Tree removal: how to dismantle a tree
Among arborists, tree removal is considered its own specialty. Dismantling technique requires a great deal of experience, intimate knowledge of tree behavior, working well as a two person team, and using the right gear. To better understand this profession, we traveled to a work site in the South of France to meet with Laurent Pierron, an arborist who took us step by step through the process.
June 24 2016
When is the decision made to remove a tree?
In some cases, felling a tree is just not possible in the environment where it is located, for example, in urban areas where a tree falling presents too great a risk. This is the case for our current work site, a property owned by the city of Valence (France). The only viable solution is to carefully dismantle the tree, which we plan to cut into pieces from top to bottom.
Preparing the work site
At tree care sites, whether pruning or any other type of work, we put together a risk prevention plan ahead of time that involves assessing the health of the tree, understanding the limitations of the surrounding environment, determining how to handle waste from the dismantling, making a gear list and deciding on the number of arborists needed, and preparing the signage for the safety perimeter.
Choosing the right weather window
Tree work requires ideal weather conditions. A tree is a living being that moves, and as such an arborist climbing through the canopy has to operate in a moving environment. Strong winds or rain can make their work a complex endeavor. Current legislation in France prohibits tree work in an orange or category 3 rated storm. If, for example, there are thunderstorm warnings, the work site is shut down immediately.
The main steps in the dismantling process
- Accessing the top of the tree by traditional means: tossing the throw line, placing the ascent rope, and then climbing.
- Installing the false crotch at the top of the tree. The climber-arborist, now operational at their workstation, takes care of setting up the block rigging system (pulleys and ropes) to guide and control the speed of the tree sections all the way to the ground. During this step, the person at the base of the tree prepares the necessary equipment on the ground: the rigging bollard, installing the pull and guide ropes, and preparing the chainsaw.
- All of the branches are cut from the base towards the top. Once the systems are installed in the tree and on the ground, the work dismantling the tree can begin. The lower branches are always cut first, and then the arborist continues to cut and climb towards the top of the tree. This technique allows each cut branch to drop directly to the ground without any obstruction.
- The trunk can be sawed into pieces. Once the top of the tree and the branches are clipped, the trunk is cut up into pieces; the length of each piece is calculated based on diameter and weight.
- An arborist is held in place at their workstation by using a reinforced adjustable positioning lanyard. The Petzl MICROFLIP, designed for tree dismantling, consists of a rope made with a cable core. It makes climbing easy and chokes the trunk by using a Prusik hitch to protect the arborist in case the trunk splits. The risk of the trunk splitting when dismantling a tree is very real. For arborists, this choking mechanism has been required in France since 2007.
- Below the reinforced lanyard, the arborist positions a second anchor using the rope and a ZIGZAG mechanical Prusik in a rigging bollard. This serves as both a backup belay system in case the reinforced lanyard is cut by the chainsaw, and as the rappel line to the ground.
- Arborists keep themselves stable by bracing their feet against the tree with the help of spikes (or spurs). Note that spikes are only used when dismantling a tree..
Carrying a chainsaw
A chainsaw often weighs more than 8kg. This is important to take into consideration when managing the physical effort that comes with dismantling a tree; it is much more comfortable to carry weight on one's shoulders than at one's waist. The shoulder straps for the SEQUOIA SRT harness take much of the chainsaw weight off the waist and distribute it onto the shoulders.
Block rigging: a delicate maneuver
The block rigging system allows a controlled lower of a tree section. A load line is tied around the middle of the section to be lowered; this rope passes through a pulley held in place by an anchor either at the base of the tree or via a zip line. At the base of the tree, a friction cylinder is installed to control the section of the trunk being lowered. Preparation consists of determining the number of times to wrap the rope around the friction cylinder. This is a critical step, requiring considerable experience to calculate the number of wraps based on the size of the load being lowered. The person at the base performs a controlled lower; the section of the tree being lowered should never just fall straight to the ground. The load should never be locked off either, which would create a great deal of swing weight for the tree and a yoyo effect on the climber. When using a block rigging system to dismantle a tree, the arborist-climber and person on the ground most coordinate with each other. The person at the base of the tree manages the friction system, and it is not always easy to see the loads tied by the climber. The climber has the responsibility of providing accurate information. Given the constant noise from the chainsaws and shredders, it is much easier to use helmets with an integrated radio.
Mémento de l’arboriste, Copalme : C. Ambiehl, A. Gourmaud, F. Salvatoni, Naturalia Publications.