Tree care industry chain saw operators work in a more challenging or at least more target-rich environment than their cohorts in the timber industry. These targets can range from the house itself to high-voltage lines all the way down to the homeowner’s prized azalea collection. Many times the tree will require climbing/aerial access and/or rigging to deal with all these obstacles, but in the interest of safety and efficiency this may not always be the case.
A tree that can be put on the ground safely by a well thought out five-step felling plan is one that is going to be finished more quickly and with minimal exposure to the crew of the dangers of climbing and rigging. Directional felling in an urban/suburban environment is often going to involve either assisting the natural lean of the tree or overcoming its natural lean to fell it in the safe and desired landing zone. Assisting lean is a topic that can be invaluable in these situations, and, once understood and practiced by crews, it can be beneficial in getting trees down safely, quickly and in the right place.
Before a crew can even consider assisting or overcoming lean, they must understand what it is and how to estimate it. Climbing arborists carrying out felling operations must evaluate lean fully and completely prior to making the first cut.
The two types of lean that will affect the fall of the tree are front or back and side lean. Lean can only be evaluated correctly out and away from the tree, where the majority, if not all, of the canopy and trunk can be seen. When evaluating lean, all of the biomass of the tree should be taken into account, meaning the entire extent of the canopy and trunk.
Forward-leaning trunks can be misleading when offset by a large amount of canopy and foliage opposite the lean. Front or back lean should be evaluated at a 90-degree angle from the desired direction of fall, while side lean should be evaluated from the intended landing zone.
Side lean is an arborist’s greatest challenge in felling operations. Although a small amount may be overcome, a far better and safer option is to attempt to fell the tree in a manner that eliminates side lean as much as possible, as the farther the tree comes over and the weaker the hinge becomes, the more the tree will tend to fall in the direction of the side lean, gravity being the law no matter where you go.
If no other option is available, significant side lean can be dealt with through the use of more sophisticated and technical techniques such as guy lines and support ropes.
The most common way to influence lean in the tree care industry is through the use of a pull or “tag” line. While most tree care crews have a great deal of experience with this method, a few basic principles will ensure the proper use of pull lines.
High – As long as the structure of the tree will support it, a line placed higher in the canopy is going to have a greater effect due to the leverage produced.
Isolation – Having the line isolated around the trunk of the tree is often what most crews attempt to obtain. However, personal experience has shown that a line placed high in the canopy with one end being used to instill the pulling force with the other following the line of the trunk and secured directly above the face notch can be just as effective.
Length – Though it might seem quite obvious, a height estimation of some accuracy is key when using pull lines. More than a few branch managers have discovered the inadequacy of their pull line length and had to explore their inner sprinter in the midst of felling jobs.
Force – In the case of pull lines, more force is not necessarily better. A large number of directional felling attempts with pull lines go south due to the use of trucks, skidders or other equipment becoming involved in the pulling process. A far better option is some form of mechanical advantage system or fiddle blocks with a sturdy anchor that allows the force to be applied gradually, nearly impossible if a foot and accelerator are involved unless your name is Danica Patrick.
Timing – Timing is everything in pull lines. Pulling on the tree too early or too late in the process can lead to everything from broken tops to barber chairs to the tree going in the opposite direction. Only after the chain saw operator has set up the desired thickness of hinge should the pulling begin, typically at the operator’s signal.
As mentioned previously, tree care crews typically have access to rigging or pull lines to assist lean in felling operations, but at times there may be situations when wedges are all that are available. Wedges can be plastic or metal, and are an excellent option in assisting lean. Plastic wedges are probably a better choice for most arborists due to their relative affordability, and the fact they cause little or no damage to the chain when inadvertently struck by the saw.
Both felling and bucking wedges are available and, as the names suggest, have very different applications. Felling wedges have small raised bumps, or “dogs,” on them, which help keep them in the kerf when being driven in to provide lift. Bucking wedges are smooth, allowing them to be removed fairly easily from a log being bucked up on the ground.
Typical-sized wedges will provide approximately 1 inch of lift at the back cut when fully driven in to the tree, thus fellers must be able to calculate how much movement that will equate to at the top of the tree to overcome existing back lean. A rough approximation of lift or movement at the top of the tree can be determined by evaluating the diameter of the tree at the location of the face notch and dividing the height of the tree into those sized sections. For example, a tree with a diameter of 12 inches remaining after the face notch has been cut that has a height of 100 feet will have one hundred 12-inch sections. This will result in 100 inches of forward movement when one wedge is driven fully into the kerf. This fairly simple calculation will help felling arborists know exactly how many wedges they need to use to overcome back lean.
An additional concern for fellers is how to effectively stack wedges when more than one is required. Wedges stacked upon each other tend to “spit” out when being driven in, particularly when the situation requires more than two. The practice of cutting slots for wedges eliminates this propensity to spit out, and allows fellers to set wedges prior to completing the back cut. These slots can be cut using a bore or plunge cut technique. If the diameter of the tree allows, the slots should be of sufficient depth to allow the wedge to be driven completely in to achieve the greatest amount of lift.
When lean is correctly evaluated during the five-step felling plan process, it should become obvious whether or not some “assistance” will be needed. While each climbing arborist will have to develop their own skills in evaluating how much lean can be overcome, the basic principles and techniques described here provide a starting point with the materials typically available in a tree truck to get that tree to fall in the desired landing zone, leaving those expensive targets untouched.