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Vegetation composition versus climate as controls of boreal-forest fire regime: Holocene records from Alaska.
Lynch, Jason*,1, Hollis, Jeremy1, Hu, Feng Sheng1, 1 University of Illinois, Urbana, Illinois
ABSTRACT- Future climatic change is projected to greatly affect boreal ecosystems, but the relative effects of climate and vegetation composition on the boreal fire regime are poorly understood. To investigate the relationships among climate, fire, and vegetation, we analyzed sediment cores from Moose Lake (61o 22.452' N, 143o 35.931' W) and Chokasna Lake (61o 22.398' N, 143o 36.138' W) in Alaska for lithology, macrofossils, pollen, and charcoal to reconstruct regional moisture availability, vegetation, and fire-return intervals (FRI). The sediment records from both lakes show a sequence of peat to alternating peat/clay layers to gyttja, indicating a dry climate before 6,000 calibrated 14C years before present (yr BP), fluctuating but low moisture availability until 4,000 yr BP, and a wet climate afterward. The early forest community was dominated by Picea glauca, which was replaced by a Picea mariana community after 4,000 yr BP. FRI was >500 years before 4,000 yr BP except for 6,500-6,000 yr BP at Chokasna Lake and 6,000-5,500 yr BP at Moose Lake when the mean FRI was 200 years. After 4,000 yr BP, FRI decreased to 207 years. Wetter climatic conditions after 4,000 yr BP should have favored higher FRI. The increased fire occurrence in the past 4,000 years was likely caused by the interaction between climate, which facilitated P. mariana expansion, and the fire-prone vegetation dominated by P. mariana, which promoted burning with increased biomass flammability and fuel availability. These long-term fire records show the importance of vegetation composition in controlling boreal-forest fire regimes.
KEY WORDS: fire history, boreal ecosystem, Picea mariana