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 (Watson
and Stokes 1989). 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.