HR: 1340h
AN: PP33B-0934    [Abstracts]
TI: Simulated and Inferred LAI, NPP, and Biomes in North America Since the Last Glacial Maximum.
AU: * Zajac, L M
EM: lzajac@uchicago.edu
AF: Leila M. Zajac, University of Chicago Department of Geophysical Sciences 5734 S. Ellis Avenue, Chicago, IL 60637 United States
AU: Williams, J W
EM: jww@geography.wisc.edu
AF: John W. Williams, University of Wisconsin-Madison Department of Geography 550 North Park St., Madison, WI 53706 United States
AU: Kaplan, J
EM: jed.kaplan@jrc.it
AF: Jed Kaplan, Institute for Environment and Sustainability European Commission Joint Research Centre, Ispra, 21020 Italy
AB: Vegetation structure and productivity are sensitive to climate change and are an important source of feedbacks to the climate system. Here we employ multiple lines of evidence to reconstruct variations in leaf area index (LAI), net primary productivity (NPP), and biomes. LAI determines the total canopy surface area available for light interception, gas exchange, and water loss, and NPP, the increase in plant carbon per unit area, measures the flux of carbon into the terrestrial biosphere. BIOME4, an equilibrium biogeography and biogeochemistry vegetation model, is used to simulate LAI, NPP, and biome distributions in North America for the past 21,000 years at 1,000-year time-steps. BIOME4 was coupled asynchronously to the Hadley Center Unified Model with a mixed-layer ocean model forced by variations in orbital boundary conditions, physiography, and atmospheric CO2 concentration (Kaplan et al. 2002). BIOME4 models LAI as a trade-off between maximizing light interception and minimizing water loss and assigns the LAI that maximizes NPP. Past LAI's and biomes, independently estimated from fossil pollen assemblages using the modern analogue technique, are compared to model results. In unglaciated eastern North America, canopy closure of the full-glacial conifer forests and woodlands in response to ameliorating climatic conditions resulted in a 80% increase in LAI's between 21 ka and 11 ka. After 8 ka, large areas of tundra and forest-tundra developed in deglaciated regions. The BIOME4 simulations show good agreement with the LAI's and biome distribution inferred from fossil pollen records. Sensitivity analyses with BIOME4 indicate that both climate and CO2 played important roles in regulating vegetation structure and productivity.
DE: 0315 Biosphere/atmosphere interactions
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting