(575a) Direct Land Use Change Greenhouse Gas Emissions Associated With Forest-Based Biofuels and Bioenergy Production in Michigan
Michigan has one of the largest amounts of timber net growth in excess of removals of any state (135.6 million cubic feet per year). Some of this excess timber growth could be a promising feedstock to address the state’s forest products industry while also creating a thriving renewable fuels industry. However, harvesting of forest resources for bioenergy production could reduce terrestrial C storage in the near term. Therefore, forest-based bioenergy LCA should incorporate forest carbon stock assessment over a long time frame to estimate the total greenhouse gas (GHG) emissions. In this study, the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) is applied to simulate the C stock change in Michigan over a greater than 200 year time frame for aspen-dominated forests, where aspen is intensively harvested for biofuel and bioenergy production. Under intensive harvesting, additional aspen biomass could produce an extra of 18.46 billion gallons of ethanol to blend with gasoline for the transport sector over the next 250 years. Alternatively, the same biomass could be used to produce 32.25 billion gallons of bio-oil by fast pyrolysis process, which can be combusted to generate electricity or upgraded to renewable gasoline and diesel. Model results show that the biofuels (ethanol or pyrolysis oil) and bioenergy (electricity) result in higher GHG emissions than using fossil fuels and business-as-usual aspen harvesting due to the forest carbon loss in the short term. However, the intensive management and harvest of aspen helps accumulates more C in the ecosystem over the long term, which results in negative dLUC emissions (credit) eventually. The time required for this initial carbon debt to be repaid is approximately 60 years for both biofuels; thereafter, this aspen harvesting and management approach accrues GHG savings compared to use of fossil fuels. This study also shows that forest carbon dynamics and dLUC emissions are highly sensitive to the assumed post-harvest growth curve, which can change the time required to overcome the initial C debt.
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