FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of carbon 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 continents 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.ornl.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 information for validating computations of net primary productivity, evaporation, and energy absorption that are being generated by sensors mounted on the NASA Terra 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 exchange models. Findings so far include 1) net CO2 exchange of temperate broadleaved forests increases by about 5.7 g C m−2 day−1 for each additional day that the growing season is extended; 2) the sensitivity of net ecosystem CO2 exchange to sunlight doubles if the sky is cloudy rather than clear; 3) the spectrum of CO2 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 CO2 exchange varies with mean summer temperature; and 5) stand age affects carbon dioxide and water vapor flux densities.

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aESPM, University of California, Berkeley, Berkeley, California.

bPflanzenökologie, Universität Bayreuth, Bayreuth, Germany.

cEnvironmental Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

dUSDA Forest Service, Durham, New Hampshire.

eSchool of Forestry, University of Montana, Missoula, Montana.

fRichardson Hall, Oregon State University, Corvallis, Oregon.

gTechnische Universität Dresden, IHM Meteorologie, Tharandt, Germany.

hDepartment of Meteorology, The Pennsylvania State University, University Park, Pennsylvania.

iDepartment of Environmental Science, University of Virginia, Charlottesville, Virginia.

jSchool of the Environment, Duke University, Durham, North Carolina.

kSchool of Forestry, Yale University, New Haven, Connecticut.

lInstitute of Ecology and Resource Management, University of Edinburgh, Edinburgh, United Kingdom.

mNOAA/Atrnospheric Turbulence and Diffusion Division, Oak Ridge, Tennessee.

nDepartment of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts.

oDepartment of Biology, San Diego State University, San Diego, California.

pLand, Air and Water Resources, University of California, Davis, Davis, California.

qPlant Biology and Biogeochemistry Department, Risoe National Laboratory, Roskilde, Denmark.

rDepartment of Geography, Indiana University, Bloomington, Indiana.

sDISAFRI, Universita de Tuscia, Viterbo, Italy.

tSchool of Natural Resource Sciences, University of Nebraska at Lincoln, Lincoln, Nebraska.

uDepartment of Physics, University of Helsinki, Helsinki, Finland.