In the world of forest management, straight-growing, upright trees are the ideal. Reality often does not respect that ideal, however. As loggers and landowners, we often have to deal with crooked, leaning trees and trees where the center of mass is substantially offset from the base of the tree. These present a particular challenge for felling, as the lean is often in a direction different from where the tree needs to be felled. Luckily, there are simple methods fellers use to fell a tree against the lean using tools such as felling wedges and felling levers. In this article, we will explain everything you need to know to be able to successfully fight gravity without putting yourself at unnecessary risk.
Please note, however, that these methods are only applicable for situations where the lean is only slight. Severe lean can create extreme hazards like barber chairs , and felling them against their lean is best left to professionals. To read more about these situations, read our article on the subject here.
Using Felling Wedges
The main tool and method used to fell a tree against the lean is the felling wedge. A felling wedge is simply a wedge (crazy, right?) that is placed in the back cut and pounded into the tree using a hammer or back of an axe. As the wedge drives deeper into the back cut, it lifts up on the stem, causing the crown (and hence center of mass) to displace toward the direction of felling. It is a simple tool that has an amazing amount of power and efficacy in displacing massive trees. You can find felling wedges here.
How Far Can a Felling Wedge Move a Tree?
A felling wedge works by displacing the crown, and so their main limitation is their ability to actually displace the crown. While wedges themselves come in sizes from small to large, with larger wedges offering more displacement, each size has a limit. The amount of displacement offered by a wedge depends on both the trees diameter and height as well as the size of the wedge itself.
The efficacy of a felling wedge can be modeled with the following formula:
(WL*H)/D=CD
Where:
- WL = Wedge Lift (thickness of the back of the wedge)
- H = Tree Height
- D = Diameter
- CD = Crown displacement
- All variable are in the same unit of measurement
So, lets using the diagram of a leaning tree below as an example.
Let’s say our wedge lift is about 1″ which is standard for most wedges. Our formula would then give us a total crown displacement of 50″–not quite enough to hit the tipping point for our example. But that’s still not necessarily a problem. There are other methods we can use to enhance the efficacy of wedges.
Using Two Wedges
If one wedge isn’t enough, it is possible to use two wedges to enhance the effects. This is done by placing the wedges about 90 degrees from one another so each wedge is about 45 degrees from the hinge itself. The proper placement can be seen in the diagram below.
This method works by effectively reducing the diameter variable in the formula discussed above, giving the wedges far more crown displacement at the cost of more difficulty driving the wedges. To compensate for the increased difficulty, alternate between hitting the two wedges into the tree. As one drives deeper, it lifts the tree slightly and makes it easier for the other wedge to move further. So keep alternating until the tree falls.
Unfortunately, this method my not work for small diameter trees, as there may not be enough room to fit one or both wedges at an angle. In these situations, it is best to use a felling lever.
Using Felling Levers
Felling levers are an amazing but under-appreciated tool for felling trees. They are, exactly as advertised, big levers that can be inserted into the back cut of a tree to allow the feller to lift up on the tree and fell it against the direction of lean. Alone, felling levers are limited to trees with only slight lean or a slightly shifted center of mass, as they depend on shear human strength to move the tree. Even so, they are able to be used and deployed much more quickly, so if you are working with small trees or conducting a larger harvest, they are an indispensable tool. You can find felling levers here.
It does not have to be either/or, however. Felling levers are a great way to finish the job when a single wedge is insufficient. If a single wedge is not enough to fully overcome the lean, they usually are able to displace the crown enough so that you can overcome the rest with a lever and your own strength. Remember, as the center of mass becomes more centered over the stem, the weight acts less as a lever on the tree itself, so it is far easier to move. You’d be surprised how much you can move a one-ton tree when it is relatively centered.
Felling levers have a secondary benefit as well: Nothing makes you feel manlier than felling a tree by deadlifting it.
Avoid Pinching Your Saw
Felling a tree against the lean also presents a unique challenge: Pinching your saw. Because the weight is shifted toward you, the tree is always going to want to close in on the back cut, potentially pinching your saw and creating a massive headache. While not a particularly dangerous situation, it can really ruin your day, especially if it is your only saw and it is really stuck in there.
Luckily, saw pinches are easily avoidable with the use of proper techniques, such as bore cutting and placing wedges in the back cut as a place holder while the hinge is still being set. This is a large topic to cover, so if you are interested in reading more about how to safeguard your saw and your sanity, we have an article on avoiding saw pinches here.
Practice Makes Perfect
When you fell a tree against the lean, it is not always a straight-forward practice. The forest is infinitely variable, and there are many factors that can affect how easily the tree will fall. Moreover, it is not always practical to solve equations every time you pick up your saw to figure out the best way a tree should be felled. Luckily, you won’t need to. As you gain experience, these solutions will become intuitive, and you will gain an eye for what needs to be done for specific trees in unique situations. First, you need a solid understanding of the basics, and second, you need experience. Third, however, you need the health to be able to keep felling, so whatever you do, be sure to stay safe so you can keep your saw running for years and decades to come.