Trees With Multiple Trunks: The Danger Codominant Stems Pose to Your Connecticut Property and How to Prevent Them

A tree with multiple trunks – also known as codominant stems – might look natural, but it usually means trouble down the road. These trees are more likely to split, especially in high winds or heavy snow, and often need careful pruning or structural support to stay safe and healthy. If you have a Y-shaped tree on your Connecticut property, especially in storm-prone areas like New Haven County, it’s worth having a professional take a look.

Key Takeaways:

• Codominant stems (multiple trunks growing from the same point) create structural weaknesses in trees that make them prone to splitting and failing during storms, particularly in Connecticut's weather conditions.
• Trees with V-shaped branch unions and included bark are at higher risk of failure, with maples, oaks, and damaged conifers being particularly susceptible to developing these structural issues.
• Early intervention through professional structural pruning when trees are young is the most effective prevention method, as it becomes increasingly difficult and expensive to address codominant stems as trees mature.
• For mature trees with codominant stems, options include reduction pruning to decrease weight and stress on weak points, or in more severe cases, professional removal may be necessary to prevent property damage.
• Connecticut property owners may be legally liable if a tree with known structural issues falls and damages neighboring property, making regular professional assessment by a CT Licensed Arborist essential for trees with codominant stems.

What is a Codominant Stem?

The term “codominant stems” refers to a tree that has grown two (or more) main stems. These tree trunks will:

• be about the same diameter,
• originate from the same point on the tree,
• grow upward at a very narrow V-shaped angle, and
• compete with each other to be the tree's primary stem (or “leader”).

Trees can also have branches that grow almost straight up from the main tree trunk. For example, Bradford pears are notorious throughout Connecticut for their narrow, V-shaped branch unions.

Codominant stems and narrow branch unions have many of the same problems, and both can present some significant issues if not dealt with quickly.

What to Look For

Look for a V-shaped angle where two or more stems of similar size come together. If you look up from there, you’ll see that the stems grow beside each other and are roughly the same height.

You may also see “included bark”. To identify included bark, look for a line or seam in the bark where the stems come together. This indicates that as the two stems have grown and pushed against each other, their bark has become trapped between the two stems. You may also see a crack in this area or bulges in the trunk. Both of these indicate that failure is more likely.

How Codominant Stems Are Formed

A tree with two trunks occurs when two apical buds at the top of a stem both grow at the same time. Instead of one becoming subordinate to the other, they both chemically act as the central leader of the tree. As a result, two stems form and become codominant.

Problems with Codominant Stems

The biggest problem with codominant stems is that they’re prone to failure. Often, trees will split apart where the two stems join, or where there are narrow branch unions, multiple stems, or many branches growing from the same spot. This is more common after tree topping, a discredited practice that a reputable company will never perform.

When two branches or stems are roughly equal in diameter, they tend to be weakly attached to each other and the main tree trunk. Included bark can also grow into the space between the branches, further weakening their attachment. The narrower the angle between the two stems, the greater the risk of failure.

Overall, the growth of a two-stemmed tree will make the entire tree much more vulnerable to high winds and stress from later growth.

WARNING: Connecticut tree laws say that if a property owner knew their tree was at greater risk of failure and it falls onto a neighboring property, the owner of the tree could be at fault. If you notice a problem with your tree, ensure you take action to either remove it or try to make it safer.

Tree Species Prone to Growing Codominant Stems

Many types of trees can develop two or more main stems, but certain tree species are more prone to growing two trunks. In Connecticut, these species are:

• Maples
• Oaks
• Conifers (especially those that sustained damage from topping or lightning strikes)

Researchers think that these species are more apt than other trees to release chemicals that cue the development of the central leader versus branches, although they’re not sure why that happens.

Catching the signs of a young tree developing multiple trunks early allows you to prune them and prevent the problem from getting worse down the road.

How to Prevent Trees from Developing Codominant Stems

Prevention is the best way to help a tree when it comes to dealing with codominant stems. These stems usually develop when a tree is young; at that point, a professional can easily prune the tree to make it safer. Most trees will respond quickly and will only need this kind of structural pruning a few times.

Structural pruning of a tree with codominant stems involves 'subordinating' all but the chosen primary leader and lateral limbs. They are cut back (“reduced”) to slow their growth, coaxing the main stem to become dominant again.

This kind of pruning is an acquired skill based on in-depth knowledge of tree physiology and mechanics and extensive experience. Do not do this yourself, as you’ll likely only worsen the problem! Instead, call in a CT Licensed Arborist who can get your tree off to the right start.

The sooner you begin structural pruning, the easier it is to change the form of the tree. It will become exponentially more expensive to correct the longer you wait.

What to Do If Your Tree Has Codominant Stems

Once a tree reaches maturity, structural pruning may no longer be viable, as cutting off one stem of a developed two-stemmed tree can cause a significant wound that may kill the tree. The tree may also be left unbalanced, putting it at risk of falling over.

Talk with an Arborist

Your first step should be to contact a CT Licensed Arborist and have them provide a recommendation for your trees. Codominant stems are not always a death sentence, and with the proper techniques, you can potentially keep a tree standing even when it has codominant stems.

To lessen the risk of tree failure, they may suggest reduction pruning to reduce the tree’s weight. If they believe the tree is too much of a risk, they’ll suggest removal to protect your residential or commercial property.

Reduce Weight with Crown Reduction Pruning

Reduction pruning is a fancy term for shortening tree branches. They can reduce the length and weight of the cut branches to make a tree more compact. This is even more useful for trees with codominant stems, as it can reduce the risk of failure at the junction where they meet.

Don’t try reducing a tree’s canopy yourself, especially for large trees. Arborists are very deliberate with where they cut the branches and how much they remove. Cutting at an arbitrary point can lead to decay or allow insects to attack the open wound.

Remove the Tree

If pruning can’t help the tree, an arborist might recommend removing it. The most frequent reason is that there’s internal decay in the tree. Internal decay is more common in multi-stemmed trees because the weak attachment between the tree stems acts as an entry point for fungal pathogens.

An arborist may also recommend tree removal if the tree is a hazard. Some of the aspects an arborist will look at to determine if your tree is a potential hazard include:

• The weight of both sides of the codominant stems
• How evenly spread the weight is between the multiple trunks
• The angle of the two stems
• Nearby structures or walkways where people commonly walk
• Apparent decay in the tree

Frequently Asked Questions About Codominant Stems and Tree Safety

We realize codominant stems aren’t the first thing on everyone’s mind when they think of their trees. To help you understand the importance of dealing with your trees that have codominant stems, we’ve answered some of the common questions homeowners have about them.

How do I know if codominant stems are a risk on my property?

If the tree is large, located near a structure, or has visible signs of stress like cracks or included bark where the trunks meet, it’s worth having a Certified Arborist inspect it. Risk depends on the tree’s condition, species, and placement.

Are codominant stems always a problem?

Not always – but they often are. The junction where the trunks meet tends to be weaker and more prone to splitting, especially during storms. It’s something a certified arborist should look at and evaluate.

Should I remove a tree with codominant stems?

Not necessarily. It depends on the tree’s size, health, location, and the severity of the structural weakness. An arborist can assess the risk and help you make the right call.

How do I prevent codominant stems in new trees?

You can help prevent codominant stems in new trees by choosing species that are less prone to this growth pattern and prune them regularly when young to encourage a single, dominant trunk.

Not Sure About Your Tree’s Structure? Rayzor’s Edge Tree Service Can Help

A codominant stem is not a death sentence for a tree, but it is a warning sign that you need to give your tree special care. Trimming a young tree can prevent the problem from developing in the first place, and reduction pruning for mature trees can make a tree safer. In other instances, removing the tree is the only thing to do to keep your property safe. When you need the best care possible for your tree, trust the experts at Rayzor’s Edge Tree Service.

Our CT Licensed Arborists can inspect your trees, offer recommendations for future tree care, and remove any trees that are beyond saving. Call us today at 203-258-5584 or request an estimate online.