Pruning Cuts and Compartmentalization of Decay in Trees (CODIT)

Notes from ISA study session

Proper pruning is essential to tree health, structural integrity, and longevity. Understanding the anatomical features of branch attachment and the biological mechanisms by which trees respond to injury allows practitioners to minimize damage and reduce the risk of decay. Central to this understanding is the concept of CODIT, or Compartmentalization of Decay in Trees, which describes how trees limit the spread of injury and decay rather than repairing damaged tissue.

Branch Attachment Anatomy

Branches are attached to the trunk at a specialized region known as the branch union, which includes the branch collar and branch bark ridge. The branch collar is a swollen area at the base of the branch where trunk tissue overlaps branch tissue. The branch bark ridge is the raised strip of bark that forms along the upper angle between the branch and the trunk.

Within the branch union lies a branch protection zone, composed of specialized cells and chemical compounds that inhibit the movement of decay organisms into the trunk. These tissues form a natural defense barrier and are critical to the tree’s ability to isolate wounds caused by pruning or branch failure.

Proper Pruning Cut Location

Correct pruning cuts are made just outside the branch collar, preserving the branch protection zone. Cuts made too far from the collar leave stubs that decay slowly, while cuts made into the collar remove defensive tissue and increase the likelihood of decay spreading into the trunk. Proper cut placement allows the tree to seal the wound efficiently and activate internal defense mechanisms.

AI interpretation of my notes: not accurate.

Pruning Cut Techniques

Large branches should be removed using techniques that prevent bark tearing and minimize injury to surrounding tissues. One such method is the snap cut technique. This involves making partial cuts on both sides of the branch, each less than half the branch’s diameter, and then allowing the branch to break cleanly. This controlled break reduces the risk of the branch tearing downward and stripping bark from the trunk.

Such techniques emphasize that pruning is not simply mechanical removal but a biologically informed practice.

Compartmentalization of Decay in Trees (CODIT)

Trees do not heal wounds in the manner of animals; instead, they compartmentalize damage. The CODIT model describes four “walls” that limit the spread of decay following injury.

• Wall 1 resists vertical movement of decay by plugging vascular tissues above and below the wound.

• Wall 2 resists inward spread toward the center of the trunk by strengthening growth ring boundaries.

• Wall 3 resists lateral spread by reinforcing ray cells that limit side-to-side movement.

• Wall 4, also known as the barrier zone, forms new tissue that isolates injured wood from healthy wood produced after the injury.

Walls 1, 2, and 3 constitute the reaction zone, which forms in existing tissue at the time of injury. Wall 4 forms later as new growth develops around the wound.

Tool Safety Considerations

Proper pruning practice also requires attention to tool safety. Chainsaw operation presents a significant hazard due to kickback, which occurs when the upper quadrant of the chainsaw bar contacts wood. Awareness of the kickback zone is essential to safe pruning and cutting operations, particularly during branch removal near the trunk.