Recent burning of boreal forests exceeds fire regime limits of the past 10,000 years
- aDepartment of Plant Biology and
- bProgram in Ecology, Evolution, and Conservation Biology, University of Illinois, Urbana, IL 61801;
- cDepartment of Forest, Rangeland, and Fire Sciences, University of Idaho, Moscow, ID 83844-1133;
- dLimnological Research Center, University of Minnesota, Minneapolis, MN 55455; and
- eSchool of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195
See allHide authors and affiliations
Edited by Thompson Webb, Brown University, Providence, RI, and accepted by the Editorial Board June 19, 2013 (received for review March 15, 2013)

Abstract
Wildfire activity in boreal forests is anticipated to increase dramatically, with far-reaching ecological and socioeconomic consequences. Paleorecords are indispensible for elucidating boreal fire regime dynamics under changing climate, because fire return intervals and successional cycles in these ecosystems occur over decadal to centennial timescales. We present charcoal records from 14 lakes in the Yukon Flats of interior Alaska, one of the most flammable ecoregions of the boreal forest biome, to infer causes and consequences of fire regime change over the past 10,000 y. Strong correspondence between charcoal-inferred and observational fire records shows the fidelity of sedimentary charcoal records as archives of past fire regimes. Fire frequency and area burned increased ∼6,000–3,000 y ago, probably as a result of elevated landscape flammability associated with increased Picea mariana in the regional vegetation. During the Medieval Climate Anomaly (MCA; ∼1,000–500 cal B.P.), the period most similar to recent decades, warm and dry climatic conditions resulted in peak biomass burning, but severe fires favored less-flammable deciduous vegetation, such that fire frequency remained relatively stationary. These results suggest that boreal forests can sustain high-severity fire regimes for centuries under warm and dry conditions, with vegetation feedbacks modulating climate–fire linkages. The apparent limit to MCA burning has been surpassed by the regional fire regime of recent decades, which is characterized by exceptionally high fire frequency and biomass burning. This extreme combination suggests a transition to a unique regime of unprecedented fire activity. However, vegetation dynamics similar to feedbacks that occurred during the MCA may stabilize the fire regime, despite additional warming.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: fshu{at}life.illinois.edu.
Author contributions: R.K., P.E.H., L.B.B., and F.S.H. designed research; R.K., M.L.C., P.E.H., I.S., and F.S.H. performed research; R.K. analyzed data; and R.K. and F.S.H. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. T.W. is a guest editor invited by the Editorial Board.
Data deposition: The data reported in the paper have been deposited in the National Oceanic and Atmospheric Administration (NOAA) Paleoclimate Database, www.ncdc.noaa.gov/paleo/data.html.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1305069110/-/DCSupplemental.
Citation Manager Formats
Article Classifications
- Biological Sciences
- Ecology