Trees Don’t Heal?
Written by: Haylee Dunn, ISA Certified Arborist WI-1486A
While trees are living organisms, just like us, there are many differences between the ways we grow, deal with stress, and recover from damage. One of the biggest differences between trees and ourselves is trees never really heal.
When you get a cut, your body creates a scab to prevent anything from getting inside. The scab will fall off and eventually heals to form a scar. Years later, it can appear as if the wound never happened. Trees respond to wounds much differently. In fact, by definition, trees don’t truly heal at all. Instead, they seal. Trees can get wounds in many ways: pruning cuts, insects, birds, storms, or even lawn mowers. Each of these wounds causes some amount of decay. Trees work to contain that decay through compartmentalization. A famous researcher, Dr. Alex Shigo, was the first to discover this process, and he named this model Compartmentalization of Decay in Trees, or CODIT for short.
CODIT is a model that works in four steps. Each step creates a wall that forms a barrier to prevent decay from taking over the tree. The first three walls prevent decay from moving upward, inward, and around the wound. This is done though chemical changes in the surrounding wood cells. The final wall, Wall 4, can actually be seen. This is when the tree grows wood in response to the wound, and seals over the problem. It is usually smooth bark tissue, often doughnut shaped. Sometimes, the tree can seal over a wound so well it may hard to notice there was even a wound in the first place. It is important to know that this sealing over, is really just covering the wound. Underneath, there will always be the initial wound, even though the tree built around it, almost like a fence around a house.
Some trees are better than others at CODIT. Hardwood tree species like White Oaks are great compartmentalizers, whereas soft wood species like Silver Maples are not. Depending on the tree species, making many, large pruning cuts can negatively impact the health of the tree. Other trees are so good at CODIT, that they can handle rigorous pruning. It is important to know the difference between trees and how to prune them properly. Ask your Certified Arborist about CODIT and how you can have your trees pruned to maximize their structure and health!