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Forest Slash
Forest slash or logging residues are the portions of the
trees that remain on the forest floor or on the landing after logging operations
have taken place. Forest slash consists mostly of tree branches, tops of
trunks, stumps, branches, and leaves. The various types are listed below:
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Logging Tops. This is the unmerchantable upper
portion of the stem. The top is typically a stick about 16-18 feet in
length with a diameter of 7 inches at the base.
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Culls. Culls are that portion of each year's growth of saw timber harvest that is classified as defective and cut and
left in the woods. The cull tree does not contain at least 25 percent
sound wood in a merchantable sawlog now or prospectively because of defect,
rot, or species.
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Precommercial Thinnings. This residue material
comes from timber stand improvement and is generally round, densely stocked
stands.
Other Forest Wood Residue
Other wood sources are stand improvements such as culling
trees, removing rotten, dead trees, or undersized trees, noncommercial tree
species removed from woodlots, and trees from thinning performed on growing
stock.
Lumber Mill Residue
Lumber mill residues or lumber processing residues consist of the slabs,
shavings, trimmings, sawdust, bark, end pieces of wood, and log cores that
result from the various processing operations occurring in sawmills, pulp mills,
and veneer and plywood plants. Generally, 85 percent of mill residue is
coarse (which includes slabs, edging, trim, and spur ends), bark, and sawdust.
The typical
moisture contents (wet basis) of bark, planer shavings,
and sawdust are 30 to 60 percent,
8 to 19 percent, and 25 to 55 percent, respectively.
Chaparral
Chaparral consists of heavily branched dwarf shrubs, the crown canopy of which
at maturity usually covers more than 50 percent of the ground. It is
mostly less than 15 feet tall, and usually evergreen. There was an
estimated 5 to 7.6 million acres of chaparral in California in 1985. The
principal genera are Adenostoma, Arctostaphylos, Ceanothus, Cercocarpus, Garrya,
and Quercus.
Quantifying the amounts and types of agricultural residues generated in each of
the forest residue categories is extremely difficult without conducting
comprehensive research throughout the state with continuous updates of the
compiled data. Without ongoing data collection, any quantification
estimates would only be valid for the time frame in which the study was done and
would be susceptible to ongoing market changes. Therefore, the
quantification of forest residue tonnages should be viewed with these inherent
limitations in mind and the tonnages quoted should not be considered absolute
values.
In generating estimated quantities, three primary sources
were used. The first source of information was the United States
Department of Agriculture (USDA) Forest Products Laboratory?s (FPL) report,
Recovery of Paper and Wood for Recycling: Actual and Potential. The second
source was the CEC?s 1991 Biomass Resource Assessment Report for California.
The last source of information was the Quincy Library Group?s (QLG) report
titled Northeastern California Ethanol Manufacturing Feasibility Study (1997).
USDA FPL Data
Primary timber processing facilities (i.e. sawmills and plywood mills) in the
United States generate large quantities of wood residues in many forms, such as
bark, chips, sawmill slabs and edgings, sawdust, and peeler log cores. In
1991, it was estimated that 26 million tons of bark and 74.5 million tons of
wood residues were generated by primary timber processing facilities in the U.S.
However, most of these wood residues were already being used as fuel or as fiber
raw material to produce other products, primarily pulp and paper products.
Only about 6 percent of the wood residues and 5 percent of the bark residues
were not being used in 1991, creating a disposal burden of only 4.3 million tons
of wood waste and 1.4 million tons of bark waste
CEC Data
The information and data collected for the CEC report mainly pertains to
quantities of forest wood residue that are available for use as biomass fuel.
The materials covered in this report included forest slash, lumber mill residue,
and chaparral (see Table B, below). Lumber mill residue seems to have the
greatest tonnages but probably has decreased over the past nine years. The
decrease would be due to the overall downsizing of the industry, a trend in
exporting bulk lumber in lieu of finished products, and the advancements of
lumber mill technologies, such as thinner blades, which leads to less waste.
The decrease in the quantity of mill residue is a minor issue because the
majority of mills have power plants built on site to assist in their individual
energy needs or the waste is dedicated to a specific reuse and is rarely
destined for landfills.
Table B: Biomass Resources in California
(CEC, Biomass Resource Assessment Report,
1991)
|
Materials
|
Annual Amount (tons)
|
% Residue
|
|
Forest Slash |
5,232,971
|
11.22
|
|
Lumber Mill Waste |
5,468,286
|
11.73
|
|
Chaparral |
7,651,000
|
16.41
|
|
Fruit and Nut Crops |
1,880,105
|
4.03
|
|
Food Processing Waste |
1,743,267
|
3.74
|
|
Vegetable Crops |
919,140
|
1.97
|
|
Nursery Crops |
24,878
|
0.05
|
|
Field and Seed Crops |
6,618,782
|
14.20
|
|
Energy Crops |
508,310
|
1.09
|
|
Urban Yard Waste |
3,054,411
|
6.55
|
|
Livestock Manure |
11,901,829
|
25.53
|
|
Urban Wood Waste |
1,621,118
|
3.48
|
|
Total |
46,624,098
|
100.00
|
Quincy Library Group (QLG) Report
The QLG report titled Northeastern California Ethanol
Manufacturing Feasibility Study (November 1997), was organized and put together
by the QLG along with other public and private stakeholders. The Quincy
Library group is an ad hoc association of local environmentalists, timber
industry representatives, elected officials, trade associations, and residents
that started meeting in 1993 to devise a plan to retain community economic
stability, which is largely based on the timber industry. Also in the
goals of the group are improvement of forest health and reduction of the risk of
catastrophic wildfires.
The Quincy Library Group Biomass Fuel Supply study area
includes most of Lassen and Plumas National Forests, and the Sierraville
District of the Tahoe National Forest, all of which encompasses approximately
2.4 million acres. The above areas are associated with existing or former
sawmill sites. The average moisture content of the forest residue is
estimated to range from 45 to 50 percent, depending upon the species harvested
and the time of year.
Wood residue is generated as a part of normal logging
operations of merchantable timber. Typical logging operations in this area
remove the larger high quality portions of the trees for sale to sawmills.
The remaining tops, limbs, and undersized trees too small for sawlogs can be
chipped for biomass feedstock or left in the forest. The amount of
material generated for biomass depends on the particular stand of timber and the
harvesting methods and ranges from 6 to 25 bone dry tons (BDT) per acre.
This study estimated that approximately 1.97 BDT of
recoverable forest residue is generated for each thousand board feet of saw logs
harvested. This estimate is based on the assumption that if a chipper was
available on the logging operation to chip tops and damaged trees, one load of
chips could be generated for each load of logs that was removed.
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