The Science

As the Arctic continues to warm and become increasingly dry, severe wildfires outbreaks are becoming more frequent. Wildfire onset leads to the combustion and loss of carbon from soil and vegetation, and the continual export of soil nutrients to waterways. This research used a mathematical ecosystem model to better understand how quickly these ecosystems recover from wildfire and how soil nutrient availability underpins that recovery.

The Impact

Arctic soils contain enormous amounts of carbon that is vulnerable to climate change impacts. Predicting the fate of these soil carbon stocks under long-term warming also requires accounting for short-term disturbances, including more frequent wildfires. An urgent need exists for developing models that accurately represent wildfire impacts on tundra ecosystems against a backdrop of climate change. This study shows how increased soil nutrient availability enables quicker recovery of plant communities and soil carbon.

Summary

Researchers used a well-tested, process-rich model, ecosys, to simulate the response of the soil carbon and nutrient cycles to acute wildfire onset and chronic changes in climate. The foundation for the model spin-up was the 2007 Anaktuvuk river fire, one of the largest (and most comprehensively sampled) wildfires in high-latitude systems. Model performance was evaluated by comparison to site data and included pre-and post-fire net primary productivity, soil carbon stocks, and physicochemical variables. Once benchmarked, several questions were addressed, including: (1) What are the long-term ramifications of fire disturbance against the backdrop of ongoing climate change across the 21^st century? (2) What role does the belowground microbial community play in enabling the recovery of the aboveground plant community? 

This study shows that over the first 5 years post-fire, fast-growing bacterial heterotrophs colonized regions of the soil previously occupied by slower-growing saprotrophic fungi. The bacterial heterotrophs mineralized organic matter, releasing nutrients into the soil. This pathway outweighed new sources of nitrogen (e.g., nitrogen fixation), reestablished biogeochemical equilibrium, and facilitated the recovery of plant productivity. 

Principal Investigator

Nick Bouskill
Lawrence Berkeley National Laboratory
njbouskill@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research was supported by the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy’s (DOE) Office of Science to Lawrence Berkeley National Laboratory (LBNL) as part of the Next-Generation Ecosystem Experiments–Arctic (NGEE–Arctic) project. 

References