What’s a Codominant Stem? Why Is It Bad?

February 18, 2022
February 18, 2022 Ryan McFadgen

What’s a Codominant Stem? Why Is It Bad?

Have you noticed that some trees tend to grow in a V shape? This shape seems to provide the perfect spot for climbing kids to grab hold, and maybe your pet cat likes to hang out in spots like these. But they’re actually an undesirable shape for trees, and catching this trait in young saplings is definitely the way to go.

It’s called a codominant stem, and the V shape essentially creats a significant weak spot in the tree. The stem that splits from the main trunk is usually not well attached, and there are weight issues as well. The result is that in high winds, or simply over time from age and disease, the codominant stem will become weaker and break.

In many cases the tree is so damaged by the split that the entire thing must then come down. These can be dangerous jobs if the codominant stem hasn’t totally separated, because there will be tension behind it. Don’t ever try to “finish off” a split tree trunk that hasn’t completely fallen yet! Leave this job to the experts. In addition, trees that have lost their codominant stem will often become unstable, because their weight balance is now very different. The remaining part of the tree might now be prone to falling.

Even if the tree survives a severe loss such as this, it is unlikely to end up very attractive afterward. Sometimes, trees whose codominant stem has broken off must be taken out for aesthetic reasons.

When a sapling is young, structural pruning can prevent the development of codominant stems, so that your tree can enjoy a nice long life. But if an existing mature tree has this shape, pruning probably won’t be a good idea. The solution in those cases is often to offer structural support, via cabling, to improve wind resistance and reduce the odds of breakage.

Give us a call if you have a tree with codominant stem, or if one breaks. We can assess the damage and help you decide what to do next.


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