Tree Cable Installation Systems Lessen Target Impact From Tree Failure

Summary: Sharon Lilly of the International Society of Arboriculture and E. Thomas Smiley of Bartlett Tree Research Laboratories discuss tree cable installation.

Cobra cable system provides dynamic support for American elm (Ulmus americana): Joseph O'Brien/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images

Tree cable installation systems adjust excessive branch movement, alleviate loads on overextended branches and anchor unions, according to Considerations for Installing Cables in Trees in the October 2014 issue of Arborist News.

Sharon Lilly of the International Society of Arboriculture and E. Thomas Smiley of Bartlett Tree Research Laboratories build three benefits into dynamic and static cable usage. Dynamic soft and static steel cabling systems cut risks of failure, likelihood of impact and consequences of failure and impact for decay-, defect-weakened branches and unions. One European standard demands eight-year lifetimes for dynamic rope, often made of hollow-braid polypropylene used with bands, belts, overload indicators, sheaths, shock-absorbing rubber splices and straps.

Ropes ease shock-loading from stress moving forcefully in opposite directions and entail no drilling even though they encourage foraging birds and squirrels, girdling and ultraviolet degradation.

Anchors, brace rods, connectors and terminators fit multi-strand aircraft and wire rope and seven-strand common-grade and extra-high-strength steel into box, direct, hub-and-spoke or triangular system arrangements.

Availability of load-holding solid wood and branch and leader sizes give exact placements for anchors, at two-thirds branch union to branch or leader to tip distances. Anchors and cables have to accommodate brace rods for tree cable installations into branch unions weakened by decay or such defects as sharp bends or splits. The lesser of a 12-inch (30.5-centimeter) separation or of the branch diameter identifies the minimum distance between two anchors to minimize the risk of splitting branches.

Aligning anchors and cables and avoiding hole elongation and metal fatigue from off-center, side-loaded pull justify shining laser pointers into one drilling to sight the second.

Low-hold, low-strength J-lags, called lag hooks, and lag eyes keep lower profiles as anchors than amon-eye nuts on threaded rods, cable-stop termination devices and eye bolts.

Drop-forged, high-strength eye bolts last in branches whose decay maximizes at 70 percent of branch diameter when the remaining solid 30 percent is "nearly equally distributed." Drill-bit diameters must equal or slightly exceed diameters of bolts and machine-threaded hardware in through-bolt installations but lag behind diameters of lag-threaded hardware in dead-end installations.

All tree cable installations need anchors to support unions maximally with direct and triangular systems, minimally with box and, when leaders are unusable, multiply with hub-and-spoke. Box, direct, hub-and-spoke and triangular system arrangements respectively offer branch connections in groups of four or more, of three or more, of two and of three.

Handmade eye splices with inserted galvanized or stainless-steel thimbles left closed prove to be common attachments to, or terminations with, anchor hardware when cables are common-grade.

Manufactured dead-end grips with heavy-duty, inserted galvanized or stainless-steel thimbles left open qualify as proper terminations for extra-high-strength cables provided that EHS and grip sizes match. Aircraft cable and wire rope require cable clamps in the United Kingdom and, in the United States, oval swage sleeves with closed galvanized or stainless-steel thimbles. Bronze or stainless-steel connector multi-purpose clamps and heat-treated, heavy-duty washers respectively service grounded cable and lightning protection systems and stop through-bolt installations from pulling through trees.

Tree cable installations always take into consideration how little or how much movement turns branches ruled by wild forces into branches beguiled into milder, human-friendly configurations.

cabling an oak tree (Quercus spp.): Joseph O'Brien/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

Cobra cable system provides dynamic support for American elm (Ulmus americana): Joseph O'Brien/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ http://www.forestryimages.org/browse/detail.cfm?imgnum=5038024

cabling an oak tree (Quercus spp.): Joseph O'Brien/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ http://www.forestryimages.org/browse/detail.cfm?imgnum=5044025

For further information:

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

Lilly, Sharon; and Smiley, E. Thomas. October 2014. "Considerations for Installing Cables in Trees." Arborist News 23(5): 12-17.
Available @ http://viewer.epaperflip.com/Viewer.aspx?docid=369ebf1d-20ba-43a8-8748-a3b501031677#?page=12

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