Why Weak Branch Unions Fail in Spring Storms

Spring storms can be rough on trees, especially those with hidden structural weaknesses. One of the most common trouble spots is a weak branch union—the point where a branch attaches to the trunk or where two stems grow together poorly. These areas often look fine from the ground, but when strong wind, rain, or heavy wet snow hits, they can split fast and fail hard. Extension and arboriculture sources consistently identify codominant stems, narrow V-shaped attachments, cracks, and included bark as major structural defects tied to storm breakage.

What makes a branch union weak?

A strong branch attachment forms when trunk wood and branch wood are well-connected, usually with a visible branch bark ridge and a proper branch collar. Weak unions often happen when two stems grow upright together at a tight angle and become codominant, meaning neither stem stays clearly subordinate. In these cases, bark can get trapped between the stems instead of wood knitting them together. Arboriculture references call this included bark, and it acts more like a wedge than a solid connection.

Why spring storms expose the problem

Storms usually do not “create” the weakness—they expose one that was already there. When spring weather brings gusty winds, saturated soil, and extra leaf and branch movement, pressure builds at those weak attachment points. If the union has included bark, a crack, or poor structural development, the stress concentrates right where the branch is already vulnerable. That is why trees with codominant stems and bark inclusions are much more likely to split during storms.

Included bark is a major red flag

Included bark prevents the two stems from forming a strong wood-to-wood bond. Instead of reinforcing each other, the stems press against trapped bark as they grow larger. Over time, that weak seam becomes more dangerous because the canopy gets heavier and the leverage increases in wind events. Purdue Extension notes that included bark unions are prone to splitting and decay, and Colorado State Extension notes that codominant trunks lacking a branch collar are structurally weak and more prone to storm damage.

Signs homeowners should watch for

Some warning signs are easier to spot than people think. Look for:

• A narrow V-shaped union instead of a wider U-shape
• Two large stems of nearly equal size growing from the same point
• Bark pinched tightly between stems
• Visible cracks or separations where the stems meet
• Past storm damage, decay, or heavy end weight on one side of the canopy

These are common indicators of a weak attachment and elevated failure risk.

Why failure matters

When a weak union fails, it usually does not break cleanly. It can tear downward into the trunk, leaving a large wound that is much harder for the tree to recover from. In some cases, one half of a codominant tree tears out completely, creating a serious hazard for homes, driveways, vehicles, fences, and people nearby. Because the wound is often large, the remaining tree may also be left more vulnerable to decay and future structural problems.

Can weak branch unions be prevented?

Yes—especially when trees are younger. Structural pruning is one of the best ways to reduce future storm problems. Proper early pruning helps encourage one dominant leader, reduces competing stems, and limits the development of weak unions before they become major hazards. Several extension sources recommend addressing codominant stems and included bark through careful pruning strategies while the tree is still manageable.

What to do if you see one

If a tree has a suspicious branch union, do not wait for the next storm to find out how strong it is. A qualified arborist can assess the union, determine whether pruning can reduce the load, and decide whether cabling, bracing, monitoring, or removal is the safer option. The sooner the issue is caught, the better the chance of reducing risk without major damage.

Final thoughts

Weak branch unions are one of the most overlooked reasons trees fail in spring storms. From the outside, a tree may still look healthy and full. But hidden structural defects like codominant stems, included bark, and tight branch angles can turn a normal storm into a costly tree failure. A professional inspection and proactive pruning can go a long way toward keeping trees safer, stronger, and more storm-resistant.