(Cabling and Crown Stabilization)
(Also since proper cable height is critical, the equipment and training to work aloft safely is needed.)
It should be noted also that any tree support system will need to be periodically inspected and adjusted as the tree continues to develop and grow. The cabling, bracing and guying of large trees is a job best left to professionals (no offense to the very capable do it yourselfers out there). The necessary supplies are not available at your average builder’s polygon type hardware store. These often have to be purchased from supply houses and only in large quantities.
It is also important to mention that cabled trees on which lightning protection equipment has been installed, should be electrically bonded to reduce the risk of electrical charges traveling in between the two systems, and causing tree damage. Under extreme conditions, even the best tree support systems can fail, however I have never seen a properly installed cable system fail. I have on the other hand seen many home - made or substandard systems fail, or otherwise make the tree more hazardous than it was before cabling. In some cases where wire, chain or cable was wrapped around the limb-work the tree became girdled and died.
Guying is another type of support system used to stabilize poorly anchored trees that have substandard, partially decayed or otherwise damaged root systems.
If rot or decay is found in a tree, an examination to determine the extent of damage must be conducted before any attempt at cabling or bracing is made. Generally speaking trees or parts of trees with less than 30% to 40% sound wood fiber are at high risk of failure, and should be slated for removal.
The point where cable attachment is made must be large and solid enough to provide adequate support for the hardware. The type of support system needed will depend largely on the unique characteristics and structure of the tree in question. For instance the most common system is the direct cable, which is basically used to join two co-dominant stems or weak branch unions. In trees with more than two competing stems or leaders, a triangular or box type system may be required. Also there is the hub and spoke system, but this system is not often used due to it’s lack of lateral support, and difficulty of installation.
The location of the different cabling and bracing system components is of critical importance. Too high and a ballooning effect may be created below the cable. Too low and it will offer little or no support. Generally speaking, anchors for cabling should be located approximately 2/3 the distance from the damaged or otherwise weak union to the ends of the branch or trunk. Exact placement will depend on the location of lateral branches and defects.
These are high strength machine threaded rods used in conjunction with compression washers and amon-eye nuts to secure a split fork or cracked limb, and to reduce the chance of further degradation.
Cabling restricts the distance that branches can move in relation to each other. Installed across a weak branch union, they can greatly reduce the risk of failure. Installed on over extended branches they can be used to provide supplemental support.
Trees with a tendency to form upright branches such as elm (Ulmus), maple (Acer) and some species of oak (Quercus) often produce weak branch unions.
Ideally many of the factors that contribute to structural failure can be eliminated or mitigated by proper pruning and training, such as the removal of or subordination of co-dominant stems or leaders early on in the first 10 to 25 years of growth, or the removal or subordination of elongated limbs and branches that have out grown the basic shape of the tree creating an imbalance.
Alternately the branch may crack due to the forces of tension and compression. These failures often occur when the branch is subjected to heavy loading such as wind, snow or ice.
Another condition that is associated with structural problems is the presence of long heavy or over extended limbs. These are limbs that are unusually long for the particular species, or grow horizontally or downward with most of the foliage concentrated towards the end of the branch. Breakage resulting from these conditions often occurs at the junction of the branch and stem.
The presence of co-dominant stems is actually one of the most common risk factors associated with structural failure in trees. It is basically where two or more competing stems or leaders are allowed to develop and become large, which in many cases creates a narrow forked branch union. As the tree continues to grow, this branch union inevitably becomes weaker. This is caused by the presence of ingrown or (included bark), which becomes trapped between competing stems or leaders, thus preventing the formation of consistently strong connective wood fiber that would other wise anchor the competing stem to the tree.
Certain conditions predispose trees to structural failure. Some of these are: Tree species, poor tree architecture i.e. (co-dominant stems, trunks or leaders, narrow V- shaped branch unions, root damage and uneven growth. Rot or decay and storm damage can be other factors as well.
Cabling, bracing and guying are tree support and stabilization systems used to provide supplemental support to trees or parts of trees, that are failing or at risk of failure. These systems are designed to reduce the risk of structural failure and the potential for flying lawsuits that can sometimes be associated.
A few of the ways Mother Nature takes care of trees is by allowing weak or defective ones to decay, break and die. It’s a good plan that works well in the forest.
The trees in our urban environments however are another matter altogether. These trees are often growing along our streets, in parks or around our homes and businesses. Sometimes they are grand specimen trees, or are of important historical value. Sometimes they are in high traffic areas where people or animals congregate. It is therefore important to ensure the optimal stability of these trees.
(Trees such as this one are prone to failure because the co-dominant trunks were never addressed early on in the trees life)
(Overly elongated limbs should be subordinated or removed to reduce the likley hood of failure)
(When we install brace rods in trees we use extra high strength non corrosive stainless steel rods like the ones shown here)
(An example of an amon eye nut)
There are also some synthetic poly propylene rope systems coming out of Europe and the US some of these are Cobra, Tree save and Libra. They are faster, non-invasive and are showing great promise. They are dynamic systems that differ from traditional static systems, in their ability to greatly reduce shock loading by creating a bungee cord like effect. These types of systems should generally be used for cabling limb-work that will not put them under constant strain. Ideally they should only come into play when sufficient load is applied.
( Assessing the extent of decay is an important aspect of safe tree cabling )
(Tree Cavity Repair Work)
The subject of tree cavity repair is indeed one filled with differing opinions. Before I cover this issue, it is essential to have a basic understanding of the C.O.D.I.T. model an acronym for compartmentalization of decay in trees. When trees are injured, they respond by a process known as compartmentalization. This theory was developed and greatly expounded by the late Dr. Alex Shigo, who is considered by many among academic circles to be the father of modern forestry techniques.
It is basically a concept of how trees are viewed. Can a tree really heal itself? This was indeed the million dollar question, and subsequently the tree began to be viewed as a highly compartmented system. Each growth ring was a compartment and each compartment was divided into smaller compartments by radial sheets of parenchyma cells. Indeed a single cell by itself is another still yet smaller compartment.It is basically a concept of how trees are viewed. Can a tree really heal itself? This was indeed the million dollar question, and subsequently the tree began to be viewed as a highly compartmented system. Each growth ring was a compartment and each compartment was divided into smaller compartments by radial sheets of parenchyma cells. Indeed a single cell by itself is another still yet smaller compartment.
(Cross sectional veiw of a hardwood tree showing various layers)
(Veiw of living parenchyma cells under magnification)
This process of compartmentalization begins as the tree responds to injuries by setting chemical boundaries that resist the spread of decay causing micro-organisms. By producing and trans-locating certain chemical inhibitor compounds to the cells in the area of wounded tissue (mostly phenols in broadleaf trees and turpenes in conifers). The tree attempts to slow down the spread of potential pathogens. These chemical boundaries also serve to buy the tree enough time to produce a new layer of woody tissue thereby containing or sealing off the infected area, and so they do not heal as do animals and people they form barriers around wounds and abrasions.
(The pruning wound on this eucalyptus tree has compartmentalized very well)
This does not come without a cost to the tree however as it sacrifices the infected areas and can no longer use this space for storing or accessing energy reserves. There are four barriers or walls that form after injury wall 1 resists vertical spread of pathogens. Wall 2 resists inward spread, and wall 3 resists lateral spread. Wall 4 resists outward spread. Walls 1 through 3 are chemical boundaries, and wall 4 is the next layer of wood tissue formed after injury. Wall 1 is the weakest and wall 4 is the strongest. This is due to anatomical features. Shown here is Dr. Shigo’s C.O.D.I.T. model.
Improper pruning techniques namely flush cuts where the entire branch protection zone is removed, are a major contributor to the formation of large cavities that do not compartmentalize.
(Flush cuts like the ones shown here are major contributors to the formation of decay cavities in trees) (The example in the center clearly shows how removal of the branch collar impedes wound closure in this case the branch collar was left intact only at the sides depicted by the arrows)
These defects then become infection courts giving aggressive pathogens un-obstructed access to the tree.
(Here you can clearly see the infected wood in this cross section of an oak tree stump. The infection was started 10 years earlier when a flush cut was made to remove a large basal branch. Notice that only tree growth after the time the cut was made appears normal (no discoloration or decay). This is a fine example of the boundry setting principle at work)
That being said proper pruning techniques would go a long way towards reducing the incidence of large open tree cavities in our urban forests. In most cases tree cavities should be left alone and not tampered with.
There are instances however, where a tree cavity can be effectively repaired. If and when we treat tree cavities we do not fill them we seal them by using a heavy fiberglass matting and resin with a hardening agent to implement repairs. This provides the new cambial growth with a smooth interface of reduced size to grow and develop on thereby speeding wound closure.
(A properly repaired tree cavity)
(This disection of a tree branch shows the demarcation line between the healthy sapwood that formed after the flush cut was made. Note this in contrast to the discolored wood that developed as a result of improper pruning)
In the old days tree cavities were often filled with concrete foam or some other substrate this is not a practice that we would recommend, as it can create breeding areas for harmful insects fungi and bacteria along the interface between the living tree itself and the medium used to fill the cavity.
(Before and after pictures of a properly repaired tree cavity)
(Pictured here are some examples of different cavity repair jobs. The two on the left were done with concrete obviously not a good choice if future pruning and cutting are to be done. The example on the right was done with expansion foam which only serves to trap moisture and create conditions favorable to the development of mold and certain bacteria)
Also there was the drilling and installation of drainage tubes to remove standing water from tree cavities. This practice should also be avoided, as it will only serve to spread decay further outward into the developing new woody tissues. In-fact the presence of standing water in a tree cavity often creates a sterile environment that helps to resist further degradation.
Tree species is another important consideration, regarding the treatment of tree cavities as not all trees are good candidates for this procedure. When deciding to repair a tree cavity it is advisable to hire a professional. It is critically important not to disturb existing boundaries when preparing a tree cavity for repair. Only the removal of punky partially digested wood tissue is advised.
It is important to remember that the improper treatment of tree cavities can do more harm than good. When in doubt doing nothing is better than acting. If you have a tree cavity that you are concerned about don’t hesitate to call us. We can advise you on whether or not treatment is necessary or even a good idea. When it comes to crown stabilization, tree support systems and tree cavity repair, Hurricane Tree Specialists has the knowledge and experience to ensure a safe quality job. We can advise you on which trees will benefit and can properly design and install the correct system for your particular application.
(Dr. Alex Shigo photo courtesy of the shigo family)
Because one cable will not necessarily prevent a branch from twisting or shearing off at the junction, it is sometimes a good idea to install more than one cable or a combination of cables and brace rods.