Treat vs Remove vs Monitor: Included Bark on Codominant Stems Decision Matrix

Why this matters

A codominant union with included bark is the most common structural defect a tree service has to make a call on, and the call (mitigate with a structural prune or cabling, remove, or monitor) drives both the safety outcome and the customer's bill. Codominant stems are two or more nearly equal leaders competing for the central position; when bark gets pinched between them instead of true wood forming a strong branch-bark ridge, the union has no interlocking grain and is prone to splitting under wind, ice, or its own weight. The severity of that defect varies enormously, and so should the response. A young tree with a developing codominant can be trained out cheaply; a mature tree with a deep included-bark seam over a target is a different conversation. This matrix sorts the response by defect severity, target, and tree age so the recommendation is defensible under ISA tree-risk practice.

The options

Mitigation by structural pruning means reducing one of the codominant stems to subordinate it, shifting dominance to a single leader and reducing the end weight and lever arm on the weak union. On young and early-mature trees this is the highest-value intervention because it corrects the architecture while the tree is small. Mitigation by support system means installing a cable or brace per ANSI A300 Part 3 to reduce the chance the union splits, used when the stems are too large to subordinate without an unacceptable wound and the tree is worth retaining. Removal eliminates the hazard entirely and is the call when the defect is severe, the target rating is high, and mitigation cannot reduce the risk to an acceptable level. Monitoring means accepting the current state with a documented re-inspection interval, appropriate when likelihood of failure or the target is low.

When mitigation (prune or cable) wins

Structural pruning wins on young to early-mature trees where one stem can be reduced or removed to establish a single dominant leader before the union grows large; this is preventive arboriculture and the cheapest durable fix. Subordination pruning also wins on larger trees where end-weight reduction on the heavier stem meaningfully lowers the load on a moderate union without removing so much live crown that you stress the tree. Cabling or bracing wins when the union is structurally significant, the stems are too large to subordinate cleanly, the tree has high retention value (heritage, shade, screening), and a support system can credibly reduce failure likelihood; it is a long-term commitment because hardware must be inspected and maintained per ANSI A300 Part 3, and it reduces but never eliminates risk. Mitigation is the right band when the defect is moderate, the tree is otherwise healthy, and the target justifies keeping it.

When removal wins

Removal wins when the defect is severe and over a high-occupancy target: a deep included-bark seam with visible cracking, a bulge or rib indicating the union is already separating, prior partial failure, or decay tracking into the union from the included-bark pocket. It wins when the codominant stems are large, the lever arms are long, and no realistic prune or cable brings the risk to acceptable. It wins when the tree is in overall decline so that mitigation would be throwing good money after a tree that is failing anyway, and when the customer cannot or will not commit to the ongoing cabling inspection that retention would require. The defining inputs are defect severity, the consequence of failure (target), and whether mitigation can actually move the needle; when severity is high, target is high, and mitigation is marginal, removal is the defensible recommendation.

When monitoring wins

Monitoring wins when the likelihood of failure is low or the target is low enough that the consequence does not justify intervention. A codominant union with a sound branch-bark ridge and no included bark may need only periodic observation. An included-bark union on a tree in a low-occupancy setting (a back corner of a large property, no structures or paths within the failure zone) can often be monitored with a documented interval rather than treated, since the cost and the wounding of intervention are not warranted by the risk. Monitoring is also the interim call while a customer decides on a larger removal, provided the documented interval is honored. Monitoring is never the call for a severe defect over a high-occupancy target; that combination forces mitigation or removal.

Field decision flow

Score the defect first: how deep is the included bark, is there a crack, bulge, prior failure, or decay, and how large are the stems and their lever arms. Score the target second: what would the failure hit and how often is that space occupied. Score the tree third: age, vigor, and retention value. Then map: young tree, any target, train it out with a structural prune. Mature tree, moderate defect, retainable, target present: subordinate or cable. Mature tree, severe defect, high target, mitigation marginal: remove. Low target or low likelihood: monitor on a documented interval. Document the inputs and the recommendation per ISA Tree Risk Assessment BMP so the record shows the reasoning, not just the outcome.

References

• ANSI A300 (Part 3) Supplemental Support Systems, Tree Care Operations Standard, Tree Care Industry Association.
• ANSI A300 (Part 1) Pruning, Tree Care Operations Standard, Tree Care Industry Association.
• ANSI A300 (Part 9) Tree Risk Assessment, Tree Care Industry Association.
• ISA Best Management Practices: Tree Risk Assessment, International Society of Arboriculture.
• ISA Best Management Practices: Tree Support Systems (Cabling, Bracing, and Guying).
• USDA Forest Service, How to Recognize Hazardous Defects in Trees, NA-FR-01-96.