Comparing Life-Cycle Carbon and Energy Impacts for Biofuel, Wood Product, and Forest Management Alternatives*

The different uses of wood result in a hierarchy of carbon and energy impacts that can be characterized by their efficiency in displacing carbon emissions and/or in displacing fossil energy imports, both being current national objectives. When waste wood is used for biofuels (forest or mill residuals and thinnings) fossil fuels and their emissions are reduced without significant land use changes. Short rotation woody crops can increase yields and management efficiencies by using currently underused land. Wood products and biofuels are coproducts of sustainable forest management, along with the other values forests provide, such as clean air, water, and habitat. Producing multiple coproducts with different uses that result in different values complicates carbon mitigation accounting. It is important to understand how the life-cycle implications of managing our forests and using the wood coming from our forests impacts national energy and carbon emission objectives and other forest values. A series of articles published in this issue of the Forest Products Journal reports on the life-cycle implications of producing ethanol by gasification or fermentation and producing bio-oil by pyrolysis and feedstock collection from forest residuals, thinnings, and short rotation woody crops. These are evaluated and compared with other forest product uses. Background information is provided on existing life-cycle data and methods to evaluate prospective new processes and wood uses. Alternative management, processing, and collection methods are evaluated for their different efficiencies in contributing to national objectives. Sustainably managed forests remove carbon from the atmosphere during their growth cycle, transferring that carbon by harvesting and processing to product carbon stores or fuels that displace fossil fuel–intensive products and fuels. The increasing storage of carbon in products extends the carbon stored in the forest to growing carbon pools outside of the forest, offsetting some fossil fuel– intensive product and fuel emissions. The use of wood products and biofuels to substitute for fossil fuel–intensive nonwood products or fossil fuels directly reduces the oneway flow of fossil fuel carbon emissions to the atmosphere. Wood products and wood-based biofuels are coproducts of The authors are, respectively, Professor Emeritus and Denman Professor of Bioresource Science and Engineering, College of the Environment, School of Environmental and Forest Sci., Univ. of Washington, Seattle ([email protected] [corresponding author], [email protected]); Professor, Dept. of Wood and Paper Sci., North Carolina State Univ., Raleigh ([email protected]); Professor, Dept. of Forest Products, Mississippi State Univ., Starkville ([email protected]); Senior Research Associate, College of Environmental Sci. and Forestry, State Univ. of New York, Syracuse ([email protected]); Research Scientist, College of the Environment, School of Environmental and Forest Sci., Univ. of Washington, Seattle ([email protected]); Professor Emeritus, Univ. of Idaho, Moscow ([email protected]); Consultant, WoodLife Environmental Consultants, LLC, Corvallis, Oregon ([email protected]); and Project Leader, USDA Forest Serv., Forest Products Lab., Madison, Wisconsin ([email protected]). This paper was received for publication in February 2012. Article no. 12-00017. * This article is part of a series of nine articles addressing many of the environmental performance and life-cycle issues related to the use of wood as a feedstock for bioenergy. The research reported in these articles was coordinated by the Consortium for Research on Renewable Industrial Materials (CORRIM; http://www.corrim.org). All nine articles are published in this issue of the Forest Products Journal (Vol. 62, No. 4). Forest Products Society 2012. Forest Prod. J. 62(4):247–257. FOREST PRODUCTS JOURNAL Vol. 62, No. 4 247 sustainable forest management along with the other values forests provide such as clean air, water, and habitat. Producing multiple coproducts with different uses that result in different values complicates carbon mitigation, accounting for both policy and investment decision makers, especially because so many of the values, including carbon, have no clear market value, thereby increasing the risk of investing in biofuels production. The potential to divert feedstock to uses that may produce unintended consequences is an ever-present risk, such as burning wood for fuel when it might result in significantly greater carbon mitigation if used in engineered wood products that also use low-valued resources. The different ways to produce and use wood result in a hierarchy of carbon and energy impacts that can be characterized by their efficiency in using wood to reduce carbon emissions and/or to reduce fossil energy imports. Effective policy and investment decisions must consider how forest management and wood use impact fossil energy use and carbon emissions. Using life-cycle inventory (LCI) measurements for every input and output for every stage of processing followed by life-cycle assessments (LCAs) of key human health and ecosystem risks provides consistent comparisons between alternative materials, processes, and engineering designs in search of environmental improvement opportunities. The focus of this article is on characterizing the hierarchy of alternative uses of biomass that reduce global warming potential (GWP) measured by greenhouse gas emissions (GHG) in units of CO2 or C equivalence and on characterizing the impact of liquid biomass fuels that can also directly reduce energy dependence. Comparisons of interest include biofuels from lower grades of wood that are not substituting for fossil fuel– intensive products but can still substitute directly for fossil fuels, including liquid fuels that are being imported, contributing to energy dependence. Producing ethanol from short rotation woody crops such as willow provides both the benefits of higher yield per acre, shorter rotations, productive use of marginal agricultural land, and less forest waste, while contributing directly to energy independence as well as carbon mitigation. Collecting forest residuals left to decompose because the cost of removing them may exceed their market value provides the opportunity to displace emissions from fossil fuels. Thinning stands to improve wood quality or reduce fire risks can also contribute substantially to biomass feedstock for carbon mitigation and energy independence goals. Alternative Scenarios Spanning the Range of Impacts on Carbon Mitigation and Energy Independence To reduce the number of wood and biofuel use alternatives to a manageable range that would reveal the hierarchy of wood uses and improvement opportunities, the US Forest Service sponsored the Consortium for Research on Renewable Industrial Materials (CORRIM 2010) to assemble a workshop of experts to develop a research plan. The series of articles published in this issue of the Forest Products Journal reports on life-cycle assessments for the biofuels and their feedstocks selected for the research plan along with comparisons to other wood uses. The options selected included three liquid fuel alternatives: pyrolysis bio-oil from whole trees (thinnings or restoration) compared with residual fuel oil (RFO), ethanol from thermochemical gasification from forest residuals, and biochemical fermentation from a short rotation woody crop (willow) compared with gasoline. Pyrolysis was selected as the conversion process that might be economical on a smaller scale that could better match local supply regions. Fermentation was selected as the likely best use for high yield, high moisture short rotation crops. Gasification was considered more likely able to handle variation in the quality of the forest residual feedstock. These alternatives were compared with the prior LCI/LCA evaluations for wood product uses. Biofuels are usually a jointly produced coproduct with wood products requiring analysis of the integration back to the managed forest to assess impacts on total carbon. These recent studies of the life-cycle implications of biomass collection and biofuel processing opportunities provide the data needed to extend the evaluation of potential benefits from products to fuel use and to identify those options that produce improvements that would contribute to the national goals of carbon mitigation and energy independence as promulgated by the Energy Independence and Security Act (Sissine 2007). The LCI/LCA data used in this article for biofuel feedstock collection and production were developed and are published in the series of articles in this issue of the Forest Products Journal. The findings were extended in this article to include the integration from forest management through feedstock collection, product processing, and end use. Various wood products and biofuels are compared with alternative nonwood products and fuels in order to identify best options to effectively improve environmental performance while acknowledging the lack of polices that promote carbon values in the US market relative to fossil fuel taxes in Europe and carbon taxes in British Columbia. To gain perspective on the carbon benefits for various uses of wood, the highly leveraged impact of using wood products to substitute for energy-intensive steel products, such as the carbon impact of substituting engineered wood product (EWP) I-joists for steel joists in residential floors, is introduced first. There is a hierarchy of wood uses, with some uses having a much higher impact on reducing fossil fuel emissions than others. The comparison between alternatives relies on using LCI data for each stage of processing and time event with conservative end of life assumptions, i.e., the finally discarded wood products for this example are burned with no energy recovery. Lippke et al. (2011) demonstrated that substituting EWP I-joists for steel floor joists produced one of the higher leveraged carbon mitigation opportunities, although only indirectly contributing to energy independence. Life-cycle data have been collected over the last decade for most primary products, providing a database to make carbon emission/ carbon storage comparisons between wood and nonwood products. Data for each type of steel and wood product are available from the US LCI database (National Renewable Energy Laboratory 2012). These data are representative of national markets that are served by regional exports. With the newly collected life-cycle data on biofuel collection and processing options reported in this issue of Forest Products Journal, the product alternatives now include pyrolysis of woody feedstocks to bio-oil and thermochemical gasification or biochemical fermentation to ethanol. Life-cycle data on each stage of processing are linked to the time profile for growing trees, harvesting, transporting, wood processing