Forest Engineering – Timber Preparation - Sappi

forest engineering 

CONTENTS 

4.1 Felling 

4.2 Debarking 

4.3 Debranching 

4.4 Cross-cutting 

4.5 Infield stacking 

4.6 Mechanised timber preparation 

4.7 Mechanised felling 

4.8 Mechanical debarking 

Timber preparation normally includes the activities of felling, debranching, topping, debarking, cross-cutting 

and stacking. These activities can be done motor-manually or mechanically. A major portion of felling in 

South Africa is still done motor-manually. 

4.1 Felling 

As with all other forestry operations, fellers must be suitably trained for the job. 

Further information regarding chainsaw operations can be found in the South African Chainsaw 

Safety and Operating Handbook published by FESA. 

4.1.1 Equipment for motor-manual felling: 

� chainsaw; 

� felling lever. 

4.1.2 Personal protective equipment: 

� approved hard hat with visor and earmuffs; 

� brightly coloured T-shirt and/or high visibility vest; 

� appropriate gloves – if required; 

� approved cutter pants; 

� steel capped safety boots; 

� First Aid kit and pressure pad (bomb bandage), 

� rain suit when required. 

chapter 4 

timber preparation 

4.1.3 Other: 

� tool pouch with required tools (round file, flat file, combination spanner, depth gauge tool); 

� fuel and oil container; 

� cloth or brush for cleaning purposes; 

� fire extinguisher; 

� first aid kit. 

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chapter 4: timber preparation 

4.1.4 Felling technique: 

� Ensure that no other person is within the felling danger zone of at least two tree lengths 

radius from the tree to be felled. The danger zone is 360° around the tree to be felled. 

� Determine an appropriate escape route. Normally 45° away from the felling direction. 

� Ensure the escape route is open and clear of obstacles. 

The following schematic drawing shows the danger zone and the escape route around the tree 

to be felled (see Figure 4.1). 

Felling direction 

Two tree length radius 

Check the possible felling direction by taking into account the following: 

� the angle at which the tree is leaning; 

� crown size and overhang; 

� neighbouring trees; 

� wind direction; 

� planned extraction direction; 

� slope on which the tree is growing; 

� environmental considerations; 

� silvicultural requirements. 

Fell the tree using the following three cuts: 

� directional notch (top cut); 

� directional notch (undercut) - angle to be at least 45°; 

� felling cut. 

Escape route 

Figure 4.1: Schematic representation of felling danger zone and escape route. 

The tree is steered in the desired direction by creating a felling hinge. Figure 4.2 below shows 

the three felling cuts. 

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Felling cut 

Hinge 


Felling direction 

Figure 4.2: Schematic representation of felling cuts. 

Directional notch 

4.1.5 Felling production 

Felling operations are normally controlled by giving a pre-determined minimum production (task) 

level. 

The following factors could influence felling productivity: 

� safety considerations; 

� tree size; 

� tree diameter; 

� espacement; 

� terrain; 

� tree species; 

� debarking percentage (where applicable); 

� stem form; 

� crown shape and size; 

� lean of the tree; 

� felling direction; 

� undergrowth; 

� serviceability and suitability of equipment; 

� operator skills; 

� cutter working alone or with an assistant; 

� subsequent operations to be completed by the operator and assistant (where applicable); 

� environmental considerations; and 

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� silvicultural considerations. 


The production levels for Eucalyptus and Acacia felling, debarking and stacking, which are 

given in Annexure “B”, are based on the following task descriptions: 

� The cutter and an assistant are responsible for felling, cross-cutting, debranching and 

stacking of brushwood. 

� The debarkers are responsible for debarking the logs. 

� The stackers are required to build stacks for further extraction or transport. 

Guidelines for task determination for Eucalyptus grandis can be found in Annexure “A”, and 

tasking guidelines for pine species can be found in Annexure “C”. 

4.2 Debarking 

Debarking is the process of removing the bark from Eucalyptus and Acacia species after felling. This 

can be done manually or mechanically. 

4.2.1 Manual debarking 

Manual debarking is normally performed with a sharpened hatchet. The bark is detached either 

as long or short strips or small plates. As far as possible, effort should be made to ensure that 

logs are free of cambium. 

Debarking spuds (hoe type piece of equipment) and shaped spades can also be used to 

debark. Either tree lengths or logs can be debarked. 

4.2.2 The following is seen as the minimum protective clothing that must be worn by manual 

debarkers: 

� overalls; 

� hard hat; 

� safety boots; 

� leg protectors; 

� rubber gloves; 

� eye protection. 

Manual debarking is a strenuous job with an awkward posture and debarkers must be trained in 

the correct debarking techniques. 

4.2.3 Debarkers must take note of the following: 

� Always debark on the far side of the log away from feet and legs. 

� Always use a properly maintained debarking tool. 

� Always chip away from yourself. 

� Do not walk or stand on wet logs. 

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4.2.4 Debarking percentage 

Debarking percentage is the term used to express the ease of removing the bark from freshly 

felled Eucalyptus and Acacia species. It is the percentage of cleanly debarked logs in a total 

number of debarked logs. 

Debarking % = (number of cleanly debarked logs ÷ total number of logs sampled) x 100 

Cleanly debarked logs are logs where no cambium or less than 30% cambium remains on the 

log. Chiselled or shaved logs are where more than 30% cambium remains and the bark has to 

be chiselled off in small pieces. See Photo 4.1 and 4.2 below: 

Photo 4.1 (left): Cleanly stripped log. 1 

Photo 4.2 (right): Chiselled log. 1 

Debarking is expressed in classes as shown in the following table. Note that the table gives the 

debarking class, the corresponding debarking percentage and the debarking percentage as you 

will find it in the tasking sheets in the annexures. 

Debarking class Debarking % Task Table 

1 0 -40 40% 

2 41 – 55 50% 

3 56 – 75 60% - 70% 

4 76 – 85 80% 

5 86 - 100 90% 

Table 4.1: Debarking classes. 

Rip-stripping is a term used where the debarkers rip the bark off in long strips from standing 

trees. This practice is only viable when trees are debarking well. Debarkers should be on the 

lookout for falling branches and premature breaking of the bark when rip-stripping. 

1 

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Photo 4.3: Ripped stripped trees. 1 

The stripability percentage can be influenced by the following factors: 

� species; 

� growing site; 

� season of stripping; 

� time of day; 

� temperature; 

� time after felling; and 

� whether the trees are stressed (drought, disease) or not. 


Debarking tasking tables are presented for Eucalypts grandis, Eucalyptus macarthurii, 

Eucalyptus smithii as well as Acacia mearnsii. 

4.2.5 Preparing wattle bark 

Wattle bark is normally stacked in bundles of approximately 40cm x 40cm x 231 or 240cm. Thin 

strips of bark are used to tie the bundle. 

Bundle size is determined by the specifications of the receiving bark mill. Bark bundles vary in 

mass from 25kg to 40kg per bundle. Photo 4.4 below is an example of a bark bundle being 

prepared. 

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Photo 4.4: Preparing a bark bundle. 1 

Bark thickness is an important factor as mills pay a premium for thicker bark. 


The tables in Annexure “E” 2 give an indication of bark mass and volume for different bark 

thicknesses. 

4.3 Debranching 

Debranching is the process of removing the branches from felled trees. 

4.3.1 When debranching by axe the following should be noted: 

� Work from the butt-end of the tree towards the top. 

� Always debranch from the far side of the log. 

� Axe strokes should be with the angle of the branch and not against it. 

� Only debranch merchandisable timber. Do not waste effort to debranch above the 

minimum diameter mark. 

� Debranchers should be outside the danger zone of two tree lengths from felling 

operations. 3 

Debranching by chainsaw is the preferred method to remove branches. There are mainly two 

different methods to approach debranching, namely the six point lever method and the sweep 

method. 4 See Figure 4.3 and 4.4. 

4.3.2 Irrespective of which method is used, the following basic rules should be observed: 

� Work at a comfortable height and try to avoid bending over. This can be achieved by 

planning ahead and by correct felling. Use already felled trees, rocks or the terrain to 

create a comfortable working height. 

� Get a firm foothold and work with the chainsaw close to your body. 

� Flex your knees and not your back. 

� Do not move your feet when you are sawing on the same side of the tree as you are 

standing. 

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� The weight of the saw should be against the tree and not your leg. 

� Lead with your left leg when starting to debranch. 

Figure 4.3 (left): Six point lever method of debranching. 

Figure 4.4 (right): Sweep method of debranching. 


4.4 Cross-cutting 

Cross-cutting is the process whereby felled trees are cut into marketable lengths infield or at landings. 

It is important to use the correct technique when cross-cutting. Using the wrong technique can cause 

accidents, pinching of the saw or splitting of the log. 

4.4.1 Observe the following when cross-cutting: 

� Determine the stresses the stem is under, example upward, downward or sideways. 

� Observe carefully how the timber reacts to being sawn. 

� Be aware of where you are standing when you cross-cut. 

� Stand off to one side instead of right in front of the cut. 

� When cross-cutting stems with sideways tension one must always stand on the inside of 

the curve when cutting. 

Figure 4.5, 4.6 and 4.7 demonstrate the cutting technique for the most common tensions a stem 

can be subjected to. 3 

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Figure 4.5: Stem with downward tension. 

Method to use: 

1. Start by making a cut downwards until the cut begins to pinch the guidebar. 

2. Continue the cut from the bottom upwards. Try to make the two cuts meet. 

Figure 4.6: Stem with upward tension. 



1. Start by making a cut upwards until the cut begins to pinch the guidebar. 

2. Continue the cut from the top side downwards. Try to make the two cuts meet. 

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Figure 4.7: Stem under sideways tension. 



1. Cut an open directional wedge on the inside or non-stressed side of the stem. 

2. Start at the top and saw in stages until the stem breaks. 

3. Remember to always stand on the inside or non-stressed side of the stem. 

Guidelines for cross-cutting can be found in Annexure “F”. 

4.5 Infield stacking 

Infield stacking is the process whereby logs are grouped infield for further loading. The size of the 

stack is determined by the available volume, the log size and the loading method that will be used. 

Stacking can be done by hand or mechanically. As excessive infield disturbance of the soil is not 

good practice, mechanical stacking by 3-wheeler should be minimised where possible. 

Stackers should always ensure that the stacking area is free of bark, branches or other debris. 

Building the stack on bearers will ensure that minimum debris is picked up at loading. 

4.5.1 Stacking productivity and quality may be influenced by the following factors: 


� log length; 

� piece size and mass; 

� available volume per hectare; 

� terrain conditions; 

� stacking area; 

� stacking method; and 

� machinery employed. 

Positioning of the stack is an important element. If the stack is positioned in between stumps 

or standing trees, it could negatively affect the loading of the timber. The stack must be 

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created in such a position that the section of the stack at the point where the grab of the 

loading machine secures the logs is free of all obstacles. 

All stackers should be issued with logging tongs and should be trained in the proper use of 

them. 

Photo 4.5: Logging tongs. 

4.5.2 Stack types 

Depending on the terrain, stacking method, piece size and loading method, there are different 

types of stacks that can be constructed. 

4.5.3 Rough-lining of timber 

In this method the timber is just turned so that it all faces the same direction. The timber is 

normally not stacked but lies on long roughly aligned rows. See Photo 4.6. 

Photo 4.6: Roughlined timber. 

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4.5.4 Classic stack 

This type of stack is constructed by laying down two bearer logs approximately 2m apart. 

Uprights are hit into the ground to support the stacked timber. Depending on the loading 

and/or extraction method, stack size may vary anything from 2 to 5 tons per stack. See 

Photo 4.7. 

Photo 4.7: Classic stack. 

4.5.5 Diamond stack 

This type of stack does not require any uprights to be driven into the ground for support. The 

stack is built to supply its own support. This type of stack works well in flat areas. See 

Photo 4.8. 

Photo 4.8: Diamond stack. 

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4.5.6 Stacking production 

Stacking production is a function of the log size (length and volume), available volume, terrain 

and the type of stack to be built. Task tables for stacking of Eucalyptus are given in 

Annexure “D”. These tasks are based on building a classic stack. 

4.6. Mechanised timber preparation 

Mechanised timber preparation is gaining acceptance throughout our industry. Various equipment 

manufacturers are actively importing harvesting machines and related equipment. 

The mechanised timber preparation system can be classified into semi-mechanised and fullymechanised 

systems. See flowchart below. 

Semimechanised 

Mechanised 

harvesting 

Fully 

mechanised 

Wheeled based Tracked base Cut to length Multi stem 

Wheeled 

leveling / nonleveling 

Purpose built Hybrid Wheeled 

Tracked 


Wheeled 


Tracked 


Figure 4.8: Classification of mechanized harvesting systems. 

Semi mechanised systems are defined as a combination of motor-manual felling and mechanical 

debarking or further processing. The debarking, for example, can be done by a debarking head or 

other mechanical means like flail debarkers. Photo 4.9 shows a locally developed debarking head 

and Photo 4.10 a small flail debarker. 

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Photo 4.9: Locally designed debarking head. 

Photo 4.10: Locally manufactured flail debarker. 


Fully mechanised systems are systems where the felling and further conversion of the tree is done by 

fully mechanical means. The full mechanical system can further be categorised as Cut to Length (CTL) 

or multi stem systems. 

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CTL systems normally use equipment that can process one tree at a time. The tree is felled, 

debranched, debarked (where applicable) and cross-cut into lengths and deposited ready for loading by 

one machine. See Photo 4.11. 

CTL systems can furthermore be classified into so-called hybrid systems or purpose built systems. The 

hybrid systems are set up utilising an excavator or other suitable carrier together with a harvesting 

head. 

Purpose built systems are specifically designed to perform a harvesting function. 

Photo 4.11: Tracked single stem harvester (CTL system). 

Multi stem systems can process more than one stem at a time. See Photo 4.12. The multi stem system 

normally uses a felling and bunching piece of equipment, an extraction piece of equipment, a cross-cut 

or debarking system or even a chipping system. 

Photo 4.12: Equipment used in a multi stem harvesting system (feller buncher, grapple skidder, 

slasher deck). 

4.7 Mechanised felling 

Mechanised felling has the following advantages over motor manual felling: 

� Increased safety of the felling operation. 

� Increased felling production and productivity. 

� Improved downstream extraction activities due to improved directional felling and 

bunching. 

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� Multi shift felling allows for better equipment utilization. 

The following factors could influence mechanised felling productivity: 


� tree species; 

� tree size; 

� tree diameter; 

� espacement; 

� terrain; 

� underfoot conditions; 

� debarking percentage (where applicable); 

� stem form; 

� crown shape and size; 

� number and size of branches; 

� equipment type; and 

� operator competence. 


Mechanical felling heads use either a shear or a non-shear function to cut through a tree. 

Shears cut through a tree like scissors. See Photo 4.13. Non-shear disks cut through the tree using 

either a rotating disk or a bar and chain. See Photo 4.14. 

Photo 4.13 (left): Shear type felling head. 5 

Photo 4.14 (right): Felling head utilizing bar and chain. 1 

4.8 Mechanical debarking 

There are various types of mechanical debarking heads on the market. They all work on the principle 

of grooved rollers rotating the stem under pressure, which causes the bark to be stripped off as the 

stem passes through the rollers. Cutting knives shear off the branches in front of the rollers (see 

Photo 4.15). 

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As with manual debarking there are various factors that could influence the debarking production and 

quality. Such factors include: 

� species; 

� roller feed speed; 

� roller pressure; 

� tree form; 

� number and size of branches; 

� operator competence; and 

� terrain. 

1 Photos by A. Immelman. 

Photo 4.15: Felling/debarking head. 1 

Photo 4.16 (left): Mechanically debarked timber. 1 

Photo 4.17 (right): Timber presentation from mechanical felling, debarking and cross-cutting. 1 

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2 

Tables taken from De La Borde’s Timber Harvesting Manual – 1992. 

3 

Zaremba - 1976. 

4 

Husqvarna undated. 

5 

Photo by G. van Huysteen. 


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Forest Engineering – Timber Preparation - Sappi

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