Cabling and bracing trees

May 22, 2012 Comments Off by

Central Texas Tree Care has installed hundreds of cables in Austin area trees over the last 10 years and I am very proud of our record. My staff is highly trained and seasoned in this area and we now properly install more cables every year than just about any other local company. The purpose of this article is not to be overly technical, but rather to explain to the average person that we know exactly what we are doing, what standards to follow and what hardware to use.

Cabling and bracing trees are scientifically approved methods for supporting trees with split crotches, or for trees that have limbs or crotches that are predisposed to failure. The International Society of Arboriculture, ISA standards for tree cabling that we follow are called the ANSI (American National Standards Institute, Inc.) A300 standards for supplemental support systems. When done properly, cabling and bracing will often save limbs or entire trees. They are generally considered permanent solutions, although constant re-inspection and monitoring/pruning is always recommended.

Cabling trees is generally done to tie in either limbs that are overextended (too long and heavy), or to tie in large limbs in the upper canopy to support weak or split main crotches. Cables are almost always installed in conjunction with canopy thinning to reduce the end weight of large horizontal sections.  Sometimes, come-alongs are also used to help pull together split crotches so the cables can be properly tied  in. Often with split trees, (although not always necessary) threaded through-bolts are installed through the split crotch for added support.

Through-bolts are used as anchors. These are galvanized metal bolts, with a fully enclosed ‘welded’ eye and are installed right through the limb to be supported. A hole is drilled through the limbs at exactly the right angle and then the bolt is slid through the limb. After the bolt is in place, a washer and a nut is then put into place on the back side of the limb. This practice makes for a very solid and permanent anchor solution that will not pull out of the tree or rust. Nor will it interfere with the natural expansion of the limb. Additionally, the ring on the inside will not break. With cheaper hardware, often the ring is not a welded eye and the cable pulls out during the first storm.

Once the anchor bolts have been installed, then the cables are tied to the anchor bolts using thimbles.  The two strongest ways to do this are either with ‘dead-end grips’ or twisty ties as we call them, or by bending and splicing the cable itself through and around the eye ring, then splicing it. Both of these methods are extremely strong and effective.

Most (not all) cables I see installed by other companies in the Austin area are installed incorrectly.  Almost every time, besides using inferior hardware, the cables are installed either too low in the tree or too far down the limb they are supposed to support. ANSI A300 standards specifically state that cables should be installed a minimum of two-thirds of the way from the crotch to the end of the limb being anchored.

The cables and bolts need to be the right size for the job. Large trees and limbs require larger bolts and larger diameter cables. Smaller trees require smaller diameter bolts and cables. Limbs that are being used to anchor the tree require large enough diameters to support the bolts, but conversely putting bolts that are too long into large diameter wood is often not correct either (too far down the limb).

Safety factors such as proximity to power lines or other utility lines are paramount. Metal cables conduct electricity and must never be installed in trees where power lines contact the tree. Also, metal cables can rub against themselves or tree limbs, so they must always be installed free from obstructions.

Trees with multiple large limbs and weak crotches often require multiple cables. Often triangle, box or ‘wheel and spoke’ systems have to be installed.  When more than one cable has to be anchored to the same limb, more than one anchor bolt must be installed (one for each cable). The anchor bolts must NOTbe closer together than the diameter of the limb being drilled. Note: For safety and power, we use gas powered drills with forward and reverse settings, instead of electric drills that require a dangerous power cord.

Although lag bolts are on the approved list of hardware for ANSI A300 cable systems, we prefer to stick to through-bolts. As an arborist with more than 15 years experience installing support systems, I find lag bolts to be unpredictable and weak anchors, especially in large trees. They often pop out in storms.  Although they work better, for example, in oak limbs that have stronger wood, and are significantly easier to install, I have seen them come out or generally fail too many times in stormy weather. I would NEVER recommend lag bolts in softer wooded trees other than oaks, mesquite or black walnut trees in this area and prefer not to use them at all.

Often cables are not necessary at all, and I have seen cables installed when they are not needed with startling regularity. Always get your trees evaluated first to see if they even need cabling or bracing. I often see other tree companies promoting them because the crews need the work and not because the tree in question actually needs a cable. Beware of unnecessary tree work! Contact us if you want an honest professional evaluation.

Arborist's Journal, Knowledge Center

About the author

Co-owner of Central Texas Tree Care, Andy was educated at Virginia Tech, one of the nations top forestry schools. While earning his degree, Andy interned with a large lumber and paper company in Northern Florida for two years. After graduation, he decided to make a transition over to urban Forestry, finding it more interesting and personally rewarding. Andy has been saving and protecting trees for private homeowners ever since.
Comments are closed.