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. / Thesis (Master, Biology) -- Queen's University, 2009-01-29 12:15:32.137

Quantifying charcoal particles preserved in sedimentary environments is an established method for estimating levels of fire activity in the past, both on human and geological timescales. It has been proposed that the morphology of these particles is also a valuable source of information, for example allowing inferences about the nature of the vegetation burned. This thesis aims to broaden the theoretical basis for these methods, and to integrate morphometric study of sedimentary charcoal with its quantification. Three key questions are addressed: firstly, whether the elongation of mesocharcoal particles is a useful indicator of fuel type; secondly, whether different sedimentary archives tend to preserve different charcoal morphologies; and finally, the critical question of how morphology affects charcoal quantification. The results corroborate the idea that grasses and trees produce mesocharcoal with distinctly different aspect ratios. However, the application of this as an indicator of vegetation change is complicated by the inclusion of species which are neither grasses nor trees, and by considerations of the effects of transportation. Charcoal morphotypes in diverse sedimentary environments are shown to be influenced by vegetation types, transportation history, and nature of the fire that produced them. Previous research has treated charcoal quantification and charcoal morphology as separate issues. Here it is shown that understanding morphology is essential for the accurate quantification of charcoal, since it affects the relationship between volumes and the two-dimensional areas from which measurements are taken. Understanding this relationship could allow such measurements to be used not just as relative measures of past fire activity, but to enable the accurate quantification of the charcoal sequestered in soils and sediments. This has important implications for our ability to understand the effects of fire on carbon cycling, and the role that fire plays in the Earth system.