PARENT SESSION
Contributed Oral Session 77: Paleoecology
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal
Pre- and post-settlement vegetation change on a Wisconsin outwash plain.
Calcote, Randy1, Hotchkiss, Sara2, Lynch, Beth3, 1 University of Minnesota, Minneapolis, MN2 University of Wisconsin, Madison, WI3 Luther College, Decorah, IA
ABSTRACT- Logging, fire and agriculture have dramatically changed vegetation assemblages since European settlement. White pine abundance has decreased in northwestern Wisconsin and aspen and oak have increased. General Land Office (GLO) survey data provide the best data available about pre-European vegetation and it is often assumed that the distribution of vegetation at the time of European settlement represents a fairly constant natural vegetation determined by climate and soils. We use pollen percentage data from sediment cores to test the sensitivity of the pollen record to postsettlement vegetation changes and to test the stability of vegetation over several hundred years before European settlement. We use nonmetric multidimensional scaling (NMS) ordination of pollen percentage data from 15 lakes on a 145,000 ha sand plain to plot the trajectories of vegetation change before and after European settlement (increase in ragweed pollen). Postsettlement assemblages show a consistent directional shift in the ordination space toward increased oak and aspen, consistent with the known regional vegetation change. Changes in presettlement samples were more variable with most sites changing little. A few sites had directional changes in several consecutive samples before settlement, sometimes as much in the few hundred years before settlement as in response to European land use. Longer records at those sites indicate that the range of assemblages in the last few hundred years covered about the same range of ordination space as the same sites in the last 1000 yrs, suggesting century scale periods of change, rather than millennial scale directional change. Pollen/vegetation changes do not necessarily correlate with charcoal peaks in sediment. Vegetation at most sites is relatively stable on the scale of a few hundred years, but occasionally changes occur that are believed to be associated with successional changes.
Key words: pollen analysis, Pinus banksiana, vegetation change, outwash plain