THE EFFECTS OF LANDCOVER CHANGE ON POLLEN-VEGETATION RELATIONSHIPS IN THE UPPER MIDWEST

Pollen assemblage data are widely used to infer past vegetation community composition. This type of analysis assumes a stable relationship between pollen and vegetation, however, and little research exists on the changing dynamics between these variables over time. This study investigates the changes in pollen-vegetation relationships in the Upper Midwest from the time of Euro-American settlement to the present day, encompassing changes in land use, climate, and fire regime. This research brings together three significant ecological databases to understand the changing dynamics of pollen, vegetation, and land use. Pollen data were obtained from the Neotoma Paleoecological Database (http://neotomadb.org) by taking samples from immediately prior to identified 'settlement horizons’, records of vegetation prior to major Euro-American land clearance in the upper Midwest were obtained from the Public Land Survey System, and modern forest composition data were obtained from the Forest Service's Forest Inventory and Analysis Program.

By investigating the effects of taxon and land use on pollen-vegetation relationships, we show that dynamics shift significantly for several taxa: beech, birch, hemlock, oak, pine, and spruce. These results suggest that pollen-based estimations of past vegetation will under-predict the presence of some taxa (beech, birch, oak, pine, hemlock, and spruce), and over-predict others (ash, basswood, and maple). These distortions imply a need for careful consideration of pollen-based reconstructions of past vegetation.