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The Center for Native Grasslands Management

Title: Interactions of climate and fire at two sites in the northern Great Plains, USA
Year: 2004
Author(s): Umbanhowar, C. E.
Source Title: Palaeogeography Palaeoclimatology Palaeoecology
Source Type: Journal
pages: 141-152
Original Publication: http://  
Abstract: The relationship of fire and climate in explaining the origin and maintenance of the grasslands of the northern Great Plains has long been of interest. I examined the hypothesis that burning was more frequent during wet years using charcoal to reconstruct fire histories near Coldwater Lake in southcentral ND, and Rice Lake in northcentral ND and published records of ostracod Mg/Ca ratios as a proxy for climate at these same two sites. Over the past 10 000 years, charcoal influx rates for Coldwater (0.045.68 mm2 cm−2 year−1) greatly exceeded influx rates for Rice (<0.011.91 mm2 cm−2 year−1). Both sites showed strong, significant periodicities of ∼15001800, ∼800900 and ∼130140 years but charcoal maxima and minima were only similar at ∼4200 cal years BP. Charcoal influx during the past 2000 years also revealed strong periodicities of between 310400 and 140 years at both sites. Comparison of smoothed charcoal influxes and ostracod Mg/Ca ratios suggests that both proxies are responding to changes in climate. When smoothed with a 320400-year window, increases in charcoal influx typically preceded rises in ostracod Mg/Ca ratio by ∼50100 years, and further smoothing (140-year window) of the residuals suggested a variable relationship between Mg/Ca ratios and charcoal influx. These results do not clearly support or reject the fuel limitation hypothesis, and this lack of clear support may result from (a) climate-driven shifts in the mix of C3 and C4 grasses resulting in maximum productivity at intermediate moisture levels, (b) possibly different responses of charcoal and Mg/Ca ratios to summer vs. winter precipitation, or (c) ground-water driven lags in the response of Mg/Ca ratios to shifts in climate. Comparison of the results from this study with other studies suggests that links between fire and fuels at finer time scales (0100 years) may be broadly constrained by longer term (∼5002000 years) patterns of climate in the northern Great Plains.