Depending on management, forests can be an important sink or source of carbon.  The recent increase in frequency of large and severe fires due to past fire suppression and ongoing climate change represents risk in forest carbon offset investment.  Under current carbon accounting mechanisms, all forest carbon offset projects are equivalent (i.e., a unit of carbon has the same value) provided they meet additionality and permanence standards. Risk of loss from wildfire is not incorporated into quantifying permanence, even though some forests are at greater risk than others and management actions can directly influence that risk.  For example, many western forests are being treated to reduce the risk of catastrophic fire.  We sought to determine the carbon implications of fuels reduction treatments on wildfire emissions and develop a metric for quantifying the carbon loss potential resulting from high-severity fire.  We modeled stand growth and carbon stocks for a range of management actions over a 100-year period and simulated high severity wildfire at year 50 in Sierran mixed-conifer forest. 

Results/Conclusions

We found that aggregating carbon in fewer larger trees makes the stand more resistant to carbon loss from high-severity fire events.  We also discounted the market value of forest carbon as a function of the risk of loss due to wildfire using the fire regime condition class (FRCC) departure index and mean fire return interval (mFRI) data products developed for the LANDFIRE project.  With this approach, the discounted value of carbon varies by forest type and condition. For example, a unit of carbon in fire-prone southwestern ponderosa pine forests is worth only 24% of that in redwood forest.  FRCC departure can be altered by fuel-reduction treatments, making this equation robust to management actions and allowing for site specific quantification of the carbon market value of a management action.  Although both thinning and prescribed fire incur an immediate carbon cost, when properly implemented they can significantly reduce large fire emissions.  To accurately assess a forest’s climate mitigation benefit, accounting policies and carbon valuation need to include emissions from disturbance.