HR: 0800h
AN: GC31A-0111    [Abstracts]
TI: Evaluating Paleoecological Patterns Using Paleoenvironmental Proxies: The Promise and the Peril
AU: * Jackson, S T
EM: jackson@uwyo.edu
AF: AU: Booth, R K
EM: rkb205@lehigh.edu
AF: Lehigh University, Department of Earth & Environmental Sciences, Bethlehem, PA 18015, United States
AB: For the past seven years we have been studying the vegetational history of the western Great Lakes region in the context of mid- to late Holocene climate change and variability. Our work has included diverse archives and proxies for both paleoecological and paleoclimatic inference. The former consist of pollen, plant-macrofossil, and charcoal records from sediments of small lakes and peatlands. Paleoclimate inferences have been based on lake-level records, peatland-inception dates, dune and lakeshore dynamics, and paleohydrological reconstructions from ombrotrophic and kettle peatlands. Our greatest success has been in pairing lake-based paleoecological records with peatland-based paleohydrological records. Peatland hydrology is sensitive to annual and seasonal moisture variation, and peatland-sediment archives contain diverse proxies including testate-amoeba assemblages, humification, organic biomarkers, stable isotopes, and plant macrofossils. Our work has resolved old controversies while unveiling unforeseen patterns. Examples include: (1) A mid-Holocene decline in hemlock populations, long attributed to a pest/pathogen outbreak, coincided with a rapid, unprecedented drop in peatland water levels. However, the decline shows complex structure in time, both ecologically and climatically. Hemlock's final demise 5000 yr BP was preceded by several centuries of multidecadal hydrological fluctuation accompanied by time- lagged hemlock fluctuations. (2) A late Holocene decline in beech populations, variously attributed to human-set fires and the Little Ice Age, occurred during a series of severe multidecadal droughts. This event is also structured in time and space: in some areas the droughts were dampened and beech increased, and at sites where beech decline and droughts occurred, beech pollen, charcoal concentrations, and water-levels fluctuated dramatically between 1000 and 700 yr BP. (3) Yellow birch populations expanded rapidly across a broad swath of Upper Michigan and Wisconsin during an extended pluvial period (4000-3000 yr BP) that followed on a drought of extraordinary duration and severity (4200-4000 yr BP). Continued expansion of yellow birch, as well as hemlock and beech, after 3000 yr BP was mediated by edaphic mosaics and centennial-scale pluvial events. Our experience indicates that integrated paleoecological and paleoclimatological studies have payoffs for ecology, paleoecology, and paleoclimatology. Perils, though real, are no different from those encountered in other interdisciplinary enterprises in the historical sciences. We identify six key challenges for continued progress in this area: (1)identifying, refining, and applying paleoclimate proxies that are sensitive to the same climate variables and at the same timescales as the ecological systems of interest. (2) correlating events in time among records, particularly when paleoecological and paleoclimate data derive from different archives. (3) identifying and modeling lags in ecological response to climate forcings. (4) determining proximal mechanisms of past ecological responses to climate changes. (5) assessing indirect responses to climate forcing, and interactions between climate and other factors (e.g., pests, wildfires). (6) determining "when to quit" – when to conclude that climate forcing of an observed ecological event is insupportable (versus assuming that the proxies examined to date simply aren't sensitive to whatever the ecological system is responding to). Meeting these challenges will require engagement and collaboration among paleoecologists, paleoclimatologists, geochronologists, and ecologists.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0476 Plant ecology (1851)
DE: 0497 Wetlands (1890)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1630 Impacts of global change (1225)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting