Session Information
| Session | Poster Session | | Date | Monday (2008-04-07) | | Time | 5:00 PM - 7:00 PM | | Room | Grand Terrace |
Presentation Information
| Presenter | Sara Hotchkiss | | Title | Paleoecological perspective on landscape scale vegetation patterns on the northwestern Wisconsin sand plain: How representative is pre-European settlement vegetation of the last 2000 years? | | Affiliation | University of Wisconsin | | Authors | Sara Hotchkiss, Randy Calcote, Elizabeth Lynch | | Keywords | Climate change, Fire breaks, Paleoecology, Vegetation dynamics, Wisconsin | | Presentation Type | Poster | Abstract:
Maps of vegetation composition and structure generated from the Public Land Survey provide insight into landscape-scale vegetation patterns before widespread land clearance. However these patterns represent a snapshot in time that may not be typical of conditions over longer time periods. We used pollen and charcoal from sediment cores from eight small, deep lakes to investigate how landscape context (soil texture and abundance of fire breaks) affected the spatial and temporal variability of vegetation over 2000-4000 years on a sand plain in northwestern Wisconsin.
Twenty sites on the sand plain were classified by the soil texture and abundance of fire breaks (lakes and wetlands) within a 25km2 area around each site. Cluster analysis defined three site types. 1: Xeric sites characterized by excessively- to well-drained soil and few lakes and wetlands, 2: intermediate sites located at the border between xeric and mesic regions of the sand plain, and 3: more mesic sites characterized by moderately well- to somewhat-poorly drained soils and abundant wetlands and lakes. The mesic and intermediate sites exhibited greater change in species composition over 2000-4000 years. Over the past 2000 years oak has generally decreased and jack-red pine increased. A rapid switch from oak- to pine-dominated vegetation occurred at several sites about 1500 years ago. At the beginning of the Little Ice Age (LIA) about 700 years ago, white pine increased at the expense of more fire-adapted jack and red pines, and the PLS vegetation types became established and remained relatively stable after that. Charcoal influx rates were low during the LIA, consistent with the shift from jack and red pine to white pine. Sites on xeric soils changed less, with jack and/or red pine dominating the pollen assemblages throughout the last 2000-4000 years. Although xeric sites changed little in species composition, the relative abundances of pollen types continued to change throughout the LIA and charcoal influx increased at the most exposed site, suggesting an increase in fuel production or extent of fires.
Our results demonstrate that vegetation on the sand plain has been dynamic at a landscape scale over the past 2000 years, apparently responding to relatively small climatic fluctuations. Landscape context influenced the sensitivity of vegetation to Little Ice Age climate change, with less change on sites with coarse soils and little protection from fire. |
|