Did fires drive Holocene carbon sequestration in boreal ombrotrophic peatlands of eastern Canada?

Abstract

Wildfire is an important factor on carbon sequestration in the North American boreal biomes. Being globally important stocks of organic carbon, peatlands may be less sensitive to burning in comparison with upland forests, especially wet unforested ombrotrophic ecosystems as found in northeastern Canada. We aimed to determine if peatland fires have driven carbon accumulation patterns during the Holocene. To cover spatial variability, six cores from three peatlands in the Eastmain region of Quebec were analyzed for stratigraphic charcoal accumulation. Results show that regional Holocene peatland fire frequency was ~2.4fires1000yr−1, showing a gradually declining trend since 4000cal yr BP, although inter- and intra-peatland variability was very high. Charcoal peak magnitudes, however, were significantly higher between 1400 and 400cal yr BP, possibly reflecting higher charcoal production driven by differential climatic forcing aspects. Carbon accumulation rates generally declined towards the late-Holocene with minimum values of ~10gm−2yr−1 around 1500cal yr BP. The absence of a clear correlation between peatland fire regimes and carbon accumulation indicates that fire regimes have not been a driving factor on carbon sequestration at the millennial time scale.