HR: 16:35h
AN: GC54A-03    [Abstracts]
TI: Late Holocene Decline of Beech Populations in the Central Great Lakes Region: Drought- Induced Vegetation Change in a Humid Region.
AU: * Booth, R K
EM: rkb205@lehigh.edu
AF: Earth & Environmental Science Department, Lehigh University, 31 Williams Drive, Bethlehem, PA 18015, United States
AU: Jackson, S T
EM: jackson@uwyo.edu
AF: Department of Botany and Program in Ecology, University of Wyoming, 1000 E. University Ave, Laramie, WY 82071, United States
AU: Taylor, M
EM: mtaylor3@uwyo.edu
AF: Department of Botany and Program in Ecology, University of Wyoming, 1000 E. University Ave, Laramie, WY 82071, United States
AU: Pendall, E
EM: Pendall@uwyo.edu
AF: Department of Botany and Program in Ecology, University of Wyoming, 1000 E. University Ave, Laramie, WY 82071, United States
AU: Sousa, V A
EM: vas206@Lehigh.EDU
AF: Earth & Environmental Science Department, Lehigh University, 31 Williams Drive, Bethlehem, PA 18015, United States
AB: A large decline in beech populations ( Fagus grandifolia) has been well-documented from pollen records in southeastern Michigan and Southern Ontario between 1000 and 600 BP. These records reveal that declines in beech pollen were generally associated with increases in oak ( Quercus) and pine ( Pinus). The beech decline probably extended eastward into western Pennsylvania and New York, although beech populations in Upper Michigan remained unaffected or even expanded during this time period. The causes of these forest changes and their spatial patterning is not completely understood, although they have been variously attributed to anthropogenic disturbance, climatic cooling, or drought. Recent paleoclimate evidence from the region indicates that the most severe droughts of the last 2000 years occurred between 1000 and 700 BP. However, direct attribution of drought as a cause of the decline has been problematic because of uncertainties associated with comparison of radiocarbon-dated chronologies. We have conducted tandem investigations of pollen, charcoal, hydroclimate proxies (testate amoebae, humification), and a temperature proxy (d¹⁸O of Sphagnum cellulose) from the archives contained in three Sphagnum-dominated peatlands of the region. Two of these peatlands were located within the region of the beech decline (eastern, lower Michigan) and the other was outside the decline region (Upper Michigan). Our results reveal that a series of large droughts, likely the combined result of decreased summer precipitation and warm temperatures, were associated with the beech decline. Large wildfires were also associated with the droughts. Neither droughts nor beech declines were recorded in Upper Michigan. High-resolution analysis of beech pollen and hydroclimate proxies at sites that experienced the droughts reveals complex dynamics at multidecadal timescales between 1000-700 BP, with large fluctuations in beech pollen, available moisture, and charcoal concentrations. Our study demonstrates the potential of using the tandem application of pollen, charcoal, and a wide variety of vegetation-independent climatic proxies to assess ecological responses to climate variability at multidecadal timescales. Although moisture variability is not generally recognized as a driver of ecological change in humid regions, our data indicate that ecologically significant thresholds have been crossed in the recent past.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1630 Impacts of global change (1225)
DE: 4914 Continental climate records
DE: 4950 Paleoecology
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting