sexually, asexually, or both, and some lichens can live up to 4,000 years.
Lichens play a role in the first step of weathering the rocks on which they live by creating tiny crevasses into which water’s freezing and thawing action can occur. The rock disintegration provides the raw material for soil building. In these cryptobiotic soils, lichens bind soil particles together. This crusty soil will trap blowing dust, preventing erosion and adding nutrients. The decay of dead lichens adds nitrogen to the soil.
Mammals such as caribou, mule deer, mountain goats, moose, and pronghorn forage on lichen, particularly in winter. Birds, including hummingbirds, use them in their nest building. Lichens have been used to make dyes and are used in perfume. Lichen growth patterns can also be used for dating stone structures.
During my hike a few weeks back, I was watching a two-year-old mountain goat grazing for a while before moving over the rocks. For just a few seconds, it stopped on rocks covered by lichens. I quickly got my camera, pointing it at the goat and making sure I zoomed out to include the lichens as well. Just a note: the goats do not feed on the lichens shown in the picture; they instead feed what is called white foam (or snow) lichen.
