Soil organic carbon change can reduce the climate benefits of biofuel produced from forest residues

Because biomass residues do not cause land -use change, soil carbon changes are commonly not considered in life cycle assessments (LCAs) of biofuel derived from forest residues adopted by regulatory agencies. Here, we investigate the impacts of soil organic carbon (SOC) changes caused by removing forest residues in the Southern US on the carbon intensity of biofuels. We show that the average greenhouse gas (GHG) emissions by SOC changes over 100 years are 8.8-14.9 gCO2e MJ-1, accounting for 20.3%-65.9% of life cycle GHG emissions of biofuel. These SOC-associated GHG emissions vary by time frame, site conditions, and forest management strategies. For land management, converting forest residues to biofuel is more climate beneficial than on -land decay or pile burning, depending on fossil fuel substitution and site conditions. Our results highlight the need to include soil carbon assessment in biofuel LCAs, policymaking, and forest management, even when forest residues are used and no land -use change is involved.