Felling on a slope is dangerous and accident-prone. Here is a guide from forestry practice, which allows safe and effortless work.
A) Cutting sequence in cross section: 1) drop notching; 2) shaping of support bar and break bar with incoming chain on the left side; 3) shaping of support bar and break bar with outgoing chain on the right side; 4) setting support wedge; 5) cutting through support bar with incoming or outgoing chain ©Ralf Grieber Dangerous situations caused by sliding or rolling trees – felling, sawing off or turning conifers on slopes is one of the most accident-prone jobs in forestry. If there are obstacles in the felling path (z. B. Crest, block overlay, etc.), there is also a risk that the tree will jump up or to the side at the base of the trunk. These dangerous situations often lead to serious accidents. Such hazards should be eliminated in advance of the actual work by a precise assessment of the tree and the felling path.
The steps in detail
B) The backsliding place should be outside the crown projection. ©R. Grieber Before assessing the tree to be felled, place the tool at right angles to the rough felling direction or. parallel to the slope. Then it must be determined which influences play a role in felling. Important are:
– the tree height (danger zone, impact point),
– the crown of the tree (weight distribution, zwiesel),
– the course of the trunk (center of gravity outside the base of the trunk),
– the trunk diameter (gives information about felling technique, chainsaw bar length),
– the branches (scrawny branches hanging in the crown can fall down),
– Neighboring trees and surroundings (felling path),
– enough space for the tree to fall without danger, or. it is to be paid attention to the fact whether the tree to be felled can get stuck or carry away another tree,
– the state of health (are there any indications of felling or. back damage, woodpecker holes and rotting).
From the points mentioned above, it is possible to determine the appropriate felling direction in each case.
The series of photos shown in this article shows a tree with an evenly shaped crown, but with a trunk that is not straight. The tree hangs slightly forward from the vertical in the direction of felling (Fig. B). In case of intended felling towards the slope (uphill), this means that the tree is likely to start falling prematurely before the break line can be formed cleanly. Therefore, in this case, it is advisable to fell the tree using the support band technique (diagram A).
When assessing the felling line in this case, it was found that the tree falls over a knoll that slopes towards the left side in the felling direction. Here there is a danger that the base of the trunk will swing upwards and to the left side.
In order to be able to move quickly and surefootedly on slopes, it is advisable to wear cutting shoes that are suitable for difficult terrain. These usually have a strong profiling of the sole, walkers on the sole (z. B. folding handle) and are suitable for step irons, (z. B. Lowa F3 with crampons Austria Alpin). Furthermore, a trip-free working environment should be ensured by clearing the work area and the switchback. The switchback is placed on the right side, perpendicular to the felling direction parallel to the slope and outside the crown projection (hardwoods six to ten meters, softwoods four to six meters). After clearing the switchback, it is advisable to walk along it again to the switchback location in order to memorize its position exactly. Before the actual felling work, the log should be cleaned of dirt so that the sharpness of the chain is maintained.
Felling direction, felling notch and felling cut
C) Sawing of the root approach (left) and creation of the drop notch (right) ©R. The direction of felling is now indicated by the rail. Saw the root approach in the direction of felling at the same level as the trunk (Fig. C, left) – this is particularly important in order to be able to create the notch properly. the stick height is determined by the top of the slope. In steep terrain, the cutting of the roots and the felling cut must often be carried out at waist height.
With the meter stick, the felling depth and the exact felling direction can now be determined and marked. The felling notch size should be a quarter to a third of the trunk diameter. Now the drop notch sole cut is to be carried out up to the set marking.
Next comes the drop notch roof cut, which is sawn out at a 60° angle in the sole with the help of marking sticks (Fig. C, right). The roof cut ends a little above the marking sticks, so that the fall notch can finally be cut out with a splitting axe (Fig. D, left). Now the exact course of the grain becomes visible. If it is slanted, the felling notch must be re-sawed so that one can get deeper into the trunk roll and form the felling notch chord neatly. After the case notch has been created, the direction of the fall should be checked again and corrected if necessary.
Now the break line and felling cut are to be marked, each one tenth of the diameter. Before starting the felling cut, the first call for attention including all-round view is made. The felling cut is now made at a distance of one tenth of the diameter above the bottom of the fall notch. Since there is a danger that the tree will swing to the left side, start the felling cut on the left side and leave the support band so that it can be cut from the right side and the saw operator is not in the danger zone while doing so. This also has the advantage that most of the felling cut can be sawn with the chain running in.
The felling cut can then be started on the left side of the trunk by making a plunge cut far enough away from the support bar and piercing with the rail tip to the right side. Then the chainsaw bar is pulled back to the half of the log roll and the breaking bar is formed on the left side with the chain running in.
Now a support wedge can be placed on the left side so that the felling cut does not close if the tree assessment was not accurate. This wedge should be far enough from the support bar so that it can be cut without touching the wedge (Fig. A or. Figure D, right). Make sure that the wedge is only driven so far into the felling cut that the felling cut remains open. Now switch to the right side and form the support band and the break line with the chain running out. As long as the tree is still standing securely, the second call for attention is made with an all-round view. Now the support bar is cut. As soon as the tree leans in the felling direction, the forester immediately goes back on the switchback to the switchback place, so that he stands outside the crown projection. At the same time, what was foreseen during the tree assessment happens – the tree deflects upwards (image series E). The forester waits on the back soak until all the crowns in the felling line have swung out.
Always limb from the uphill side
D) The felling notch cut (left) is followed by the felling cut (right). ©R. Grieber When limbing on a slope, one should never stand in the line of fall of potentially rolling or sliding log sections. Where there is a risk of the log rolling off during delimbing, always (!) delimb from the uphill side.
If coniferous logs are cut downslope, then most of the delimbing must be done from top to bottom. As a result, the log is farther away and the posture is not optimal (Fig. F, left). Furthermore, the risk of tripping and falling is greater and one may have to fell the tree against the natural direction of the slope (increased wedge work). If the tree is cut upwards on the slope, then most of the delimbing can be done in an optimal position (Fig. F, right).
Cutting only from the safe side
E) After cutting the support bar, the worker looks for the back switch. The series of pictures clearly shows how the tree swings upwards. ©R. Grieber When cutting down a felled tree, always work from the "safe side" (Fig. If a trunk could roll off after being cut, the cut should always be made from the top of the slope. At most, a first narrowing cut can be made with the chain running in from the bottom of the slope (dangerous side) (Fig. A, cut 1). Then switch to the upper side of the slope and make cut 2 with the chain running in as a narrowing cut on the pressure side (beware of the danger of jamming)!). Cut 3 is made on the pull side with the chain running in as a separating cut with outstretched arms. It is important that all three cuts meet each other.
Ralf Grieber, Ravensburg
F) Limbing downslope (l.) is more dangerous than working upslope (r.). ©R. Grieber
G) cut 1 = narrowing cut; cut 2 = narrowing cut from the pressure side; cut 3 = separating cut ©R. Grieber