Assessing net ecosystem carbon exchange of U.S. terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations

Authors: XIAO, J. - PURDUE UNIVERSITY; ZHUANG, Q. - PURDUE UNIVERSITY; LAW, B. - OREGON STATE UNIVERSITY; BALDOCCHI, D. - UNIV. CALIFORNIA BERKELEY; CHEN, J. - UNIVERSITY OF TOLEDO; RICHARDSON, A. - UNIV. OF NEW HAMPSHIRE; MELILLO, J. - MARINE BIOLOGICL LAB; DAVIS, K. - Pennsylvania State University; HOLLINGER, D. - Us Forest Service (FS); WHARTON, S. - University Of California; OREN, R. - Duke University; NORMETS, A. - North Carolina State University; FISCHER M., L - Lawrence Berkeley National Laboratory; VERMA, S. - University Of Nebraska; COOK, D. - Argonne National Laboratory; SUN, G. - Us Forest Service (FS); MCNULTY, S. - Us Forest Service (FS); WOFSY, S. - Harvard University; BOLSTAD, P. - University Of Minnesota; BURNS, S. - University Of Colorado; CURTIS, P. - The Ohio State University; DRAKE, B. - Smithsonian Environmental Research Center; FALK, M. - University Of California; FOSTER, D. - Harvard University; GU, L. - Oak Ridge National Laboratory; HADLEY, J. - Harvard University; KATUL, G. - Duke University; LITVAK, M. - University Of New Mexico; MA, S. - University Of California; MARTIN, T. - University Of Florida; MATAMULA, R. - Argonne National Laboratory; MEYERS, T. - National Oceanic & Atmospheric Administration (NOAA); MONSON, R. - University Of Colorado; MUNGER, J. - Harvard University; OECHEL, W. - San Diego State University; THA PAW, U. - University Of California; SCHMID, H. - Indiana University; Scott, Russell - Russ; STARR, G. - University Of Alabama; SUYKER, A. - University Of Nebraska; TORN, M. - Lawrence Berkeley National Laboratory

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2009
Publication Date: 11/1/2010
Citation: Xiao, J., Zhuang, Q., Law, B.E., Baldocchi, D.D., Chen, J., Richardson, A.D., Melillo, J.M., Davis, K.J., Hollinger, D.Y., Wharton, S., Oren, R., Noormets, `., Fischer M., L., Verma, S.B., Cook, D.R., Sun, G., Mcnulty, S., Wofsy, S.C., Bolstad, P.V., Burns, S.P., Curtis, P.S., Drake, B.G., Falk, M., Foster, D.R., Gu, L., Hadley, J.L., Katul, G.G., Litvak, M., Ma, S., Martin, T.A., Matamula, R., Meyers, T.P., Monson, R.K., Munger, J.W., Oechel, W.C., Tha Paw, U.K., Schmid, H.P., Scott, R.L., Starr, G., Suyker, A.E., Torn, M.S. 2010. Assessing net ecosystem carbon exchange of U.S. terrestrial ecosystems by integrating eddy covariance flux measurements and satellite observations. Agricultural and Forest Meteorology. 151: 60-69.

Interpretive Summary: More accurate projections of future carbon dioxide concentrations in the atmosphere and associated climate change as well as carbon accounting and climate policy-making depend on improved scientific understanding of the terrestrial carbon cycle. Despite the consensus that U.S. terrestrial ecosystems act as a carbon sink, the size, distribution, and interannual variability of the sink remain uncertain. Here we report total terrestrial carbon uptake in the conterminous U.S. at -0.68 Pg C yr-1 with the majority of the sink in regions dominated by evergreen and deciduous forests and savannas based on novel estimates of net ecosystem carbon exchange with high spatial (1km) and temporal (8-day) resolution derived from flux tower measurements and wall-to-wall satellite observations. We find that the U.S. terrestrial ecosystems could offset 40% of the fossil-fuel carbon emissions. The dominant sources of interannual variation of the carbon sink include extreme climate events and disturbances, with droughts in 2002 and 2006 reducing U.S. net ecosystem carbon uptake by ~20% relative to a normal year, and disturbances including wildfires and hurricanes resulting in reduced carbon uptake or carbon release into the atmosphere.

Technical Abstract: More accurate projections of future carbon dioxide concentrations in the atmosphere and associated climate change as well as carbon accounting and climate policy-making depend on improved scientific understanding of the terrestrial carbon cycle. Despite the consensus that U.S. terrestrial ecosystems act as a carbon sink, the size, distribution, and interannual variability of the sink remain uncertain. Here we report total terrestrial carbon uptake in the conterminous U.S. at -0.68 Pg C yr-1 with the majority of the sink in regions dominated by evergreen and deciduous forests and savannas based on novel estimates of net ecosystem carbon exchange with high spatial (1km) and temporal (8-day) resolution derived from eddy covariance flux tower measurements and wall-to-wall satellite observations. We find that the U.S. terrestrial ecosystems could offset 40% of the fossil-fuel carbon emissions. Our results show that the U.S. terrestrial carbon uptake varied between -0.51 and -0.70 Pg C yr-1 over the period 2001-2006. The dominant sources of interannual variation of the carbon sink include extreme climate events and disturbances, with droughts in 2002 and 2006 reducing U.S. net ecosystem carbon uptake by ~20% relative to a normal year, and disturbances including wildfires and hurricanes resulting in reduced carbon uptake or carbon release into the atmosphere. Our novel approach can be applied to other regions of the globe to refine the global terrestrial carbon budget.