Cabling and Bracing

Tree Cable Systems 

If you decide to install one or more cables, make sure that they are professionally installed. Sometimes the best strategy is to lightly thin the tree’s crown in conjunction with cabling. There are presently two kinds of available cables: Static steel cables and Dynamic synthetic cables.

Both types of cables are used to support weak unions in the tree, almost always in the case of co-dominant stems (“double” trees) or a cracked branch union. The cable should be installed about 2/3 of the distance from the weak union to the end of the stem. The design and installation of both are described below.

These high-strength steel wires, usually between 1/8″ to 3/8″ in diameter, are attached with hardware into the trunk of the tree.

For small stems, a J-lag screw should be installed to the full length of the threads. Any large branches or trunks should have drop-forged eye bolts extending through them and held with a washer and nut on the back side. Cables should be swaged or dead-ended to a thimble that goes around the J-lag or eye bolt. The thimble prevents severe bending of the wire. Cables are installed with enough tension to remove all slack from the cable.

There are sometimes complications arising from steel cabling. Because trees naturally add wood to their circumference every year, they annually strengthen themselves to compensate for co-dominant stems, large limbs or other imbalances. They strengthen themselves by adding wood where it is most needed, reducing the stress in that area. Known as the axiom of uniform stress, this follows from the observation that trees always have much thicker growth rings in areas of high stress. Adding a cable can help support the tree, but may result in less wood formation to support that part of the tree that has been cabled. Thus, steel cables once installed must be maintained and replaced when necessary.

In general, steel cables are recommended where the union is prone to a sudden failure, such as in very brittle trees, or in the case of partially cracked unions, or unions that have a well-defined plane of crack propagation.