In California, I saw a sign on a tree that was covered with lichens and surrounded by dead trees. It seemed a plea for help. But according to the Hastings Biological Field Station of the University of California, lichens can capture airborne nutrients and return them to the soil. That is considered good. Another website paints a more complex picture, suggesting lichens may sometimes be associated with the death of trees in California. Read it here.
Suzanne's Mom's Blog 