Determining a Tree’s Lean

Illustrations by Joseph Smith

Since only a very few trees grow absolutely vertically, determining and adjusting for the lean of a tree is an important skill for any sawyer preparing to fell a tree. For the sake of discussion, we’ll consider the word “lean” to mean that the center of a tree’s mass is not plumb above the center of the stump.

Lots of times, you’ll want to fell a tree in a different direction than its lean. It is usually not difficult to compensate for a little bit of lean, by using either wedges or a change in aim. Severe lean, or even moderate lean in a tree whose trunk has weakening defects can be cause for concern. Lean in any direction of more than five feet is considered severe and can adversely affect the integrity of the hinge. As always, if you feel you don’t have the skill and experience, don’t cut the tree.

The following steps will help you determine how much lean the tree presents.

Step one is to walk out to where you would like your tree to fall. Estimate where the very top of the tree will land on the ground and plant a stake there. Then, standing at the stake, and using some sort of plumb bob (it’s easy to improvise one with a piece of string and a weight tied to its end), close one eye and line up your fingers at the top of the plumb bob with the center of the crown’s mass, a point that is equidistant from the
top and both sides of the crown.

Use your open eye to follow down the plumb bob and looking past it toward the tree, note how far from the center of the base of the tree your plumb bob reaches the ground. This is your side lean. So, for example, if your plumb bob hits a spot two feet to the left of the tree’s base, you’ve got two feet of side lean.

You can compensate for this lean in your cutting plan by changing your aim. For example, if you have two feet of lean to the left, move your stake two feet in the opposite direction of the lean. This will change the location of your notch and compensate for the side lean.

The final step is to plumb your front/back lean. Go back to the tree and then walk away from it at a 90-degree angle from the direction of your stake. When you get far enough away to see the crown of the tree, use the plumb bob again in the same way. If the plumb bob hangs on the side you want the tree to be felled, you’ve got front lean, making your job a bit easier. If the plumb bob is on the back side of the tree, then you have back lean, and you’ll need to use your wedges and maybe shims to jack the tree over. To calculate how much you will have to jack the tree to reach the apex where it can
begin to fall in the direction you want it to, see the Autumn 2005 Tricks of the Trade column.

Carl Demrow is a trail consultant and carpenter when he’s not busy tending his woodlot in Washington, Vermont.

 
Discussion
  1. Kati → in Kensington, MD
    Mar 14, 2013

    Is there a process of “pinning” a tree and using string so it can be determined if the tree is shifting which would determine need for removal?

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