Fuel availability not fire weather controls boreal wildfire severity and carbon emissions


Carbon (C) emissions from wildfires are a key terrestrial–atmosphere interaction that influences global atmospheric composition and climate. Positive feedbacks between climate warming and boreal wildfires are predicted based on top-down controls of fire weather and climate, but C emissions from boreal fires may also depend on bottom-up controls of fuel availability related to edaphic controls and overstory tree composition. Here we synthesized data from 417 field sites spanning six ecoregions in the northwestern North American boreal forest and assessed the network of interactions among potential bottom-up and top-down drivers of C emissions. Our results indicate that C emissions are more strongly driven by fuel availability than by fire weather, highlighting the importance of fine-scale drainage conditions, overstory tree species composition and fuel accumulation rates for predicting total C emissions. By implication, climate change-induced modification of fuels needs to be considered for accurately predicting future C emissions from boreal wildfires.

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Fig. 1: Map of studied ecoregions and field sites.
Fig. 2: Average above- and belowground pre-fire and combusted carbon (C) pools for each ecoregion group.
Fig. 3: SEM results testing a hypothesized network of top-down and bottom-up controls on C combustion.

Data availability

The data used in this manuscript are archived at the Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC). https://doi.org/10.3334/ORNLDAAC/1744.

Code availability

No custom code or mathematical algorithms were used in the analyses of these data. The R code for our statistical analyses is available from the authors upon request, and each of the R packages used is referenced in the Methods.


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This synthesis work for this project was supported by funding from the NASA Arctic Boreal and Vulnerability Experiment (ABoVE) Legacy Carbon grant NNX15AT71A awarded to M.C.M. The original field studies were supported by funding in the United States from NSF DEB RAPID grant no. 1542150 to M.C.M., NASA ABoVE grant NNX15AT83A to L.B.-C., NASA ABoVE grant NNX15AU56A to B.M.R., S.V. and M.T., Joint Fire Science Program grant 05-1-2-06 to J.F.J., NSF grant 0445458 to M.C.M., NSF support to the Bonanza Creek LTER (DEB-0423442); and in Canada from NSERC Discovery Grant funding to J.F.J. and M.R.T.; Government of the Northwest Territories Cumulative Impacts Monitoring Program Funding project #170 to J.L.B.; NSERC PDFs to N.J.D. and C.M.D.; GNWT logistical and financial support through the Laurier-GNWT Partnership Agreement; Polar Knowledge Canada’s Northern Science Training Program funding awarded to Canadian field assistants; S.V. acknowledges Vidi grant support from the Netherlands Organization for Scientific Research (NWO).

Author information




M.C.M. and X.J.W. conceived the study with help from B.M.R. and S.V. Field data were contributed by L.B.-C., W.J.d.G., C.M.D., E.H., E.S.K., B.M.R., M.C.M., X.J.W. and E.W. Additional data were contributed by B.M.R., E.H., L.K.J., S.P., and S.V. X.J.W. combined the datasets and analysed the data with help from M.C.M., B.M.R. and S.V. X.J.W. led the writing in collaboration with M.C.M., J.F.J., B.M.R. and S.V. All authors read and edited this manuscript.

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Correspondence to X. J. Walker.

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Peer review information Nature Climate Change thanks Gregory Dillon, Matthew Hurteau, Rachel Loehman and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–6, Tables 1–9, discussion and references.

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Walker, X.J., Rogers, B.M., Veraverbeke, S. et al. Fuel availability not fire weather controls boreal wildfire severity and carbon emissions. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-00920-8

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