Forwarders are extraction machines that remove material from the woods fully suspended in bunks.
Forwarders are articulated machines consisting of an operator’s cab and a log bunk. They are basically tractors pulling a wagon load of wood. Forwarders currently exist having up to eight wheels. The cab may be fixed or capable of rotating on the chassis. Many forwarders have a boom mounted grapple for loading and unloading material.
Traction and flotation can be increased by adding tracks that slide on over the dual wheels or by opting for wider tires. Tire chains may also be applied for additional traction in snow or mud.
Slope: Tracked harvesters can operate on slopes up to 55%. Wheeled harvesters are generally limited to less than 40% slope. Rough, broken ground will limit the slopes on which they can operate. The tracked, articulated harvester is reportedly capable of operating on slopes up to 80%.
Soil Conditions: When operating on wet soils, tracks or high flotation tires should be used to minimize soil disturbance. Since the load is fully suspended, soil disturbance caused by dragging material is minimized.
Forwarders generally work with a system that is processing material in the woods, permitting the use of smaller landings which minimizes soil disturbance.
Extraction Distance: The ability of forwarders to accumulate large payloads makes the cost of forwarding less sensitive to extraction distance, compared to skidding.
Tree Size: The forwarder should be matched to the log length and stem volume being extracted. Tree length forwarders are capable of forwarding tree length material. Their large size means that they require large areas to maneuver.
Forwarders usually operate in a fully mechanized system where all the workers are enclosed in cabs. Workers are generally protected from falling or flying debris. Operating on slopes introduces the biggest hazard to forwarder operation.
Forwarders are capable of operating in partial cuts where tree spacing allows passage. They work well where multiple products are being produced in the woods since they are capable of sorting and extracting material by product. Forwarding systems, other than tree-length systems, generally have smaller landing requirements since processing occurs in the woods.
Forwarders are limited to extracting processed material. They are typically operated with a harvester capable of producing cut to length material. The harvester is also capable of stacking the processed logs near a skid trail accessible to the forwarder. Manual felling and processing does not have this capability which limits the forwarders productivity.
Compared to skidders, forwarders cost more to purchase which requires a higher rate of productivity to justify the cost.
A typical cut to length system will use either self loading trucks or the forwarder will load the log trucks. Roadside landings can be used since there are no space requirements for a loader or processor. The forwarder can simply unload into decks at the roadside, facilitating subsequent loading of the log trucks.
The following is a selection of representative research studies and reports done on harvest systems that include forwarders. These reports may be used to get an idea of productivity and impacts of different systems and uses of forwarders as well as some of their limitations. When reading these reports, keep in mind that they describe specific systems and stand treatments. Trying to apply the lessons learned from these reports to systems and treatments outside of the studies’ scope may have unintended or unforeseen consequences.
This is not a complete listing of research on forwarders. Additional information can be found at the USDA Forest Service Treesearch website. This site provides reports on research performed by Forest Service Research and Development scientists and their collaborators.
Title: Effect of slash on forwarder soil compaction
Author: McDonald, Timothy P.; Seixas, Fernando
Description: A study of the effect of slash on forwarder soil compaction was carried out. The level of soil compaction at two soil moisture contents, three slash densities (0, 10, and 20 kg/m2), and two levels of traffic (one and five passes) were measured. Results indicated that, on dry, loamy sand soils, the presence of slash did not decrease soil compaction after one forwarder pass, but did provide some protection from subsequent passes. The density of slash (over 10 kg/m2) did not affect compaction. On the same soils in a wetter condition, however, slash density at 20 kg/m2 was significantly less than on bare plots. At 10 kg/m2, the increase in bulk density after five passes was smaller than on the bare plots, but not significantly so.
Title: Comparison of two thinning systems. Part 2. Productivity and costs
Author: Lanford, Bobby; Stokes, Bryce J.
Description: A side-by-side comparison of two popular thinning systems, a skidder system and a forwarder system, was made during winter logging conditions in southern Alabama. The first report of this study addressed stand and site impacts of these two thinning systems. This report focuses on productivity and costs while thinning an 18-year-old loblolly pine plantation. The skidder system used a feller-buncher with a shear head followed by a grapple skidder that transported bunches of trees and delimbed them with a grade delimber. A loader/slasher combination processed trees into 7.5-foot lengths and loaded tractor trailers. The forwarder system used two machines: a harvester and a forwarder. The harvester felled, delimbed, and bucked trees into 7.5-foot or cut-to-length pulpwood. The forwarder loaded processed wood and transported it to setout trailers. Production rates were sampled using time and production studies for each machine in the two systems. Production rates and estimated costs were combined for each system to give overall system costs. System production was limited by the woods transport vehicles, the single skidder for the skidder system, and the forwarder for the forwarder system. Weekly production rates were 261 cords for the skidder system and 249 cords with cut-to-length wood and 200 cords with 7.5-foot wood for the forwarder system. Cost per cord was slightly lower for the forwarder system using cut-to-length wood as compared to the skidder system, a difference of $0.14, and higher for the forwarder system in 7.5-foot wood, a difference of $3.77.
Title: Tree Diameter Effects on Cost and Productivity of Cut-to-Length Systems
Author: Holtzscher, Matthew A.; Lanford, Bobby L.
Description: Currently, there is a lack of economic information concerning cut-to-length harvesting systems. This study examined and measured the different costs of operating cut-to-length logging equipment over a range of average stand diameters at breast height. Three different cut-to-length logging systems were examined in this study. Systems included: 1) felier-buncher/manual/forwarder; 2) feller-buncher/processor/forwarder, and 3) swing-to-tree harvester/forwarder. Operating costs were calculated by generating stands with the stand generator program PCWThin. Once stands were generated, costs for thinning were determined using a computer spreadsheet model known as the Auburn Harvester Analyzer. Each individual system followed different cost trends; however, for all systems, tree size had a significant effect on unit cost of wood produced. As tree size increased, unit cost of wood produced decreased. The swing-to-tree harvester system was much more expensive for small-diameter trees than the other two systems due to individual stem processing and small volume per tree but approached the unit costs of the other systems at larger tree sizes.
Title: Evaluation of a cut-to-length system implementing fuel reduction treatments on the Coconino National Forest in Arizona
Author: Klepac, John; Rummer, Bob; Thompson, Jason
Description: A Cut-to-Length (CTL) system was evaluated for production and cost while implementing fuel reduction treatments in two stands on the Coconino National Forest in Arizona. Product recovery and fire behavior within each stand after treatment were also examined. Only trees less than 16 inches diameter breast height (DBH) were harvested. After logs were forwarded to a landing, the remaining slash in each stand was removed by the forwarder for fire hazard reduction. Time-and-motion data collected revealed the harvester produced 364 cubic feet (cf) per Productive Machine Hour (PMH) while harvesting sawlogs and 33 cf per PMH while harvesting biomass. Forwarder productivity averaged 690 cf per PMH while transporting sawlogs and 160 cf per PMH while transporting biomass. System cost, with profit and overhead, was estimated at 208 per Scheduled Machine Hour (SMH). Unit costs were $0.88 per cf while harvesting sawlogs and $9.62 while harvesting biomass.
Title: Soil compaction effects of forwarding and its relationship with 6- and 8-wheel drive machines
Author: Seixas, Fernando; McDonald, Tim.
Description: A study was done to determine the impact, if any, of a range of drive train options on the soil compaction effects of forwarders. The purpose of the study was to evaluate the cost of optional forwarder equipment versus its ability to reduce detrimental soil physical property changes. Tests were done on forwarders equipped with wide and narrow tires, rear steel tracks, and 6 or 8 tires. The configurations differed, at the extremes, by a factor of about 2 in expected ground pressure. Despite that, results showed little difference in bulk density, soil strength, rut formation, or porosity changes (pre- versus post-traffic) between any of the tested options. The implication was that, for the moisture conditions encountered in the study, the use of the tested options did not alter soil compaction impacts substantially. A drop in macroporosity was observed, however, which may have been evidence that traffic affected soil structure without compacting it by a detectable amount.
Title: Cut-to-length harvesting of short-rotation Eucalyptus
Author: Hartsough, Bruce R.; Cooper, David J.
Description: Traditional whole-tree harvesting systems work well in short-rotation hardwood plantations, but other methods are needed where it is desirable to leave the residues on the site. We tested a system consisting of a cut-to-length harvester, forwarder, mobile chipper, and chip screen to clearcut a 7-year-old plantation of Eucalyptus viminalis. Three levels of debarking effort by the harvester (minimal, partial, and full), and two levels of screening (with and without) were evaluated. The harvester had the lowest production rate and highest cost of the system elements. Harvester production rate was strongly affected by tree size and somewhat by debarking level. Bark contents for full debarking averaged 1.5 percent; screening apparently did not reduce bark content any further. Estimated stump-to-truck costs (without screening) for the system in stands of good form varied from $19 per bone dry ton (BDT) for 1l-inch DBH trees to $72/BDT for 3-inch trees. For trees in the 5- to 1l-inch range, and an average forwarding distance of 500 feet, a balanced system would include three harvesters, two forwarders, and one chipper. The system may be cost competitive with whole-tree systems.
Title: Comparison of mechanized systems for thinning ponderosa pine and mixed conifer stands
Author: Hartsough, Bruce R.; McNeel, Joseph F.; Durston, Thomas A.; Stokes, Bryce J.
Description: We studied three systems for thinning pine plantations and naturally-regenerated stands on the Stanislaus National Forest, California. All three produced small sawlogs and fuel chips. The whole tree system consisted of a feller buncher, skidder, stroke processor, loader and chipper. The cut-to-length system included a harvester, forwarder, loader and chipper. A hybrid system combined a feller buncher and harvester to produce bunches of small whole trees for fuel, and bunches of long, delimbed sawlogs. The hybrid bunches were skidded to a landing where they were chipped or loaded. The cut-to-length system had higher costs per unit of material and yielded less fuel than the other systems. The cut-to-length system damaged fewer trees in the natural stand than the other systems, but damage levels were low for all systems. Other environmental impacts - on soil, fuel levels, insect activity and stand growth - are still being evaluated.