Higher burn severity stimulates postfire vegetation and carbon recovery in California

As the climate continues to warm, the severity of wildfires is increasing. However, the potential impact of higher burn severity on ecosystem resilience and regional carbon balance is still not clear. There are ongoing debates regarding whether increased burn severity stimulates or delays postfire vegetation and carbon recovery. In this study, we utilized remote sensing data to analyze burn severity and vegetation observations, as well as model simulations to assess wildfire carbon emissions and ecosystem carbon fluxes. Our focus was on examining the dynamics of vegetation and carbon flux following wildfires spanning up to 16 years in California, a region that has experienced significant intensification in burn severity over the past two decades. Our findings revealed that more severe burns resulted in greater vegetation damage and carbon releases. However, they also facilitated faster postfire vegetation and carbon recovery. In comparison to the average burn severity, the most severe burns caused an additional 62–128 % loss of vegetation, 21–80 % higher instant wildfire carbon emissions, and 45–110 % more postfire carbon sources. Nonetheless, high-severity burns exhibited accelerated postfire recoveries in both vegetation growth and ecosystem carbon sink. Carbon sinks, which persisted for up to 15 years after high-severity burns, partially offset a significant proportion of the extra postfire carbon sources, ranging from 84 to 107 % (excluding instant emissions). However, this offset effect was insufficient to fully compensate for the combined impact of postfire carbon sources and instant wildfire carbon emissions. Consequently, on the decadal time scale relevant to regional climate policies, the increasing severity of fires poses a threat to the objective of maintaining California's natural and working lands as a net carbon sink. Moreover, it exacerbates climate warming by enhancing carbon releases from ecosystems.