Without a photo example of what you're seeing, it's hard to tell, but we suspect you're looking at lichen (moss is different and usually green), both of which are harmless to trees. Lichen might grow more abundantly on some trees if they are in decline, not because the lichen caused any damage, but because the dying tree has fewer leaves blocking light and rain from the lichen. Nothing needs to be done about removing lichen, and attempting to do so might actually harm the tree if it damages the bark.


Tree decline has many causes, and sometimes it begins without obvious symptoms years before any branch dieback or leaf loss is noticeable. Chronic stress from weather (years of excessive rain, like 2018, or drought, like 2024) can cause root dieback that can weaken a tree, and acute injury from a range of factors (mowers hitting the trunk base and damaging bark, herbicide exposure from a nearby lawn, lightning strikes, storm damage that isn't pruned off, etc.) can all predispose trees to attack by secondary pest insects or fungal infections. They take advantage of weakened trees, but often are not the primary cause of decline. Heat reflected from pavement, limited root space, air pollution, and other environmental conditions also contribute to long-term tree stress. Some that are planted too deeply develop girdling roots, which can eventually "strangle" part of the trunk and cause significant canopy dieback.

If there are trees on your property that you'd like to have evaluated, we recommend having them assessed by a certified arborist or licensed tree expert. While they cannot treat or cure every condition, they can help to make a diagnosis and determine if the tree needs to be taken down for safety in cases of advanced decline or wood decay.

Miri