E-mail : brigitte.talon@univ.u-3mrs.fr

Reconstruction of the long-term fire history of an old-growth deciduous forest in Southern Québec, Canada: from charred wood in mineral soils

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Charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes. In this study, we used botanically-identified and radiocarbon-dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale. Charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long-term fire history of an old-growth deciduous forest in southern Québec. Charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters. Spruce (Picea spp.) fragments dominated the charcoal assemblage, along with relatively abundant wood fragments of sugar maple (Acer saccharum) and birch (Betula spp.), and rare fragments of pine (Pinus cf. strobus) and white cedar (Thuja canadensis). AMS radiocarbon dates from 16 charcoal fragments indicated that forest fires were widespread during the early Holocene, whereas no fires were recorded from the mid-Holocene to present. The paucity of charcoal data during this period, however, does not preclude that a fire event of lower severity may have occurred. At least 8 forest fires occurred at the study site between 10,400 and 6300 cal. B.P., with a dominance of burned conifer trees between 10,400 and 9000 cal. B.P. and burned conifer and deciduous trees between 9000 and 6300 cal. B.P. Based on the charcoal record, the climate at the study site was relatively dry during the early Holocene, and more humid from 6300 cal. B.P. to present. However, it is also possible that the predominance of conifer trees in the charcoal record between 10,400 and 6300 cal. B.P. created propitious conditions for fire spreading. The charcoal record supports inferences based on pollen influx data (Labelle and Richard, 1981) of the early arrival of spruce and sugar maple in the study area shortly after deglaciation. We conclude that macroscopic charcoal analysis of mineral soils subjected to disturbance by tree uprooting may be a useful paleoecological tool to reconstruct long-term forest fire history at the stand scale. This type of analysis including botanically-identified and radiocarbon-dated charcoal macrofossils at the site scale should be encouraged because it yields direct evidence of past fire activity indeed in the sites that are currently affected by fire but not enough considered in the paleoecological literature.

Publication

Talon, B., Payette, S., Filion, L., Delwaide, A., 2005. Reconstruction of the long-term fire history of an old-growth deciduous forest in Southern Québec, Canada: from charred wood in mineral soils. Quaternary Research, 64: 36-43.