Hazard or danger trees are one of the most dangerous challenges tree crews with chain saws face. They represent a challenge that can quickly and violently go bad with catastrophic results, particularly if not recognized as hazard/danger trees in the first place, but even more so if removal or release is attempted with the usual tools/techniques used in standard felling operations. The hazard/danger trees being discussed here are not the upright, still-standing specimen firmly rooted in the ground. These trees are ones that, through natural forces or otherwise, have lost their bearings and footing, and are lodged on a utility line or pole, a house or structure or simply in another tree.

This type of hazard tree could be created by the high winds of a storm or a heavy snow load, snapping the tree’s trunk or causing a complete root failure and subsequent fall into or onto whatever it hangs up on. They may also be created by errors in judgment or technique in felling operations, where the side lean was a bit more than reckoned, or the height estimate just a tad short, leaving the tree not on the ground, but also not upright like it once was. Regardless, the forces at play throughout it have changed radically, and a failure to recognize and evaluate these forces in order to use specialized cutting techniques to release or lessen them can often result in a chain saw operator dancing around with the tree trying to avoid the impact of large, woody debris. A few basic principles and techniques can help tree crew members avoid this less-than-pleasant experience.

The two primary forces within a tree that chain saw operators need to be aware of are compression and tension. These are present whether the tree is upright, horizontal on the ground or lodged atop Mr. Smith’s ranch house portico. The difference is that as the tree’s orientation changes, so does the location of these forces, along with the reactions they produce when released, intentionally or otherwise. On a broad scale, trees develop tension and compression wood to compensate for varying conditions and needs, providing strength and support where needed. A simple example of these forces would be a tree with a lean to the right as it is looked at.

The wood on the right side of the trunk (under or with the lean) will most likely be under compression, while the wood to the left side of the trunk (opposite the lean) will most likely be under tension. Now, say this same tree has been blown over in the direction of its lean and the top is lodged in another tree. In all likelihood, the compression is now on the upper or left side of the tree with the tension on the lower or right side of the tree. A failure to recognize these changed forces and adapt the cutting plan to them will lead to stuck or pinched bars at best, and serious injuries at worst. An excellent acronym to remember the order in which to sever fibers under tension or compression, developed by the instructors at Arboriculture Canada Training and Education, is CUT.

  • C: Begin the cut on the compression side,
  • U: “U” are in the middle,
  • T: Finish the cut on the tension side.

A key notch completed with wedges in the bottom horizontal cut. The wedge on the side being pulled toward would need to be removed prior to pulling. Photo: Michael Tain

The dance floor

Accident statistics in felling operations have shown that 90 percent of injuries or deaths occur in the first 15 seconds of movement within a 5-foot circle of the stump; this is a dance floor arborists don’t want to be “busting a move” on. An easy way to remember this is as the 5-15-90 rule: 5 feet of the stump, first 15 seconds of movement, 90 percent of accidents. While every action possible should be taken to move off that dance floor quickly during standard felling operations, it is, if anything, even more vital when dealing with a hazard or danger tree due to the instability of the tree and changes in the tension/compression forces. The use of cutting methods and release techniques that allow arborists to be outside this 5-foot circle when everything breaks loose is highly recommended, and should be attempted whenever possible. Push sticks, ropes, winches and mechanical advantage systems are tools that will assist in releasing cuts that have already been setup, and doing so from a safe distance.

Mismatch cut

The simplest cutting technique to use on a danger tree is the mismatch or bypass cut. It is similar to the technique used when snapping off wood aloft in “cut and chuck” operations, with one major exception. Operators should not attempt to snap off the hazard or danger tree by hand. Rather, the use of a pull rope or push stick allowing the operator to be well away from the 5-foot circle at the moment of release is much safer, and in many cases, easier. The mismatched cuts are made from opposite sides of the tree, much like on a horizontal branch when aloft, thereby avoiding the tension and compression fibers, typically on the top and bottom of the tree, as much as possible; and the amount of overlap or bypass, along with the distance between the cuts, will vary with diameter and wood strength. Users will find it much easier to snap off the cut if it is pulled or pushed in the direction of the side with the lower cut.

This technique, slightly more complicated than the mismatch, is used to attempt to fell the tree out of, or off of, the obstacle it is lodged in (it can be quite useful when dealing with trees on utility lines). An open-face notch of at least 90 degrees of opening is cut on the upper side of the tree, after which a hinge equal to 5 percent of the diameter of the tree is created through the use of a bore or plunge cut. In a standard felling operation with an upright tree, the holding strap would be severed at level or below the hinge, but in a hazard/danger situation, this would require staying on the dance floor, a location to be avoided. This can be accomplished by using a mismatched back cut beneath the level of the hinge. Wood strength and diameter will once again affect the distance between the two cuts, but, in general, the further below the bore cut, the greater the amount of force that will be required to release the cut. The knee cut or knee hinge demands a full evaluation of the tree’s forces prior to being implemented, as factors such as the root plate still being attached or a great deal of top or weight overhanging a utility line will prevent the cut from working correctly, making a different specialized cutting technique a better option.

Side view of a knee cut or hinge. The final mismatched back cut would be stepped down below the level of the hinge/bore cut. Photo: Michael Tain

This technique, the most complicated and gear-intensive of the ones discussed here, can be extremely useful in particular hazard/danger tree situations. Through the use of bore cuts and standard cuts, a tongue or key is created within the tree that “locks” the two parts of the tree together, allowing them to be pulled apart from a safe distance at a time of the user’s choosing. The weight and forces involved will most likely, if not definitely, require a winch or some form of mechanical advantage to pull apart, so if those tools are not available, a different technique would be a better option. The tongue or key created should be at least the diameter of the tree, with a tongue of greater length providing more friction, strength and security. The tree is divided visually into thirds from the side: the center third will be the key, with the outer edges of it being the initial two bore cuts to the desired length of the key. The next step after completing the bore cuts outlining the sides of the key is to make a horizontal bore cut at one end or the other connecting both sides of the key.

Placing wedges in this horizontal bore from both sides will add support, and help prevent “pinching” when the final two cuts are completed. The first of the final cuts is made from the outside of the tree to the edge of the vertical bore cut that created the key on the compression side of the wood, a wedge in this cut may be helpful when carrying out the final cut. This final cut is then made on the tension side of the wood from the outside of the tree to the other vertical bore cut. If done correctly, the tree should now be severed into two parts, but secured or locked together by the key or tongue and groove created. Once the wedges have been removed from the side it’s being pulled toward, it can now be pulled apart from a safe distance with a winch, mechanical advantage or other appropriate force.

These specialized cutting techniques can be valuable, but they must be understood and practiced extensively prior to their use in a live situation, as a misstep or fall is one the chain saw operator might not get back up from. However, with practice and training, the principles and techniques discussed here can help tree care professionals deal with a wide variety of hazard and danger trees quickly, efficiently and, most important of all, safely.