Comparisons of two methods of harvesting biomass for energy

Two harvesting methods for utilization of understory biomass were tested against a conventional harvesting method to determine relative costs. The conventional harvesting method tested removed all pine 6 inches diameter at breast height (DBH) and larger and hardwood sawlogs as tree length logs. The two intensive harvesting methods were a one-pass and a two-pass method. In the one-pass method, all material 1 inch DBH and larger was simultaneously harvested. Pines 1 to 6 inches DBH and hardwoods 11 inches DBH and less were chipped for energy wood and all other stems were logged tree length. With the two-pass method, the energy wood (same description as in the one-pass) was harvested in a first pass through the stand, and the commercial size wood being removed as tree length logs was harvested in a second pass. The conventional harvesting system recovery averaged 52 percent of the standing biomass while the one-pass and two-pass methods recovery averaged 85 percent and 76 percent of the standing biomass, respectively. The conventional system had an average harvesting cost of $8.75 per green ton onto the log truck while the one-pass and two-pass methods had average costs onto log trucks and chip vans of $7.60 and $8.85 per green ton. Both the one-pass and two-pass methods produced energy chips into vans at a cost which was well below the value of the material as a fuel source at the mill. Kluender reported that in 1980 the pulp and paper industry depended on fossil fuels for 52 percent of its energy needs (3). It is currently estimated that this industry is using fossil fuels for only 25 percent of its energy needs. This trend of nondependence on fossil fuels will continue in the near future since there is an ample supply of biomass to provide the needed fuel, Most pulp‘and papermills can obtain energy wood for their boilers from the residues of their manufacturing process and from small sawmills nearby which need outlets to dispose of their residues. Other wood products firms, such as large sawmills, are adapting heavy energy consuming operations, such as kilns, to rely on wood residues as an energy source. Logging residues have long been acknowledged as a potential source of additional energy wood, but the high costs of harvesting these materials have restricted their use. Machines have been developed for the specific purpose of capturing these residues. Examples of this are Georgia-Pacific’s Jaws II machine (7) and the Nickolson-Koch Mobile Chip Harvester (4, 6). Harvesting crews with portable chippers have also been used to recover the material normally left during harvest. Chipping harvesting crews have produced as much as 90 percent additional material over the cruise of merchantable volume (2). Another advantage of fuel chip harvesting operations is that the better utilization of the resource reduces the cost of preparing the site for the next stand of trees (8). The objective of this study was to identify ways to reduce site preparation cost by utilizing conventional harvesting equipment to capture logging residues. The study was accomplished in two phases. The first phase quantified the harvesting costs associated with reducing residue during harvest. In this phase, several test blocks were harvested using conventional utilization The authors are,,respectively, Associate Professor, ?ep,t. of Forestry,Mississippl Agri. and Forestry Expt. Sta., M~sslssippi State, MS 39762; Engineer, USDA Forest Serv., Southern Forest Expt. Sta., Andrews Forestry Sci. Lab., Devall St., Auburn Univ., AL 36849.; and Assistant Forester, South Branch Expt. Sta., Mississippi Agri. and Forestry Expt. Sta., Leakesville, MS 39451. The.authors wish to acknowledge the invaluable assistance ofScott Paper Company’s Southern Operations in the successful completion of this study. This paper was received for publication in April 1985. Q Forest Products Research Society 1986. Forest Prod. J. 36(4):63-68. FOREST PRODUCTS JOURNAL standards and other test blocks were harvested where all material 1 inch diameter at breast height (DBH) or larger was utilized. The second phase assessed the costs of appropriate site preparation methods at the various levels of harvesting residue. The results of the second phase will be reported in a subsequent publication.