Weak Branch Unions (Included Bark): Atlanta Guide

What Are Weak Branch Unions?

A branch union is the point where a branch connects to the trunk or where two stems originate from the same point. In a strong union, the wood of the branch and trunk grows together in an interlocking pattern, creating a connection that can withstand significant mechanical stress. In a weak union—often called "included bark"—bark becomes trapped between the two stems, preventing the wood from fusing properly. Instead of interlocking wood fibers, the junction is held together only by surface contact, much like pressing two pieces of bark together.

Included bark unions are one of the most common structural defects in urban trees and one of the leading causes of catastrophic branch and stem failure. The defect is essentially a hidden failure point that may go unnoticed until a storm, heavy snow, or simply the increasing weight of the growing canopy causes the union to split apart.

How to Identify Weak Branch Unions

• V-shaped crotches: Co-dominant stems that emerge at acute angles (forming a tight "V" rather than a wide "U") are the primary indicator. The narrower the angle, the more likely bark is included.
• Bark ridge pushed inward: At a strong union, the bark ridge between stems is pushed outward, creating a raised line. At a weak union, the bark is pushed inward, creating a crease or seam between the stems—bark is being trapped rather than expelled.
• Visible crack or seam: A line of separation between the two stems, sometimes with darkened or wet tissue, indicates the union is already beginning to fail.
• Unequal stem sizes: When co-dominant stems are nearly equal in diameter, neither can suppress the other's growth, and the included bark defect tends to worsen over time.

Which Atlanta Trees Are Most Susceptible?

• Water Oak: Frequently develops multiple co-dominant stems with included bark, creating a high failure risk that increases with the tree's size. Many Atlanta water oaks have this defect.
• Red Maple: Red maples are genetically predisposed to co-dominant stem development. Without corrective pruning when young, they commonly develop weak included-bark unions.
• Sweetgum: Similar to red maple, sweetgums frequently produce co-dominant stems that are prone to included bark formation.

Many other species develop included bark, including Bradford pear (notorious for it), silver maple, elm, and willow oak. Any tree with co-dominant stems may have this defect.

Treatment Options

• Structural pruning (young trees): The most effective treatment is early intervention. When trees are young, an arborist can subordinate one of the competing stems by reducing its length, allowing the other stem to become the dominant leader. This is best done when the tree is still small enough to prune easily.
• Cabling and bracing: For mature trees with included bark that provide significant landscape value, supplemental support systems (high-strength steel cables or synthetic cables installed in the upper canopy) can reduce the risk of splitting by redistributing mechanical stress. Cables do not fix the defect—they manage the risk.
• Weight reduction: Pruning to reduce the end-weight on co-dominant stems decreases the leverage forces that cause splits. This "crown reduction" or "weight reduction" pruning is a common arborist approach for managing included bark risk.
• Risk assessment and monitoring: Regular professional risk assessments monitor whether the defect is progressing (cracks widening, wood deterioration at the union) and whether the current risk level is acceptable given the tree's location and the consequences of failure.
• Removal: When the risk of failure is high and the target area below is frequently occupied (over a home, driveway, play area), removal may be the safest and most responsible option.

Prevention Strategies

• Structural pruning at planting: Establish a single dominant leader at planting time. Remove or subordinate competing stems while the tree is young and the work is simple.
• Regular formative pruning: During the first 10 to 15 years of a tree's life, periodic pruning to maintain good structure prevents included bark from developing. This small investment early yields enormous returns in reduced risk later.
• Species selection: When planting, choose species or cultivars known for good branch architecture over those prone to co-dominant stems.
• Nursery stock evaluation: When purchasing trees, select specimens with a clear central leader and well-spaced lateral branches rather than those with multiple competing stems.

When to Call an Arborist

Call an ISA-certified arborist if you notice V-shaped stem unions, visible bark creases between major stems, or any cracking at branch attachment points on your trees. Risk assessment is especially important for large trees overhanging structures, parking areas, or high-traffic zones. Our TRAQ-qualified arborists evaluate included bark severity and recommend appropriate management—from cabling to removal—based on the specific risk profile.

Atlanta-Specific Considerations

Atlanta's frequent severe thunderstorms put extreme stress on weak branch unions. Wind loads during storms are the most common trigger for included-bark failures, and Atlanta's storm season coincides with full canopy conditions (maximum wind resistance). Trees that have survived for decades with this defect can fail suddenly during a single strong storm.

Many of Atlanta's most common residential tree species—water oaks, red maples, and sweetgums—are predisposed to co-dominant stem development, making included bark one of the most prevalent structural defects in the metro area's urban forest. Proactive structural pruning of young trees is one of the highest-return investments Atlanta homeowners can make in their landscape.

EastLake Tree Services offers structural assessment, corrective pruning, cabling installation, and risk management for Atlanta trees with included bark defects. Call 404-850-1174 or request a consultation.