I have heard that question a lot this year.
The answer is lichen, a fungal/algal growth that can be found growing on trees, rocks, sidewalks, roof shingles, and many other places that are relatively undisturbed.
Lichen does not root itself well, and can easily be displaced, which is probably why we don’t see it growing in more places. It likes an undisturbed environment, and does not tolerate pollution very well, which might explain why it grows ubandantly in a forest.
So why does it grow on my tree or roof? Well, it’s just a good place to grow.
Lichen does not cause any harm to your tree. It does not feed off the tree, not does it inject a toxin- it is purely a good anchorage point. I tend to see it more in shady areas- tree trunks, and rooftops that are under cover of tree limbs, as well as landscape rocks. Lichen is part fungus and part algae- while many lichens are a symbiotic relationship, some are saprophitic or parasitic.
I have also seen moss growing on trees as well. Like lichens, moss does not feed on the tree; however, there is the potential for large accumulations of moss to trap moisture against a tree, promoting decay or rot diseases. Moss is usually found in shady, damp areas of a property. Lately, moss has gained a lot of attention as a groundcover in the landscape- once it is established, it needs little to no maintenance, and lasts a long time.
If you are not sure of something that you find in your garden or see something weird growing on your trees, give us a ring!