Bark Inclusion Present but No Crack Yet: Reduce Now vs Monitor Condition Decision Tree

Why this matters

Included bark is the classic structural defect that arborists see every day and homeowners rarely understand. Two stems grew up together, bark got pinched in the union instead of strong xylem fusion, and now you have a V-shaped union that is genuinely weaker than a U-shaped one but has not failed yet. The question is whether to reduce one stem now, install a structural support, or document and monitor. This decision tree gives the framework to land that call defensibly.

Section 1: Identify what you are actually looking at

Not every tight union is included bark, and not every included bark union is high risk. Confirm before recommending.

Walk the union and look for:

• The shape of the union from multiple angles: a U-shape with a visible branch bark ridge is normal and strong; a V-shape with bark turned inward at the union is included
• A visible branch bark ridge (the raised line of bark where the stem and trunk meet): present and well-formed means normal union; absent or pushed inward means inclusion
• Bulging or swelling at the union: trees often respond to a weak union by laying down extra wood; this is reaction growth and is informative but not a guarantee of safety
• The diameter ratio of the two stems: stems of nearly equal diameter at the union are codominant; one stem much smaller than the other is a normal lateral and far less of a concern
• The angle of attachment: tight angles less than approximately 30 degrees are higher risk; wider angles are stronger

Section 2: Assess the load and exposure

A weak union on a sheltered ornamental in a courtyard is a different problem than the same union on an exposed shade tree over a driveway.

Consider:

• Wind exposure: prevailing wind direction relative to the union plane (a union perpendicular to prevailing wind takes more leverage)
• Crown size and asymmetry: a heavy crown on one of the included stems multiplies the load on the union
• Sail area: dense, fine-twigged species (some maples) catch more wind than coarse-twigged species
• Position in the canopy: a low union with most of the crown weight above it is loaded differently than a high union with light terminal weight
• Recent loading changes: removal of an adjacent tree, structure, or windbreak that previously sheltered the tree
• Target consequence: structures, vehicles, walkways, play areas in the failure path

Section 3: Look for active failure indicators

A union with included bark and no other indicators is a watch item. A union with included bark and any of these is closer to an act item.

Active indicators:

• Visible longitudinal crack at the apex of the union or extending down either stem
• Sap exudation, bleeding, or discoloration at the union
• Movement between the stems under wind load (watch the union during a gust; visible separation is a critical finding)
• Decay at the union confirmed by sounding, drilling, or sonic tomography
• Reaction growth that suggests the tree is responding to mechanical stress (bulging, but combined with any other indicator)
• Previous failure on the same tree (a tree that has shed a codominant stem before is more likely to do it again)

Section 4: The decision matrix

Combine union characteristics, load, and indicators to land the call.

Reduce now (subordination pruning of one stem):

• Included bark confirmed
• Codominant stems of similar diameter
• One stem can be reduced by 20 to 30 percent of its length without producing more than approximately 25 percent live tissue removal from the whole tree (ANSI A300 Part 1 prudent limit)
• Crown weight asymmetry favoring one stem (reduce the heavier or the more exposed stem)
• High-consequence target zone

Install structural support (cabling or bracing per ANSI A300 Part 3):

• Included bark with elevated risk but reduction would remove too much live tissue
• High-value mature tree where retention is the customer priority
• Customer accepts the ongoing inspection commitment that supports require
• Bracing rod added below the union if the inclusion is at or near the apex, with cable above to share load
• Cable rated and installed per ANSI A300 Part 3, with documented inspection cadence

Monitor with documented inspection cadence:

• Included bark present, no other indicators
• Low to moderate target consequence
• Customer informed and accepts the monitoring plan in writing
• Inspection at least annually, more frequently after major wind events

Remove:

• Included bark plus visible crack, decay, or movement under load
• High-consequence target with no acceptable reduction or support option
• Tree in overall decline with the union as one of multiple defects
• Customer cannot or will not restrict the target zone during a monitoring or support strategy

Section 5: How to do the reduction correctly

If reduction is the call, do it right or do not do it at all. A topping cut on a codominant stem is not subordination pruning; it accelerates failure by adding sprouting load above an already weak union.

Reduction principles:

• Reduce the stem by removing length back to a lateral branch at least one-third the diameter of the cut stem
• Make the cut just outside the branch collar of the retained lateral
• Spread reduction across multiple cuts over the length of the stem, not one large heading cut
• Do not exceed approximately 25 percent live tissue removal from the whole tree in one season
• Plan a follow-up reduction in 2 to 3 years if the goal is progressive subordination over time
• Document the cuts taken and the percentage of live tissue removed

Section 6: Structural support, when it is the right call

Cabling and bracing buy time on a tree the customer wants to keep. They do not make a defect safe; they reduce the probability of catastrophic failure while ongoing decay or further inclusion development is monitored.

If you install support:

• Follow ANSI A300 Part 3 for hardware selection, placement, and installation
• Use through-bolt brace rods for bracing at or below the union if the inclusion is at the apex
• Install dynamic or static cable above the union at approximately two-thirds the distance from the union to the top of the stems
• Document the install with photos, hardware type, and load rating
• Set the customer expectation: support is not permanent, inspection is required at least annually, hardware may need replacement, and a failure can still occur

References

• ANSI A300 (Part 1) - Pruning Standard, Tree Care Industry Association
• ANSI A300 (Part 3) - Supplemental Support Systems Standard, Tree Care Industry Association
• ISA Best Management Practices: Tree Support Systems, International Society of Arboriculture
• ANSI Z133 - Safety Requirements for Arboricultural Operations, Tree Care Industry Association