Solving Tree Defects Through Pruning
When an Arborist makes an assessment of any given tree, there are two primary factors considered. The overall vigor of the tree and its structural integrity. Pruning trees directly impacts both of these factors and is the foundation of urban tree care. Through the practice of pruning trees we can correct, prevent, treat and even eliminate structural defects. We’ll be taking a look at some common defects in trees, why they occur and how pruning helps manage them.
Tree Structure
You may be wondering, why bother pruning trees in the first place, they seem to do just fine in a natural forest setting. It is important to understand trees in the forest develop a different structure as compared to stand alone landscape trees. This has to do with millions of years of evolution and a wonderful phenomenon we know as phototropism. In simple terms phototropism is the growth response of trees to sun light. Trees in the forest will develop a tall slender structure because of close neighbours and light stimulus mainly from above only, creating less opportunities for structural deficiencies to develop. Landscape trees have little to no neighbouring trees and light stimulus from all angles which create growth responses more prone to the structural defects we regularly combat with pruning. Furthermore, there are two categories of growth habits trees fall into we call excurrent and decurrent. Excurrent trees tend to form a uniform strong single stemmed structure naturally. Decurrent trees will form a broad multi-stemmed canopy which will be more susceptible to structural defects. Decurrent trees generally require more maintenance pruning as compared to excurrent trees however, both will benefit greatly from structural pruning especially at a young age.
Excurrent Tree Form
single dominant stem
Decurrent Tree Form
broad canopy with multiple stems
Now that we have some understanding of tree structure lets look at some defects we commonly encounter in the canopy that you can easily learn to recognize yourself.
Codominant Stems
Growth shoots originating from the same node compete and grow equally to try and become a primary stem. This creates a weak branch union known as codominant stems which is particularly susceptible to failure, especially with bark inclusion and should be treated with pruning.
Codominant Stems Mature Tree
Removal of a stem is not tolerated well by a mature tree. Instead, we aim to reduce the weight of stems through reduction pruning. This reduces the forces on the union making it less likely to fail.
Codominant Stems Young Tree
When caught early, as long as the tree can tolerate the wound, we can eliminate the defect by removing one of the stems.
Some species will be more susceptible to growing codominant stems, and pruning can not eliminate all instances entirely. The aim in treating such trees is to make sure codominance does not form on primary leaders. Ideally, we do not want to see codominant stems supporting heavy amounts of tree mass. Mature trees with existing codominant stems should not be allowed to get too big or heavy and will require regular reduction pruning for optimal safety and failure resistance.
Dead Branches
As trees grow they routinely develop and shed dead branches. Dead branches eventually succumb to gravity and you’ll want to prune them off before that happens to avoid injury or property damage. We also prune dead branches to expedite the trees healing process. The quicker a tree heals over a wound, the less chance disease has for setting in. Dead branches are fairly easy to spot in the growing season as they simply will be bare with no foliage growing.
Broken or Cracked Limbs
Through the forces of gravity and wind, tree branches can sometimes fail. Broken or cracked branches should be removed as soon as discovered to eliminate the danger of a falling branch and again to initiate the healing process. In both young and mature trees we remove the offending branches to eliminate the defect. Large diameter wounds resulting from treatment will need to be monitored for decay and regularly examined by your Arborist.
Dead Cracked Branch
We treat dead branches in young and mature trees alike, removing them as soon as they form. Large diameter wounds resulting from a removal cut will need to be monitored for decay and regularly examined by your Arborist.
Dead Branch Trapped in Canopy
Remove as soon as possible.
Branches Rubbing Each Other
Branches that rub against each other can create a weak point in a tree, very much susceptible to failure. You’ll want to eliminate the defect by simply removing one of the branches. Generally, the weaker less dominate branch should be removed.
Rubbing Limbs in a White Oak
We remove one of the rubbing branches, ideally the weaker of the two. However, if the tree can not tolerate branch removal, we treat through reduction pruning to lessen the weight of the branches. This will reduce the likelihood of failure at the rubbing weak point.
After the Rubbing Branch was Removed
Here we were able to remove the offending weaker limb and eliminate the tree defect. You can see some damage at the point of friction, but the tree will recover.
Branch Stubs
Branch stubs exist in trees as a result of failed branches or poor pruning practice. Stubs can significantly increase the healing process for a tree, this is bad because it gives diseases more time to infect a wound. In both young and mature trees we remove stubs as soon as discovered. In some cases we may leave a stub if significant healing has already taken place as cutting into new layers of growth formed can end up slowing down the whole process.
Stub as a Result of a Break
Cut back to branch collar as soon as possible.
Stub as a Result of Poor Pruning
Cut back to branch collar as soon as possible.
Lions-tailed Trees and Branches with Dense Ends
Sometimes through phototropism, aggressive branches can develop elongated with the majority of growth at it’s end. But most often we see dense branch ends as a result of poor pruning practice. These are called lions-tailed trees because after being stripped of all its secondary and scaffold branches the structure resembles a loins tail. When all growth and weight are at the ends of branches, weight is not distributed evenly and the tree or branch has little ability to distribute the forces of gravity and wind. Lions-tailed trees are much more susceptible to failure and are a common result of novice tree pruners.
Lions-tailed Tree as a result of Poor Pruning Practice
Through strategic pruning we can train and restore a more uniform growth pattern. Correction of lions-tailed trees will usually take a series of pruning sessions over the course of some seasons.
Lions-tailed Tree as a result of Poor Pruning Practice
We can sometimes correct this defect through pruning in older trees. Severe cases in mature trees are often past the possibility of correction and may either require frequent maintenance pruning to keep weak points in check or potentially be removed if the risk of failure is deemed unacceptable.
Ideally we want to address defects in trees as early as possible. By developing a pruning plan specifically suited to your trees needs it’s even possible to eliminate defects before they ever have a chance to form.
If you need assistance with any of your tree maintenance we’d be glad to help. Simply fill out our contact form and we’ll get back to you as soon as possible.
