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Watch Out For Lichens


There are many visible signs that serve to indicate the health of a tree. While they can be hardy and survive extreme weather conditions, trees can also be remarkably sensitive to changes in temperature, soil pH, and air quality.

Watch Out For LichensAs the environment changes, the trees themselves show various signs of stress that serve as clues to their overall health. These signs may include shedding bark, losing leaves, or any number of other visible indicators. You should keep an eye out for any indicators of failing health in your tree. If you do notice any signs of poor health, you may need to summon a tree surgeon to look into the problem for you. In the Oregon area, a service such as Mr. Tree can help to diagnose and treat health problems in trees.

There are many things to keep an eye out for when you are inspecting your tree’s health. One sure way to observe the health of a tree is to watch out for the growth of lichens.

What Are Lichens?
Lichens are considered a composite organism; that is, they are formed from the symbiotic relationship of two different species. Lichens are created when an algae or cyanobacteria merges with a fungus.

They tend to grow in calm areas that are not usually disturbed; rocks, fence posts, and slow growing trees often make a home for lichens. They can be found in a variety of environments; lichens can grow almost anywhere in the world and have been found everywhere from here in Oregon all the way to the frozen Arctic. Despite this hardiness, they are also very sensitive to temperature changes, soil changes, and other environmental factors, which is what makes them a great indicator for the health of your tree.

Since lichens are made from fungus, they should not be confused with mosses, which may appear similar. Despite often growing in similar conditions, mosses are not fungi but in fact plants; as such they have roots, stems and leaves which fungi do not.

How To Recognize Lichens
There are several types of lichens that you or your tree surgeon may find growing on your tree.

Foliose, or leafy lichens are the ones that are most easily confused for moss, as their structure resembles leaves somewhat closely. As they mature, they form “cups” called apothecia in their structures; these lichens can come in a variety of colors but are often green.

Fruticose, or “shrubby” lichens often resemble small shrubs or hanging strands. They may be coral-like in appearance due to their small branches.

Crustose, or crusty lichens, appear less like plants and more like cracked crusts spreading across the area they have taken hold on. As they don’t have any leaflike structures or rootlike structures that can be easily plucked, it is difficult to remove them without damaging the surface they are attached to.

Leprose lichens are a type of crustose lichen and have a powdery surface and no discernible structure. All of these varieties, with the exception of fruticose lichens, grow very slowly. The circles they form on trees are measured to chart their growth; the fruticose lichens can be measured as they grow outward from their branches.

If left undisturbed, lichens can survive for a very long time. In fact, some of the crustose lichens discovered in the Arctic were found to be about 9,000 years old. Although lichens are often found on trees, they can grow on many different structures and derive their food supply from photosynthesis. They also absorb nutrition that they need from rain and fog. Because they use their environment as a food supply, they are excellent indicators of environmental health.

What Lichens Can Tell You
Lichens do not harm your tree. Unlike certain parasitic fungi, lichens are simply growths that do not leach nutrients or water from the substrate they grow on. Despite this, you should take care to observe the growth of lichens on your trees, as there is much they can tell you about the health of your environment.

Lichens, not being plants, lack many of the protective features that plants have – such as waxy cuticles – and therefore are far more sensitive to environmental changes. For example, one common air pollutant is nitrogen; many lichens are poisoned and killed off by excessive nitrogen in the atmosphere, but the candle-flame lichen (a green crustose lichen) thrives with it. If you note a distinct lack of shrubby lichens in favor of a vast growth of crusty lichens, this may be one indicator that the air around you is polluted with nitrogen.

Besides pollution, lichens can also demonstrate the acidity of the environment. Trees are sensitive to soil acidity; lichens even more so. Some species thrive in an acid environment while others cannot. If you think you notice unusual growth of lichens – or a lack thereof – contact a tree surgeon to advise you on what this may mean for your environment. Lichens can also indicate how much water is available in your environment. While there are many varieties of lichen, only some can tolerate drought conditions.

When you are observing lichens, take into account any other factors you may notice as well. Since lichens don’t normally appear on fast growing trees, consider the species of tree you have. If it’s a fast growing tree such as a pine, but is covered in powdery lichens, something may be wrong. If it seems to have a growth all over but doesn’t have any leaves, or has weak, brittle branches, call your tree surgeon to come and have a look.

What To Do Next
Lichens only serve as an indicator of the environment. Removing them will not solve any of your problems; you will have to contact a tree surgeon for that. Mr. Tree serves Portland and the surrounding Oregon area and can have specialists diagnose and treat issues with your tree. A skilled arborist can make recommendations as to what changes you may need to make and how to implement them in order to ensure optimal health for all of your trees.