CODIT | Tree Biology

Terms: CODIT, compartmentalization, reaction zone, (ring) shake, barrier zone

CODIT stands for Compartmentalization Of Decay In Trees. It’s a model of decay/damage progression in trees by Alex Shigo, a US Forest Service pathologist, based on dissection of tens of thousands of trees. D can also stand for damage or dysfunction. “Compartmentalization” means that the tree responds by trying to form compartments around the issue to prevent its progression.

It features 4 walls:
Wall 1 is the plugging of xylem vessels (“top” and “bottom” of the compartment).
Wall 2 is last year’s annual ring.
Wall 3 is made up of rays - the side walls.
Wall 4 (aka barrier zone) is the only wall not already in existence; it’s the wood made in the following season and is much more robust from a defense standpoint. Because it does not allow rays across the new annual ring, the wood is less complex and may separate along the annual ring (called a “ring shake” or “shake”).

A parallel defense feature is the reaction zone, which forms ahead of the infection/attack/damage. Protective chemicals are produced in this zone.

CODIT USFS Bulletin No. 405: https://www.nrs.fs.usda.gov/pubs/misc...

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