PARENT SESSION
Poster Session 21: Paleoecology
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Macroscopic charcoal morphology provides an indication of fuel source.

Lynch, Elizabeth^*,1, Jensen, Kathryn¹, Merten, Steffen¹, Calcote, Randy², Hotchkiss, Sara³, ¹ Luther College, Decorah, IA² University of Minnesota, Minneapolis, MN³ University of Wisconsin-Madison, Madison, WI

ABSTRACT- The northwest Wisconsin sand plain historically supported a gradient of ecosystems, ranging from oak-pine savannas in the south, to jack pine barrens in the central region, to mixed pine forests in the north. Our objective is to reconstruct spatial and temporal patterns in fire regimes across this vegetation gradient using both quantitative and qualitative analysis of macroscopic charcoal in lake sediments. To build a reference library of charcoal types we burned samples of plant materials from dominant taxa, including grasses (Poaceae) and the leaves, bark, and wood of oak (Quercus) and pine (Pinus). Samples were burned in an open crucible. Charcoal fragments were gently crushed, then given the same treatment as fossil charcoal samples, including soaking in 6% H₂O₂, and sieving to remove fragments <125m. While most of the charcoal produced does not differ by source material burned, there are three distinct types that we observe in both the reference burns and in fossil charcoal from lake sediments. Grass cuticles are clearly identifiable by the arrangement and shape of epidermal cells, although burned sedge (Carex) leaves are similar to some grass fragments. Bordered pits in conifer tracheids are clearly visible in burned samples of pine wood. The charred veins in oak leaves have a characteristic branching structure, although other broad-leaved species with well-lignified veins may also show similar patterns. Fluctuations in the proportions of these charcoal types in lake sediments may reflect changes in vegetation and/or the prevalence of cool surface fires vs. hot crown fires over time.

Key words: charcoal analysis, charcoal morphology, fire history, paleoecology