|| WORLD BOREAL SCIENCE & INNOVATION ||
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 |
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.
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 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:
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.
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
to produce clean chips for transport to pulp and paper, or panel mills
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
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).
of logging methods, %
volume reported 1000 m3
Figure 1.Logging method
use trends for Canada east of Alberta (C.P.P.A. and FERIC data).
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.
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:
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
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
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
there must be minimal impact
on the site
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.
skidder (limited use)
||no slash left
|Roadside landing requirements
off-road transport distance
& grapple skidders - 300 m
skidder - 600 m
& grapple skidders - 16.7 m/ha
skidder - 8.3 m/ha
|Area with vehicular
& grapple skidders - heavy
skidder - moderate
|Ground disturbance - dry
|Ground disturbance - frozen
|Ground disturbance - wet
|Protection of residual trees
Table 3. Applicability
of harvesting methods to silvicultural systems and operations.
|clearcutting with standing
snags and live trees
|alternate strip cutting
|progressive strip cutting
|seed tree cutting
|individual tree selection
|group selection cutting
|over-story removal (shelterwood
and seed tree)
LOGGING SYSTEMS OPERATIONAL
AND COST COMPARISON
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
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
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
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.
full tree system
|Total roadside cost
||Total roadside cost
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.
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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