Cabling and Bracing

We normally use steel through-hardware and Treesave Brand elastic rope cable. http://www.sherrilltree.com/ for more information.

cable sizes:  
10 mm cable 5,000 lb breaking strength
13 mm cable 11,000 lb breaking strength
10 mm spectra cable 20,000 lb. breaking strength

Traditional steel cable is thought to have the following problems:

  1. Fixing trunks rigidly to one another reduces the tree’s ability to dissipate high wind forces through deflection of the crown. Also, high wind conditions can create slack in the cable which, when suddenly taken up can result in failure of the cable or of the trunks above the cable.
  2. The supported parts of the tree come to rely on the cable’s support. Should the cable break the tree might be less able to hold itself together than before the cable was installed.

The Better Cable

Connecting parts of a relatively elastic structure (the two parts of a tree in need of cabling) to each other is more effectively done using an elastic material such as rope. Using a relatively inelastic one (steel) results in higher forces at the attachment points, which can cause breakage there. It also acts as a crutch, diminishing the tree’s further growth of wood to support the fault.

Rope cable has so far been employed mostly with non-invasive terminations (slings around the trunks rather than bolts through them), but I see no reason not to use it with invasive terminations*. Non-invasive terminations have serious drawbacks, despite their tree-friendly ring. These include risk of girdling stems if not periodically loosened, and a risk of causing large loss of bark and all-important cambium during storms. Through-bolts, on the other hand, only expose a small column of wood to decay.


*Sling terminations, however, should not be used with relatively inelastic material because this will increase the forces at the sling-bark interface.