Wildfire and fuel treatment effects on carbon storage, eastside Cascade Range, Washington, USA

Sequestration of carbon in forests has the potential to mitigate effects of global climate change by offsetting future emissions and greenhouse gas concentrations in the atmosphere. In dry temperate forests, however, wildfire is a natural disturbance agent with the potential to release large fluxes of carbon into the atmosphere. Climate-driven increases in wildfire frequency, extent, and severity are expected to increase the risks of reversal to carbon stores and affect the potential of dry forests to sequester carbon. Fuel treatments that successfully reduce surface fuels in dry forests can mitigate the spread and severity of wildfire, while reducing both tree mortality and emissions from wildfire. However, heterogeneous burn environments, site-specific variability in post-fire ecosystem response, and uncertainty in future fire frequency and extent complicate assessments of long-term (decades to centuries) carbon dynamics across large landscapes. Results of studies on the effects of fuel treatments and wildfires on long-term carbon retention across large landscapes are limited and equivocal. Current stand-scale studies, empirical and modeled, describe a wide range of (1) total treatment costs (12--116 Mg C ha-1) and (2) reductions in wildfire emissions between treated and untreated stands (1--40 Mg C ha-1). Conclusions suggest the direction (source, sink) and magnitude of net carbon effects from fuel treatments are similarly variable (-33 Mg C ha -1 to +3 Mg C ha-1). Studies at large spatial scales have shown that the low probability of high-severity wildfire events for any given treated stand can negate any expected carbon benefit.