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GEOMORPHIC CONTROLS ON MEADOW ECOSYSTEMS IN THE CENTRAL GREAT BASIN
GERMANOSKI, D., J. MILLER, M. LORD, D. G. JEWETT, J. CHAMBERS, W. TROWBRIDGE, K. STURTEVANT, AND G. BAKER. GEOMORPHIC CONTROLS ON MEADOW ECOSYSTEMS IN THE CENTRAL GREAT BASIN. Presented at 2007 International Meeting of the Society for Range Management, Reno, NV, February 12 - 16, 2007.
To inform the public.
Wet meadows, riparian corridor phreatophyte assemblages, and high-altitude spring-fed aspen meadows comprise a very small percentage of the total landscape of the mountain ranges in the central Great Basin however, they represent important ecological environments. We have used satellite images, aerial photographs, field reconnaissance, geophysics, drill cores, geologic and topographic maps, and detailed hydrogeologic and geomorphic field measurements to determine the controls that govern the distribution of these unique features. Wet meadows are dominated by grasses such as sedges and rushes, riparian corridor vegetation assemblages are dominated by willows, water birch, wild rose, and cottonwoods, and headwater source vegetation assemblages are dominated by quaking aspen, cottonwoods, and grasses. Our work shows that these ecosystems require high groundwater tables and that rapid channel incision can lower the water tables and lead to degradation of these features. Headwater source meadows are situated in zero- or first-order basins and are supported by discrete spring sources or from snow packs sheltered in the high elevation hollows. Riparian corridor willow and water birch vegetation are supported by the downstream flux of water adjacent to mountain streams. Wet meadows form where some combination of the following factors produce elevated groundwater tables: side-valley alluvial fans prograde into axial valleys, constrict the flux of sediment downstream and facilitate the accumulation of relatively fine grained sediment with low hydraulic conductivity; bedrock constrictions (sometimes related to local faulting) facilitate the accumulation of relatively fine grained sediment with low hydraulic conductivity and constrict the down-valley flux of groundwater; groundwater tables are elevated by high discharge from multiple groundwater springs located along the valley sides.