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University of Montana ScholarWorks at University of Montana Numerical Terradynamic Simulation Group Publications Numerical Terradynamic Simulation Group 11-2001 FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities Dennis Baldocchi Eva Falge Lianhong Gu Richard Olson D. Y. Hollinger See next page for additional authors Follow this and additional works at: https://scholarworks.umt.edu/ntsg_pubs Let us know how access to this document benefits ou.y Recommended Citation Baldocchi, D. D., Falge E., Gu L., Olson R., Hollinger D. Y., Running S. W., Anthoni P., Bernhofer Ch., Davis K. J., Evans R., Fuentes J., Goldstein A., Katul G., Law B. E., Lee X., Malhi Y., Meyers T. P., Munger J. W., Oechel W. C., Paw U K. T., Pilegaard K., Schmid H. P., Valentini R., Verma S., Vesala T., Wilson K. B., and Wofsy S. C. (2001). FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem- Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities. Bulletin of the American Meteorological Society, 82: 2415-2434, doi: 10.1175/1520-0477(2001)082<2415:FANTTS>2.3.CO;2 This Article is brought to you for free and open access by the Numerical Terradynamic Simulation Group at ScholarWorks at University of Montana. It has been accepted for inclusion in Numerical Terradynamic Simulation Group Publications by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. Authors Dennis Baldocchi, Eva Falge, Lianhong Gu, Richard Olson, D. Y. Hollinger, Steven W. Running, Peter Anthoni, Ch. Bernhofer, Kenneth Davis, Robert Evans, Jose Fuentes, Allen Goldstein, Gabriel Katul, Beverly Law, Xuhui Lee, Yadvinder Malhi, Tilden Meyers, William Munger, Walt Oechel, K. T. Paw U, Kim Pilegaard, H. P. Schmid, Riccardo Valentini, Shashi Verma, Timo Vesala, Kell Wilson, and Steve Wofsy This article is available at ScholarWorks at University of Montana: https://scholarworks.umt.edu/ntsg_pubs/112 FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities Dennis Baldocchl,® Eva Falge,’’ Llanhong Gu,® Richard Olson,^ David Floiilnger,'’ Steve Running,® Peter Anthonl,f Ch. Bernhofer,^ Kenneth Davis,'' Robert Evans," Jose Fuentes; Allen Goldstein,® Gabriel KatuI,) Beverly Law,f Xuhul Lee," Yadvlnder Malhl,' Tllden Meyers,"' William Munger," Walt Oechel,° K. T. Paw U, p Kim Pllegaard,®i FI. P. Schmld,'^ RIccardo Valentlnl," Shashi Verma,* TImo Vesala," Kell Wilson,"' and Steve Wofsy" ABSTRACT FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of car­ bon dioxide, water vapor, and energy between the biosphere and atmosphere. At present over 140 sites are operating on a long-term and continuous basis. Vegetation under study includes temperate conifer and broadleaved (deciduous and evergreen) forests, tropical and boreal forests, crops, grasslands, chaparral, wetlands, and tundra. Sites exist on five con­ tinents and their latitudinal distribution ranges from 70°N to 30°S. FLUXNET has several primary functions. First, it provides infrastructure for compiling, archiving, and distributing carbon, water, and energy flux measurement, and meteorological, plant, and soil data to the science community. (Data and site information are available online at the FLUXNET Web site, http://www-eosdis.oml.gov/FLUXNET/.) Second, the project supports calibration and flux intercomparison activities. This activity ensures that data from the regional networks are intercomparable. And third, FLUXNET supports the synthesis, discussion, and communication of ideas and data by supporting project scientists, workshops, and visiting scientists. The overarching goal is to provide infor­ mation for validating computations of net primary productivity, evaporation, and energy absorption that are being generated by sensors mounted on the NASATerra satellite. Data being compiled by FLUXNET are being used to quantify and compare magnitudes and dynamics of annual ecosystem carbon and water balances, to quantify the response of stand-scale carbon dioxide and water vapor flux densities to controlling biotic and abiotic factors, and to validate a hierarchy of soil-plant-atmosphere trace gas ex­ change models. Findings so far include 1) net CO^ exchange of temperate broadleaved forests increases by about 5.7 g C m“^ day^ for each additional day that the growing season is extended; 2) the sensitivity of net ecosystem CO^ exchange to sunlight doubles if the sky is cloudy rather than clear; 3) the spectrum of CO^ flux density exhibits peaks at timescales of days, weeks, and years, and a spectral gap exists at the month timescale; 4) the optimal temperature of net CO^ exchange varies with mean summer temperature; and 5) stand age affects carbon dioxide and water vapor flux densities. ^ESPM, University of California, Berkeley, Berkeley, California. "Department of Earth and Planetary Sciences, Harvard University, Cam­ *^Pflanzenokologie, Universitat Bayreuth, Bayreuth, Germany. bridge, Massachusetts. Environmental Science Division, Oak Ridge National Laboratory, Oak "Department of Biology, San Diego State University, San Diego, Califomia. Ridge, Tennessee. PLand, Air and Water Resources, University of California, Davis, Davis, ^USDA Forest Service, Durham, New Hampshire. Califomia. ^School of Forestry, University of Montana, Missoula, Montana. Elant Biology and Biogeochemistry Department, Risoe National Labo­ 4lichardson Hall, Oregon State University, Corvallis, Oregon. ratory, Roskilde, Denmark. *Technische Universitat Dresden, IHM Meteorologie, Tharandt, Germany. ‘‘Department of Geography, Indiana University, Bloomington, Indiana. ^Department of Meteorology, The Pennsylvania State University, Univer­ DISAERI, Universita de Tuscia, Viterbo, Italy. sity Park, Pennsylvania. ‘School of Natural Resource Sciences, University of Nebraska at Lincoln, ‘Department of Environmental Science, University of Virginia, Lincoln, Nebraska. Charlottesville, Virginia. "Department of Physics, University of Helsinki, Helsinki, Finland. ^School of the Environment, Duke University, Durham, North Carolina. Corresponding author address: Dennis Baldocchi, Department of Environ­ •^School of Forestry, Yale University, New Haven, Connecticut. mental Science, Policy and Management, Ecosystems Science Division, 151 Institute of Ecology and Resource Management, University of Edinburgh,Hilgard Hall, University of Califomia, Berkeley, Berkeley, CA 94720. Edinburgh, United Kingdom. E-mail: [email protected] ■"NOAA/Atmospheric Turbulence and Diffusion Division, Oak Ridge,In final form 27 Eebmary 2001. Tennessee. ©2001 American Meteorological Society Bulletin of the American Meteorological Society 2415 1. Introduction growth of atmospheric CO^. Typical values of inter­ annual variability are on the order of 0.5-3.0 ppm y r f Large-scale, multi-investigator projects have been On a mass basis, these values correspond with a range the keystone of many scientific and technological ad­between 1 and 5 gigatons C yr '. Potential sources of vances in the twentieth century. Physicists have year-to-year changes in atmospheric CO^ remain a leamed much about the structure of an atom’s nucleustopic of debate. Studies of atmospheric and dis­ with particle accelerators. Astrophysicists now peer tributions imply that the terrestrial biosphere plays an deep into space with the Hubble Space Telescope andimportant role in this interannual variability (Ciais an array of radio telescopes. Molecular biologists are et al. 1995; Keeling et al. 1996). Sources of this vari­ decoding the structure of our DNA with the Humanability have been attributed to El Nino/Ea Nina events, Genome project. which cause regions of droughts or superabundant Ecosystem scientists need a tool that assesses the rainfall (Conway et al. 1994; Keeling et al. 1995), and flows of carbon, water, and energy to and from thealterations in the timing and length of the growing terrestrial biosphere across the spectrum of time- and season (Mynenietal. 1997a,b; Randersonetal. 1997). space scales over which the biosphere operates (see Rising levels of CO^, and other greenhouse gases, Running et al. 1999; Canadell et al. 2000). Similarly,are of concem to scientists and policy makers because atmospheric scientists need a tool to quantify surfacethey trap infrared radiation that is emitted by the energy fluxes at the land-atmosphere interface, asearth’s surface. Potential consequences of elevated these energy fluxes influence weather and climateCO 2 concentrations include a warming of the earth’s (Betts et al. 1996; Pielke et al. 1998). In this paper, wesurface (Hansen et al. 1998), melting of polar icecaps report on such a tool. It consists of a global array of and a rising sea level, and an alteration of plant and micrometeorological towers that are measuring fluxecosystem physiological functioning and plant com­ densities of carbon dioxide, water vapor, and energyposition (Amthor 1995; Norby et al. 1999). between vegetation and the atmosphere on a quasi- With regard to plants and ecosystems, short-term continuous and long-term (multiyear) basis. The ob­experiments with elevated CO^ show increased rates jectives of this paper are to introduce the FLUXNET of photosynthesis and plant growth and lowered sto- project and describe its rationale, goals, measurementmatal conductance (Drake et al. 1996). The long-term

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