Thursday, August 9, 2007

PS 64-118: A 3000-year fire history from Corner Lake, north-central Wisconsin, and its relationship to vegetation and climate change

Benjamin H. Von Korff, Samantha W. Kaplan, and Sara C. Hotchkiss. University of Wisconsin

We reconstructed fire history in Germain Hemlocks State Natural Area, Oneida County, Wisconsin, using sedimentary charcoal from Corner Lake, to contribute perspective for fire management at the site. The role of fire in the failure of white pine regeneration following 1880s logging is of particular management concern. Charcoal was sieved from contiguous samples representing approximately 12-year intervals over the last 3000 years. Two plant fragment samples were 14C dated and the ambrosia rise was identified to establish a chronology. Fractions 125-250μ and >250μ were counted to reconstruct local fire events and classified into conifer wood with bordered pits, graminoid cuticle, and unidentified types. LOWESS smoothing and a Gaussian mixture model separated peaks in charcoal accumulation rate (CHAR) from a slowly varying background. CHAR peaks from the >250μ size fraction occurred on average once every 125 years between 3000 and 2500 BP – about twice as frequently as the 125-250μ size fraction. In the 125-250μ size fraction CHAR peak frequency doubled from 1600-1100 BP, but fires were absent between 1100 and 800 BP, coinciding with the Medieval Warm Period. The highest charcoal peak frequencies occurred during the Little Ice Age, between 800 and 100 BP, with the last peak in the 125-250μ size fraction at 400 BP and circa 100 BP in the >250μ size fraction. Increased occurrence of charcoal with bordered pits suggests that the relative importance of conifers increased from 650 BP until present. The lack of fire in the last century may have resulted from fire suppression efforts. These data reveal a temporal correlation among changes in climate, vegetation and fire regime, and a counterintuitive increase in fire frequency during the Little Ice Age. Results suggest that fire may be important for white pine restoration.

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