In a previous column (December 1, 2010) I discussed the problems that wet, heavy snow can cause for trees and shrubs – particularly evergreens. In response my colleague Terry Ettinger mentioned a cabling technique discussed in the 2nd edition of Arboriculture (1991). I think it’s worth looking at the science behind this practice and some of the unintended consequences.
Harris’s Arboriculture text is considered the bible for landscape professionals, including certified arborists. In the late 1990’s, Dick Harris was joined by Jim Clark and Nelda Matheny, two other gifted academics who have crossed over into practical writing. In the 4th edition of this book (published in 2004), the authors caution about routine use of cables and other support systems for tree crowns. They state that “evidence for the use of support systems to strengthen tree structure is anecdotal” and based on my reading of the scant scientific literature on the topic I must agree.
Older articles and texts tend to provide how-to instructions and diagrams on various cabling and bracing techniques, but little to no evidence supporting the practice. More recently, studies have provided evidence that drilling holes for cables, wires, bolts etc. increase the likelihood of introducing disease into otherwise sound wood. As the tree continues to grow and change over time, even the best of these systems may need to be modified or replaced. In fact, the systems should be inspected and maintained annually. Crown cabling is not a permanent, one-time fix – and sometimes it isn’t even a fix. Failures still occur, often just above the point of attachment of bolts and cables. In fact, many arborists believe cabling should be the choice of last resort.
Some current research is exploring noninvasive methods of securing crowns, such as belt systems, that provide support without creating additional problems. As with any new technology, long terms studies are pending. Given the potential risks and lack of reliable benefit, I would not recommend cabling or bracing unless there were no other choices for saving the crown of a tree.