Assessing changes in pollen assemblage and charcoal accumulation during known changes in climate from c. 5,400 to 3,300 Years Before Present at the forest-prairie ecotone in Alberta, Canada
Lorenz, P. Christopher J.
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The ecotone between aspen parkland and mixed-grass prairie in mid-eastern Alberta is a climatically-sensitive area that has been subject to periods of enhanced aridity occurring at multi-decadal to centennial-scale cycles throughout much of the last 6000 years. To assess the ecotonal response to changes in effective moisture, as inferred by diatom-inferred salinity, temporal variations in pollen and charcoal preserved in a sediment core from Chauvin Lake were analyzed over several diatom-inferred moisture-cycles from c. 5,400 to 3,300 YBP. Changes in landscape vegetation were inferred by variation in both the percent relative abundance and influx rates of pollen taxa found in a sediment core from Chauvin Lake. Variation in sediment charcoal accumulation rates for both total charcoal and morphotypes, as well as the percent relative abundance of charcoal morphotypes, were used to infer changes in landscape fire regimes during these aridity cycles. One-way ANOVAs were used to determine significant differences in average accumulation rates or relative abundances between the arid and more mesic periods. Changes in the relative abundance of Cyperaceae and Ambrosia pollen between wet and dry periods suggests a shift in the spatial arrangement of vegetation, and a decrease in the sediment influx of most taxa, suggests a decrease in production of landscape vegetation during periods of aridity. Charcoal morphotype analysis, especially variation in Type M, Type D and Type B, suggests fewer, more intense fires during periods of drought. Lack of change in total charcoal may be related to increased secondary sedimentation of charcoal during periods of drought due to increased soil erosion. This study suggests that the spatial arrangement and production of landscape vegetation is dependent on climate, and fire prevalence decreases during periods of drought due to reduced fuel availability.