Will cabling a tree’s crown make it stronger?

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.

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

15 thoughts on “Will cabling a tree’s crown make it stronger?”

  1. This time winter is heavy in my country as well. I am thinking of ways to preserve my balcony and terrace plants. Some have already frozen and withered.I don’t know how to preserve them? I am searching for ways..

  2. Is this cabling advice specific only to avoiding the chance of tree failure due to snow build up? Cabling, or belting, is used a lot in Australia for guarding against tree failure, particularly for undesirably bifurcated trees. There’s a specimen of Araucaria bidwillii on the city campus of the University of Melbourne that is about 30m tall but formed co-dominant leaders from about the
    620
    six-foot mark. The two crowns are tethered together near the top to guard against the tree splitting in two in high winds, and so far so good. I’m all for this kind of intervention, but as far as putting bolts through the limbs of trees in order to address a problem I’m cautious of. For one thing, you’re wounding the tree in an attempt to improve it, which is something I’ve always been taught to avoid at all costs when it comes to all things arb.

  3. Jimbo, the cabling info is generic (though it was originally snow issues I was addressing). Noninvasive belting seems that it might be a better long-term choice than cables and bolts, but until there are some of those long-term studies looking at failure rates we just don’t know yet.

  4. It seems to me that belting systems have the potential to disrupt bark and sub tissues seriously, rub bark raw so to speak. To be honest I too am very hesitant to recommend very costly treatments whose track record of success is so questionable. Hopefully well soon some sound research results on all artifical support systems that give us better guidance on the efficacy and value of the various methodologies.

  5. Wes, so far these belt systems appear to be ok. Here’s a snippet from one article about them: “Wood-biological investigations on beech trees (Fagus sylvatica) in an
    19e0
    urban forest near Osnabrück, Germany, with six-year-old double-belt systems showed that neither discoloration nor fungal attack occurred in the wood and bark under the belts. The cambium beneath the belts apparently was not impaired either.”
    Six years isn’t long term in my book, but at least it’s a start.

  6. I’m flattered by your reference, Linda! To clarify, however, I was attempting to specifically address the issue of protecting relatively small, multi-stemmed evergreens – such as the arborvitae pictured in your December 1st post, as well as Taxus, etc. – from the consequences of heavy, wet snowfall. In the TV segment I referenced, I was working on an `Emerald’ arborvitae, which matures at roughly fifteen feet tall and five to seven feet wide. I would absolutely agree that cabling large trees is an inexact science/art – at best. More often, when performed by a skilled arborist, I think greater storm protection is derived from improving the overall structure of a tree via selective pruning to open the canopy, rather than the installation of cables, braces, etc. We must always remember that trees with broad canopies are, in many instances, not exhibiting their naturally evolved form – which tends to be more upright and narrow – due to competition (and protection from straight line winds) from nearby trees in a forest setting.

  7. Please let me get this straight. You are suggesting that even on bad, codominant, double leader trees cabeling is not recommended?

    I have used cables on split, very old apple trees where we lifted a huge section back up that would otherwise have to be removed- badly deforming a specimen tree. I know retroactive cabling was affective in these 2 cases and I only wish I’d done the cabling before the trees split. Seems to me if a cable can hold a split tree together it can certainly stop a tree from splitting in the first place.

  8. Alan, invasive cabling (that which involves drilling into the tree) is not recommended as a proactive treatment. Current research on belt systems appears to be promising, though the long term studies aren’t completed.

  9. Linda, if you don’t mind, what is the basis for this change in recommendations? Can you lead me to some data?

    I’ve never seen a cabled tree break at the point of cabling due to rot from drilling and insertion and I am on properties and even in trees every single working day that are loaded with such cable work (and I work during blizzards and sometimes heavy rain!).

    I have no ax to grind here as I don’t perform cabling in my business but researchers and their interpreters routinely over reach the actual scope of research, especially when it contradicts conventional wisdom. That’s the kind of research we all find most interesting.

    I’m not suggesting that’s what you’re doing as I’m generally a big fan of your consistently logical interpretations but on this one I’m left highly skeptical.

  10. Alan, here’s one reference that you should be able to access easily: Stobbe, H.; Dujesiefken, D.; Schröder, K.; Miller, R. W. 2000. Tree crown stabilization with the double-belt system Osnabrück. Journal of Arboriculture, 26(5): 270-274.

  11. http://www2.tree-consult.org/images/pdf/eng/crown_support_balt.pdf

    Thanks Linda, I found this by googling for a few minutes and it contains the rationalization for the new belting systems very convincingly.

    The studies of the superiority of a bracing system that allows the trees to flex seem to fall short of conclusive evidence of the type required in the field of, say, medicine, but I’m very thankful for you enlightening me on this issue. I wonder if any of my local arborists are tuned into this.

    I’ve long known that flexible support of transplanted trees is helpful to their structural development so this idea seems like an extension of that.

  12. Can you provide references that will help me evaluate a commercial arborist’s recommendation that my otherwise very healthy, 75-year-old (?) red oak be cabled to prevent future storm damage?

  13. I would totally agree with your assessment of the current state of affairs. I recommend cables as a commercial arborist very rarely. If I do install one, it is a dynamic system. Trees build themselves for the environment in which they are growing in response to the stimuli received. The unfortunate development of an included bark co-dominant stem may lead to a potential failure. Frequently a cable is installed to support these unions. Follow-up care is rarely performed and nothing is done to change the architecture of the tree that is the cause of the problem.
    I will use an analogy to highlight my point about growth. If you fracture your leg, a cast goes on to support your movement until the fracture has healed. When the cast comes off, the muscles, from disuse, have atrophied. You would in no way shape or form want a cast permanently on your leg. Granted, trees do not heal, they seal. They do take the stimuli of movement to “decide” how much wood is needed for support. I have numerous times in my career encountered situations where the support system failed (cable broke) then the tree failed shortly thereafter. Other times a failure occurred because the tree used the cable as a fulcrum and failed immediately below or above the cable.
    The research is indeed limited/non-existent. In the Journal of Arboriculture, one article involving a computer simulation. Not an evaluation in the HIGHLY dynamic environment in which trees grow. What we are working off of is an opinion, not verif
    iable research.

  14. Be careful when trying to preserve trees. If the tree already has dead limbs or it is dangerously close to house, consider tree removal for that specific one. Sometimes the tree isn’t worth keeping if it is going to fall on your house.

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