THE POTENTIAL FOR SHORT-ROTATION WOODY CROPS TO REDUCE UNITED-STATES CO-2 EMISSIONS

Short-rotation woody crops (SRWC) could potentially displace fossil fuels and thus mitigate CO2 buildup in the atmosphere. To determine how much fossil fuel SRWC might displace in the United States and what the associated fossil carbon savings might be, a series of assumptions must be made. These assumptions concern the net SRWC biomass yields per hectare (after losses); the amount of suitable land dedicated to SRWC production; wood conversion efficiencies to electricity or liquid fuels; the energy substitution properties of various fuels; and the amount of fossil fuel used in growing, harvesting, transporting, and converting SRWC biomass. Assuming the current climate, present production, and conversion technologies and considering a conservative estimate of the U.S. land base available for SRWC (14 x 10(6) ha), we calculate that SRWC energy could displace 33.2 to 73.1 x 10(6) Mg of fossil carbon releases, 3-6% of the current annual U.S. emissions. The carbon mitigation potential per unit of land is larger with the substitution of SRWC for coal-based electricity production than for the substitution of SRWC-derived ethanol for gasoline. Assuming current climate, predicted conversion technology advancements, an optimistic estimate of the US. land base available for SRWC (28 x 10(6) ha), and an optimistic average estimate of net SRWC yields (22.4 dry Mg/ha), we calculate that SRWC energy could displace 148 to 242 x 10(6) Mg of annual fossil fuel carbon releases. Under this scenario, the carbon mitigation potential of SRWC-based electricity production would be equivalent to about 4.4% of current global fossil fuel emissions and 20% of current US. fossil fuel emissions.