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A key component of the five-step felling plan is the lean of the tree. Lean must always be evaluated when formulating the plan to get the tree on the ground. But then the crew must also have the skills, tools and techniques to manage the existing lean, or even overcome it, in order to get the tree safely and efficiently on the ground in the chosen landing zone.

Managing Lean in Felling Operations

By Michael “House” Tain


A key component of the five-step felling plan is the lean of the tree. Not only will a lean ignored likely make for a much longer day for a tree crew with possible property damage, it is often a culprit in injury accidents — and sadly even deaths — among tree crew members. Lean must always be evaluated when formulating the plan to get the tree on the ground. But then the crew must also have the skills, tools and techniques to manage the existing lean, or even overcome it, in order to get the tree safely and efficiently on the ground in the chosen landing zone.

The Tree Felling Primer does an excellent job of introducing and explaining the basic components to getting a tree on the ground; and explains how to evaluate the lean and determine the “good” and “bad” side of the tree. This article will help tree care professionals understand some of their options in dealing with the lean they have just discovered in their evaluation of the targeted tree.


Directional felling and lean

Directional felling is simply a fancy term for an activity that most professional arborists are intimately familiar with — getting a tree, large piece of wood, or even top to fall in the direction desired in a fairly controlled manner. Obviously, the first step in directional felling is determining in which direction to fell the tree. Factors such as height, hazards, obstacles, chipper access and others will all play a role in figuring out where the crew wants the tree to end up on the ground, but lean of some sort will always be the most important part of this evaluation.


Side lean


Above: A tree with obvious side lean to the left side of the picture.
Below: The same tree but from a different angle, thereby turning the dangerous side lean into back lean that can be overcome with mechanical advantage, pull lines and wedges.

This type of lean is the largest challenge that production tree crews face during felling operations. To ignore its existence, or not even notice it, can only lead to bad things happening. A basic description of side lean would be that it is visible lean or canopy weight to one side or the other of the direction of fall. Side lean is so challenging to overcome and manage for the simple reason that gravity is the law on this planet, regardless of the state or province in which the tree crew is working. As a tree comes over in felling operations, even if it is straight up and down, the hinge is weakening, fibers are popping and cracking as they bend, and the additional gravitational pull line of side lean to one side or the other is insistently dragging the mass of the tree that way as the hinge weakens. Many crews have watched a tree begin its graceful journey to the earth in exactly the arc desired, only to see it suddenly head off to one side or the other before it hits the ground. The explanation — side lean that was not prepared for or managed overcame the fibers of the hinge before the tree could get all the way down, and gravity finished the job. Although a certain degree of side lean may be overcome through the use of more technical methods such as guy lines and support ropes, the simplest way to deal with it is to eliminate it by turning it into front or back lean.


Front or back lean

This is a type of lean that is visible standing out and away from the tree at a 90-degree angle from the direction of fall. In its most basic form, front or back lean would seem to either help or hinder the safe and efficient felling of the tree. Although both have individual challenges that must be dealt with, in general, front or back lean of a fairly large, though still not insane, amount are much more easy to deal with than a smaller amount of side lean. For this reason, whenever possible, the crew should decide on a direction of fall that eliminates side lean altogether or turns it into its friendlier cousins of front or back lean.


How much is the lean

As has been discussed in other articles, and as is mentioned in the Tree Felling Primer, taking the whole canopy of the tree into account and using an imaginary “plumb line” through the center is imperative for determining just how much lean is being presented as a challenge. Although some may view knowing how many feet or meters of lean are being dealt with as a bit “over the top,” this information can be vital to making sure the top ends up in the right place. A knowledge of how much lean exists, whether side, front or back, is extremely important in determining such factors as aiming point adjustments for side lean, barber chair tendencies in front lean, and wedge needs/mechanical advantage requirements in back lean. Wherever the center of the imaginary “plumb line” falls from the base of the tree is the amount of lean that has to be dealt with. Discovering once the sawdust is flying that the “good enough” estimate was a bit off is not the route to tree felling success.


Pull lines

The use of some form of line is the most common way to overcome lean in the tree care industry; and though most crews are probably more than a little bit familiar with this method, a few basic principles can help make its use more successful and safe.

Line placement: Although an isolated line — one maneuvered in such a way that it is around the trunk of the tree’s top is certainly desirable — it is not strictly necessary. A line high into the canopy — as long as it is over some significant and strong enough branches, then returned to the ground to be tied above the chosen felling notch point around the trunk — will often prove more than adequate in pulling the tree over. In fact, there is some thought that this manner is more effective by pulling all along the length of the trunk instead of just isolated at the top. In addition, higher in the tree almost always provides more leverage, with care obviously taken to avoid putting too much pull on too small or too weak a top. So effort should be made to use those throwline skills to place the line where some true leverage will be available.
Pulling: One of the most common issues in pull line use, and often with the best of intentions by the pullers, is “over” pulling or pulling too soon. Very little pressure, if any, should be put on the pull line until the cut is set-up and ready to go. The feller or chain saw operator should be the sole person in charge of determining when pull needs to be applied, and some form of communicating that to the pullers should already have been determined and in place. Should the tree settle back on the saw pinching it, the feller can have the crew put some more pressure on the line lifting it off, but over pulling early can create some dangerous hinge and wood fiber problems including barber chair.
Force: Using equipment, whether it be trucks, skid-steers, or some other mechanized monster, though tempting, is a recipe for broken lines, broken tops, and broken crew members. The reality is that even the best driver in “The Chase” would be hard pressed to “dial in” exactly the amount of force and tension to pull over a tree under control in felling operations. A much better option is using ropes, blocks and pulleys to create mechanical advantage, and more easily adjustable manageable force to pull the tree over. Should equipment still be used, the operator should keep in mind that all that is required is enough force to slowly get the tree headed in the desired direction, a well cut notch/hinge, and gravity will take care of the rest of the motion.



As already mentioned, tree crews are most often going to overcome the lean of the tree through the use of pull lines, but there may be occasions where going “old school” with wedges is the only option, perhaps after an aspiring Smoke on the crew broke the pull line with the truck; and another tool, such as wedge use, in the mental toolbox is always valuable.

Types: Though wedges are available in both plastic and metal, plastic wedges are probably the most economical and saw-friendly choice for arborists, with the additional advantage of being lighter weight. Wedges also come in either bucking or felling forms, with bucking wedges intended for use in bucking up logs or wood on the ground and felling wedges, as the name suggests, for use in felling trees. Bucking wedges are smooth to allow them to be knocked out of a severed log fairly easily, while felling wedges have “dogs” or small raised bumps on them that are intended to assist in keeping them in the chain saw kerf while being driven in to provide lift.
Lift: As stated earlier, the feller needs to know how much lean he or she has to overcome; and this information in turn will help them determine how many wedges are needed. A typical wedge will provide about one inch of lift at the back cut when driven in all the way — thereby providing a rough approximation of how much the top of the tree will move. In general, a 50-foot-tall tree that is 12 inches in diameter at the face notch will have about 50 12-inch sections in it, so each wedge driven all the way in should move the top about fifty inches forward, so one wedge can overcome about fifty inches or four feet and change of back lean. Once again, this is a rough approximation, and depends on how well the lean, height, diameter of the tree, etc. were determined. So if the calculations say one wedge should be enough, a second would be a very good idea.
Stacking: Trying to stack wedges atop one another in the chain saw kerf is often a quite challenging process; and wedges “spitting out” when the feller is trying to drive the tree over can make for stressful days. A better option is to cut slots for the wedges even prior to the back cut, this will help prevent the wedges spitting out; and enables the chainsaw operator to use as many wedges as required for lift. The slots should be fairly close together and in line as much as possible, as this will allow the wood between them to split and lift upward.


Just as evaluating for lean is a key component to a well-designed five-step felling plan, managing whatever lean is discovered is vital to getting the tree safely and successfully on the ground. Although lean management can provide particular challenges, a knowledge and understanding of the techniques and methods described here, coupled with hands-on training and practice, will lead to overcoming it in the safest, most efficient way possible.


Michael “House” Tain is a contract climber, splicer, educator and writer associated with North American Training Solutions www.northamericantrainingsolutions.com  and Arbor Canada Training and Education www.arborcanada.com. He is currently located in Lancaster, Ky., and can be reached via e-mail at house@houseoftain.com

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