Do Lichens Cause Harm to Trees?

Lichens are often thought to be a pest or disease to trees and shrubs.
Do Lichens Cause Harm to Trees? - Videos


Forest Resources Wood Products Kiln Drying Lumber

More by Scott Weikert 

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- [Scott] Lichens are interesting organisms.

They can be found living on just any inanimate object.

Oftentimes when people see them on trees they immediately begin to think the tree has some sort of disease.

Or if the tree appears to be unhealthy in some way they assume the lichens are causing the problem with the tree.

Let's take a look at what lichens are and whether they adversely affect the health of trees.

Lichens are complex organisms created through a symbiotic relationship between two separate organisms.

Each organism relies on the other for survival.

One of the organisms that make up this partnership is a fungus, while the other is either a green algae or a blue-green algae called cyanobacteria.

Unlike plants, fungi do not produce their own food, thus relying on some other source from which to get the nutrients it needs.

A common example of this would be a fungus that is decomposing dead wood, such as the fungus shown here.

Algae, unlike fungi, are capable of producing their own carbohydrates for food through photosynthesis.

They can survive in fresh water or salt water individually, but when they're part of a symbiotic relationship with a fungus, they can survive in almost any environment.

Lichens do not have roots, stems, leaves, or any sort of vascular system to move nutrients and water.

Lichens rely on rain and the air in their environment to get the water and nutrients it needs to survive.

In order to survive, lichens need water, light, air, nutrients, and a substrate on which it can grow.

They get water from rain, fog, and can even absorb water vapor from the air.

Lichens are not capable of conserving water during dry periods so they become dormant during periods of dry weather.

When they get wet again, either from rain or heavy fog, they start to grow again.

The fungus is primarily responsible for absorbing water so that the algae can survive.

Like plants, light is needed so the algae can photosynthesize to create food it needs to survive.

The algae produces carbohydrates through photosynthesis and the fungi uses those carbohydrates to grow.

Lichens need clean, fresh air to survive.

They absorb the air from their environment, which includes the nutrients it needs to survive, as well as any harmful toxins that may be in the air.

Lichens absorb nitrogen, oxygen, and carbon from the air.

And finally, lichens need to have a substrate on which to live.

This could be a tree, rock, soil, old cars, or just about any inanimate object.

When taken into consideration how lichens get their nutrients and water that is needed to survive, they pose no danger to the trees on which it grows.

They only use the bark on the tree as a place to live and grow.

They do not penetrate into the inner bark of trees, and they take no nutrients or water from the tree.

Oftentimes the lichens are simply not noticed until the tree appears unhealthy.

If you see a tree that appears to be in poor health or dying, don't blame the lichens.

The only thing they are killing is time.


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