Harvesting forests for biofuels likely to yield a near-term increase in atmospheric CO2

Background/Question/Methods The capacity for forests to aid in climate change mitigation efforts is substantial but will ultimately depend on their management.  If forests remain unharvested, they can further mitigate the increases in atmospheric CO₂ that result from fossil fuel combustion and deforestation.  Alternatively, forests can be harvested for biofuels production, which could generate a significant amount of energy via biomass fuels or when converted to cellulosic ethanol.  Both energy sources could serve as a substitute for traditional fossil fuels, but harvesting forests will reduce terrestrial carbon sequestration and thereby increase atmospheric CO₂ concentrations in the near-term.  Here we determined the minimum amount of time required for a utilization of forest biomass for biofuels production to result in an offset of atmospheric CO₂ by modeling the effects of forest biomass harvest on both potential bioenergy production and long-term carbon storage for different harvesting regimes, initial landscape conditions, and biofuel types.  

Results/Conclusions Regardless of initial landscape condition and harvesting intensity (50-100%), forests that were harvested for biofuels every 25 to 50 years required over 100 years to achieve a net offset of atmospheric CO₂.  Harvesting forests for biofuels production lowers carbon storage without providing an equitable offset of fossil fuel CO₂, since the amount of energy released per unit of carbon in biofuels is considerably lower than that in fossil fuels.  Consequently, repeated harvests over a long time period are required to achieve a net offset of atmospheric CO₂, indicating that a substitution of forest biomass for fossil fuels is unlikely to provide any significant near-term amelioration of rising atmospheric CO₂ concentrations and associated threats from continued climatic change.