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.
Carbon Emission Reduction Impacts from Alternative Biofuels
Maureen E. Puettmann
John F. Katers
Timothy A. Volk
The heightened interest in biofuels addresses the national objectives of reducing carbon emissions as well as reducing dependence on foreign fossil fuels. Using life-cycle analysis to evaluate alternative uses of wood including both products and fuels reveals a hierarchy of carbon and energy impacts characterized by their efficiency in reducing carbon emissions and/or in displacing fossil energy imports. Life-cycle comparisons are developed for biofuel feedstocks (mill and forest residuals, thinnings, and short rotation woody crops) with bioprocessing (pyrolysis, gasification, and fermentation) to produce liquid fuels and for using the feedstock for pellets and heat for drying solid wood products, all of which displace fossil fuels and fossil fuel–intensive products. Fossil carbon emissions from lignocellulosic biofuels are substantially lower than emissions from conventional gasoline. While using wood to displace fossil fuel–intensive materials (such as for steel floor joists) is much more effective in reducing carbon emissions than using biofuels to directly displace fossil fuels, displacing transportation fuels with ethanol provides the opportunity to also reduce dependence on imported energy. The complex nature of wood uses and how wood fuels and products interact in their environments, as well as the methods needed to understand these impacts and summarize the relative benefits of different alternatives, are discussed herein. Policies designed to increase biofuel use by subsidies or mandates may increase prices enough to divert biomass feedstock away from producing products, such as for composite panels, resulting in increased emissions from fossil fuel–intensive substitutes. Policies that fail to consider life-cycle implications are discussed, identifying their unintended consequences.