Recently we had a question come to our mailbox about white spots on their trees’ bark.
MLF Tree Expert Carl Mansfield replied:
Your tree appears to have lichens growing on the outer bark.
Lichens are colourful crusts found growing on trees, rocks and other objects. They are often thought to be a pest or disease of trees and shrubs, but not so.
Lichens are non-parasitic plant-like organisms that pose no harm to the trees on which they grow. They use the outer bark of trees as a place to live and grow. They do not penetrate into the inner bark of trees and take no nourishment or water from the trees.
A lichen consists of two different organisms engaged in a symbiotic relationship. One is a fungus, whose job it is to anchor the lichen to an object where it will grow. The other is a bluish-green algae that turns sunlight into food for the lichen. There are many kinds of lichens. They are spread by spores and tiny bits of lichen, blown on the wind.
Lichens aren’t often noticed until a tree appears to be unhealthy or dying; don’t blame the lichens. The only thing they’re killing is time.
- Carl Mansfield, MLF’s Tree Expert