By: Anthony C. Arnoldi, Certified Arborist WI-0102A
Trees generally don’t misbehave, but there are certainly times when they need correction. Structural weaknesses often need correcting.
When trees are chosen to grow in the open as landscape shade trees, structural problems often begin to develop because of the resulting growth pattern. Lateral (side) branches turn upward and may begin to become leaders that will compete with the true leader. Then the crotch between the lateral branch and the main trunk gets tight, and bark begins to become “ingrown” there. Wood cannot be added to provide needed support because of the lack of space. With continued growth, a “seam” of separation becomes evident that often cracks open or fails altogether in a storm, resulting in a limb down on the ground, electric wires, car or other property, or even threatening personal safety.
This condition is quite common on open-grown shade trees but rare in forest trees because the proximity of other trees causes a single leader to develop without many of the bad crotches. The majority of limbs that fail do so at these vulnerable crotches. These crotches are prevented from developing if correct training pruning is done periodically when the tree is young, but if they are already there on a larger tree, either removal of the limb or reinforcing it is necessary.
Special extra-high-strength steel cable(s) can provide needed support and properly spread out the physical stresses from branch weight or storm forces. Cables are correctly installed in approximately the upper third of the tree’s crown in order to have sufficient mechanical advantage and so are usually very discrete. In fact, many clients will call us to say that they can’t find them at first.
When crotches require even more support or have cracked open, bracing rods may be used to bolt it together again and provide needed stabilization.
It is very important to use the correct cable and terminal hardware according to ANSI standards. Aircraft cable purchased at local hardware stores does not meet this criterion, but is often seen being installed by unschooled practitioners.
The ANSI committee is evaluating some newly introduced cabling systems using polypropylene slings or synthetic rope with adjustable hardware. each brings a few advantages as well as some limitations of use. As they become accepted, they may provide more options to save vulnerable trees. We will always stay abreast of cutting edge technology.
All cabling methods have both their limitations and approved uses. It requires great skill and knowledge both to determining where they are to be used and to install them correctly. Also, cables should be inspected periodically to check for materials degradation and to make sure adjustments are made as the tree gets taller and the center of gravity changes.
Cabling and bracing cannot save all trees. Every situation is unique and it is important that costs, risks and benefits be examined by a Certified Arborist. However, cabling and bracing are very useful tools to save valuable mature trees in our landscapes.
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