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CLOSE THIS BOOKWood Harvesting with Hand Tools - An Illustrated Training Manual (ILO, 1989, 128 p.)
TREE FELLING
VIEW THE DOCUMENTPREPARATION FOR TREE FELLING
VIEW THE DOCUMENTTREE FELLING WITH AXE AND BOW SAW
VIEW THE DOCUMENTTREE FELLING WITH AXE AND CROSS-CUT SAW
VIEW THE DOCUMENTPRECAUTIONS WHEN MAKING THE UNDERCUT AND THE BACK CUT
VIEW THE DOCUMENTFELLING TREES LEANING INTO THE PLANNED FELLING DIRECTION
VIEW THE DOCUMENTFELLING TREES LEANING TO THE SIDE
VIEW THE DOCUMENTTREE FELLING IN DENSE TROPICAL FORESTS
VIEW THE DOCUMENTFELLING OF TREES WITH PLANK BUTTRESSES
VIEW THE DOCUMENTWOOD WASTAGE DUE TO POOR WORKING TECHNIQUES IN FELLING

Wood Harvesting with Hand Tools - An Illustrated Training Manual (ILO, 1989, 128 p.)

TREE FELLING

PREPARATION FOR TREE FELLING

The felling direction must be carefully determined (1). This will depend on the skidding direction, the lean of the tree, the shape of the crown, the wind, and on obstacles in the way of the tree's fall, obstacles on the ground and also on the possibility of retreating safely.

When the felling direction (1a) is determined, the tools are placed opposite to the felling direction, behind the tree (1b). The working area around the tree is cleared (1c). Two escape routes are cleared, as far as is necessary to allow easy retreat, placed sideways at about 45 angles to the rear (1d).

The base of the tree must be well cleared, using the axe or a matchet in order to prevent the saw from blunting too quickly (2).


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TREE FELLING WITH AXE AND BOW SAW

Small trees are felled with an axe, cutting from both sides (1).

For slightly larger trees, axes are used for making the undercut. In this case, the horizontal cut can be done with the bow saw (2). The back cut should not be made with the axe because too much wood is wasted and it is more difficult to maintain the desired direction of fall (3).

Axe felling of larger trees is allowed only in exceptional cases.


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TREE FELLING WITH AXE AND CROSS-CUT SAW

Felling of medium- and large-sized trees is done with the axe and the cross-cut saw. This process requires special skills and experience.

A proper undercut (1a) and back cut (1b) are necessary, leaving a hinge (2a) to guide the tree into the desired direction of fall. Small lateral cuts (1c) and (2b) avoid tearing of fibres from the tree during felling. The depth of the undercut should be about 1/5 to 1/4 of the diameter; it should open at an angle of about 60. The back cut should be about 2-5 cm higher than the undercut. In very large trees, the undercut may penetrate up to 1/3 of the diameter, depending on shape, and the back cut may be 10-20 cm higher.

Wedging will be necessary to avoid pinching of the saw (3). If necessary, wedging will also force the tree to fall.


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PRECAUTIONS WHEN MAKING THE UNDERCUT AND THE BACK CUT

Accurate felling makes the job safer, facilitates subsequent operations and reduces timber wastage. Felling should therefore be done with the greatest care and precision. By looking at the stump, it can easily be seen whether a poor or a good felling job has been done.

When making the undercut, care must be taken that it points precisely into the felling direction. This can be checked by standing in front of the undercut (1). If necessary, the undercut should be corrected.

Sufficient holding wood which acts as a hinge must always remain in order to maintain control of the tree so that it does not fall in any direction other than that intended (2). 2a shows the correct depth of the back cut. If the cut penetrates as deeply as indicated by 2b in the picture, the tree is practically loose and a gust of wind may push it anywhere.

If trees have buttresses, it is necessary to remove them before making the undercut and back cut, which can then be made with more precision and ease (3). The buttresses should also be removed to facilitate transport and handling of the log. To make sure that the cuts are placed in the right position, it helps if they are marked with an axe.


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FELLING TREES LEANING INTO THE PLANNED FELLING DIRECTION

Trees leaning into the planned felling direction (1) have to be felled particularly carefully in order to avoid danger to the workers, damage to the saw and wastage of timber.

In such a case, the undercut (2) must penetrate more deeply into the tree. This may entail preparing the undercut in two steps (3) and (4). When the saw starts pinching, work should continue with the axe.

The back cut (5) must be done from both sides and only the remaining wood (6) be sawn parallel with the hinge.


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FELLING TREES LEANING TO THE SIDE

A tree can also be felled at an angle of about 30 from the lean. In this case, the undercut (a) should face the intended felling direction (b). The hinge (c) should be kept smaller on the side of the lean (d) and larger on the side to which the tree is to be felled. In addition, a wedge (e) placed on the side of the lean will help to direct the fall of the tree.

Felling larger trees against the lean is only justified in exceptional cases (e.g. to save young tree growth or near buildings) and requires special skills, techniques and equipment (e.g. winches).


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TREE FELLING IN DENSE TROPICAL FORESTS

Felling in dense tropical forests can be particularly dangerous. Dense undergrowth makes it difficult to retreat from the tree during its fall. Dead branches may be hidden in the crown, which is often not visible. For the same reason, it may be difficult to assess the lean of the tree.

Trees may be over-mature and may therefore have hollow or rotten centres.

Trees are often connected to each other with climbers. When the trees fall, they frequently pull down other trees (1). Branches from the falling tree or from neighbouring trees (2, 3) are broken off and may swing backwards (4). Climbers are torn off or may break and snap back (5).

The accident risk when felling trees in dense tropical forests is considerably reduced if the area around the base of the tree and the escape routes are well cleared.

Two paths are cleared to a length of 20-30 m beyond the reach of the crown opposite the felling direction. The angle between them should be about 45.

Climbers attached to the tree must also be cut before sawing begins,

It will often be necessary to clean the base of the tree to remove bark and dirt deposited by termites.

Tree harvesting in natural tropical forests still continues to some extent with hand saws although in the large commercial operations chain saws have taken over.


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FELLING OF TREES WITH PLANK BUTTRESSES

Plank buttresses are common in tropical trees. They occur in many tree species once they have grown large.

Large trees with plank buttresses often attain a cylindrical shape only at a height of 3-5 m above ground level (1). At ground level the cross-section becomes larger and more irregular (2), (3).

Trees with large plank buttresses may be felled at a convenient working height while the workers are standing at ground level.

If felling from the ground is not possible, it may be necessary to build a platform (4), especially in steep terrain. Experienced workers will be able to do this quite quickly with material available locally. The platform should permit a sufficiently comfortable and safe working position.


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If felling is done through the buttresses, the tree is usually felled into the direction of lean.

The undercut is made to a depth of about one-third of the diameter (1a). First the horizontal cut is made and then the oblique cut. The back cut is made about 20 cm higher (or more) than the horizontal cut of the undercut. The cut begins on the side buttresses (1b) and is finished on the rear buttress (1c). Wedging may be necessary on the lateral buttress in order to stabilise the tree and on the rear buttress to push the tree into the direction of fall (1d).

This technique must be adapted to the particular shape of the tree. The undercut may, for instance, have to be made in two buttresses (2a). If there are also two buttresses opposite the felling direction which have to cut one after the other, the smaller one should be cut first (2b) and then the larger one (2c). To assist felling, it is again advisable to insert wedges (2d).


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WOOD WASTAGE DUE TO POOR WORKING TECHNIQUES IN FELLING

High stumps are an indication of poor workmanship and insufficient supervision. Often they are the result of putting felling marks, which are to be left on the stump for control purposes, too high. Sometimes workers find it more comfortable to cut about 1 m above ground level (1a). Except in special cases (e.g. hollow or heavily buttressed trees), the stump should be as low as possible (1b). This helps to avoid wastage of wood and because lower stumps make skidding easier.

Where the wage level is low and the timber price high, the value of wood left in one stump (1c) may correspond to a week's wages or more of the operator.

The following table gives information on volume loss:

Stump recoverable height

Diameter cm


40

60

80

20

0.025

0.057

0.100

40

0.050

0.113

0.200

60

0.075

0.171

0.300

Considerable wood losses in felling can also occur if the tree is felled without an undercut or with an insufficient undercut (2). If the undercut is at the same level as, or higher than, the back cut, there is a risk that wood fibre will be pulled out of the butt end, reducing the value of the log.

If the undercut is too small (3a), this can be most dangerous because the tree's fall is no longer properly guided. The tree may split and this results in considerable wastage on the valuable bull end.


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A considerable amount of valuable wood is lost when large trees are felled across obstacles on the ground such as hollows (1), ridges (2), logs or rocks (3). Most species break if they hit such obstacles. Although the broken part may be small, the loss caused by cutting out the break can be considerable.

The experienced worker will look carefully for obstacles and, when determining the felling direction, he will try to avoid them. This will be possible in many cases. Remember that even heavily leaning trees can be felled to a point about 30 on either side of the lean.

Efforts to avoid obstructions not only reduce waste but also facilitate work because unnecessary cross-cutting is avoided.

The breaking of a tree can cause serious losses, especially for valuable hardwood species.


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