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Bill Pramuk, Trees and People: Tree cables need professional installation and maintenance
Trees and People

Bill Pramuk, Trees and People: Tree cables need professional installation and maintenance

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Almost six years ago I got a call from a property owner, concerned about the big trees on their property. One had fallen, which raised concern about the risk of others falling.

When I visited to examine the remaining trees I saw the fallen tree and the resulting, horrifying damage. Fortunately, no one was injured.

The new owner of the property did not know this big oak had a severe structural defect and an old, non-standard cable system holding it together.

In calm early spring weather, as the live oaks were blooming and generating new growth, the two-trunk tree split down the middle in spite of the cable system. Weather records show there had been some heavy wind in February. Maybe that was when the failure began.

I took some time to look closely at the fallen tree. Most obvious was the split, double trunk. It had deeply “included bark” — a common defect where the bark of two trunks is pinched inside their attachment. It is inherently weak and growth pressure can lead to self-wounding and subsequent decay, which was the case here.

Half the tree had fallen onto a country road while the other half fell into the residence parking area and onto a parked car, severely crushing it.

I noted a steel tree cable attached to one of the big limbs, now in the process of being bucked for firewood. Scouting other parts of the tree I found an old eye lag, with new bark and wood embedding it and no cable attached. The remnants of the old cable system consisted of “bent” — not forged— eye lags, and cable attached with wire rope clips (two-piece clamps consisting of a saddle and a threaded u-bolt), and only one per attachment point. There were no “thimbles” over the eye lags. The cable rides in the thimble to reduce strain and wear.

In addition, the installer had broken a rule of wire rope clip installation: “Never saddle a dead horse!” It means never put the saddle portion of the clip on the dead-end section of the cable. The saddle goes on the load-bearing side of the cable. The U-bolt goes on the dead-end section.

According to the International Society of Arboriculture “Best Management Practices,” that kind of cable hardware “is not used in North America to form terminations on any cable larger than 1/8-inch diameter.”

Where it is used commonly in the UK and Australia, three clips are prescribed for each termination. The cable in this incident was one-quarter inch and the installer used only one clip, installed backward.

In other words, the cable system was old and overloaded because the tree had grown and gained a lot of weight. The hardware was inappropriate, not properly installed, and the owner did not know what trouble was brewing.

I have seen coast live oaks that large and with similar structural defects, which were saved by judicious pruning and well-designed cabling or bracing systems.

I believe this failure and property damage could have been prevented by good professional care. Or, perhaps, the new owner might have chosen to have the tree removed if they had known the risk and the options.

ISA and the American National Standards Institute (ANSI) provide the specifications for “Tree Support Systems”. Tree work contractors should be familiar with the standards and inform their clients about options for risk management.

After cable systems are installed, they must be inspected periodically and adjusted or revised as the trees grow heavier or the cable system components wear or corrode. A three -year inspection cycle is typical in our region.

And a final question: At the time of sale, shouldn’t someone — the seller or the buyer’s realtor — exercise due diligence with respect to big trees? It could be a matter of life or death.

WATCH NOW: NAPA COUNTY WILDFIRES TAKE A TOLL ON LANDSCAPE

Thousands of fire-damaged trees are being removed at a cost of millions of dollars in the wake of Napa County wildfires.

CHECK OUT: NAPA’S BURNING PROBLEM

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The Napa Valley Register takes an in-depth look at Napa County's vulnerability to wildfires in this four-part series.

Bill Pramuk is a registered consulting arborist. Visit his website, www.billpramuk.com. Email questions to info@billpramuk.com, or call him at 707-363-0114

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