Figure1: Figure 1: Identifying safe and hazardous areas and preparing escape routes. (To view click on image)

Figure 2: Estimating the height of a tree and where it will fall. (To view click on image)

Figure 3: Dimensions of cuts.

Figure 4: Undercut and back cut.

Figure 5: Using props and Samson poles to assist the direction of fall. (To view click on image)

Figure 6: A flexible tree under tension is hazardous. (To view click on image)

Figure 7: The danger of weakened tree trunks.

By Cleve Cheney

Trees are used for many purposes, some of the most important being to provide timber for dwellings and the manufacture of furniture, boats, wagons, tools or implements. Trees can be felled using a chainsaw, handsaw or axe. Whatever tool is used, it must be remembered that felling trees can be dangerous.

We touched on this in a previous article, but it is important enough for us to expand on the subject.

Felling trees
There is a procedure to follow for safely chopping down a tree.
By careful observation, try to determine which way the tree is likely to fall, taking into consideration its direction of lean, wind, foliage distribution and slope.

Look at the site and identify danger areas and the most obvious escape route. Carefully clear this route of any obstructions which might hinder a quick getaway (see Figure 1). Estimate the height of the tree and the distance it will fall (see Figure 2).

Clear any obstructions around the tree that might hinder your work.
Make the first cut – referred to as the undercut – in the direction in which you expect the tree to fall. The top part of the cut should be angled at about 45 degrees. Subsequent cuts are made at a similar angle, but move through the wood in small increments of a few centimetres at a time. The width of the gap of the undercut should be about equal to the diameter of the tree. The depth of the undercut may vary from one third to one half of the trunk thickness, depending on the soundness of the tree, its lean, and the wind strength. If the undercut is made too deep, the tree may fall in the opposite direction before the back cut is made, resulting in a dangerous situation. The cut should be made straight across, as a slanted one makes a poor hinge (see Figures 3 and 4).

The back cut is made slightly higher and on the opposite side. Retaining a few centimetres of wood as a hinge will prevent the tree trunk from slipping back off the stump or rotating. If the undercut is not deep enough or if the back cut is too high above the undercut, the tree may fall in the opposite direction to that expected. If the undercut and back cut are at the same level, or if they are cut at an angle instead of opposite to one another, the tree may “kick back” opposite to the direction of fall, which is hazardous and may have fatal consequences. The width of the hinge is about two to four finger widths. To get the tree to fall away from a pronounced lean the hinge should be made wedge-shaped when viewed from the top, with the widest part of the hinge made in the direction the lean is to be shifted. Green trees may fall with a substantial hinge, while dry trees tend to fall only when the hinge is relatively thin.

As the back cut nears completion, the tree may be propped up to influence its direction of fall, or given a push to ensure that it falls in the desired direction (see Figure 5). From the moment a tree begins to fall, watch it closely and don’t stop watching until it has fallen and come to final rest. Be ready to take evasive action should anything erratic or unexpected occur. Back away from the tree as it begins to fall and if possible position yourself in a safe area, preferably behind another substantial tree. Never stand close to the base of a falling tree as many unpredictable things can happen near the stump.

Falling characteristics of different trees
Different tree species fall in different ways. The branches of densely foliated tree species may cause them to rebound back over the stump. A flexible tree under tension (for example, if another tree has fallen on it) may suddenly spring back if the tension is relieved by its being cut too low down on the trunk. This can cause serious injury. The tension must first be eased by cutting branches higher up (see Figure 6).

This is best done by making a partial cut at the central portion of the bend. Some trees have rotten cores or have been weakened by wood borers, which may cause them to fall sooner than expected or in an unexpected direction. Weakened trunks can also break as they fall and hit other branches, causing the trunk to break, fold back on itself and fall in an area opposite to that predicted (see Figure 7). Falling trees that get hung up in other trees are very dangerous and the situation requires careful inspection in order to determine how to bring the tree down safely. A hung-up tree can come down unexpectedly with fatal results, so never stand under any part of it. Rocking, rotating or prying may dislodge it, but if this proves unsuccessful, you may have to chop off sections of trunk to get the tree down. Cutting down the tree causing the hang-up is extremely dangerous and should not be attempted.