United States

Department of

Agriculture

Forest

Service

Northern

Research Station

General Technical

Report NRS-69

MECHANIZED SYSTEMS FOR

HARVESTING EASTERN HARDWOODS

Chris B. LeDoux
Abstract

In the central Appalachian region, hardwoods traditionally have been harvested 

by chainsaw felling with trees and logs extracted from the forest to landings 

by rubber-tired skidders, bulldozers, and crawler tractors. In recent years, 

mechanized systems that include feller bunchers and cut-to-length (CTL) 

processors coupled with forwarders and clambunk and grapple skidders have 

been used increasingly to harvest Eastern hardwoods. Feller bunchers fell 

trees and pile stems or logs in bunches. CTL processors fell trees and delimb 

them, buck the stems into logs, and pile them in presorted bunches. Wood piles 

and bunches are transported to landings by a clambunk or grapple skidder 

or a forwarder. These system combinations for processing and transporting 

essentially eliminate the need for woods workers on the ground, a major 

advantage from a production and safety standpoint, and greatly reduce adverse 

effects on the site compared to chainsaw felling and conventional skidding. Feller 

buncher and CTL systems are reviewed, results of environmental impact studies 

are presented, and cost equations for a range of operating conditions in Eastern 

hardwoods are provided.

Visit our homepage at: http://www.nrs.fs.fed.us/

Published by: For additional copies:

USDA FOREST SERVICE USDA Forest Service

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Delaware, OH 43015-8640

September 2010 Fax: 740-368-0152

The Author

CHRIS B. LEDOUX is a research industrial engineer with the U.S. Forest 

Service’s Northern Research Station at Morgantown, West Virginia.

Manuscript received for publication December 2009

1. Cut-to-length processor (photo courtesy of Andrew 

Whitman, Manomet Center for Conservation 

Sciences); 2. Crawler dozer (photo courtesy 

of Caterpillar); 3. Rubber tired skidder 

(photo courtesy of Tigercat); 4. Trackmounted clambunk skidder (photo courtesy 

of Andrew Whitman, Manomet Center 

for Conservation Sciences); 5. Clambunk 

skidder (photo courtesy of Tigercat); 6. Small 

forwarder (photo by Neil Huyler, U.S. Forest 

Service, retired); 7. Track-mounted feller buncher 

processor (photo courtesy of John Umstead, West Virginia University); 

8. Cut-to-length processor (photo by Kurt Gottschalk, U.S. Forest Service).

Cover Photo

1 2

3

4

5 6

7 8

The use of trade, fi rm, or corporation names in this report is for the information and 

convenience of the reader. Such use does not constitute an offi cial endorsement or 

approval by the U.S. Department of Agriculture or the Forest Service of any product 

or service to the exclusion of others that might be suitable.
CONTENTS

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Feller Buncher and CTL Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Site Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Estimating Production and Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Literature Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
GTR-NRS-69 Page 1

INTRODUCTION

Mechanized systems that include feller bunchers and cut-to-length (CTL) 

processors coupled with clambunk and grapple skidders are used increasingly 

to harvest hardwoods in the Central Appalachian region (American Pulpwood 

Assoc. 1997, Long 2003). The trend toward increased mechanization is attributed 

to the need to address concerns related to productivity, safety, environmental, and 

cost concerns (LeDoux and Huyler 2001a, Wester and Eliasson 2003). 

Daily production using machines to fell, delimb, cut to length, and bunch 

trees can exceed that achieved by crews of hand fallers. A study by the Forest 

Engineering Institute of Canada showed that a mechanized system (feller 

buncher/stroke delimber/grapple skidder) can produce a higher volume per hour 

at a lower cost per unit volume than a conventional system (hand faller/hand 

delimber/line skidder) (Phillips 1997). A study of CTL harvesting by LeDoux 

(2002) in New Hampshire, Vermont, and Maine showed that a substantial amount 

of the forest inventory would be profi table using this system.

Mechanization also helps ensure a year-round supply of timber to mills because 

the machines cited can operate in poor weather (American Pulpwood Assoc. 

1997). Some mills even help loggers acquire the necessary equipment. Using 

a feller buncher or CTL processor increases safety because the direction in 

which a tree falls can be controlled and the severed tree can be held securely 

and transported to the desired location, thus protecting operators from falling 

debris (Bell 2002, Shaffer and Milburn 1999). These machines also position 

felled trees such that hand delimbing and bucking is safer. Feller bunchers and 

CTL processors vary by type and size (Blinn et al. 1986; Greene and McNeel 

1987, 1991) to accommodate different forest types, composition of primary tree 

species, topography, e.g., steep slopes and swamps (McDonald et al. 2000, Long 

2003), site conditions, e.g., pine plantations (Aedo-Ortiz et al. 1997, McDonald 

et al. 2000) or products, e.g., pulpwood (Green et al. 1987, Greene and McNeel 

1991). In this report we review feller buncher and CTL harvesting systems, 

present results of safety and environmental impact studies, and provide equations 

that can be used to estimate costs for a wide range of operating conditions in 

Eastern hardwoods.
Page 2 GTR-NRS-69

FELLER BUNCHER AND CTL SYSTEMS

In harvesting the hardwood resource, CTL processors and feller bunchers 

(Figs. 1 and 2) can be fi tted with different felling, delimbing, and debarking 

heads (Huyler and LeDoux 1996, 1997, 1998, 1999; LeDoux and Huyler 2000, 

2001a,b), and generally are coupled with rubber-tired skidders with grapples 

(Fig. 3), dozers and crawlers with grapples (Fig. 4), clambunk skidders (Fig. 5), 

or forwarders (Fig. 6) to transport trees or logs to landings or central-processing 

areas. Such systems are best applied on gentle to moderately steep terrain. The 

CTL processor fells, delimbs, bucks a tree into logs, and debarks the stem. It 

can sort the wood as desired and build bunches according to the capacity of 

the machine used for skidding. Besides felling a tree, the feller buncher can 

accumulate multiple stems in the head, sort wood as required, and build bunches 

for transport by the skidding machine.

The machines that we studied were track-mounted with a self-leveling cab, and 

equipped with a boom that can extend the felling head a substantial distance 

beyond the machine itself. Track mounted machines are best suited for steeper, 

uneven and cut up terrain with ravines and rock outcrops. Such mechanized 

systems generally are ergonomic and highly maneuverable, and minimize soil 

disturbance and compaction and residual stand damage (LeDoux and Huyler 

2001b, Wang et al. 2005). The CTL harvester can use limbs from the delimbing 

process to form a mat to travel on, further mitigating soil disturbance and 

compaction. A clambunk skidder is commonly used in association with CTL 

processors and feller bunchers (Fig. 5). It can be mounted on rubber tires or 

tracks and are equipped with a bunk and large grapple or clam attached to the 

back of the skidder. This machine generally is used to move bunched logs to 

a landing or central-processing area, and can be equipped with a boom with 

grapple attachment that can be used to build loads, sort logs, build decks, or 

maintain landings.

Although large volumes of wood can be moved in a short time and logs can be 

transported long distances, major trails used to travel to and from the landing 

and log-processing areas can be severely impacted. The maneuverability of a 

clambunk skidder is limited because of its size. One end of the log rests on the 

bunk and is held there while the other end is dragged along the ground.
GTR-NRS-69 Page 3

Figure 1.—Large, selfleveling track-mounted, 

cut-to-length processor 

with felling and 

delimbing head (photo 

courtesy of Andrew 

Whitman, Manomet 

Center for Conservation 

Sciences).

Figure 2.—Large, selfleveling, track-mounted 

feller buncher with 

accumulating felling 

head (photo courtesy 

of John Umstead, West 

Virginia University).

Figure 3.—Rubbertired skidder equipped 

with grapple and highfl otation tires (photo 

courtesy of Tigercat). 
Page 4 GTR-NRS-69

Figure 4.—Mediumsize, track-mounted 

crawler dozer with 

grapple in back and 

blade in front skidding 

a turn of logs (photo 

courtesy of Caterpillar).

Figure 5.—Trackmounted clambunk 

skidder with boom 

attachment working 

on log deck (photo 

courtesy of Andrew 

Whitman, Manomet 

Center for Conservation 

Sciences).

Figure 6.—Small 

forwarder with rubber 

tires and chains in the 

front, tracks in the rear, 

boom, blade in the front, 

unloading and sorting 

at the landing (photo by 

Neil Huyler, U.S. Forest 

Service, retired).
GTR-NRS-69 Page 5

A forwarder generally is used to transport logs and trees in association with 

a feller buncher and CTL processor (Fig. 6) when logs and trees have been 

prebunched in the woods. Forwarders are produced in various sizes and can 

handle a range of payloads. They are typically confi gured with rubber tires 

and chains or a track-based carrier and a boom with grapple attachment for 

self-loading and unloading. Because of the increased volume it can carry, the 

forwarder is a good alternative to a rubber-tired or dozer skidder when skid 

distances are long and the terrain is gentle to moderately steep (Erickson 1992).

Forwarders can sort logs or trees by species or product type while loading in the 

woods or at the landing. They are slower than rubber-tired skidders but they can 

transport larger payloads than skidders and dozers. Wood is carried on bunks 

and not dragged along the ground. Overall impact on the site is relatively light, 

though soil disturbance and compaction can be signifi cant on the most heavily 

traveled skid roads and trails.

Rubber-tired skidders (Fig. 3) or dozers and crawlers (Fig. 4) equipped with 

grapples transport bunched logs to landings or central-processing areas. The use 

of grapples is best matched with prebunched wood, i.e., bunched by the feller or 

CTL processor. Logs generally are dragged along the ground. As with forwarders, 

skidders and crawlers are best suited to gentle or moderate terrain and can 

increase soil disturbance and compaction on the most heavily used skid trails.

Seventy percent of current harvesting systems require the use of chainsaws to 

fell, buck, limb, and top trees1

. They also are used to bump knots and clean and 

dress-up logs at the landing before hauling to processing plants. Unfortunately, 

the use of chainsaws in the woods has resulted in serious and even fatal 

injuries. In fact, the chainsaw is the largest contributor to logging accidents 

and injuries, according to the Occupational Safety and Health Administration 

(www.osha.gov). Where they are used, mechanized harvesting systems have 

dramatically reduced numerous risks associated with chainsaws by eliminating 

the need for chainsaw operators and other woods workers (Bell 2002, Shaffer 

and Milburn 1999).

1

 LeDoux, C.B. Harvesting systems for eastern hardwoods. Unpublished report on fi le at 

the Northern Research Station, 180 Canfi eld Street, Morgantown, WV 26505.
Page 6 GTR-NRS-69

SITE IMPACTS

Despite the diligent use of “best management practices,” some harvesting 

systems create a certain amount of stand damage, including soil disturbance 

and compaction. Excessive disturbance along with severe rutting on moderate 

to steep slopes can be long-lasting and result in erosion and sedimentation. The 

use of mechanized harvesting systems can greatly minimize adverse impacts 

on residual stand because trees can be felled directionally, they are not dragged 

through the stand, and stems marked for cutting can be easily removed from 

within clumps or tangles with minimal damage to residual trees (LeDoux and 

Huyler 2001b). Delimbing occurs in front of the machines, so limbs and slash 

can be used as a mat upon which a machine can travel. As a result, the use of 

track-mounted feller bunchers and CTL processors cause less soil disturbance 

and compaction than traditional skidder-based systems. Although rubber tires 

are available for use on gentle terrain (McDonald et al. 2000), track-mounted 

machines operate primarily on moderate to steep slopes (Huyler and LeDoux 

1996, 1997, 1998, 1999; LeDoux and Huyler 2000, 2001a,b; Long 2003; Wang 

et al. 2005).

These machines simply drive themselves from tree to tree where conventional 

logging systems would require skid trails to be built or logs to be winched 

through the stand to form a load. Studies have shown that mechanized, 

track-mounted systems resulted in less soil disturbance and compaction than 

conventional systems when operating in similar conditions (Wang and LeDoux 

2005, Wang et al. 2007). The most heavily used skid trails should incur high 

levels of soil disturbance and soil compaction, particularly where multiple passes 

by loaded and unloaded machines are required in extracting trees and logs from 

the woods to landings (Wang et al. 2006).
GTR-NRS-69 Page 7

2

 LeDoux, C.B.; Wang, J. Development of general production and cost equations for 

feller bunchers in central Appalachian hardwoods. In preparation.

3

 Acronyms are defi ned in Tables 1 and 2.

ESTIMATING PRODUCTION AND COST

We developed equations2 for estimating the cost of feller bunching, CTL 

harvesting, and forwarding based on results from time and motion studies and 

simulations. These equations were incorporated into the ECOST computer 

program. ECOST was developed by the author to estimate stump-to-mill costs 

related to logging Eastern hardwoods via cable, conventional ground-based 

skidding, mechanized harvesting systems, and small tractors. The program is 

available for downloading at: http://www.nrs.fs.fed.us/tools/software.

Cost equations are included for a Valmet 524 forwarder (Table 1), Timbco 425 

and 445 feller bunchers (Table 2), Timbco T425 and JD 988 CTL harvesters 

(Table 3), and Timberjack 460 grapple skidder (Table 4). Note that cost estimates 

based on variables outside the limits listed in Tables 1-4 likely will be unreliable.

Suppose a logger wants cost estimates using a Timbco 425 feller buncher to cut 

timber and a Valmet 524 forwarder to transport wood to a landing. The travel 

distance for the forwarder is 800 feet (SYD)3

, the average diameter of the trees to 

be cut is 12 inches (DBH)3

, and the volume to be removed per acre is 2,000 cubic 

feet (VOAC)3

. For the feller buncher, the equation is:

 TreeVol= –32.0924 + 5.529 * 12 = 34.25

 VOAC = 2000

119.17

(1087.1828 + 38.0275 * TreeVol + 0.1865 * VOAC)

$ ⁄ ft3 =

119.17

(1087.1828 + 38.0275 * 34.25 + 0.1865 * 2000)

$ ⁄ ft3 =

$ ⁄ ft3

 = .0431 (~.04)
Page 8 GTR-NRS-69

Table 2.—Simulated delay-free felling and bunching cost equations for two 

 feller bunchersa.

Feller buncher Equation Variable limit

Timbco 425 $/ft3 = 119.17 DBH: 4 to 30

/ (1087.1828 + 38.0275 * TreeVol VOAC: 334 to 10600

 + 0.1865 * VOAC)

Timbco 445 $/ft3 = 138.33 DBH: 4 to 30

/ (633.3737 + 63.9942 * TreeVol VOAC: 334 to 10600

 + 352162.052 * (1 / VOAC))

a TreeVol = tree volume (ft3

); DBH = average diameter breast height (inches); VOAC = 

volume cut per acre (ft3). NOTE: If DBH = 4, TreeVol = 1.76; if DBH = 5, TreeVol = 2.37; 

if DBH = 6, TreeVol = 4.72; otherwise TreeVol = –32.0924 + 5.529*DBH.

Table 3.—Simulated delay-free cut-to-length cost equations for two CTL 

harvestersa.

CTL harvester Equation Variable limit

Timbco T425 $/ft3 = 146.7 / (7830 + 270.77 * DBH DBH: 5 to 20

 – 1.88 * DBH * HT DC: Constant at 22

 – 642.51 * DC + 11.44 * DC2)

JD 988 $/ft3 = 115.0 / (–440.25 DBH: 5 to 14

 + 201.74 * DBH – 1.85 

* DBH * HT)

a

HT = total height (ft) = 34.95428248+2.672088601*DBH; DC = average ground travel 

distance of harvester/cycle (ft) = 22; DBH = average diameter at breast height (inches). 

Table 4.—Simulated delay-free cost equation for grapple skiddera.

Grapple skidder Equation Variable limit

Timberjack 460 $/ft3 = 0.65 * ((82.17 / (466.49 SYD: 400 to 1800

 – (0.13*SYD) + (3.76*Pl) Pl: 50 to 250

 – (0.003*Pl2) – (0.36*BS) BS: 30 to 270

 + (0.003*BS2))))

a

SYD = slope yarding distance (ft); Pl = pay load (ft3); BS = bunch size (ft3).

Table 1.—Simulated delay-free cost equation for forwardera.

Forwarder Equation Variable limit

Valmet 524 $/ft3 = 110 / TP: Constant at 400

(408.9482 + 0.00241 * TP SYD : 50 to 1627.4

* SYD – 0.0006 * SYD2

) 

a

TP = turn payload (ft3) = 400; SYD = slope travel distance (ft).
GTR-NRS-69 Page 9

For the forwarder the equation is:

 TP = 400

 SYD = 800

Felling and extracting using both machines would cost about $0.18/ft3

, or 

about $17.64/cord. Be advised that these estimates are “delay free”, that is, 

theoretical production for a given machine and stand condition with no idle 

time or delay. Another way to think of “delay free” estimates is that these are 

the production levels we observed during our time and motion studies when 

the respective machines were in full production mode with no delays and idle 

time. Although these production levels are possible, they are unlikely over the 

course of a longer production cycle. Thus, all estimates must be adjusted for 

delays and down/idle time. In this example, if we assume that the logger expects 

about 18 percent delay/down/idle time for both the felling and forwarding 

operations, our estimates of $17.64/cord would be adjusted such that 

$17.64/(1–.18) = 17.64/.82 = $21.51/cord. The equations also can be 

adjusted for various combinations of machines, sites, and delay times.

110

408.9482 + 0.00241 * TP * SYD – 0.0006 * SYD2 $ ⁄ ft3

 = 

$ ⁄ ft3

 = .1382 (~.14)

110

408.9482 + 0.00241 * 400 * 800 – 0.0006 * 8002 $ ⁄ ft3

 = 
Page 10 GTR-NRS-69

CONCLUSION

Mechanized feller buncher and CTL systems have major advantages over 

ground-based skidders in that they allow sustained productivity, increase safety, 

and reduce site impacts (Wang et al. 1998, Wang and LeDoux 2003). They can 

be highly productive in cold and windy weather, rain and snow, and on muddy 

and swampy sites (American Pulpwood Assoc. 1998). The need for chainsaws 

and woods workers is virtually eliminated, thus reducing safety risks and 

hazards. Damage to the residual stand also is reduced, and soil disturbance and 

compaction are minimized compared to conventional systems.

There also are disadvantages in using mechanized harvesting systems. Feller 

bunchers and CTL processors are expensive to purchase and maintain and present 

challenges when moving from site to site due to their size. They are larger and 

wider than conventional equipment, so moving these machines might require 

special permits, the use of fl ag vehicles, and oversize, lowboy mule trains. Also, 

on some roads and bridges, dismantling of some equipment may be necessary to 

meet safety standards and/or weight limits.

Our intent is not to promote mechanized systems but to provide information that 

can be used in selecting equipment for use in alternate harvesting operations. An 

even fl ow of wood year round is imperative to generate profi ts, meet payrolls, 

and purchase equipment. The use of mechanized systems that include feller 

bunchers and CTL processors coupled with forwarders, rubber-tired or tracked 

grapple skidders, or clambunk skidders can help loggers meet this objective.
GTR-NRS-69 Page 11

LITERATURE CITED

Aedo-Ortiz, D.M.; Olsen, E.D.; Kellogg, L.D. 1997. Simulating a harvesterforwarder softwood thinning: a software evaluation. Forest Products 

Journal. 47(5): 36-41. 

American Pulpwood Association. 1997. Active cut-to-length equipment in 

northern New England. Rockville, MD: American Pulpwood Association. 

33 p.

American Pulpwood Association. 1998. In-woods processing—tree 

characteristics that impact production. Rockville, MD: American 

Pulpwood Association. 35 p.

Bell, J.L. 2002. Changes in logging injury rates associated with use of feller 

bunchers in West Virginia. Journal of Safety Research. 33(4): 463-471.

Blinn, C.R.; Sinclair, S.A.; Hassler, C.C.; Mattson, J.A. 1986. Comparison of 

productivity, capital, and labor effi ciency of fi ve timber harvesting 

systems for northern hardwoods. Forest Products Journal. 36(10): 63-69.

Erickson, M.D.; Hassler, C.C.; LeDoux, C.B. 1992. Economic comparisons of 

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meeting; 1992 December 15-18; Nashville, TN. ASAE Pap. 92-7513. 

St. Joseph, MI: American Society of Agricultural Engineers. 17 p. 

Greene, W.D.; Lanford, B.L.; Mykytka, E.F. 1987. Stand and operating effects 

on feller buncher productivity in second thinnings of southern pine.

Forest Products Journal. 37(3): 27-34.

Greene, W.D.; McNeel, J.F. 1987. Productivity, costs, and levels of butt 

damage with a Bell Model T feller buncher. Forest Products Journal. 

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Greene, W.D.; McNeel, J.F. 1991. Productivity and cost of sawhead feller 

bunchers in the South. Forest Products Journal. 41(3): 21-26.
Page 12 GTR-NRS-69

Huyler, N.K.; LeDoux, C.B. 1998. Application of cut-to-length harvesting in a 

small suburban woodlot in Vermont. Northern Logger. May: 26-36.

Huyler, N.K.; LeDoux, C.B. 1996. Cut-to-length harvesting on a small 

woodlot in New England: a case study. In: Joint Meeting of the Council 

On Forest Engineering and International Union of Forest Research 

Organizations: planning and implementing forest operations to achieve 

sustainable forests; 1996 July 29 - August 1; Marquette, MI. Gen. Tech. 

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Huyler, N.K.; LeDoux C.B. 1997. Logging technology for managing northern 

hardwoods. In: Ball, John J.; Starnes, Lawson W., eds. Proceedings, 20th 

annual meeting of the Council on Forest Engineering; 1997 July 28-31; 

Rapid City, SD. Corvallis, OR: Council on Forest Engineering: 12-16.

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U.S. Department of Agriculture, Forest Service, Northeastern Research 

Station. 6 p.

LeDoux, C.B. 2002. Assessing the feasibility and profi tability of cut-to-length 

harvests in Eastern hardwoods. In: Wagner, Robert G., comp. Eastern 

CANUSA forest conference proceedings; 2002 October 19-20; Orono, ME. 

Orono, ME: University of Maine: 53 p.

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GTR-NRS-69 Page 13

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on residual stand growth in central Appalachian hardwood forests: 

a preliminary case study. In: Proceedings, 29th annual meeting of the 

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LeDoux, Chris B. 2010. Mechanized systems for harvesting eastern hardwoods. 

Gen. Tech. Rep. NRS-69. Newtown Square, PA: U.S. Department of Agriculture, 

Forest Service, Northern Research Station. 13 p.

In the central Appalachian region, hardwoods traditionally have been harvested 

by chainsaw felling with trees and logs extracted from the forest to landings by 

rubber-tired skidders, bulldozers, and crawler tractors. In recent years, mechanized 

systems that include feller bunchers and cut-to-length (CTL) processors coupled 

with forwarders and clambunk and grapple skidders have been used increasingly 

to harvest Eastern hardwoods. Feller bunchers fell trees and pile stems or logs in 

bunches. CTL processors fell trees and delimb them, buck the stems into logs, and 

pile them in presorted bunches. Wood piles and bunches are transported to landings 

by a clambunk or grapple skidder or a forwarder. These system combinations for 

processing and transporting essentially eliminate the need for woods workers on 

the ground, a major advantage from a production and safety standpoint, and greatly 

reduce adverse effects on the site compared to chainsaw felling and conventional 

skidding. Feller buncher and CTL systems are reviewed, results of environmental 

impact studies are presented, and cost equations for a range of operating conditions 

in Eastern hardwoods are provided.

KEY WORDS: Feller buncher; cut-to-length processor; forwarder; production cost; 

 safety; site impact
www.nrs.fs.fed.us