As more than a few tree care professionals have discovered to their dismay, side lean in felling operations is one of the greatest challenges to overcome successfully. It has, unfortunately, led to more than its fair share of unintended consequences, including damaged property and, sadly, even injuries and death to crew members and civilians.

There are a variety of techniques and methods that can be effective in dealing with side lean, all of them dependent on the severity of the lean and ranging from the simple to the complex. Some have been discussed in previous columns; and though this column will discuss many of them, the primary focus will be on the most effective, yet complex one, guy lines.

The use of guy lines in felling operations, once understood and practiced, is certainly an effective way to minimize or negate the impact of side lean, but as climbing arborists work with living organisms with their own personalities and an often hidden inner structure and associated defects, care must be taken to set up and use this technique correctly to minimize risk as much as possible, otherwise the land of “bad things” may soon be visited.

A tree with obvious side lean if it was to be felled in the direction of the viewer.

Side lean

An examination of the tree to be felled for side lean is a vital and integral part of the five-step felling plan; and one that cannot be done in a haphazard manner. Side lean should be evaluated out and away from the tree, not at the base looking up the trunk, as this method can often lead to incorrect judgment of the amount of side lean. Although the best place to examine a tree for side lean is from the desired landing area, the feller should examine the tree from all sides, as this may illustrate easier felling directions; and they must take into account the entire structure of the tree, not just the lean of the trunk, as can be seen in the accompanying illustrations. The leverage provided by weighted limbs within a tree’s canopy will affect the way it wishes to fall greatly; and if ignored will most likely result in the tree landing in a different area than intended.

Side lean into back lean

This method is one of the simplest ways to deal with side lean, so simple that it often seems like a magic trick. As an example, if a tree, when examined from the intended landing area, has a significant amount of lean to the left, if possible, fell the tree to the right, thus turning the dangerous side lean into back lean. This is a much easier obstacle to overcome in felling, assuming that the tree is fairly structurally sound and has existing good wood fiber in the proposed hinge area. The use of throw lines, pull lines, mechanical advantage and wedges all make overcoming back lean without ever leaving the ground a much easier prospect than dealing with side lean in any way, shape or form.

Face notch and aiming point

Minor amounts of side lean can often be dealt with by the feller simply changing the aiming point while cutting the face notch. For example, if a tree has an estimated side lean of 3 feet, the chain saw operator would want to move the aiming point from straight out into the landing area to 150 percent, or 4.5 feet, in the direction opposite the lean.

In addition, a wedge placed firmly in the back cut on the “bad” side, or the one with the side lean, will help support the hinge as the tree is felled. This wedge should not be pounded in with any degree of vigor, as this may weaken or separate the hinge on that side; its purpose is support as the tree begins to move and tries to sag to the side with the lean. Once again, this description assumes the tree to be felled has decent structural integrity and good hinge fiber and will be nowhere near adequate when dealing with severe side lean.

An example of apparent lean when just looking at the trunk. In reality, the canopy balances out the trunk, meaning that little or no lean exists that would affect the felling plan significantly.

Guy lines

The intention of guy lines in felling operations is to support the tree as it goes over, preventing it from obeying the law of gravity and falling in its naturally intended direction, toward the existing side lean. Obviously, the guy line should be placed perpendicular to the direction of fall and opposite the tree’s side lean. The higher in the canopy the guy line is installed, the greater its effectiveness. Though this can often be easily accomplished from the ground through the use of a throw line, care should be taken not to have the guy line so high that the wood is too small to support the rest of the tree, or in a structurally unsound area.

Ropes used or intended for guy lines in felling operations should have a minimum amount of stretch, or elongation, coupled with excellent strength, due to the forces and vectors the guy line will be exposed to. As an example, a rope such as Samson Amsteel Blue with less than 1 percent elongation at 30 percent of breaking strength and excellent strength-to-size ratios is a good choice for guy line applications.

The individual felling situations and sites will dictate how far away from the tree the guy line can be anchored, but a rough guideline for guy lines is: the farther the better. The goal is to accomplish a supporting force as close to opposite of the side lean force as is possible; and a line closer to the base of the tree is pulling downward rather than horizontally. The path of the tree to be felled and the guy line tied to it should also be examined for obstacles, as the guy line hanging in another tree or on a branch during its fall to the ground could change the planned outcome dramatically.

Some method of pretensioning the guy line — mechanical advantage system, come along, GRCS — will be necessary, along with a suitably strong method of securing the tensioned guy line, such as a Port-a-Wrap. The forces the guy line may be exposed to make the use of knots or hitches at the guy line anchor point not only a point of possible failure and disaster, but should they survive the operation, may result in a “knife knot,” virtually impossible to untie without the use of a sharp-edged tool.

The tension applied to the guy line should not only remove all slack from the line itself, but also cause very slight movement opposite the side lean of the tree to be felled. Care must be taken to not over tension the guy line, possibly creating shearing forces within the wood fiber of the tree and hinge. The guy line is meant to simply be a supporting force or vector counteracting the side lean, not a pulling force overwhelming the tree’s structure.

The use of wedges on the “bad” side of the tree is still desirable when using a guy line, as it will provide additional support for the hinge wood on that side possibly preventing the hinge from collapsing, but, once again, the wedge should not be driven in with too much force as that might lift and separate the hinge on the side it is needed most.

The same tree with the side lean turned into back lean simply by changing the direction of fall.


The use of guy lines in felling operations is certainly a complex undertaking; and one that should not be undertaken lightly, or in a situation with multiple targets without additional field-based, hands-on training and practice. Both Arboricultural Canada Training and Education and North American Training Solutions offer courses in hazard and danger tree cutting and felling that cover the use of guy lines in felling operations that can provide practice in a controlled environment and face-to-face interaction with experienced users that this column cannot.

If a formal course is not a feasible option, practicing the technique on trees with less severe side leans in open areas with no targets may provide the hands-on experience and acquired knowledge necessary to use the guy line technique effectively when there is little or no margin for error. However, even when practicing, all crew members should take the necessary precautions for their own personal safety and well-being. Felling trees with side lean is dangerous, no matter the circumstances.

As stated previously, side lean is probably the professional tree crew’s greatest enemy, and even threat, during felling operations. However, by using some of the techniques and methods discussed here, arborists can confront that enemy with the tools, both physical and mental, they need to handle the situation in a safe, efficient manner.