Lightning from a thunderstorm strikes a 21 tree that falls to the forest floor and dies. During the next few years the dead tree undergoes many changes. What organisms are most likely responsible for the biological and chemical changes to the tree?

The questions have been asked in several important state and regional science exams in the United States. For example: TAKS-Texas Assessment of Knowledge and Skills, New York State Educational Department Regents exams, California Standards Test, etc.