Wednesday, February 17, 2016

Front Yard Forestry: Cabling Weak Trees

Front yeard foresteryOne of the ways Mother Nature keeps the forests healthy and strong is by “letting” trees with poor structure split during high wind or ice load events. Such trees become decayed and die young. Those with better genetics (or better luck) are the trees that reach maturity. This selection process is great for woodlands, but it doesn’t work quite the same way for trees growing in yards, streets and parks.

Trees often develop imperfections. The vast majority of these are benign, but some can be dangerous. To avoid breakage of large limbs and associated flying lawsuits and debris, trees with obvious defects are often removed. But since many problems are a result of human activities, it hardly seems fair to cut down a mature shade tree if there’s an alternative.

A common but usually correctable problem is called narrow forks. These occur where the angle of attachment between trunk and limb, or between two competing (codominant) trunks is narrow. The strongest attachments are open, somewhat “U”-shaped, with a wide angle approaching ninety degrees. Narrow forks, or unions, get weaker with age, until eventually a large tear occurs.

This type of defect can be fixed when the union is small by a mere snip of a hand pruner. If this is not done, the defect gets weaker over time. If there is a valuable target (swing set, house, Faberge egg) that could be struck if one side splits off, corrective action is needed. A professional should be called to evaluate the tree. If it is in very bad shape, it may need to go, but if is healthy other than the weak union, a cable system could be installed.

A professional should always be called to install a cable system. Cabling must be done right or the problem could be made worse. The American National Standards Institute (ANSI), which has specs for home wiring, water lines and steel bridges, also has standards for tree cabling. Cable diameter, type of eye, size and type of bolts to use are all specified.

It’s critical that the cable is installed at the right height. It should be placed two-thirds to three-quarters of the way from the weak fork to the top of the tree. The cable is not wrapped around the trunk, since that would damage the trunk and weaken or kill the tree above that point. Either drop-forged eye bolts or J-shaped lag screws are used to secure the cable ends to the tree. The correct sized hole is drilled through the tree (for bolts) or into the tree (for lags). Bolts are stronger, and are used for larger wood and for any case where decay inside the trunk is suspected. Lags are cheaper and easier to install but are acceptable only for small wood where there is no evidence of decay.

Cabling may be used in other ways, for example a whole tree with a trunk defect may be cabled to other trees to support it. And some cables today are synthetic material, rather than steel, to allow for more natural limb movement.

A proper cable system is inconspicuous. For a fraction of the cost of a removal, and a tiny fraction of the cost of emergency removal plus damage repair, most trees can get an extended life through cabling.

While under extreme conditions even a perfect system may fail.

For information on cabling, contact your local Certified Arborist or other tree care professional. Start with companies which belong to trade organizations like the International Society of Arboriculture (ISA) or the Tree Care Industry of America (TCIA). Ask for their copy of the ANSI cabling standards, and insist on proof of insurance directly from their carrier.

Photo provided by Charleston Tree Experts.

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Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.You can read more of his work at or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World

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