You may have noticed a gray, green, or even yellow mossy looking substance growing on your trees. Lichen is not moss, however, and it’s not even a plant.
So what is lichen, what is it doing on your tree, and is it harming the tree that it’s growing on?
What Is Lichen?
Lichen is unusual in that it is a symbiotic relationship between a fungus and an alga or a cyanobacterium, plus usually one other organism thrown in for good measure.
Because lichen is self-sustaining, it does not need to take any nutrients from the tree that it is on, and therefore is not harming the tree.
Lichen is also found on rocks, the ground, even tombstones and statues. It just needs a place to grow. Lichen is not a plant, so it does not have roots. It’s not burrowing into your tree, but rather staying on the surface of the bark. It gets all of the nutrients it needs from rain and the surrounding air.
Lichen is usually the first type of organism to appear after a natural disaster, such as a fire. It can survive when plants can’t and can grow on rough surfaces like rocks or old fences.
Why Is Lichen On Your Tree?
Well, there’s good news and bad news. The good news is that the lichen is not harming your tree. The bad news is that if your tree is suddenly sporting a spot of lichen, your tree is probably already in decline. Lichen is rarely found on healthy, vigorous trees.
Lichen loves sunlight and moisture, so it is often found in sunny, wet spots. If your tree has had a sudden loss of leaves or a branch, that means more light can reach the surface where the lichen is.
To reiterate: the lichen is in no way harming your tree, but the presence of lichen may point to an unhealthy or dying tree (caused by other reasons, such as pests or disease). Look at it as an indicator that it’s time to have a Certified Arborist examine your tree to see what’s wrong and what can be done about it.
Benefits of Lichen
Surprisingly, lichen can actually be of benefit. It’s a natural air quality indicator, as it absorbs everything in the environment around it, but only thrives when the air quality is clean. In fact, scientists use lichen as a measure of air quality in different areas. Lichen also converts carbon dioxide to oxygen and absorbs any pollutants that are in the area.
Lichen has been used for dyes (there are some very colorful types of lichen!), for clothing, decoration, and even for antibiotic uses – you might find it as an ingredient in your deodorant or toothpaste, for example!
Animals are fond of lichen as well – deer use it as a food source, it provides a protective cover for some beneficial insects, and birds like hummingbirds use it in their nests. Other critters, like frogs, enjoy it as a snack.
Don’t Confuse Lichen With Moss
Lichen is often confused with moss, partially because some lichens look very similar to some mosses and partially because it’s often found growing near moss. The two coexist well together although moss enjoys shady spots, while lichen loves the sun.
Adding to the confusion, “reindeer moss” or “caribou moss” is actually a lichen, and is a popular food source for caribou.
Should You Remove Lichen From Your Trees?
Lichen should not be removed from trees as removing it does more harm than good. The lichen is not hurting the tree, so there’s no reason to remove it. In fact, you’re likely to injure the bark by trying to remove the lichen, ultimately causing damage to the tree and providing entryways for diseases and pests.
If however, you really don’t like the look of lichen, the best method is prevention. Ensure that your trees remain healthy, properly pruned, and appropriately watered.
Common Colorado Lichens
Over 6% of the earth’s surface is estimated to be covered by lichens. There are over 20,000 different kinds, and they come in a variety of colors and shapes. They are found on every continent, from humid forests to frozen areas and desert sands.
Here in Colorado, there are hundreds of lichen species that exist in practically every environment imaginable, including some with interesting common names, such as pale-footed horsehair lichen, lustrous camouflage lichen, salty rock tripe, and veinless pelt (although those don’t generally grow on trees).
In the Denver foothills area, you might have noticed the lichen called old man’s beard, which looks like strings or tassels on a branch.