Landscape patterns in response to climatic change: 1000 years of vegetation change and fire history on a sand plain.
Hotchkiss, Sara*,1, Calcote, Randy2, Lynch, Elizabeth3, 1 University of Wisconsin, Madison, WI2 University of Minnesota, Minneapolis, MN3 Luther College, Decorah, IA
ABSTRACT- The effect of changing climate on vegetation is mediated through interactions with ecological factors such as soils and disturbance regimes. These factors may produce different vegetation responses at sites experiencing the same regional climate conditions. The objective of this study was to examine both spatial and temporal patterns in the response of vegetation and fire regimes at several sites across a 450 km2 sand plain in northwestern Wisconsin. We used fossil pollen and charcoal from nine small deep lakes on the northwestern Wisconsin sand plain to reconstruct vegetation and fire history over the past 1200 yr. Pollen assemblages from these small lakes correlate with vegetation within ca. 5km, while charcoal fragments >125 microns in length are probably derived from fires that occurred within a few hundred meters of the lake shore. The interpretation of Vegetation was based on comparison with pollen assemblages from modern sediments and the period just before 19th century logging at 33 lakes. At sites in the southern sand plain white pine pollen percentages increased and nonarboreal pollen decreased between 700 and 200 years ago, suggesting that tree cover increased. The timing and degree of increase in tree pollen varies from site to site. At most sites a decrease in charcoal influx preceded the increase of white pine and mesic taxa by a century or more. One site in the fire-prone central region of the sand plain showed little change in vegetation during this period and the charcoal influx increased, presumably due to increased fuel. Sites on the northern sand plain also showed little vegetation change despite decreased charcoal influx after 600-800 cal yr BP. Paleoecological records from other Midwestern sites indicate a trend toward cooler/moister conditions 700-150 cal yr BP. Our results suggest that the vegetation of the sand plain changed dramatically in response to these relatively small regional climatic changes, but that local site conditions tempered the magnitude and timing of this response. Our results also suggest that the presettlement vegetation represented by the witness tree records may have been a result of several centuries of cool, moist conditions and is not necessarily a realistic target for ecosystem restoration.
Key words: late-Holocene, sand plain vegetation, fire history
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