Climate Adaptation and Mitigation Strategies for Sierra Nevada Forests Using a Life-Cycle Assessment of Carbon Potential

The purpose of this research is to determine whether a forest thinning project conducted with the aim of reducing wildfire risk and restoring the forest to a more resilient condition can improve the carbon stores compared to a baseline, no-thin project. A life-cycle analysis was conducted on data from a case study of a fuels-reduction thinning operation at Independence Lake, a 700-acre lake north of Truckee, California in the northern Sierra Nevada. The calculation tracks the net ecosystem carbon balance, including above and below-ground carbon pools, removals from harvesting, and disturbance by wildfire. To make assessments of in-forest carbon stores, vegetation plots and a forest growth model are utilized. Trees that are removed are used to create energy and carbon that would have been emitted from comparative fossil fuel energy sources is counted. In this case study in the Sierra Nevada, with a frequent fire return interval common to mixed-conifer forests in the historic period, thinning to reduce fuels does provide greater carbon benefits than not thinning and letting the forest grow. In all cases, potential wildfire emissions are the greatest source of emissions. Direct emissions from mechanical treatments and transportation of the biomass are each about 1% of total emissions. Emissions from the combustion of biomass are slightly less than half of total emissions but less than potential wildfire emissions. The results indicate that wildfire frequency is the greatest determinant of whether or not the project provides greater carbon sequestration potential than the baseline scenario. This suggests carbon costs and benefits of reducing fuels may need to be evaluated relative to how wildfire burn risk varies with fuel loading, forest type, and stand location.