Preventing Tree Breakage

[Paul J Hetzler]

Cradles and Cables

We are a clever lot when it comes to helping our kids settle into bed at night. Apparently, the story of how Jack broke his head fetching a pail of water, with Jill falling down the well after him, or the charming bubonic plague ditty “Ring Around the Rosie,” is supposed to calm small children. The veiled threat about abandoning an infant in a tree on a windy night always made my kids hush up. “Rock-a-bye baby, in the treetop; when the wind blows, the cradle will rock. When the bough breaks, the cradle will fall, and down will come baby, cradle and all.”

When the wind blows, any cradle left in a treetop will definitely rock, which sounds like a job for Child Protective Services. Predicting whether a bough is going to break, however, is a job for an arborist. One critical factor that predisposes a tree to wind damage is inherent weakness between major unions, also called forks or crotches. Failure of a large branch-to-trunk or trunk-to-trunk union can be catastrophic, both for the tree as well as for people or structures beneath it. Luckily, most weak unions can be remedied once they have been identified.

Winter is a good time to evaluate mature hardwoods for all kinds of defects, including weak unions. It’s fortunate that unions provide clues as to their strength. The first is the angle of attachment. Branch unions close to ninety degrees tend to be strongest, while narrower ones are weaker.

A tree with two or more trunks of similar size is said to have codominant stems or trunks. Codominant trunks nearly always develop narrow forks which pose some level of risk of splitting. Such a risk increases with the age and size of a tree.

Another indicator of weakness is the presence of seams—look for cracks running down the trunk from the union. A crack on both sides of the trunk implies a far worse situation than does a seam on one side only. Decay is an important clue, but the problem is that it may not always be evident. Conks (shelf fungi) and woodpecker activity indicate serious rot, and it should go without saying that having a little “garden” of brambles and saplings growing in the fork also means extensive decay.

One of the clearest signs of weakness is a pair of ears on a fork. I should probably explain. Trees are self-optimizing; that is, they respond to stress by adding tissue in ways appropriate to the problem. The weaker a union, the more a tree compensates by adding wood, in this case outward from the trunk in a sort of ear or “clam shell” shape.

Finding one of these clues is enough to warrant hiring a professional to assess the tree, and if you identify more than one sign, make it soon. So long as a tree is in generally good condition, even the weakest union can often be stabilized with a cable brace. Because a mature shade tree is irreplaceable in one lifetime, and because it’s more than a slight inconvenience to have a large portion of one “drop in” on you suddenly, cabling is worth the investment.

With all due respect to the capable Do-It-Yourself crowd out there, the wrong cable is worse than no cable. Every component in a cable system must be load-rated, rust-proof, and sized correctly based on the situation. Cabling should only be done by someone familiar with the American National Standards Institute (ANSI) published standards for cable bracing. This is an important point, because not all tree care professionals are up to snuff on ANSI standards, which specify cable diameter, type of eye termination, and the size and type of bolts to use.

It’s critical that the cable is installed at the right height, which is two-thirds to three-quarters of the way from the weak fork to the top of the tree. Of course, the cable is never wrapped around the trunk, since that damages the trunk and weakens or kills the tree above that point. Usually, drop-forged eye bolts are used to secure the cable ends to the tree, but for small trees with no sign of internal decay, J-shaped lag screws are acceptable. The correct sized hole is drilled through the tree (for bolts), or into the tree (for lags). Bolts are much stronger, and are used for larger wood and for any case where decay inside the trunk is suspected. An arborist might also recommend a synthetic cable, rather than steel, to allow for more natural limb or trunk movement.

Lest you fear you will end up with a Frankentree in the yard, don’t worry. A properly installed cable system is inconspicuous, even to the point where you may have to squint through binoculars to find it. For a fraction of the cost of a removal, and a tiny fraction of the cost of emergency removal plus roof repair, most trees can get an extended lease on life through cabling.

While under extreme conditions even a perfect system may break, I have never seen a properly installed cable system fail, and some were more than 50 years old. I have, on the other hand, seen many homemade or substandard systems where cables have snapped, and lags ripped out of trunks.

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

Incidentally, there was a reason that cradle was rocking in a tree. In many indigenous cultures including the the Abenaki and Haudenosaune (Iroquois), mothers would secure an infant’s cradle board—the original baby backpack—to a tree while they tended crops or did other work. The child thus got a pleasant, shaded, adult’s-eye view of the world, and was always taken down if the wind became too brisk.

I hope that you and your trees “keep it together” through all sorts of weather for many years to come.