Fire-induced carbon emissions and regrowth uptake in western U.S. forests: Documenting variation across forest types, fire severity, and climate regions

• Published in: Journal of Geophysical Research: Biogeosciences Vol. 117; no. G3
• Main Authors: Ghimire, Bardan, Williams, Christopher A., Collatz, G. James, Vanderhoof, Melanie
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-09-2012; American Geophysical Union
• Subjects: Atmosphere; Biogeochemistry; Biomass; Biosphere; Burns; Carbon; carbon cycle; Dead wood; Drought; Earth sciences; Earth, ocean, space; Emissions; Exact sciences and technology; fire emissions; Fires; forest disturbance and recovery; Forests; Geobiology; modeling; net primary productivity; Regrowth; Wood; Western U.S; United States; biomass; trend-surface analysis; density; Mortality; Regional scope; focus; decomposition; climate; North America; forests; Uptake; fires; balance; combustion; drought; carbon; temperature; wood; Natural hazards
• ISSN: 0148-0227; 2169-8953; 2156-2202; 2169-8961
• DOI: 10.1029/2011JG001935

The forest area in the western United States that burns annually is increasing with warmer temperatures, more frequent droughts, and higher fuel densities. Studies that examine fire effects for regional carbon balances have tended to either focus on individual fires as examples or adopt generalizations without considering how forest type, fire severity, and regional climate influence carbon legacies. This study provides a more detailed characterization of fire effects and quantifies the full carbon impacts in relation to direct emissions, slow release of fire‐killed biomass, and net carbon uptake from forest regrowth. We find important variations in fire‐induced mortality and combustion across carbon pools (leaf, live wood, dead wood, litter, and duff) and across low‐ to high‐severity classes. This corresponds to fire‐induced direct emissions from 1984 to 2008 averaging 4 TgC yr−1 and biomass killed averaging 10.5 TgC yr−1, with average burn area of 2723 km2 yr−1across the western United States. These direct emission and biomass killed rates were 1.4 and 3.7 times higher, respectively, for high‐severity fires than those for low‐severity fires. The results show that forest regrowth varies greatly by forest type and with severity and that these factors impose a sustained carbon uptake legacy. The western U.S. fires between 1984 and 2008 imposed a net source of 12.3 TgC yr−1 in 2008, accounting for both direct fire emissions (9.5 TgC yr−1) and heterotrophic decomposition of fire‐killed biomass (6.1 TgC yr−1) as well as contemporary regrowth sinks (3.3 TgC yr−1). A sizeable trend exists toward increasing emissions as a larger area burns annually.
Key Points
Comprehensive review of fire‐induced plant combustion and mortality
Introduces detailed post‐fire carbon flux trajectories for western U.S. forests
Assesses interannual variation in regional carbon emissions and uptake from fire