A High-Resolution Paleoecological Perspective on Historical Fire Regimes in Great Lakes Barren Communities of Stockton Island, Wisconsin

Abstract Fire is an important earth-system process, which is impacted by climate, and in turn shapes plant communities and drives biogeochemical cycling. Long-term perspectives on fire history are valuable in understanding the historical role of fire inmaintaining plant communities, and paleoenvironmental methods are a primary source for this information. Great Lakes barren communities, characterized by pines and other fire-adapted plants growing in sandy, well-drained soils, are a regionally unique ecosystem type that is likely fire dependent. However, long-term perspectives on fire history are needed to inform management. In this study, I quantify multiple size-fractions of charcoal throughout a peat core to compare burning at different spatial-scales through time, comparing and contrasting fire history in the Great Lakes barren community with that of the broader island and regional mixed-deciduous forest. I compare these fire history records with a surface-moisture reconstruction developed through testate amoeba analyses to assess hydrological controls on burning, and use my data to discuss the utility of peatland fire history records and make brief management recommendations. Macroscopic charcoal influx was high throughout most of the ~6000-year record, with particularly high levels indicating periods of increased local burning 4.1-3.6 ka, 2.6-2.1 ka, and over the last ~400 years prior to fire suppression. Microscopic charcoal influx showed little correlation with the macroscopic record (r=0.17), indicating mostly distinct signals from regional and local fires respectively. However, nine instances of simultaneous local and regional fire episodes were identified, likely representing occurrences of major, widespread fires. All simultaneous regional and local fire events occurred when bog moisture was drier than average, and regional fire history was weakly correlated with bog hydrology for the past 2500 years. Results indicate that the sand barren landscape has a history of persistent local burning with an average fire return interval of about 55 years, and fire history was unrelated to local bog hydrology, although increased large fires during the Medieval Climate Anomaly and decrease large fires during the LIA suggest a possible relationship with temperature or seasonal moisture changes. Controlled burning of Great Lakes barren communities that is broadly consistent with the observed historical fire frequency of the past 400 years is most likely to maintain this rare and unique community. Finally, my results highlight the value of peatland records of fire history, which have been underutilized in paleoenvironmental studies even though these depositional systems provide some advantages over lakes.