The economics of biomass harvesting are addressed in several publications on this CD. These date from 1987 through 2003.
and others (1992) compare
the costs of transportation, harvest operations, and woodyard handling and
chipping between two operational systems (long wood operations and in-woods
chipping operations). This was a
cooperative study with Mississippi State University, Rust International
The amount of fuel (energy) consumed to
produce energy wood was analyzed in cooperation with
and others 1987b offer a
discussion on the economics of obtaining biomass from logging residues (one-
and two-pass harvesting methods) and short rotation biomass plantations. This cooperative study with
Two studies (documented in Miller and others 1985, Miller and others 1987, and Watson and others 1986b) calculated the cost of producing energywood (in dollars per green ton) for each piece of equipment used in the one- and two-pass methods. In the two-pass method, feller-buncher productivity was significantly impacted by the amount of energywood present. In the one-pass method, machine productivity was not significantly different over the range of tonnages of available biomass. The authors report that intensive site preparation leads to lower energywood tonnages. This creates a production advantage for the one-pass method as compared to the two-pass method.
In a cooperative study with Mississippi State University, the University of California, and the Bureau of Indian Affairs, Watson and others (1995) investigated the impacts of slope on the production of three different feller-bunchers (a self-leveling excavator type track machine, a tri-track wheel machine, and an intermediate sized track machine) used in a chipping operation. The thinning operation included merchandising sawtimber and pulp quality chips. Production on the wheeled machine was sensitive to slope, while the other feller-bunchers were sensitive stem size. Productivity rates for the flail/chipper, felling operation, and skidding operation are displayed in regression equations.
Two reports (Stokes 1998 and Stokes and Klepac 1998b) examine the recovery and utilization of chips from three harvesting operations: a tree-length (long wood) operation, a flail delimber/debarker and chipper operation, and a cut-to-length operation. Chip recovery and equipment production and cost were analyzed for each type of operation on three loblolly pine (Pinus taeda) stands ranging from 13- to 23-years old. Harvest costs are affected by tree size and utilization. The tree-length operation was the least sensitive to tree diameters, while the cut-to-length operation was the most sensitive.
(Gallagher and Shaffer (2002) and Gallagher and Shaffer (2003) provide an introduction to the advantages and disadvantages of green plantation storage versus traditional woodyard storage of hardwood in the South. While this study was tied to pulp production, the same ideas and concepts could be applied to managing biomass inventory. The authors explore the costs and benefits associated with using intensively managed short-rotation hardwood stands to balance the pulpwood supply during wet winter months. Typically, mills increase their inventory in preparation of the wet months. This inventory has additional costs of storage, watering, deterioration, and handling. Future related studies will explore growth and yield models and silvicultural costs (land, irrigation, site preparation, planting, annual maintenance, supervision, and harvesting) and economic feasibility of intensively managed short-rotation hardwood stands as compared to woodyard storage.
Site Preparation Costs
Harvesting understory material for biomass can rarely be accomplished profitably. In a study (Stokes and Watson 1986c and Watson and others 1984) in south Alabama, the Forest Operations Research Unit worked cooperatively with Mississippi State University to question whether conventional systems could be used to harvest biomass, and whether biomass removal reduced the site preparation costs enough to make energywood harvesting economically feasible. This study compared the site preparation costs following three harvest methods (conventional, one-pass, and two-pass). (These methods are explained in more detail under Biomass Harvesting Systems.) The conventionally harvested areas were treated by (1) a shear, rake, pile and disk treatment or (2) by a herbicide only treatment. Less mechanical treatment was necessary for site preparation on the 1-pass and 2-pass treated areas. Three site preparation treatments (single disk, double disk, or herbicide) were applied on these areas. The one- and two-pass harvesting methods removed more biomass, which translated to lower site preparation costs. The single disking application was the least costly treatment. The study area was visually inspected nine months after the site preparation treatments. The conventionally site prepared area had similar vegetation regrowth as the double-disk treatment areas. These site preparation cost savings can be considered a benefit to help offset the cost of biomass harvesting.
Both the one-pass and two-pass harvesting methods resulted in reduced site preparation costs (Watson and Stokes 1989). On the south Alabama study sites, only discing was necessary to re-establish the stands after energywood harvesting. Conversely, the site preparation treatment of shear-rake-pile-disc following conventional harvesting cost approximately $140/hectare more than energywood harvested sites.
Three different harvesting systems were used in a study in northeast Mississippi (Ragan and others 1987) which compared the costs of conventional pulpwood harvesting, conventional pulpwood harvesting plus in-woods chipping of biomass, and an intensive treatment consisting of in-woods chipping for pulp quality chips and in-woods chipping of the biomass. The results of this cooperative study with Mississippi State University and the Tennessee Pulp and Paper Company indicated that energywood harvesting is marginally feasible, but when site preparation costs are reduced due to the energywood harvest, these savings help offset the cost of energywood harvesting.