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Trees are an important part of the ecosystem but sometimes they need to be removed as part of a responsible management plan. When it comes to felling a tree, it is as much art as it is science.

Tree Felling Primer

By Cary Shepherd


 


Trees are an important part of the ecosystem but sometimes they need to be removed as part of a responsible management plan. When it comes to felling a tree, it is as much art as it is science.


Before firing up the chain saw, a plan must be put into place. Pre-operation planning for chain saw safety starts with the right equipment for the job, safety apparel, and emergency preparation. It is imperative to know the answer to the question “what needs to be done if an emergency occurs,’’ and develop a plan for specific situations. This will help identify potential hazards beforehand, and create an organized response if an emergency occurs.


A first-aid kit on site, cell phone programmed to the nearest emergency care facility, directions and distance to that facility, and local utility contact numbers are a few basic components to a good emergency plan. Whether in the back yard or the back 40, never work alone.


Although it is mandatory for professionals, anyone using a chain saw should include personal protective equipment (PPE) as part of their plan. A properly outfitted operator wears protective chaps or pants, eye and ear protection, appropriate footwear, work gloves, and a helmet with visor. The proper protective equipment cannot eliminate the risk of injury completely, but it can reduce the severity of an injury should an accident occur.


Before pulling the cord, it is important that users conduct a visual inspection of the saw, looking for any damage or leaks. Here are some core areas that need to be addressed:


External — Look for cracks, leaks, lose hardware and modifications to the saw. Check the chain tension so that it does not sag from the underside of the bar, but can still be rotated by a gloved hand. Make sure the muffler is securely attached, and check for a broken or worn starter cord.


Fluids — Fill the gas tank with fresh, correctly mixed fuel and the oil reservoir with chain oil. Fuel with an ethanol rating higher than E-10 should not be used.


Air — Check and clean the air filter regularly by blowing lightly inside to outside, brushing or tapping lightly, or soaking in water and mild detergent, rinsing and letting it dry for 24 hours.


Cooling system — Blow or brush the flywheel fins, cylinder head fins and air intake on the starter cover.


Safety features — Check that the chain brake, throttle lock control and stop switch are working and free of damage. Confirm the chain catcher is in place and the anti-vibration system is working properly. Safety features reduce the risk of accidents, but they must be fully operational to work.


Bar, chain and sprockets — The chain’s cutting teeth need to be properly sharpened and depth gauge setting is correct. Inspect for visible cracks and wear in rivets and links. Remove the bar and check for a flat top rail. File burred side rail edges of the bar, which can create drag while cutting. Clean out the bar groove and the chain oil hole that allows movement of oil from the saw to the bar groove. Rotate the bar regularly for equal wear. Check that the bar tip sprocket turns freely and that the teeth are rounded and not pointed. Check the chain drive sprocket and replace it if worn or damaged.


Preventative maintenance will help ensure the chain saw is in top operating condition and will help ensure features designed to minimize exposure to potential hazards continue to work properly and increase operator safety.


When using the chainsaw, understanding the three reactive forces — push, pull and kickback — will help prevent accidents. Never cut with the upper half of the tip of the bar. Kickback occurs when the tip of the bar comes in contact with an object or gets pinched during operation, causing the bar to “kick” up and back toward the operator, and result in a loss of control and possible injury.


That is why balance is important to safe operation. The boxer’s stance, left foot slightly forward and both knees bent, is recommended to help maintain control of the saw and minimize fatigue — even when reactive forces are experienced. 


Directional felling is the process of determining the direction a given tree will fall and making cuts to actually steer the tree as it falls. A “felling hinge” is the hallmark and the most important part of felling a tree.


When surveying the tree and surrounding area, identify potential hazards on the ground, in the tree and where the tree will fall. Clearing leaves, limbs and live saplings — or anything that will impede making a clean and controlled cut or complicate the escape route — will make it easier to work safely. Look for dead limbs and hanging branches that could possibly fall when cutting or as the tree begins to fall. Also examine the path and area where the tree will fall for hazards such as potential hang-ups or stumps.


It is exceptionally rare to find a tree that does not lean. To determine the side lean, stand back 25 to 50 feet from the tree, frame the canopy of the tree using hands extended to match the farthest reaching limbs, and imagine a plumb line running from the center of this distance directly down to the base of the tree. The distance left or right of center will determine the amount of weighted side lean. Move 90 degrees from the intended fall zone and repeat the procedure to determine the front or back lean.


The side lean will show which is the “good” side and which is the “bad” side. It is safer to make cuts from the good, or unweighted, side of the tree.  The side the tree leans toward is considered the bad side of the tree. The lean will also help determine aim when placing the tree. If a tree leans three feet to the right, you aim three feet to the left of where you want it to fall.


Trees with severe forward lean can be dangerous to fell because the tree moves in the leaning direction too quickly, splitting at the base and becoming what is known as a “barber chair.” Barber chairs can fly upwards, striking the operator with terrific force.


Next is mapping out the escape route. This is always opposite the direction the tree will be falling and should be at a 45 degree angle from the tree. Remove any obstacles and make note of any potential hazards such as holes or tree stumps. When the tree begins its descent, don’t turn your back on it, and retreat to 15 feet minimum.


Sounds like a lot of work? Abraham Lincoln is crediting with saying, “Give me six hours to chop down a tree and I will spend the first four sharpening the axe.” Preparation is central to success. It’s almost time to start cutting.


The hinge helps dictate how and where the tree will fall. Most industry experts will use a simple formula to calculate both the hinge length and thickness. To determine thickness, it is recommended to use 10 percent of the diameter of the tree at D.B.H (diameter at breast height) or 4-1/2 feet from the ground.


A tree that is 20 inches in diameter will have a 2-inch-thick hinge. Hinge thickness is reduced for thicker trees and drier wood fiber.


The length is 80 percent of the tree’s diameter at D.B.H. So, usually for a 20-inch-diameter tree, the hinge length is 16 inches.


Historically, the 45-degree face notch dominated the industry, flat on the bottom and cutting at a 45-degree angle downward to create the opening. While this will bring the tree down, there is more risk with the reduced amount of control in placing the tree. The tree can only fall 45-degrees before the notch closes and the hinge breaks.


Today, most people recommend using an open face notch which is a 70-degree opening. This gives more control since the hinge will not be broken until the tree is almost to the ground. The open face notch allows the back cut to be made level with the notch whereas the 45-degree notch will need a stepped back cut where the cut will be above the apex of the hinge.


To cut the notch, start with the top cut moving downward to the point of the hinge. Many of today’s chain saws will come with felling marks. Similar to the sight on a gun, these lines will help the operator align the cut with the direction the tree will be felled. 


Now the lower cut can be performed with careful attention to not create a bypass by cutting too far into the tree and over-shooting the top cut since this will weaken the hinge and reduce control. If progress becomes unsure, simply engage the chain brake and visually inspect the cut.


The notch is complete, and now the back cut will need to be performed. Two primary choices exist; the conventional back cut where the cut is made from the back of the tree to the front where the notch is located, or the bore cut. The bore cut method involves plunging the saw directly through the tree and working forward to make the hinge first and back second creating a back strap that helps hold the tree in place until it is time to drop it.


When used in conjunction with the conventional notch, the back cut should be above the apex of the notch to create a step that helps prevent the tree from shooting off the rear of the stump.


With the open face notch, the back cut can be performed at or near the notch line. By opening up the notch, more control is afforded since the notch does close until the tree is on the ground.


Felling wedges are extremely handy to help in preventing the chain saw bar from becoming pinched in the back cut, particularly if the tree has some back lean. Lifting a tree one-inch with a wedge at the back cut can move the top of a tree several feet. The amount that the tree top can be moved depends on the height and girth of the tree, or determining the number of vertical segments in the tree.


 

Bore cut
Photos courtesy of HusqvarnaThe bore cut is something that requires practice as it is an art form. Using the bottom edge of the bar, an initial cut will be made until the chain can bore or plunge into the tree. Never use the top corner of the bar tip as this will result in severe kick-back. Also, the bore cut should be made well behind the hinge so as to keep it safely intact.


Once the entire tip of the bar and chain are in the tree, the saw can move back and forth to cut out the proper amount while still leaving enough of the back strap. When the tree is larger in diameter than the length of the chain saw bar, bore cut only about 50 percent through from the bad side of the tree and cut up to the hinge on that side. Then, bore cut the remainder of the way from the good side of the tree and establish, slightly overlapping the first cut and out toward the back of the tree. Using the bore cut sets up the hinge first, minimizes the potential to pinch, allows quicker retreat and distance, and reduces cutting the tree while it is moving.


With the weight dispersed between the hinge and back strap, the final step is to cut the back strap, thus releasing the tree to fall. Turn off the saw and move away from the tree through the pre-established escape route to a safe position, remembering not to turn away from the tree. Safety cannot be stressed enough.


 


Cary Shepherd, CTSP is Senior Product Specialist for Husqvarna working with forestry and professional tree care business development. He is a voting member of the ANSI approved Accredited Standards Committee Z133 for Arboricultural Operations and is the Chair of the Chain Saw Sub Group.

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