Restoring surface fire stabilizes forest carbon under extreme fire weather in the Sierra Nevada

Abstract

Abstract. Climate change in the western United States has increased the frequency of extreme fire weather events and is projected to increase the area burned by wildfire in the coming decades. This changing fire regime, coupled with increased high-severity fire risk from a legacy of fire exclusion, could destabilize forest carbon (C), decrease net ecosystem exchange (NEE), and consequently reduce the ability of forests to regulate climate through C sequestration. While management options for minimizing the risk of high-severity fire exist, little is known about the longer-term carbon consequences of these actions in the context of continued extreme fire weather events. Our goal was to compare the impacts of extreme wildfire events on carbon stocks and fluxes in a watershed in the Sierra National Forest. We ran simulations to model wildfire under contemporary and extreme fire weather conditions, and test how three management scenarios (no-management, thin-only, thin and maintenance burning) influence fire severity, forest C stocks and fluxes, and wildfire C emissions. We found that the effects of treatment on wildfire under contemporary fire weather were minimal, and management conferred neither significant reduction in fire severity nor increases in C stocks. However, under extreme fire weather, the thin and maintenance burning scenario decreased mean fire severity by 25%, showed significantly greater C stability, and unlike the nomanagement and thin-only management options, the thin and maintenance burning scenario showed no decrease in NEE relative to the contemporary fire weather scenarios. Further, under extreme fire weather conditions, wildfire C emissions were lowest in the thin and maintenance burning scenario, (reduction of 13.7 Mg C/ha over the simulation period) even when taking into account the C costs associated with prescribed burning. Including prescribed burning in thinning operations may be critical to maintaining C stocks and reducing C emissions in the future where extreme fire weather events are more frequent.

Large‐scale restoration increases carbon stability under projected climate and wildfire regimes

“…Although reducing wildfire emissions requires repeated atmospheric C emissions from more frequent prescribed fires (Hurteau ; Krofcheck et al . ), prescribed fire emissions are smaller and we found support for our hypothesis that large‐scale treatments will lower fire severity and reduce wildfire emissions relative to the control (Figures and ). Inclusive of emissions from repeated prescribed fire, our large‐scale restoration treatments reduced fire emissions by an average of 0.07–0.09 Mg C ha −1 yr −1 over the 90‐year simulation, with the cumulative amount of avoided C emissions across the entire Sierra Nevada equaling 24% of California's 2020 emission limit (116 Tg; California Assembly Bill 32).…”

“…; Krofcheck et al . ). The temporal distribution of C losses demonstrated that large‐scale restoration treatments may initially incur greater C loss from the system, with the size of this near‐term C cost being a function of implementation timing (Figure ).…”

“…() and Krofcheck et al . (). The thinning and prescribed fire treatments were designed to remove a greater proportion of the youngest cohorts and shift the age distribution toward older cohorts.…”

Widespread severe wildfires under climate change lead to increased forest homogeneity in dry mixed‐conifer forests

“…❖ www.esajournals.org 4 November 2019 ❖ Volume 10(11) ❖ Article e02934 forest succession and interactions with fire, harvest, wind, and insects (Scheller et al 2008, Duveneck et al 2014, Kretchun et al 2016, Krofcheck et al 2017, Lucash et al 2017. LANDIS-II uses the life-history traits of tree and shrub species, along with soil and climate data, to simulate succession and responses to disturbances over time.…”

Quantifying carbon and species dynamics under different fire regimes in a southeastern U.S. pineland

“…The NECN extension implements succession with above-and belowground carbon and nitrogen and simulates the regeneration and growth of vegetation based on age, competition for resources (water, nitrogen, light), and disturbance. Prescribed fires are, however, only currently being simulated within the Biomass Harvest extension , Hurteau 2017, Krofcheck et al 2017, Swanteson-Franz et al 2018. Dead biomass (woody and leaf litter) and soil organic carbon (SOC) are also tracked over time.…”