Photos by Michael (House) Tain.
Unlike their peers in the logging industry, who typically work in rural, isolated locations with few objects that can be broken or destroyed other than themselves or other trees; tree care professionals working in urban and suburban settings tend to conduct their work in a “target-rich environment,” surrounded by man-made objects and structures that create a virtual maze through which they must safely get wood to the ground.
This need is often addressed by climbing or accessing the canopy through mechanical means and removing the tree in various pieces and parts through rigging techniques. However, there are more than a few occasions when a tree might be removed more efficiently and safely from the ground through the use of directional felling techniques. Directional felling techniques are quite effective with the appropriate experience, training and knowledge, but more often than not, tree crews will be presented with trees whose natural lean has no inclination to carry it into the required safe landing zone. This situation is when knowledge of some of the various methods of assisting lean can be invaluable to accomplishing a safe, efficient felling operation.
|By encompassing the entire biomass of the tree and dividing it in half, felling arborists can determine that no lean is present, even though the trunk seems to present one (left) or they can determine that a lean is present (right) even though the trunk is straight.|
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, and though 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 further 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.
Although tree crews typically have access to rigging or pull lines to assist lean in felling operations, there may be situations when wedges are all that are available. Wedges are either 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 that help keep them in the kerf when being driven in to provide lift, while 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 into 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 100 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 more than two are required by the lean situation. 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.
|Wedges are stacked to assist in overcoming an extreme back lean by using slots created through bore cuts.|
|Driving wedges stacked in slots to prevent them “spitting” out.|
The use of pull lines with equipment providing the momentum force, such as trucks or skid steers, leads to a situation where the amount of force being exerted on the top of the tree being felled is extremely difficult to determine, and can lead to catastrophic failures in ropes, trees or other gear. A much better choice would be an assortment of blocks or pulleys used to create a mechanical advantage system in which the individual’s force is multiplied to provide the momentum to pull over the tree. Although tree crews will most commonly use pull lines when assisting or overcoming lean in felling operations, an ability and knowledge to use wedges is yet another tool to have in the mental toolbox, ready and waiting for the appropriate situation to lead to a safer, more productive day.
Michael (House) Tain is a contract climber, splicer, educator and writer currently located in Lancaster, Ky.