The above high rainfall we’ve had this year seems to have caused a boost in lichens, as I’ve had several calls about them. Lichens are those flat green blotches or hair-like tufts you see growing on tree bark and rocks. Like all life on Earth, lichens have found a niche where they can grow without too much competition. Older trees in our area have a least a small colony growing somewhere.
There are several lichen species found in our area, the most common type being Parmelia. This is the one that looks like flat, crinkled splotches of green. Another common one found on trees is Old-mans’ Beard, which hangs down in small tufts of branching, pale green fibers. There may be small discs present that are fruiting bodies that produce spores. Lichen variety with more color, at least in the Spring, is British Soldiers, which grows on the ground or dead wood. It has a crusted base with small, erect hollow tubes that are capped with bright red knobs that are the fruiting bodies. Except for the red knobs, British Soldiers look moss-like. One other common lichen, found in the mountains on overhanging cliffs and large boulders is Rock Tripe. When moist, this one has large brown sheets that are leathery and attached by a stout cord. When dry it curls up and turns black. There are other lichen species that come in a variety of colors.
Lichens are a biological curiosity in that they are both plant (algae) and animal (fungus). The relationship is called “mutualism” and each partner benefits from being together. The algae produce food for itself and the fungus, and in return the fungus provides protection from adverse conditions such as drought. Some botanists disagree and think the relationship is more a host-parasite relationship in which the fungus is a weak parasite of its algal host. Either way, it makes lichen a unique life form.
Lichens have an important role of converting lifeless rock into soil that can then support other life. They can literally grow on a rock, and have acidic properties that slowly break down stone, converting it over the eons to soil sized particles. Humans have used lichens for food, medicine, and dyes. They are a very important food source for caribou in the extreme north, where conditions on the tundra are so harsh that only lichens can grow there.
I get asked now and then if lichen growing on the bark is harmful to the tree. Most tree experts say the lichen does not harm to the tree and is merely using the trunk as a high-rise apartment to get away from the more highly populated ground. I have wondered if a really high population of lichen that completely covers the bark might cause moisture retention that would soften the bark and perhaps cause mold, mildew, or bacteria issues. I haven’t found any scientific references to support this however, so my short answer is that unless you find them visually unappealing, just let them be.