Thirteen reports on this CD are categorized as pertaining to biomass harvesting systems. These date from 1988 through 2003. The early studies (Stokes and Watson 1988) compared the amount of forest biomass lost after each step of a conventional harvesting system (gate delimbing, tree-length hauling, then slashing and drum debarking at the mill before chipping and screening) to a flail/chip harvesting system (flail delimber, in-woods chipper, mill screening). In a 21-year old pine plantation clearcut, more in-woods biomass was available from the flail debarker and chipper system (17.9% of the whole tree) as opposed to the delimbing gate/tree-length haul system (10.1% of the whole tree). Additionally, the flail/chip option recovered more acceptable pulp quality chips.
A 1983 study in southern Alabama and southern Mississippi examined two methods of integrating biomass (energywood) harvest with the removal of conventional products (Watson and others 1986b and Stokes and others 1985). The one-pass method involved felling and skidding the energywood at the same time as the other products. The feller-buncher piled the energywood separately from the roundwood for the skidder. On the landing, roundwood was sorted and loaded tree length and the energywood was chipped. The two-pass method felled, skidded and chipped the energywood in the first pass, and a second operation was used to remove the merchantable roundwood. Both of these methods were compared to a conventional system that did not recover any energywood. The one-pass method had a higher utilization rate (harvested green tons per acre) than the other two methods because the limbs and tops from the merchantable roundwood were chipped along with the energywood. However, the one-pass method did not recover as much roundwood. More of the boles were left on the tops to facilitate feeding the chipper, which accounts for some of the roundwood volume loss. While the total cost of producing roundwood was similar between the one- and two-pass methods, the energywood production cost was significantly less with the one-pass method. Both of the energywood producing methods produced roundwood at a lower total cost than the conventional method in the plantation stands tested.
FOCUS MORE ON PRODUCTION RATHER THAN COST. Two publications (Hartsough and others 1994 and Hartsough and others 1997a) compared three harvesting systems used to harvest stands (one natural stand and one plantation stand) that included removal of small sawlogs and fuel chips. Slopes in the stands were generally 35% or less. The three systems were a whole-tree system (feller-buncher, skidder, stroke processor, loader and chipper), a cut-to-length system (harvester, forwarder, loader and chipper), and a hybrid system (feller buncher, harvester, skidder, loader and chipper). Analysis of these systems includes detailed time-motion results for each piece of equipment, cost comparisons, and residual damage comparisons. The hybrid system was the least expensive of the 3 systems in the plantation stand. In the plantation, the hybrid system did not use the feller-buncher because there wasn’t enough biomass to justify a first pass with the feller-buncher. The hybrid system felled all products with the harvester, skidded the sawlogs, and lastly, skidded the biomass. In the natural stand, the whole tree system was the least expensive. This system felled all of the wood, then skidded and loaded the sawlogs, followed by skidding and loading of the biomass. The cut-to-length system was the most expensive system in both stands. Damage to the residual trees was low in the plantation for all systems. In the natural stand, the hybrid had the most residual damage (15%), followed by the whole-tree system (13%) and the cut-to-length system (10%).
Hartsough and others (1995) expands the harvest system analysis from the above three systems by including two more from other studies that focus on fuel reduction treatments. Instead of focusing on the time and motion studies, this paper provides a comparison chart of criteria to consider for harvest system selection. For example, in the hybrid system mentioned above, the access roads need large radius curves to accommodate chip vans. This hybrid system has a very low residual fuel loading and leaves negligible residues at the landing. While all of the systems discussed in this publication do not recover biomass, the selection criteria chart is useful for system selection.
Another method of harvesting energywood involved a post-harvest system where the energywood was harvested after conventional operations. This method underutilized the small stems because most were knocked to the ground during conventional operations (). This report to the International Energy Agency (IEA) also included a summary of the 1-pass and 2-pass methods of energywood harvesting.
Our biomass decision-making tools research began in 1990 with a spreadsheet that was developed to estimate the cost of harvesting biomass and other products based on site and material characteristics, equipment mix and crew, and other input variables (Hartsough and Stokes 1990b). Current decision-making tools are available on the Unit’s Web Page (www.srs.fs.usda.gov/forestops/downloads.html). The Auburn Harvesting Analyzer is available on the downloads page. It is a spreadsheet template used to analyze system balance, production rates, and costs. A trucking residue simulator is available on the biomass page (http://www.srs.fs.usda.gov/forestops/biomass.html). This spreadsheet and related study are discussed under the Drying, Storing, Transporting & Roll Splitting.
Christopherson and others (1993) provides a very good introduction to forest management for biomass production. It discusses the factors to consider when planning land management, harvest scheduling, equipment selection, and managing the chip pile. Although newer, more efficient equipment has been developed since 1993, the selection considerations are still valid.
When prescribed fire cannot be safely implemented, alternative fuel reduction treatments are employed. Bolding and others (2003) reported a summary of the costs of five mechanized fuel reduction treatment systems for harvesting small stems. The lowest cut-and-haul cost ($37.06/ton) was observed in a cut-to-length system with a small roadside chipper.
Seki and others (1982) studied the harvesting system that would be needed to harvest a proposed 46,750-acre energy plantation. Four systems were analyzed for feasibility based on daily production requirements, tree size, site conditions, rainfall, and a limited labor force. The selected system included the following equipment for each of the 14 operations: two swing-to-tree feller-bunchers, two tracked clam bunk skidders with knuckleboom loaders, and one portable whole tree chipper.
Several studies reviewed the technical information on harvesting small trees and forest residues and reported the results to the International Energy Agency. Twaddle and others (1989) provides a 1989 summary of biomass harvesting from 8 countries. Stokes (1992b) updates this report which includes information from 10 countries. Integrating biomass processing with the collection of conventional products still appears to be the most promising system. Many countries continue to experiment with biomass harvesting systems based on expected future increases in prices of fossil fuels.