Wood is comprised of cellulose, hemicellulose, and lignin. Cellulose and hemicellulose make up the wood's cell walls, and lignin acts like a glue holding the cells together.  

Often, certain or many different types of wood decay fungi will dissolve all or just certain cellulose, hemicellulose, and lignin components in trees. , thus increasing the likelihood of branch or whole tree failure.  

While some species of trees can manage or compartmentalize wood decay well, others do not.

Often, these wood decay fungi will not be conspicuous, and other times, they will. In the spring or fall or any time of the year, they often produce evidence of their existence. 

All trees should be periodically inspected for deficiencies in health and structure. But if you find a tree with a fungus or fungus-like growth growing on the ground near it or protruding from it, this is direct evidence that the plant has some degree of decay along with some degree of strength loss. A Certified and Qualified arborist should investigate these conditions.