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Recent fire activity in the boreal eastern interior of North America is below that of the past 2000 yr

Justin Waito,M. Girardin,J. Tardif,Y. Bergeron,Adam A. Ali

Published 2018 in Ecosphere

ABSTRACT

. The North American boreal forest has been developing since the end of the last glaciation approximately 10,000 yr ago. With climate warming and human occupation, it is anticipated that fi re dan-ger, ignition, and activity will be increasing, compromising forests ’ bene fi ts for generations to come. In this study, we show, however, that a century of rapid climate changes and human densi fi cation has had the opposite effect in the boreal eastern interior of the North American continent, reducing biomass burning to values below two millennia of historical levels. A multi-millennial fi re history was reconstructed for eight forested landscapes from the Lake of the Woods Ecoregion (LWE) located at the boreal – prairie ecotone. Fire history was reconstructed using a combination of archival (period 1920 – 2010), tree-ring (stand initiations and fi re scars: period 1690 – 2010), and lake sediment charcoal (2500 BP to present) records. The archival record revealed recent large fi res ( > 200 ha) in 1948, 1980, and 1988. An additional 19 fi res were identi fi ed by the fi re-scar record. Fire events in 1805, 1840, 1863, and the 1890s were identi fi ed in numerous locations around multiple lakes suggesting that they were of large extents. In accordance with the tree-ring record, the charcoal accumulation rate (CHAR) peak record generally identi fi ed the major fi res but tended to lag from the tree-ring records by several decades. Within LWE, the long-term charcoal record revealed that CHAR was higher for each lake in the earlier portion of the record including the warm Medieval Climate Anomaly (AD (cid:1) 900 to AD 1000), followed by a progressive decrease toward the cool Little Ice Age period. This decline was abruptly interrupted in the mid- to late 19th century with large synchronized fi res, also reported over western and central North America, and resumed approximately four decades later. Fire disturbance level is today below the historical range, despite the accentuated climate warming. Aging of the forest landscape may create biodiversity loss notably in fi re-adapted species while at the same time setting the tone for major fi res in upcoming decades if no action is taken for managing fuels.

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