HR: 08:30h
AN: B31B-03    [PDF]
TI: Impacts of N-depostion on biodiversity in a grassland ecosystem
AU: * Weiss, S
EM: stubweiss@netscape.net
AF: Creekside Center for Earth Observations, 27 Bishop Lane, Menlo Park, CA 94025 United States
AU: Luth, D
EM: dcluth@yahoo.com
AF: Eco-Business Decisions, 726 18th Ave, S an Francisco, CA 94121 United States
AB: Nitrogen deposition threatens biodiversity in many ecosystems across the globe, and poses a range of scientific and policy challenges. Grassland ecosystems on nutrient-poor serpentine soils provide a model system for understanding local and regional impacts of N-deposition on biodiversity. A population of the threatened Bay checkerspot butterfly crashed from 3500 butterflies in 1997 to likely extinction in 2003. Non-native annual grass crowded out larval hostplants over much of the habitat, primarily driven by nitrogen deposition from tailpipe emissions of NH3 from 100,000 vehicles per day on a roadway bisecting the habitat. NH3 levels (measured with passive monitors) are elevated adjacent to the roadway, but are near background levels 400 m away. Grass cover was higher closer to and downwind of the road, and hostplant cover was inversely related to grass cover. Results from a first-order model show that N-deposition levels adjacent to the roadway are similar ($>$10 kg-N ha-1 yr-1) to levels downwind of the heavily urbanized Santa Clara Valley (where grass invasions have led to the extinction of large populations via vigorous grass invasions). This local butterfly extinction is unexpected fallout of the adoption of three-way catalytic converters in 1990s. The only known occurrence of an endangered plant, Pentachaeta bellidiflora, exists west of the freeway and may be at long term risk. Invasions of nitrophilous grasses and other weedy species into N-limited grasslands and shrublands appear to be a common response to increased atmospheric deposition in semi-arid areas.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1851 Plant ecology
DE: 3322 Land/atmosphere interactions
DE: 4805 Biogeochemical cycles (1615)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting