by Brent Kahn, Certified Arborist WI-0302A
Some trees can have conditions or structural defects that potentially lead to branch or tree failure. The result could mean damage to the tree or surrounding trees, damage to your property, or even personal injury. When your arborist detects one of these defects, they may recommend a tree support system, also referred to as a cable or brace. A support system, when installed properly, can help to reduce these risks by minimizing the distance that branches can move in relation to each other
A support cable system consists of a set of anchors installed into two parts of a tree with a steel cable connected between them. They are generally placed at 2/3 the distance from the weak point to the ends of the branches (meeting ANSI standards). This means they are located in the upper canopy of the tree and not always easily seen from the ground. Depending on the tree, more than one cable may be needed.
There are two primary reasons your arborist may recommend a support cable system:
A Co-dominant Stem also referred to as a “V” branch union
- This is a very common structural defect with a high risk of failure
- A tight “V” with bark grown into the branch union is a visible sign of this condition
- The branch union tends to break or pull directly apart
Extremely long, heavy, or “overextended” branches
- The resulting damage will be branch breakage or a horizontal split that occurs in the middle of the branch.
- The cause of this damage can be related to tree species, excessive foliage toward the ends of a branch, high winds, or snow/ice loading.
Your arborist may recommend pruning in conjunction with a support cable system. This can help reduce branch weight and leverage forces. It can also help to correct branch structure to minimize future defects.
A Bracing support system is used to support a branch union that has a visible split. It can also be used to support a split that occurs in the middle of a branch. They consist of a threaded rod that is drilled through the defective area, and terminated on each end with a heavy duty washer and nut. More than one brace may be needed. A support cable system is usually recommended, for additional support, in conjunction to a brace.
These support systems do not eliminate the problem. They are a means to add support to an already existing condition and to help minimize risk. This system will need to be inspected regularly (every 1-5 years depending on the severity of the condition) by a certified arborist.