There are two main reasons for installing a Structural Support System in a tree:
1. Prevention: to reduce the chance of failure in a healthy tree with structural weakness or to reduce the potential hazard of a tree.
- Example: a specimen bur oak in good condition but having large limbs with poorly formed “V-unions”
- Example: a picturesque multi-stemmed hickory that towers over a picnic shelter
2. Restoration: to prolong the existence of a damaged tree
- Example: a large sugar maple that lost one of its leaders in a storm, leaving the others suddenly exposed and vulnerable to further damage
- A union or crotch which has partially failed and there is a crack evident.
There are 2 types of structural support systems for trees; Static and Dynamic.
The Static System is made up of steel cables and bolts, which are used to support limbs or branch unions that have been visibly split, usually due to a storm event. In a case like this the limbs can be pulled together in order to close the opening at the branch union. A support system would be installed in the form of a bolt and steel cable.
The bolt would be installed near the weakness to reduce movement of the branch and a steel cable would be installed between the two limbs above the weakened union, usually at about 2/3 of the distance from the union to the top of the tree. A hole is drilled through each limb to allow for bolts to anchor the steel cable.
The Static System does not allow for movement at the failed union.
The Dynamic System is known as Cobra Cable. Dynamic cables are installed when there is a weakness in the branch union with no signs of failure. These cables are made from a UV protected synthetic braided rope and are installed approximately 2/3 of the distance from the weak union to the top of the tree. The cable is wrapped around the limbs eliminating the need for drilling through the wood.
Cobra cables can be used preventatively if they are installed prior to a split in co-dominant trees or on limbs with potentially weak unions. These cables provide support while encouraging ongoing strong, healthy growth.
Cobra cables have a shock absorber built into the cable to allow for more branch movement. Slight branch movement allows the limb to maintain its natural range of motion but limits the extremes to which it can move, especially during storm events, and therefore reduces the risk of limb failure.
Cobra cables will require replacement every 7-10 years.
We highly recommend that these Support Systems be inspected annually to ensure they are still functioning properly. These inspections are usually in the early spring, after the treat of winter storms and prior to leaf out.
In some cases, such as the recent ice storm, we will inspect them more often.
In some cases, as the tree grows, additional cables may have to be installed higher in the tree.