Control of the multimillennial wildfire size in boreal North America by spring climatic conditions

Wildfire activity in North American boreal forests increased during the last decades of the 20th century, partly owing to ongoing human-caused climatic changes. How these changes affect regional fire regimes (annual area burned, seasonality, and number, size, and severity of fires) remains uncertain...

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Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 51; pp. 20966 - 20970
Main Authors:	Ali, Adam A, Blarquez, Olivier, Girardin, Martin P, Hély, Christelle, Tinquaut, Fabien, El Guellab, Ahmed, Valsecchi, Verushka, Terrier, Aurélie, Bremond, Laurent, Genries, Aurélie, Gauthier, Sylvie, Bergeron, Yves
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 18-12-2012 National Acad Sciences
Series:	From the Cover
Subjects:	Biological Sciences Biomass Biomass burning Boreal forests Canada Charcoal Climate Climate change Climate models climatic factors Computer Simulation drought Ecosystem Environmental conditions Environmental Sciences fire regime fire season Fires Forest & brush fires Forest fires Global Changes global warming Human influences Lakes Models, Statistical Normal Distribution North America Paleoclimatology Pollen Seasons solar radiation Spring summer Temperature Trees Wildfire seasons Wildfires North America Canada
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Summary:	Wildfire activity in North American boreal forests increased during the last decades of the 20th century, partly owing to ongoing human-caused climatic changes. How these changes affect regional fire regimes (annual area burned, seasonality, and number, size, and severity of fires) remains uncertain as data available to explore fire–climate–vegetation interactions have limited temporal depth. Here we present a Holocene reconstruction of fire regime, combining lacustrine charcoal analyses with past drought and fire-season length simulations to elucidate the mechanisms linking long-term fire regime and climatic changes. We decomposed fire regime into fire frequency (FF) and biomass burned (BB) and recombined these into a new index to assess fire size (FS) fluctuations. Results indicated that an earlier termination of the fire season, due to decreasing summer radiative insolation and increasing precipitation over the last 7.0 ky, induced a sharp decrease in FF and BB ca . 3.0 kyBP toward the present. In contrast, a progressive increase of FS was recorded, which is most likely related to a gradual increase in temperatures during the spring fire season. Continuing climatic warming could lead to a change in the fire regime toward larger spring wildfires in eastern boreal North America.
Bibliography:	http://dx.doi.org/10.1073/pnas.1203467109 PMCID: PMC3529026 1A.A.A. and O.B. contributed equally to this work. Edited by Robert E. Dickinson, University of Texas at Austin, Austin, TX, and approved October 24, 2012 (received for review March 1, 2012) Author contributions: A.A.A., S.G., and Y.B. designed research; A.A.A., O.B., M.P.G., and C.H. performed research; A.A.A., O.B., M.P.G., C.H., F.T., A.E.G., V.V., A.T., L.B., and A.G. analyzed data; and A.A.A., O.B., M.P.G., and C.H. wrote the paper.
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.1203467109