What is CODIT?

How the model works

A tree does not heal an injury the way a person does. It surrounds the injured wood with chemical and physical barriers and grows new wood outside them. The model describes four walls: one stops decay moving up and down, one stops it moving inward toward the center, one stops it moving sideways around the trunk, and one, the strongest, is the barrier zone formed by the cambium after the wound. The three inner walls are weak points, and the fourth is the line the tree builds.

The practical point is that a tree's response is limited. A big wound, or many wounds in one place, can overwhelm it. See woundwood.

Why it matters in Northern Nevada

Trees here make their walls on little water, and species differ. Species differ in how well they compartmentalize, and a stressed tree does it less well. That is one reason a tree that lost a limb to a snow storm and a flush cut can decay years later, and why old trees seem fine until a limb drops. It also explains why a hollow tree can stand: the wall around the decay may be sound. See cavity.

This is a general model and individual trees vary, which is why an assessment looks at the tree in front of you.

What an arborist does about it

CODIT is behind the standard advice: make small, correct cuts at the branch collar, avoid unneeded wounds, never use a flush cut, and avoid cutting more than a tree can seal. It is also behind the recommendation against filling cavities and against painting cuts. The arborist reads old wounds to see whether the tree is coping, and recommends monitoring, support or removal on that basis.