HR: 11:00h
AN: A42A-03    [Abstracts]
TI: Impacts of lake-effect snow on forest communities in the Great Lakes region
AU: * Henne, P
EM: phenne@life.uiuc.edu
AF: University of Illinois at Urbana-Champaign, Room 265 Morrill Hall 505 S Goodwin Ave, Urbana, IL 61801 United States
AU: Hu, F
EM: fshu@life.uiuc.edu
AF: University of Illinois at Urbana-Champaign, Room 265 Morrill Hall 505 S Goodwin Ave, Urbana, IL 61801 United States
AB: Lake-effect snow (LES) increases winter precipitation in the Great Lakes snowbelts by up to 100%. The ecological effects of LES remain poorly documented. We coupled GIS and lake-sediment analyses to examine how spatial and temporal variations in LES interact with glacial landforms to impact forest communities in northern Lower Michigan. GIS analysis reveals that snowfall is the most important among several environmental variables (e.g. landform, summer precipitation) influencing the spatial distribution of upland forest types. Mesic forests dominate on all landforms (e.g. outwash, till) in areas receiving LES, but they are restricted to fine-textured (primarily till) soils in nearby areas outside the snowbelt. Oxygen isotopes and pollen preserved in lake sediments suggest that temporal changes in upland vegetation relate to the snowbelt establishment during the Holocene. We compared paleorecords from two lakes inside the snowbelt (Huffman Lake, HL, and Clifford Lake, CL) and two lakes outside the snowbelt (O'Brien Lake, OB, and Horseshoe Lake, HS). HL and OB are situated in outwash whereas CL and HS are situated in till. Thus the four lakes are juxtaposed such that the effects of LES versus glacial landform can be evaluated. At HL, a stepwise decline in \delta$^{18}$O of 2\permil occurs between 6500 calibrated years before present (BP) and 4000 BP followed by a slight decline (0.2\permil) in the past 4000 years. The major \delta$^{18}$O decline probably reflects the establishment of snowbelts because LES is depleted in $^{18}$O. Outside the snowbelt at OB, \delta$^{18}$O declines gradually by 1.2\permil between 6500 BP and the present, with no stepwise shift between 6500 BP and 4500 BP. Detrended correspondence analysis of pollen percentages reveals two distinct vegetation types in the past 6500 years: a xeric type dominated by {\it Pinus}, and a mesic type dominated by northern hardwoods (e.g. {\it Fagus, Tsuga}). At HL and CL a clear shift from xeric to mesic vegetation occurred around 5000 BP. A similar shift never occurred at HS or OB. Differences in vegetation between snowbelt and non-snowbelt sites were far greater than those between the two landforms. Pollen percentages of mesic taxa are higher on till (32% at HS) than on outwash (25% at OB), but neither site approaches the 70% mesic taxa attained at HL (snowbelt outwash). The marked difference in the magnitudes of vegetation change between the snowbelt and non-snowbelt sites cannot be attributed to a mid-Holocene climatic shift throughout the region and/or soil-substrate effects. These data suggest that LES is a dominant factor controlling the spatial and temporal patterns of forest communities around the Great Lakes. They also imply that the mesic plant communities in that region may be in jeopardy if snow is diminished by anthropogenic climatic warming.
DE: 3329 Mesoscale meteorology
DE: 3344 Paleoclimatology
DE: 1655 Water cycles (1836)
DE: 1851 Plant ecology
DE: 1863 Snow and ice (1827)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting