An evaluation of the impact of forest biomass harvest for biofuels on carbon storage in the US west coast states under different management scenarios

Mitigation strategies to reduce fossil fuel emissions of carbon dioxide have lead to investigation of alternative sources of fuels. National and state forest policies have been implemented to both reduce risk of wildfire and promote use of forest biomass as a secondary biofuels energy source. However, the cost and biomass availability have been estimated without quantifying the impact on current and future terrestrial carbon balances. This study uses a combination of Federal Inventory Analysis data (FIA) and supplementary plot data for Washington, Oregon and California to quantify the current forest carbon stocks, net ecosystem production (NEP), and net biome production (NBP = NEP - removals) for the period from 2001-2006. Varying management treatments were applied to determine the net cost, carbon debt, and biofuels energy potential. The treatments were designed to meet multiple objectives emphasizing carbon storage, economic gain, or energy production. The hazardous fuels reduction treatment minimizes carbon loss by only harvesting biomass in forested areas classified by moderate to high risk fire condition classes (FRCC class). This scenario assumes no additional harvest in ecoregions characterized by long fire return intervals (>100 years) such as the Coast Range and the West Cascades and limits removals to an 18 in diameter at breast height (DBH). The energy production treatment maximizes biomass removal by harvesting areas regardless of FRCC class and allows removals up to a 24 inch DBH. Statewide estimates of carbon for 2001-2006 prior to harvest scenarios for California, Oregon, and Washington respectively are as follows: 1) Total land-based carbon stocks (excluding soils) averages 1680, 1663, and 1278 Tg C; 2) NEP is positive in most ecoregions averaging 213, 180, and 191 g C m-2 yr-1; 3) Actual harvest removals averaged 2.7, 6.5, and 5.1 Tg C yr-1 for the same period. In Oregon, the amount of biomass available for biofuels varies from 128 g C m-2 in the hazardous fuels reduction treatment versus 185 g C m-2 in the energy production treatment. Removal of this biomass over the next 20 years is estimated to result in an additional 4 Tg C yr-1 (a 60% increase) in harvest removals for the hazardous fuels reduction treatment and an additional 14 Tg C yr-1 (216% increase) for the energy production treatment. Even in a minimal removals scenario and assuming no other disturbance losses (i.e. insects and fire), Oregon forest NBP will be significantly reduced with the potential to become a carbon source.