Technical Tree Felling – A Historical Perspective (Article 1)
In the first of a six-part series on felling, Dwayne discusses how the legacy from the days of the axe & crosscut still influences modern techniques
Tree felling has been taking place for thousands of years because trees have provided resources necessary for the survival of humankind. This is the very reason why it is such a controversial and varying subject. In the past trees were in some cases burned to the ground. This required a lot of time and tending and when it was finally weakened enough by the flames, the tree would fall in any direction. This method gave way to chopping at trees with stone implements, like tomahawks. In the not-so-distant past, felling accuracy, tree placement and landing improved with the use of a crosscut saw and axe.
Tree felling techniques date back beyond the advent of the modern day chainsaw. Unfortunately some techniques and practices used to fell trees have not kept up with the technology of the chainsaw itself. For example, it is often thought that there is a safety or wood quality reason for the common 45 degree notch opening. But the fact is that this notching technique originates back to the crosscut saw and axe. In order to notch in a tree with a cross cut saw and an axe you have to make the under cut first and then chop out the wood above the cut. It is easiest for an axe to remove wood in this situation at a 45-degree angle and that is the very reason why a 45-degree face notch is so common. In other words, it is a legacy from long-ago.
The wood left uncut during the felling process is called; “hinge wood”. It is formed by cutting a notch and using a back cut to release the wood behind the notch. The purpose of the hinge wood is to provide control during the arc of the fall. This control is only available as long as the hinge is intact and working. Many things can work against the hinge wood and cause it to break prematurely resulting in a loss of control of a falling tree. Some other things that cause hinge failure are side lean, hinge too thick, wood fiber decay, by-pass and uneven hinge wood, all of which I will discuss later in the series. I have not met anyone that fells trees that wants to lose control of a tree.
The most common method of notching trees today is the 45-degree face notch. The flaw in this is that it only allows your hinge to work for about half of the arc of the fall of the tree. A tree generally grows 90 degrees to the ground with the exception of slopes and uneven terrain and even then the trunk is parallel or in line with the force of gravity acting downward along its length. When a tree begins to fall, the angle of the trunk to the ground closes and in order for the hinge to bend from start to finish, the tree must have gone from standing to laying on the ground. The hinge can only provide this control if it can remain intact through the entire arc of the fall. And the only way to maintain control of the tree being felled using a hinge is to allow the hinge to work or hinge through the entire arc of the fall. Control of the tree can only be achieved if the hinge is allowed work through the entire arc of the fall, and this requires a notch opening of 70 degrees.
In this series I will expand on a five-step tree felling planning process that allows anyone felling trees to remain in control of trees they are felling and also be as safe as possible during any tree felling process. If you are interested in learning about control and accuracy when it comes to tree felling then look for my next article where I will touch on the first step in the plan which is evaluating site hazards, tree risk indicators and tree placement considerations such as tree height, felling site location and placement.