Common greenshield lichen

Common greenshield lichen, about 25-years old growing on white pine tree bark. This species grows about 5 mm a year, so can be roughly aged. Lichens are perhaps the most obvious overlooked component of our landscape even though they are all around us — providing you live in areas with clean air.

Before we can like a lichen, we must answer the question, “What is a lichen anyway?” Here is a simple answer to what otherwise could quickly become a confusing, complex answer because lichens are complex organisms.

Lichens are compound organisms of algae and fungi living together in a close relationship known as symbiosis. Organisms that cooperate with others of their own kind, or different species, are often more successful than those that do not. This mutual relationship benefits them both. In other words, one cannot live successfully without the other.

Fungi provide protective cover and water for their algae partners. Fungi are incapable of photosynthesis to produce food because they lack food-producing chlorophyll. Thus, fungi must seek their nutrition from the algae that does have chlorophyll. Chlorophyll uses sunlight to synthesize foods, used by both algae and fungi, from carbon dioxide and water. A byproduct of photosynthesis is oxygen and, of course, we all know how important oxygen is for life to survive.

There are at least 13,500 species of lichens in the world, maybe even up to 17,000 or more, so they must somehow provide an important role in our environment. And they do, as described by lichen expert and author, Joe Walewski: “Many animals utilize lichens at some point in their lives. For example, ruby-throated hummingbirds use shield lichens in nest construction and camouflage. Northern parula warblers construct nests of draping beard lichens. Spruce grouse, white-tailed deer, moose, and flying squirrels all eat lichens. Mites, springtails, bark lice, silverfish, slugs, and snails dine on lichens too. Some insects and tree frogs capitalize on the camouflage provided by lichens.

“As pioneers in a young landscape, lichens degrade rock surfaces and prepare areas for mosses, grasses, and trees to follow. Some can even make significant contributions to soil fertility — especially regarding useable nitrogen. All of this may take hundreds of years, but lichens patiently make their contributions.

Many lichen species are sensitive to air pollution and other environmental changes, so their absence, presence, or health may be able to tell us what is happening to an ecosystem according to Gordon Grice as illustrated in the following example.

Several years ago, Mary Lou and I were on a forest pathology field trip in Norway when we first got introduced to the importance of lichens as bioindicators of air quality. It was pointed out on that field trip that lichens were missing from the forest we were visiting because of air pollution from an aluminum plant in the vicinity. If not for that pollution, the forest would ordinarily be full of lichens. We found out that lichens are sensitive to atmospheric pollution including nitrogen and sulfur dioxide emissions that produce acid rain and are also sensitive to toxic lead and mercury emissions. This is because lichens absorb water and minerals from rainwater and the atmosphere. Thus, lichens can be used as an inexpensive filtering system to monitor the spread of dirty air from factories, power plants, and urban areas.

Since that experience in Norway, we have become more aware of lichens wherever we go, knowing that air quality must be good if we do see lichens. And see them we do, all over the trees, rocks, and ground of our Northwoods. So, the next time you see them, take a good whiff of our clean northern air and be thankful for our lichens. We know you will get to like’um and appreciate them for what they do for us.

And PS! If you are depending upon using lichens for a compass to find your way out of a woods because they are said to grow only on the north side of trees, forget it — they grow on all sides. Also, lichens do not harm trees, they are not pathogens or parasites, and do not cause disease.

For more information on our fascinating lichens, look for the book “Lichens of the North Woods” by Joe Walewski published in 2007. It is a wonderful field guide to 111 northern lichens.

(Copyright © 2019 APG Media)

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