Over the holidays, I was fortunate enough to spend two weeks visiting friends and family in the great state of Washington. If you know anything about the Pacific Northwest, your mind is sure to conjure up images of dense green forests-trees surrounded by ferns and covered in moss. As an arborist, this region of the country has always fascinated me with its unique landscape. On this latest visit, I began to wonder about the relationship between trees, moss, and lichen. While the trees on the east coast rarely if ever see the moss coverage that trees in Washington do, I figured there’s probably some interesting tidbits of information that can be garnered from this subject.
Firstly, let’s identify what exactly moss and lichen are. Mosses are a small, non-vascular plant that do not have traditional plant roots. They rely on dense clustering to create an anchor to surfaces such as tree bark and rocks. There are over 12,000 known species of moss in the world! Moss typically appears in areas with higher humidity, cooler temperatures, and more moisture. In the Pacific Northwest, this is pretty much the entire landscape. Here in Virginia, we tend to see mosses grow in specific areas or on particular sides of trees where these conditions become present. I’m often asked if moss is harmful to a tree. Moss is and of itself is not harmful to trees, but its presence can sometimes be a sign of other issues. Because it’s synonymous with moisture, moss can appear on trees that might be suffering from rot and decay. In extreme cases, moss can also add excessive weight to a tree, increasing the risk of tree or branch failure (although this would be extremely rare here in central Virginia).
Lichen is even more fascinating to me. A combination of a fungus and an algae, lichen is a truly unique organism. There are over 20,000 types in the world!! Like moss, lichen needs a surface to grow on- whether it be rocks, tombstones, sand, or trees. And just like moss, lichen does not inflict harm to trees. It thrives in moist areas, with more direct sunlight. We often see lichen growing on older trees or trees in decline. Why is this? A major reason is that younger trees are actively growing, or growing more rapidly. This leads to a less consistent surface for the lichen to latch onto. Another reason is that trees in decline may have thinner canopies, allowing for more sunlight through them- presenting more favorable growing conditions for lichen.
To conclude, I think it’s important to stress that moss and lichen are important to our ecosystem. They do not harm your trees, but can be a potential indicator or other underlying issues. If you’ve got moss or lichen growing on your trees, it’s never a bad idea to have them checked out by one of our certified arborists!
