How do trees "heal" after they have been wounded?

Trees and woody plants don’t heal. A healed wound has had the tissue repaired or replaced, which would be evidenced by a scab or scar on skin. Trees are not capable of replacing or repairing damaged tissue, but instead, they attempt to “seal” off damaged tissue from the healthy, live tissue.

“Compartmentalization of Decay in Trees” (CODIT) is the process a tree or other woody plant employs to seal or “wall off” wounded tissue in an effort to reduce the risk of decay or disease from spreading to healthy tissue. A  good arborist will tell you, “Trees don’t heal. They seal.”  – Alex Shigo