INTERACTION OF MILLENNIAL-SCALE CLIMATE VARIATIONS, CO2, MEGAFAUNAL EXTINCTIONS, AND FIRE ON ECOSYSTEM TRANSFORMATIONS AND DISAPPEARANCES IN FLORIDA

Understanding the interactions among climate, megaherbivory, and fire in driving vegetation change in the past has direct implications for developing models of future climate-driven environmental change. However, few lacustrine records in eastern North America extend prior to the Last Glacial Maximum. In this talk, we present results from new cores from Lake Tulane, Florida, USA. The previously collected 61,000-year pollen record at Tulane shows oscillations of pine and oak-dominated vegetation, with peaks in pine closely aligned with Heinrich events. This suggests that Heinrich events resulted in warm and wet climates in central Florida, in contrast to the cool, dry conditions experienced elsewhere in the Northern Hemisphere. We augmented the existing pollen record with new analyses of coprophilous fungal spores and sedimentary macroscopic charcoal. We incorporated these data into new quantitative approaches, using topic modeling to classify the pollen assemblages into four community types and a newly developed state-space model to test hypotheses about the close regulation of vegetation dynamics by the interacting effects of climate, fire, and megafaunal extinctions. Millennial-scale climate variation and CO2 were the strongest predictors of vegetation changes, with Heinrich events being the strongest predictors of high pine abundances and high CO2 being the strongest predictor of oak abundances. Additionally, disturbances such as fire appear to play important roles in catalyzing ecosystem transformations, particularly the establishment and loss of pine woodlands. A diverse oak-forb woodland was prevalent under Pleistocene conditions of low CO2 and high megafaunal abundances. This ecosystem vanished between 15,000 and 10,000 years ago, coinciding with megafaunal extinctions, rising CO2 levels, and the arrival and expansion of human populations. These findings provide a refined understanding of the complex interactions between climate, fire, and megafaunal dynamics, elucidating the mechanisms behind major vegetation changes over the last 61,000 years. Ultimately, this work highlights the critical role of large herbivores in maintaining biodiversity and ecosystem structure, informing modern conservation strategies aimed at rewilding and restoring herbivore populations.