Codominant stems – potential future tree failures
By Ralph E. Mitchell
As you are driving around Charlotte County, you probably don’t give a second look to the structure of our trees – they tend to just blend into the background. However, if you look carefully you might see a defect called a codominant stem. This is a place where two or more stems (branches/leaders) have come together. Now it may look like they are connected, but they are not and could eventually pull apart in a storm like a giant wishbone. This can be a big problem when there is a target nearby such as a car or house. Codominant stems can lead to future tree failures.
How do codominant stems get started and what do they look like? Often, certain trees produce abundant branches which rapidly grow and begin to crowd each other. Codominant stems form when two nearly equal branches grow side-by-side and begin to push up against each other. Look for a “V” shaped union in the area where they come together. Here you will also see what is called “included bark”. This area of included bark shows a definite line or seem where the two stems come together and begin to push against each other – cracks may even develop. If this is noticed when very young, it can be careful pruned out. Further down the road, it could even be corrected with what is called “subordination” where one stem is selected to remain and the other is pruned down in steps to remove the branch over a period of years. This action slows down the offending stem and speeds up the growth of the remaining stem. Eventually the good stem is dominate and the extra one is totally removed and out of the way. This helps develop a full, well-structured tree.
In general, a tree should have one central leader and four to five scaffold branches aligned around the tree in a whorled pattern. If you were able to look down on the tree from above, it would look like the branches were spaced out like the spokes on a wheel. Over the years your goal is develop a dominant leader through proper pruning and structural development of sound, well-placed branches and no codominant stems.
If you have missed your chance to deal with codominant stems while they are small or relatively small, you really have only a few options left. To prune out extra stems would leave a gaping wound that would never seal up properly allowing decay to enter. You will probably need the services of a Florida Certified Arborist at this point – please see here – http://www.floridaisa.org/. Florida Certified Arborists can complete work such as bolting or bracing codominant stems. This will structurally enhance the individual tree and keep it from tearing apart in a windstorm. Remember that anyone you hire should have the proper insurance and references.
Trees benefit from proper pruning and training as they grow. The resulting structurally sound trees are safer trees! For more information on trees and pruning, please call our Master Gardener volunteers on the Plant Lifeline on Mondays, Wednesdays and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer. Don’t forget to visit our other County Plant Clinics in the area. Please check this link for a complete list of site locations, dates and times – http://charlotte.ifas.ufl.edu/horticulture/Plant%20Clinics%20Schedule.pdf.
Gilman E. F. & Bisson, A. (2017) Chapter 12—Developing a Preventative Pruning Program: Young Trees. The University of Florida Extension Service, IFAS.
Gilman E. F. & Bisson, A. (2017) Chapter 13—Developing a Preventative Pruning Program: Mature Trees. The University of Florida Extension Service, IFAS