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abstracts
Natural and anthropogenic influences on the Holocene fire and vegetation history of the Willamette Valley, northwest Oregon and southwest Washington
Megan Walsh, Cathy Whitlock, Patrick Bartlein
The debate concerning the role of natural versus anthropogenic burning in shaping the prehistoric vegetation patterns of the Willamette Valley of Oregon and Washington remains highly contentious. To address this, pollen and high-resolution charcoal records obtained from lake sediments were analyzed to reconstruct the Holocene fire and vegetation history, in order to assess the relative influence of climate variability and anthropogenic activity on those histories. Two sites provided information on the last 11,000 years. At Battle Ground Lake, shifts in fire activity and vegetation compared closely with millennial- and centennial-time scale variations in climate. In contrast, the fire and vegetation history at Beaver Lake (near Corvallis) showed relatively little vegetation change in response to both millennial- and centennial-scale climate variability, but fire activity varied widely in both frequency and severity. A comparison of this reconstruction with archaeological evidence suggests that anthropogenic burning near the site may have influenced middle- to late-Holocene fire regimes. The fire history of the last 1200 years was compared at five sites along a north-south transect through the Willamette Valley. Forested upland sites showed stronger fire-climate linkages and little human influence, whereas lowland sites located in former prairie and savanna showed temporal patterns in fire activity that suggest a significant human impact. The results of this research contribute to our understanding of long-term vegetation dynamics and the role of fire, both natural- and human-ignited, in shaping ecosystems, as well as provide an historical context for evaluating recent shifts in plant communities in the Willamette Valley.
Megan Walsh, Department of Geography, University of Oregon,1251 University of Oregon, Eugene, OR, 97403-1251, United States, mwalsh2@uoregon.edu
Cathy Whitlock, Montana State University, Department of Earth Sciences, Bozeman, MT, 59717, United States
Patrick Bartlein, University of Oregon, Department of Geography, Eugene, OR, 97403, United States
Session: F4: Human-Climate-Ecosystem Interactions
Download Talk:
> YSM09_OralG_Walsh.pdf
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