In the eastern United States, forest plant communities that were present 17,000 to 12,000 years ago are no longer represented on the landscape. This project will determine whether these historic assemblages of vegetation arose from: 1) unusually high temperature seasonality, 2) low atmospheric carbon dioxide concentrations, and/or 3) herbivory by now-extinct ''megafauna'' (e.g. mammoths, mastodons). This project integrates paleoecological data and mechanistic vegetation models. Specifically, this project will study lake-sediment cores from seven mid-continental sites from Tennessee to Minnesota and model climatic and carbon dioxide controls on vegetation composition. Sediments will be analyzed to infer ecological histories of vegetation, fire, and megafaunal population density and determine the timing of key ecological events.
This study of past environmental change has direct implications for current climate-change concerns. In particular, for planning purposes, there is an urgent need for accurate ecological forecasts, but the robustness of current ecological models, when applied to environmental conditions outside the range of modern observations, is poorly understood. Moreover, climates at the end of the 21st century will likely include combinations of temperature and precipitation unlike any observed today. The well-documented anomalous late-glacial climates and ecological communities are a good testing ground for evaluating the adequacy of current models of ecological response to complex environmental change. This work will support student training and outreach activities for high school teachers and students.
The last deglaciation offers a model system for studying how species distributions and abundances are affected by environmental change. A key phenomenon during the last deglaciation was the reshuffling of species into associations not seen at present. Understanding the processes controlling the assembly and disassembly of these ‘no-analog’ communities is directly relevant to current efforts to conserve species and ecosystem services during the climate changes expected for the 21st century. In this project, conducted in collaboration between the University of Wisconsin-Madison (principal investigator Dr. John W. Williams) and the University of Wyoming (principal investigator Dr. Stephen T. Jackson), we sought to better understand the causes of the formation and disappearance of no-analog plant communities during the last deglaciation by collecting a series of high-resolution and well-dated lake sediment records from the central US and analyzing these sediments for indicators of past vegetation composition, fire history, and megafaunal population density. We collected seven new records (Anderson Pond, TN, Appleman Lake, IN, Cupola Pond, MO, Jackson Pond, KY, Kirchner Marsh, MN, Silver Lake, OH, and Spicer Pond, IN) and analyzed all records for fossil pollen and spores, sedimentary charcoal, physical sedimentology, and radiocarbon dates. These records show that the formation of plant communities with no modern analog was time-transgressive, beginning first in the south-central US ca. 16 thousand years ago and in the upper Midwest between 14.5 and 13.9 thousand years ago. This pattern strongly suggests that the formation of the no-analog communities is linked to rising temperatures. However, at several sites in the upper Midwest, declining abundances of spores from the dung fungus Sporormiella coincide with or just precede the formation of the no-analog plant communities. We and others have shown that in modern grazed systems, high abundances of Sporormiella spore are an indicator of megafaunal grazing intensity, albeit one that is also sensitive to taphonomic processes. Hence, the observed association between Sporormiella declines and the formation of no-analog plant communities provides tantalizing evidence that the formation of the no-analog plant communities in the upper Midwest was partially shaped to the end-Pleistocene population declines and ultimate extinctions of megaherbivores, perhaps via a release of palatable tree species from herbivory. Hence, this project has led to a new working hypothesis in which the formation of the no-analog plant communities was jointly shaped by a combination of climatic and megafaunal controls. More work is needed to further test the importance of megaherbivory on past plant community dynamics. This work directly bears on current ‘rewilding’ projects in which land managers are reintroducing species, or close equivalents of extinct species, with the goal of enhancing ecosystem function and biodiversity. All fossil pollen and radiocarbon data has or will soon be made publically available by submission to the Neotoma Paleoecology Database (www.neotomadb.org). This work has supported six graduate students and thirteen undergraduate students, including four first-generation college students and students from populations traditionally underrepresented in the sciences. We have participated in programs designed to provide undergraduate research experiences, particularly from underrepresented groups. These include the Wyoming EPSCoR Summer Research Apprentice Program, Undergraduate Research Fellowship Program, and Honors Thesis program; the Wisconsin Undergraduate Research Scholars, Integrated Biological Sciences Summer Research Program, Pathways Scholars Program, and Hilldale Scholars Program; and several undergraduate theses. PhD student Jacquelyn Gill won the prestigious Braun and Cooper Awards from the Ecological Society of America. We also helped host and gave presentations at a "Teaching Climate Change" workshop for teachers in summer 2010 (co-sponsored by this grant, Carleton College, the US INQUA National Committee, and the American Quaternary Association). Both Williams and Jackson teach at the undergraduate and graduate level and regularly communicate with the general public through public presentations, social media, and traditional media outlets.
