PARENT SESSION
Tuesday, August 8, 5:00-6:30 pm
Poster Session 10 - Genetics, evolution, and paleoecology
Exhibit Hall, Ballroom Level, Cook Convention Center
Simulated and inferred LAI, NPP, and plant functional types in North America since the last glacial maximum.
Zajac, Leila*,1, Williams, John2, Kaplan, Jed3, 1 University of Chicago, Chicago, IL, United States2 University of Wisconsin-Madison, Madison, WI, United States3 University of Bern, Bern, Switzerland
ABSTRACT- 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 plant functional types (PFTs). 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 PFT 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 net primary productivity. Past LAIs and PFTs, independently estimated from fossil pollen assemblages using the modern analogue technique and calibrated against the MODIS data set, are compared to model results. The BIOME4 simulations show good agreement with the LAIs and PFT distributions inferred from the fossil pollen records. In unglaciated eastern North America, canopy closure of the full-glacial conifer forests and woodlands in response to ameliorating climatic conditions resulted in an 80% increase in LAIs between 21 ka and 11 ka. After 8 ka, large areas of tundra and forest-tundra developed in deglaciated regions. Sensitivity analyses with BIOME4 indicate that both climate and CO2 played important roles in regulating vegetation structure and productivity.
Key words: BIOME4, LAI, NPP, Vegetation Structure, Biogeography