The U.S. forestry industry, in the process of harvesting and converting wood into consumer products, generates a number of residue and waste materials that could be used for bioenergy and bioproducts. Among the resources obtained from the harvest of forest and timberland areas are logging residues which are the portions of harvested trees not utilized and left in the woods after operations. Logging residue data is available online through the Timber Product Output (TPO) database (http://www.fia.fs.fed.us) compiled by the USDA Forest Service Forest Inventory and Analysis Program (FIA) which is charged with tracking and reporting on the fate of wood harvested from U.S. forests. The FIA collects data through surveys and questionnaires sent to forest owners and harvesters, and by on-site measurements of the material felled and removed and/or left during harvesting operations. The TPO database provides estimates of logging residue quantities generated by county. Data is provided by inventory source (i.e., total and growing stock), by tree species, and by land ownership class in cubic feet and board feet.
Logging residue quantities for the RPA (Resource Planning Act) survey year 2007 by ownership class and tree class are presented in table 1. About 4.51 billion ft3 (63.04 million dry tons) of logging residues were generated from all sources, with about 44% of the residues from softwood tree species and the remainder from hardwood species. About 8% of the material came from national forests and other public lands. The distribution of logging residues generated in RPA survey year 2007 is shown in figure 1.
The FIA data form the basis of the estimated available logging residue quantities found in a number of studies such as Perlack, 2005; Southern States Energy Board, 2006; Western Governors’ Association, 2006; Encyclopedia of Southern Bioenergy Resources, 2006; 25x25 Initiative, 2006; and Walsh, 2007.
The TPO database is limited to historical data and does not project potential quantities of logging residues for future time frames. The Forest and Rangeland Renewable Resources Planning Act (RPA) of 1974 directs the Forest Service to conduct a study every 10 years that projects the future cost and availability of timber products, evaluates emerging issues, and examines impacts of policy options. According to this assessment, logging residues have been a declining portion of the total removals from the growing stock inventory, decreasing from 9.8 to 6.4% of softwood removals and 22.2 to 12.4% of hardwood removals between the years 1952 and 1997. This trend is projected to continue (to 6% of softwood removals and 9% of hardwood removals by 2050) due to higher prices which make it more economical to remove lower quality material, to changes in harvesting methods, and to the increased use of fuelwood (Haynes, 2003). The analysis accounts only for logging residues from growing stock. Of the 3.25 billion cubic feet of logging residues generated in RPA survey year 2002, 41% (1.34 billion cubic feet) were from growing stock sources, with the remainder from other sources. Using the FIA logging residue data, and projected harvests and percent logging residue removals from the RPA assessment, Perlack (2005) estimated the availability of 46.4 million dry tons of logging residues by mid-century, but conducted no economic analysis.
Few studies attempt to estimate supply curves (i.e., quantities available as a function of price) for logging residues for either current or future time frames. Costs are thought to be relatively similar to pulpwood harvest and transport costs. Some analysts have constructed local or regional supply curves. (e.g., Kerstetter, 2001). The Antares Group (1999) estimated the availability 72.2 million green tons of forest residues at prices of less than $4.00/MMBtu, but did not separate the residues by type. Walsh (2000) estimated state forest residue supply curves (including logging residues) and summed the state data to obtain total U.S. forest residue quantities at several prices (e.g., 44.9 million dry tons at a delivered price $50/dt).
Walsh (2007), using RPA assessment projections and FIA estimates of current logging residue quantities and distribution, estimated future logging residue collection cost schedules at several price levels (table 2). Future quantity estimates were based on the projected changes in regional softwood and hardwood timber harvest quantities from forest lands (Haynes, 2003; Haynes, 2007). Estimated costs of collecting logging residues were based on a regional distribution of logging residue collection costs obtained from a somewhat updated version of a model originally developed by McQuillan (1988) which includes forest inventory data, logging and chipping costs, wood types, site accessibility, site slope, and equipment operability constraints to estimate nine regional supply schedules for softwood and hardwood chips for the base (1983) and future years. The analysis suffers from the inability to fully update the original economic model, to fully account for structural changes in the timber industry or shifts in stumpage prices over time, to fully disaggregate regional data to county data, and to account for new harvest and collection technologies. It should also be noted that collection costs are not the same as the market prices paid for the materials which fluctuate in response to supply and demand conditions (e.g., changes in housing construction) and which typically vary from year to year. For example, delivered (to the mill) pulpwood prices for the first quarter of 2007 ranged from $60 to $100/dry ton depending on region (International Woodfiber Report, RISI).