Shifting zonal patterns of the southern boreal forest in eastern Canada associated with changing fire regime during the Holocene |
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| Authors: | Guillaume de Lafontaine Serge Payette |
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| Affiliation: | 1. Smithsonian Environmental Research Center, P.O. Box 28, 647 Contees Wharf Rd, Edgewater, MD 21037, United States;2. Earth and Environmental Science Department, Lehigh University, United States;3. Department of Geography, University of California, Los Angeles, United States;1. Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh, PA, USA;2. Department of Earth and Environmental Sciences and Large Lakes Observatory, University of Minnesota Duluth, Duluth, MN, USA;1. GEOTOP — Université du Québec à Montréal (UQAM), C.P. 8888 Succursale Centre-ville, Montreal, Québec H3C 3P8, Canada;2. Département de biologie — Université Laval, 1045 avenue de la Médecine, Québec G1V 0A6, Canada;1. Chaire Industrielle en Aménagement Forestier Durable UQAM-UQAT, Institut de recherche sur les forêts, Université du Québec en Abitibi-Témiscamingue, 445 boul. de l''Université, Rouyn-Noranda, QC J9X 5E4, Canada;2. Laboratory of Tree-Ring Research, University of Arizona, 1215 E. Lowell Street, Tucson, AZ 85721, USA;3. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S, P.O. Box 10380, Stn. Sainte-Foy, Quebec, QC G1V 4C7, Canada;4. Norwegian Institute for Nature Research, P.O. Box 5685, Torgarden, NO-7485 Trondheim, Norway;5. Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, P.O. Box 49, SE-230 53 Alnarp, Sweden |
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| Abstract: | This research aims at uncovering the stand-scale Holocene fire history of balsam fir forest stands from two bioclimatic zones of the boreal forest and assessing the existence of a sub-continental shift in past fire activity that could have triggered a change in the Holocene zonal pattern. In eastern Canada, the extant closed-crown boreal forest corresponds to two ecological regions separated along 49°N, the northern black spruce zone and the southern balsam fir zone. We sampled balsam fir stands from the southern fir zone (n = 7) and among the northernmost patches of fir forest located far beyond the fir zone boundary, into the spruce zone (n = 6). Macrofossil analysis of charcoal in mineral soils was used to reconstruct both the stand-scale and regional Holocene fire histories. Data were interpreted in the context of published palaeoecological evidence. Stands of the balsam fir zone were submitted to recurrent fire disturbances between c. 9000 and 5000 cal. yr B.P. Local fire histories suggested that four sites within the fir zone escaped fire during the Holocene. Such fire protected sites allowed the continuous maintenance of the balsam fir forest in the southern boreal landscape. Stands of the spruce zone have been affected by recurrent fires from 5000 cal. yr B.P. to present. Local fire histories indicated that no site escaped fire in this zone. Published palaeoecological data suggested that balsam fir migrated to its current northern limit sometime between 7300 and 6200 cal. yr B.P. A change of the fire regime 5000 years ago caused the regional decline of an historical northern balsam fir forest and its replacement by black spruce forest. The consequence was a sub-continental reshuffling of the fir and spruce zones within the closed-crown boreal forest. The macrofossil analysis of charcoal in mineral soils was instrumental to the reconstruction of stand-scale Holocene fire history at sites where no other in situ fire proxies were available. |
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