What is CODIT and why is it important?

Compartmentalization of Decay in Trees = CODIT.

This concept was developed by a man named Alex Shigo in the 1960s. He also wrote that  “trees must be touched to be understood,” which adorns our website.

Shigo studied not just the outside of trees but mostly the insides of trees, specifically how they responded to injury. He purposely damaged trees by drill, screw, nail, etc. then went

back years later to see what the tree did in response. He cut the tree longitudinally (like you were milling a log). This type of cut exposes the layers of wood from inside to out, and shows the fibers of wood running up and down the tree. 

What Shigo found was that trees are really good at compartmentalizing themselves to stop the spread of infection. Similar to how a ship or a submarine will compartmentalize a leaky part of the boat, walls are formed in the fibers of the tree that box in the infection. These walls are made out of cells injected with phenols (a six carbon ring with a hydroxyl group). Phenols are antimicrobial and paradoxically poisonous to the tree. In a way, the tree is poisoning part of itself to save the rest. The walls go up to prevent the infection from spreading in all directions: up, down, inward and outward. Four walls in total. 

Shigo summarizes this and many other findings in a very accessible tome called “A New Tree Biology”. This book is fascinating and very applicable to the arboricultural industry. In fact, he is known as the father of modern arboriculture. 

So why does all this matter? 

Shigo discovered the best way to prune a tree, such that it experiences the least amount of damage in the process. He literally wrote the book on pruning. We all need to prune trees in our modern environment.

Our desire to bring trees into our concrete infrastructure means there is bound to be conflict. Safety, clearance from structures, clearance for height, aesthetics, and tree health are all reasons to prune. Thanks to Alex Shigo, we can do this in a way that doesn’t hurt the tree. 

Check out my tips on how to prune in my other posts, like when to prune a fruit tree, how to begin pruning, and what types of cuts to use depending on your goals.