Landscape-level fuel treatments alter pyrogenic carbon emissions but reduce long-term carbon storage

Background/Question/Methods A century of fire suppression in US forests has led to a significant accumulation of understory fuels, particularly in disturbance-prone ecosystems throughout the west.  Such an extensive development of understory fuels has resulted in wildfires of uncharacteristic severity and areal extent.  Efforts have thus been made to reduce understory fuels throughout much of the affected landscapes.  However, current rates of fuel reduction within these landscapes range from 1-2% of the affected area, meaning that the treatment implementation times are in excess of the natural fire return intervals, thus they could ultimately prove to be ineffective.  Furthermore, there are concerns about the extent to which such fuel reduction treatments will reduce long-term C storage, which could continue to serve as an offset to increasing atmospheric CO₂ concentrations. We tested the extent to which various fuel reduction treatments, when applied at various annual treatment areas, altered pyrogenic C emissions and long-term C storage.  For this we used the LANDCARB model, which models forests on a stand-by-stand basis and can simulate complete stand harvests as well as partial disturbances including salvage logging, partial harvests, and prescribed fires. 

Results/Conclusions For fuel reduction treatments to be effective, they must be applied over landscape areas far larger than current extents. Furthermore, the necessary reduction in total landscape C storage is substantially larger than the amount of pyrogenic C emissions that are avoided by a reduction in fire severity.  We suggest that strategies aimed at reducing all fuel accumulation may ultimately prove to undermine the role of these forests as a C storage medium, and we recommend that fuel reduction treatments instead be placed strategically throughout this and possibly other landscapes with similar conditions.  We also propose that future research investigate the effects of various spatial arrangements of fuel reduction treatments across the landscape.