Given the right environmental conditions all trees present some level of risk. The level a particular tree presents should be determined, and a decision should be made as to whether that level of potential risk is acceptable or not.
When the solution is too costly, or if it is too destructive to implement and still maintain the tree in a condition adequate to be a contributing asset, removal is usually the only remaining option to consider.
However, there is another possible solution that may deliver a lower risk without destructive pruning or removal. This option is “structural enhancement” of the tree to reduce risk of failure.
Unfortunately, trees can fall apart with catastrophic consequences. While they may appear safe and solid from the outside, the reality can be quite different. It is important to have large trees with the potential to damage structures or injure people evaluated by a qualified arborist.
Structural enhancement may include cabling, rodding or bracing of the tree’s trunk(s) and limbs to provide the support necessary to reduce the risk of failure to an acceptable level.
Not only must a certified arborist design the system to address each limb’s length and weight, but they must also anticipate and prepare for constantly changing factors including wind load and decay.
To do this successfully, the arborist must be able to visualize how the observable aspects of the external tree interact with unobservable, hidden defects within the tree.
The arborist must also be knowledgeable about how various tree species differ in their structural characteristics and how they differ in their ability to react to decay and other conditions which may compromise their structural integrity.
Future growth, which will continually change both the length and weight of each limb, means the system must be routinely monitored and updated as required.
This is not the kind of knowledge which can simply be “learned” by reading a book or attending a lecture. It takes practical knowledge which must be gained through extensive hands-on experience working with trees.
It requires the ability to evaluate potential problems and correctly assess the risk factors. Properly done, cabling and bracing is a valid alternative to the removal, or mutilation by over pruning, of trees which otherwise might be considered unsafe.
Cabling is a procedure which involves connecting two or more trunks or limbs together in the crown of a tree with steel cable or other approved materials. This may be necessary to reduce failure due to decay, excessive limb movement or other factors that may lead to trunk or limb failure in the tree.
Cabling can often reduce risk of wind damage in areas with high storm potential (such as tropical storms or hurricanes). Decay or genetic defects in the trunk, or at the junction of major limbs, can make risk of failure too high.
Rodding involves the addition of steel rods in the trunk or major supporting limbs when they are structurally inadequate due to injury, decay or genetic defect. Most often this remedy is used to prevent the separation or splitting apart of multi-trunk trees.
The bracing technique uses limb or trunk support systems to keep trunks and major limbs from failing. Leaning trees may be given lateral support to prevent falling when root support is lost due to mechanical injury, rot or disease.
Bracing is a technique which can support a tree’s structural integrity and extend the life of a valued landscape asset.
Trees in wet sites may need additional support due to root slippage caused by excessive water in the soil. Major lateral limbs growing from the trunk may also need support due to wind damage, decay or poor limb attachment at the trunk.
Newly planted palm trees often need support around the trunk to keep the palm vertical until an adequate root support system can be reestablished.
It is also essential that qualified experts be utilized to evaluate, design and correctly install any type of structural support when attempting to reduce the risk of tree failure when targets of value are threatened.
Sometimes structural engineers work in collaboration with ISA (International Society of Arboriculture) Certified Arborists who are qualified professionals trained to design and install structural support systems in trees.
Finally, these structural systems are generally done in conjunction with the installation of an approved lightning protection system. The metallic materials used in the installation do not attract lightning, but they can direct the charge if one does hit.
As such, when struck, trees with structural cables and rods installed may receive significantly more damage. To minimize the possibility of damage, ground all metal parts to a lightning protection system.
Installing lightning protection also helps to protect your primary investment in the structural support system.
Sam Hand, Jr. is an Associate Professor of Landscape Design, providing extension services at Florida A & M University. He is a “Certified Arborist” by the “International Society of Arboriculture” (ISA) and is also a “Registered Consulting Arborist” with the “American Society of Consulting Arborists” (ASCA).
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