Technical Tree Felling – Assessing Lean (Article 3)


 By Dwayne Neustaeter

An important step of any falling plan (and one I believe that is often the most overlooked) is assessing the lean. In almost all cases whenever possible it is best to fell a tree in the direction it is naturally leaning. That is to say that if all of the strength of the wood fibres holding the tree up against gravity were to be severed or be instantly released then the tree would fall exactly where gravity is taking it. Therefore, if you can fell a tree in the direction of its natural lean gravity will ensure it falls that direction.

In my last article, I touched on height measure and how, if you have determined how tall the tree is and accurately assess the lean, then there is little that can cause the tree to fall anywhere other than planned.

 Assessing lean is much more than the angle of the trunk.  Other factors must be considered.  I tell my students to consider the entire ‘bio-mass’ of the tree as this is what truly creates bendin gon the trunk.  The ‘bio-mass’ is all of the parts of the tree combined – every branch and trunk.  This is best assessed as part of your outer perimeter survey s described in the previous article.

 The bio-mass and lean is best assessed from a distance from the tree.  In your mind’s eye, draw a line around the entire tree, being sure it touches the tips of every branch, start at the base of the trunk and then proceed left or right around the entire canopy or bio-mass of the tree.  Once you have this visualized, split that shape in half (it usually is an oval or egg shape) and imagine a line plumb down the center.  The distance this line is in relation to the notching area of the trunk tells you how much lean you are dealing with.

This tree shows about 5 - 7 feet of lean.

This tree shows approximately 1 foot of lean

 It is important to look at the tree from all sides and assess lean as you go because the lean will change from different viewing locations.  Using this method the natural lean may be determined and the fell should proceed in that direction.  If there are obstacles in the way of this natural lean, then other technical felling or rigging techniques are needed and worked into the plan.

 What I have just described is how to calculate ‘forward lean’.  There is another aspect of lean that is also important to evaluate.  Once the ‘forward lean’ is established, it is important to eliminate any side lean in relation to your direction of fall.  Often side lean is not considered.  The problem is when obstacles are in the way of the ‘natural-lean’, the faller must obviously choose to fell the tree away from the obstacle.  In doing this – side lean becomes a factor.

 Side lean is lean that is perpendicular to the felling notch and hinge.  This is important because wood is much weaker in the vertical plane than the horizontal (imagine trying to split a log by hitting along the side, yet when you hit it from an end, it splits relatively easily).

 Gravity acts on the hinge much the same way; as the tree falls it can cause the hinge to break prematurely, sending the tree once again in the direction of the ‘natural lean’.  Therefore, once natural forward lean is determined, be sure that there is no side lean acting on your hinge 90 degrees to your direction of fall.

 Mastering how to perform a lean assessment will ensure all of your trees fall exactly where you want them to.  By using the outer and inner perimeter survey and height measure you can predict accurately and confidently where the top of the tree will land.

 There are more factors to consider in your felling plan and in my next article I will discuss establishing and using an escape route.

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