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Cut-to-length, Tree Length or Full Tree Harvesting?
Source: Dr. Reino Pulkki, R.P.F.
Lakehead University, Faculty of Forestry

| HARVESTING METHODS AND SYSTEMS DEFINED |


INTRODUCTION

The objective of this paper is to generally compare the advantages and disadvantages of cut-to-length to tree-length and full tree harvesting methods and systems. Since there is considerable misuse of the terminology related to harvesting methods and systems they are briefly defined and described. The various equipment configurations and application of the methods to silvicultural systems are then presented. Finally, a one-grip harvester/forwarder system is compared to a conventional full tree system with feller-buncher, grapple skidder, stroke-delimber and slasher. A tree-length system is not considered since it lacks the clear advantages of the other two, with the exception that when compared to a full tree system the slash is distributed over the cut-over.

In any case, the choice of a harvesting method and system depends on the form of wood required at the receiving mill. For example, if a company is geared to accepting only tree-length wood due to the use of portal cranes, etc., a shift to a cut-to-length system would be a monumental change in wood receiving and handling at the mill. For this reason the comparison assumes either tree-length or log-lengths can be received at the mill. Also, it is assumed that roundwood is being delivered to the mills, thus chain flail-delimber-debarker chipper operations are not dealt with in this paper.
 

HARVESTING METHODS

A harvesting method refers to the form in which wood is delivered to the logging access road, and depends on the amount of processing (e.g. delimbing, bucking, barking, chipping) which occurs in the cut-over. The different harvesting methods are:

Cut-to-length (shortwood) - Trees are felled (cut-off above the stump with stump height less than one-half butt diameter), delimbed and bucked to various assortments (pulpwood, sawlog, veneer bolt, etc.) directly in the stump area. In softwoods, trees can be topped down to a 5 cm top diameter and limbs and tops can be left in windrows or spread over the cut-over. Logging can be fully mechanized or motor-manual. Off-road transport is usually by forwarding (i.e., wood is carried off the ground), although cable skidders are sometimes used. The cut-to-length method can be utilized in all silvicultural systems (e.g., clear felling, thinning, individual tree selection logging). Roadside landings are minimal since all processing is done in the cut-over and high roadside piles can be made. The method also allows for better sorting and storage of various wood assortments. Since the wood is carried off the ground the possibility of breakage and dirt contamination is much less than with the full tree and especially the tree-length methods. The cut-to-length method can be used efficiently even when in-woods inventory levels are minimal (i.e., hot-logging is very applicable). This method is re-establishing itself in North America due to its "softer" environmental impact, and now accounts for about 20 percent of the volume harvested east of Alberta.

Tree-length - Trees are felled, delimbed and topped in the cut-over. Delimbing and topping can occur in the stump area or at a point before roadside. The slash is distributed over the site. In softwoods, trees can be topped down to a 5 cm top, however, topping generally occurs at a 7 to 10 cm top. Trees are mainly skidded to roadside with cable or grapple skidders. Crawler tractors and clam-bunk skidders are also used to some extent. The tree-lengths are bucked to pulpwood and logs at roadside, or can be left as tree-lengths for tree-length hauling to the mill. The tree-length method is most applicable to clear felling, and can be used in row thinning. Landing requirements at roadside are much greater than for the cut-to-length method.

Full tree - Trees are felled and transported to roadside with branches and top intact. Transport to roadside is mainly by cable or grapple skidders. The full trees are processed at roadside or hauled as full trees to central processing yards or the mill. Roadside processing of full trees can include:

  • full tree chipping and hauling of full tree chips to the mill
  • delimbing and topping to produce tree-lengths for hauling to the mill
  • delimbing, topping and bucking to produce wood assortments for hauling as pulpwood to pulpmills or pulpwood using panel mills, and logs to sawmills or veneer mills
  • chain flail-delimbing-debarking-chipping to produce clean chips for transport to pulp and paper, or panel mills
With the full tree method the limbs, tops and wood residue, and in the case of the chain flail-delimber-debarker-chippers also the bark, are left in piles at roadside and must be disposed of. The slash can be raked into piles and burned, or left as is for natural breakdown. Another alternative is to spread the slash or delimber-debarker mulch back into the cut-over. The full tree method is most applicable to clear felling operations, and in some cases to first commercial thinning where the material is transported to roadside by forwarder. The landing requirement is the highest with this method. The full tree method is currently the most widely used method in Canada east of Alberta.

Whole tree - There is much confusion in the use of this term. For example, in the U.S., the term whole tree logging is equated to full tree logging. However, in this paper a broader international definition of the whole tree method is used. In the whole tree method, full trees including the stump are removed to roadside for processing and utilization. This method is seldom used in Canada.
 

Complete tree -Full trees, including stump and major roots are removed to roadside for processing and utilization. This method is seldom used.

Table 1 presents statistics on the use of the various logging methods in Canada in 1990 based on a survey done by the C.P.P.A. of member companies. This data represents about one-third of the total harvest in Canada. Figure 1 presents the development in the use of the major logging methods in Canada east of Alberta. An important development has been the shift back towards in-stand delimbing and the use of tree-length and cut-to-length methods.
 

Table 1. Statistics on the use of logging methods in Canada in 1990 (C.P.P.A. 1992, Survey of Member Companies).
Province Use of logging methods, % Harvest volume reported 1000 m3
Full tree Tree-length Cut-to-length Multiple log length
Newfoundland 0 51 49 0 1464
Nova Scotia 32 29 39 0 1551
New Brunswick 69 13 17 0 4535
Quebec 71 20 9 0 10565
Ontario 92 8 0 0 9136
Manitoba 34 66 0 0 756
Saskatchewan 70 23 7 0 1278
Alberta 0 99 1 0 4437
B.C. Interior 42 36 1 21 15003
B.C. Coast 1 1 0 98 14806
Total Canada 43 24 5 28 63531


Figure 1.Logging method use trends for Canada east of Alberta (C.P.P.A. and FERIC data).

HARVESTING SYSTEMS

A harvesting system refers to the tools, equipment and machines used to harvest an area. The individual components of the system can be changed without changing the harvesting method (i.e., the form in which the wood is delivered to roadside). A typical cut-to-length logging system could employ a one-grip harvester which fells, delimbs and bucks the trees right in the stump area, and a forwarder to carry the pulpwood and logs to roadside. With the tree-length method a common system would include motor-manual (chain saw) felling, delimbing and topping, tree-length skidding to roadside, and roadside slashing. A typical harvesting system used in full tree harvesting would include a feller buncher, grapple skidder, stroke delimber and slasher.

EQUIPMENT CONFIGURATIONS AND APPLICATIONS

Tables 2 and 3 summarize equipment configurations for the three methods, and their applicability to various silvicultural systems. As can be seen from the tables the cut-to-length method and systems are the most versatile. This has resulted in almost 100% use of cut-to-length systems in the Nordic countries since:

  • logging areas are small (e.g. <2 ha) and widely scattered
  • landing area is minimal
  • road right-of-ways are narrow
  • there is a need for use of the equipment in individual tree selection thinning, shelterwood and seed tree cuts
  • minimal (<2%) or even no damage in many cases is allowed to residuals in partial cuts (e.g., commercial thinning, shelterwood cuts)
  • there is a requirement to protect advanced regeneration when removing the over-story in seed tree and shelterwood cuts
  • there must be minimal impact on the site
Optimum forest access road densities required by the various logging systems generally vary from 8.3 to 16.7 m/ha (i.e., the length of road required on average to access an area for logging). A road density of 16.7 m/ha is equivalent to a maximum straight-line off-road transport distance of 300 m (i.e., 10000/(density x 2)). The optimum road spacing and thus maximum off-road transport distance is a factor of skidding/forwarding machine cost, driving speeds empty and loaded, load size, volume removed per hectare, and access road construction and maintenance cost.

Logging systems using grapple and cable skidders generally cannot work past a 300 m skid distance and remain economical. Often, however, with full tree systems excessive road is built and access road density can be in excess of 30 m/ha. This is especially true in larger clear-cut areas, with high volumes, since roads and spurs must be built to provide sufficient landing space.

Forwarders and large clam-bunk skidders can effectively operate to off-road transport distances in excess of 600 m (8.3 m/ha) due to their large load size (i.e., >15 m3/load). In areas where the construction of an individual spur is required when using skidders, the maximum economical off-road transport distance with a forwarder can extend up to 1,200 m. It is important that the forwarder is used to its fullest off-road capacity since at this point its production is more or less in balance with a one-grip harvester. If too short an off-road transport distance is used, the road cost is excessive and the forwarder has excess capacity. Thus, a major benefit of the system through reduced road cost and reduced area covered by roads is lost.

Similarly, when using a one-grip harvester to produce tree-lengths or delimbing in the cut-over with a processor to produce tree-lengths, the advantages associated with both the full tree systems (e.g., high productivity and concentrating processing at roadside) and cut-to-length systems (e.g., extended off-road transport distances, cleaner wood, minimal roadside landings) are lost. For this reason, the following comparison is only between a convention full tree system (feller buncher, grapple skidder, delimber, slasher) and cut-to-length system (one-grip harvester, forwarder) producing logs and pulpwood.
 

Table 2. Configurations and characteristics of the major logging methods.
CHARACTERISTIC Cut-to-length Tree-length Full tree
Felling equipment chain saw chain saw chain saw
one-grip harvester feller buncher feller buncher
two-grip harvester one-grip harvester
two-grip harvester
Off-road transport equipment forwarder cable skidder
cable skidder (limited use) grapple skidder
clam-bunk skidder
cable yarder
Delimbing and topping location stump area stump area roadside
within cut-area not delimbed
Bucking location stump area roadside roadside
centralized yard centralized yard
mill mill
not bucked not bucked
Slash distribution evenly spread evenly spread Roadside piles
windrows small piles no slash left
Roadside landing requirements & impact small large largest
Maximum effective off-road transport distance 

(straight-line)

600 m cable & grapple skidders - 300 m
clam-bunk skidder - 600 m
Access road requirement 8.3 m/ha cable & grapple skidders - 16.7 m/ha
clam-bunk skidder - 8.3 m/ha
Area with vehicular traffic low cable & grapple skidders - heavy
clam-bunk skidder - moderate
Ground disturbance - dry low moderate heavy
Ground disturbance - frozen minimal low low
Ground disturbance - wet moderate heavy heavy
Protection of residual trees & regeneration good moderate poor

Table 3. Applicability of harvesting methods to silvicultural systems and operations.
Operation Cut-to-length Tree-length Full tree
EVEN-AGE SILVICULTURE SYSTEMS
clearcutting Good Good Good
clearcutting with standing snags and live trees Good Good Good
patch cutting Good Good Good
alternate strip cutting Good Good Good
progressive strip cutting Good Good Good
shelterwood cutting Good Moderate Poor
seed tree cutting Good Good Moderate
UNEVEN-AGE SILVICULTURE SYSTEMS
individual tree selection cutting Good Poor Poor
group selection cutting Good Moderate Poor
OTHER SILVICULTURAL CUTTING OPERATIONS
selection thinning Good Poor Poor
row thinning Good Moderate Poor
over-story removal (shelterwood and seed tree) Good Moderate Poor

LOGGING SYSTEMS OPERATIONAL AND COST COMPARISON

One-grip Harvester/Forwarder System Operation

A typical working unit for a cut-to-length logging system is a one-grip harvester and forwarder. In general, the production of a full-size one-grip harvester and forwarder (e.g., 14 t payload) is in balance. This assumes the off-road transport capacity of the forwarder is used to its fullest (i.e., forwarding distance up to 600 m). If this is not the case the forwarder will have excess capacity and one of the major advantages of the system through less roads per hectare is lost.

The annual production capacity of the system with experienced operators, on double shift, and an average tree size of 0.2 m3/stem is about 50,000 m3 (i.e., 15 m3/PMH). In general, this is also close to the annual capacity of a haul truck running on an 80-100 km haul. In the Nordic countries annual production capacities of 60,000 m3 are typical when operating in clear felling conditions, and from 40,000 to 50,000 m3 when working in a mix of clear felling and partial cutting (e.g., thinning) conditions. Since the components of the system are in balance, it is not uncommon in Finland or Sweden to see wood felled and processed in the morning, forwarded to roadside by the afternoon and hauled to the mill in the evening.

A major disadvantage with the one-grip harvester is its complexity and thus the high operator skill required. For this reason training operators is very expensive and it may take up to two full years for an operator to become totally competent in its operation. However, within several months most operators become sufficiently proficient. A general comment often heard in the field is that "old" feller-buncher operators do not make good one-grip harvester operators. However, I am aware of no research which supports this general comment though.

A major problem noticed with new operators is the unwillingness to use the reach of the boom to its fullest. In many cases they prefer driving closer to the trees than use the 9 to 10 m reach capacity. Thus, productivity is lost through excessive machine driving and positioning time. In addition you end up with more vehicle traffic on site, as opposed to machine trails with a spacing of 15 to 20 m. Also, with inexperienced operators hang-ups, trees felled on top of the machine, broken components, etc., can easily occur.

Operating a one-grip harvester has been found to be a high stress job. For this reason, on some operations the harvester and forwarder operators switch machines half-way through the shift. In this way harvester productivity is maintained at its maximum, and operator health maintained. Another benefit is that the operator generally ends up forwarding the wood he harvested, and thus can only blame himself for piles that a too small, sloppy or badly placed. This type of arrangement assumes that both operators are proficient on the harvester, and that any contract agreements (e.g., union agreements) allow this.

A one-grip harvester's productivity is greatly influenced by tree-size. Thus, there has been development work on heads which can fell and process multiple trees. Since a forwarder can pick up multiple trees, its productivity is not influenced by tree size to the same extent. For both machines, however, the length of the bolts has a major impact on productivity. For this reason, every attempt should be to process long-length logs and pulpwood. In this type of operation the logs can be merchandised from the stem, and the top is kept as one long pulpwood piece of 5.1 to 6 m in length. Both harvester and forwarder productivities drop considerably if a lot of 100 inch pulpwood is produced.

Another advantage of the one-grip harvester/forwarder system is the buffer inventory between the harvester and forwarder can be minimal and still allow smooth running of the operation (i.e., equipment delays due to mechanical failure or equipment congestion at roadside). This allows for hot-logging operations. Also, hot-logging with cut-to-length operations is important in winter since the processed wood piles in the cut-over can be easily lost under snow if left for extended periods of time.

A full-size one-grip harvester and forwarder system of Nordic design costs about $1 million (including training package and some spare parts), with the price for the harvester being about $550,000, while for an eight-wheel forwarder it is about $450,000. However, this varies by manufacturer and the accessories/design of the equipment, with North American designed and built equipment being somewhat cheaper. Assuming a $1 million purchase price, the initial investment cost is approximately $20/m3 of annual production.

Conventional Full Tree System

A convention full tree operating unit generally consists of 2 feller-bunchers, 2 large- size grapple skidders, 1.5 roadside delimbers and 1.5 slashers. This varies depending on the logging chance factors, season, quality of the equipment used (i.e., mechanical availability) and the operational expertise. However, in general the above mix holds true.

In most cases it is the feller-bunchers which are the major influence on overall productivity of the system. On average, the annual productivity for a feller-buncher working a double shift is about 90,000 m3, or 180,000 m3 for the operating unit. Tree size is an important factor which influences productivity, but not to the same extent as with one-grip harvesters due to continuous sawheads and multiple tree capabilities.

A major operational advantage of the conventional full tree system is the robustness of the equipment, ease of operator training and ready availability of equipment and parts. There is also the general familiarity of the equipment due to historic reasons, although much of the initial development of both cut-to-length and tree-length one-grip and two-grip harvesters occurred in Northern Ontario during the 1960's and early 1970's. Another advantage is that the cut-over is generally clear of slash and logging residues. This eases site preparation and planting operations. When relying on natural regeneration in jack pine and black spruce, however, this is a disadvantage since the natural seed source in the cones is removed.

A major operational disadvantage is the many phases and pieces of equipment used. For the system to work efficiently there generally needs to be a buffer of approximately a half to one week's supply of wood between all phases. Otherwise, equipment breakdowns and traffic congestion can cause major operational delays. With the one-grip harvester/-forwarder system the wood can theoretically be delivered to the mill on the same day, while with the conventional full tree system a minimum four week period from felling to delivery to the mill is generally required.

The overall average investment cost for the operating unit is about $2.15 million ($400,000 per feller-buncher, $225,000 per grapple skidder, $350,000 per delimber and $250,000 per slasher). This is an initial investment cost of about $12/m3 of annual production.

SYSTEM COST COMPARISON

Using a standard equipment costing model, with the above purchase prices and system productivities, operating costs per m3 were determined (Table 4). No allowance has been given for profit and the same wages, fuel costs, interest rates, etc. were used. The annual capital cost is calculated as the Capital Recovery Depreciation. In addition to equipment operating costs, the costs of roads/landings and roadside debris pile disposal were added. The road and landing construction cost is assumed to be $20,000/km or $20/m, the average volume removed per hectare is 100 m3, and the road density is at the optimum for each system. In must be noted that the costs are estimates based on standard input data, and will vary depending on the purchase price of the equipment, productivity, salaries, fringe benefits paid, etc. It is also assumed that all overhead, planning and forestry costs are similar between the systems, although they should be cheaper for the one-grip harvester/forwarder system.

Table 4. Logging systems cost comparison (softwoods) assuming starting with new, top of the line equipment: no allowances for profit, overheads, planning and silvicultural costs, or differences in wood utilization and quality included.
One-grip harvester/forwarder system Conventional full tree system
$/m3 $/m3
Harvester 

Forwarder

8.65 

7.15

Feller-buncher 

Skidding 

Delimbing 

Slashing

4.00 

3.10 

2.50 

2.10

Extraction cost 15.80 Extraction cost 11.70
Roads 1.66 Roads 3.34
Debris disposal 0 Debris disposal 0.50
Total roadside cost  17.46 Total roadside cost 15.54

From the points of view of initial capital investment ($12 vs $20 per m3 of annual production) and overall roadside cost ($15.54 vs $17.46 per m3), the conventional full tree system seems to have a clear cost advantage, when compared to the one-grip harvester/forwarder system. The high capital cost for the Nordic cut-to-length equipment is a major disadvantage.

The costs per m3 are sufficiently close, however, that any number of the above factors could result in a competitive advantage for either system. For example, in areas where the cut areas are becoming smaller and more widely dispersed, the moving and set-up costs for the conventional full tree system becomes a major problem. Therefore, it is important that each case is analysed based on the conditions present and productivity levels achievable.

CONCLUSION
 

The need for "softer" logging techniques which can operate in smaller and more widely dispersed logging areas, and in partial cutting situations, has resulted in a resurgence of cut-to-length logging in North America. As outlined in the paper both full tree and cut-to-length logging systems have their advantages and disadvantages. Thus, the most appropriate system to use must be determined through a thorough analysis of each individual situation. However, there is a need for the price of one-grip harvesters and forwarders to be reduced, since an initial capital investment cost of $20 per m3 of annual production is clearly too high.

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