Boreal forest CO2 exchange and evapotranspiration predicted by nine ecosystem process models: Intermodel comparisons and relationships to field measurements

Authors

Jeffrey S. Amthor, Oak Ridge National Laboratory
J M. Chen, Canada Centre for Remote SensingFollow
Joy S. Clein, University of Alaska, Fairbanks
Steve Frolking, University of New Hampshire - Main CampusFollow
M L. Goulden, University of California, Irvine
Robert F. Grant, University of Alberta
John Kimball, University of Montana, Missoula
A W. King, Oak Ridge National Laboratory
A D. McGuire, University of Alaska, Fairbanks
Ned T. Nikolov, Oak Ridge National Laboratory
Christopher S. Potter, NASA Ames Research Center
S Wang, University of AlbertaFollow
Steven C. Wofsy, Harvard University

Abstract

Nine ecosystem process models were used to predict CO₂ and water vapor exchanges by a 150-year-old black spruce forest in central Canada during 1994–1996 to evaluate and improve the models. Three models had hourly time steps, five had daily time steps, and one had monthly time steps. Model input included site ecosystem characteristics and meteorology. Model predictions were compared to eddy covariance (EC) measurements of whole-ecosystem CO₂exchange and evapotranspiration, to chamber measurements of nighttime moss-surface CO₂release, and to ground-based estimates of annual gross primary production, net primary production, net ecosystem production (NEP), plant respiration, and decomposition. Model-model differences were apparent for all variables. Model-measurement agreement was good in some cases but poor in others. Modeled annual NEP ranged from −11 g C m⁻² (weak CO₂source) to 85 g C m⁻² (moderate CO₂ sink). The models generally predicted greater annual CO₂sink activity than measured by EC, a discrepancy consistent with the fact that model parameterizations represented the more productive fraction of the EC tower “footprint.” At hourly to monthly timescales, predictions bracketed EC measurements so median predictions were similar to measurements, but there were quantitatively important model-measurement discrepancies found for all models at subannual timescales. For these models and input data, hourly time steps (and greater complexity) compared to daily time steps tended to improve model-measurement agreement for daily scale CO₂ exchange and evapotranspiration (as judged by root-mean-squared error). Model time step and complexity played only small roles in monthly to annual predictions.

Department

Earth Sciences, Earth Systems Research Center

Publication Date

12-27-2001

Journal Title

Journal of Geophysical Research: Atmospheres

Publisher

Wiley

Digital Object Identifier (DOI)

10.1029/2000JD900850

Document Type

Article

Recommended Citation

Amthor, J. S., et al. (2001), Boreal forest CO2 exchange and evapotranspiration predicted by nine ecosystem process models: Intermodel comparisons and relationships to field measurements, J. Geophys. Res., 106(D24), 33623–33648, doi:10.1029/2000JD900850.

Rights

Copyright 2001 by the American Geophysical Union.