By Dennis Baldocchi, Bev Law and David Hollinger
Ameriflux is a network of long-term, eddy flux measurements stations, historically located in the contiguous United States, Alaska, Canada, Costa Rica and Brazil, but now expanding throughout the Western Hemisphere. The network was established to provide data from field sites representing the many climate and ecological biomes in this hemisphere, including crops, tundra, grasslands, desert, shrublands (e.g., chaparral or sagebrush in Great Basin), savanna, and conifer, deciduous and tropical forests.
The AmeriFlux network was launched in 1996, after the vetting of making long term flux measurements was made at an international workshop in La Thuile, Italy, in 1995, where some of the first year-long flux measurements were presented (Baldocchi et al., 1996). The AmeriFlux network started with a group of ad hoc flux towers already operating in such locales as Harvard Forest in Massachusetts, Walker Branch Watershed in Tennessee, Howland Forest in Maine, and at the Camp Sherman site in Oregon. By 1999 new towers were established at Duke Forest loblolly pine plantation and deciduous forest in North Carolina, on the Wind River Crane in Washington, at Morgan Monroe State deciduous forest in Indiana, on Niwot Ridge in subalpine forest of Colorado, near Douglas Lake at the University of Michigan Biological Station, at agricultural sites in Oklahoma and Illinois, over a slash pine plantation in Florida, a grassland near Fort Peck, Montana, at a chaparral in southern California, and at a ponderosa pine plantation in northern California.
Early support for the network came from the U.S. Department of Energy’s Terrestrial Carbon Program, DOE’s National Institute of Global Environmental Change (NIGEC), NASA, NOAA and the U.S. Forest Service. The network grew from about 15 sites in 1997 to over 90 active sites in 2007 (Boden et al., 2013). Today, over 110 active sites are registered, and 61 other sites have been partners in the past.
Goals of the network
- Quantify the magnitude of the carbon sources and sinks for diverse terrestrial ecosystems in the Americas, and evaluate how the carbon sources and sinks are influenced by disturbance, management regimes, climate variability, nutrients, and atmospheric pollutants
- Advance understanding of processes regulating carbon assimilation, respiration, and storage
- Collect critical new information to help define the current global CO2 budget
- Enable improved predictions of future concentrations of atmospheric CO2
At the network’s start, it was governed by a science chair and a steering committee. Dr. David Hollinger, who led the effort to set up the pioneering Howland Forest site, was the first leader of the AmeriFlux network. In 2001, Beverly Law assumed leadership of the network for the next decade. In 2012, with the U.S DOE’s decision to support ongoing and stable long-term AmeriFlux core sites and to support expanded data and technical capabilities, Margaret Torn of LBNL became the new leader of the network and the new U.S. DOE-sponsored AmeriFlux Management Project, which provides technical and data resources, expertise and support to all AmeriFlux sites and community members.
A unique attribute of the AmeriFlux network was its early establishment and use of a roving system of standard flux instrumentation to produce an intra-network calibration (Schmidt et al., 2012). The roving systems discovered sensor problems, established calibration standards and gave confidence in the different instrumentation configurations in use across the network. The network also pioneered data archiving, uniform processing, and distribution through the data portal at Oak Ridge National Lab’s CDIAC (Boden et al., 2013).
The AmeriFlux network and its community are national and international intellectual contributors. AmeriFlux is a key member of the global FLUXNET network of networks (Baldocchi et al., 2001) and a key component of the North American Carbon Program (Schaefer et al., 2012). Data from AmeriFlux have been used to validate new satellite-based estimates of carbon exchange from the NASA MODIS sensors on the Terra and Aqua satellites (Running et al., 2004; Sims et al., 2008), and to validate and parameterize models that are used to simulate land-surface processes in climate models, and carbon and water exchange in ecosystem and biogeochemical models (Schaefer et al., 2012; Schwalm et al., 2010).
To build a robust community, several science workshops have convened to share ideas on making and interpreting long term flux measurements and to produce synthesis papers with the AmeriFlux data in hand. The first workshop was held at Flathead Lake in Montana in 1997 (Running et al., 1999), followed by the Marconi Workshop in California (Gu and Baldocchi, 2002). Bi-annual meetings with the DOE Terrestrial Carbon program also provided opportunities for scientists to interact, share experiences, and brainstorm future research priorities and synthesis goals.
Special issues in journals like Agricultural and Forest Meteorology produced highly cited findings on the eddy covariance method (Massman and Lee, 2002), flux footprint theory (Schmid, 2002), and synthesis of flux data among climate and ecological gradients (Falge et al., 2002; Law et al., 2002). The 2002 Workshop on Flux Diagnostics and Standardization produced a Handbook on Micrometeorology (Lee et al., 2004).
In 2012, the US Department of Energy changed the funding structure of the network and contracted Lawrence Berkeley National Laboratory, under the leadership of Margaret Torn, to guide investigator-operated AmeriFlux core sites, and provide long-term stable funding to support state-of-the-art instrumentation and staffing to optimize site operations and resulting data quality. The new AmeriFlux Management Project (AMP) [link to About/About AMP] continues to provide annual QA/QC site visits using their roving calibration systems, to offer open-access data to the broad scientific community, and to standardize data processing, gap filling and flux partitioning (Agarwal et al., 2010), while pursuing continuous improvement in processes to achieve higher quality data and better service to the AmeriFlux community.
- Agarwal, D.A. et al., 2010. A data-centered collaboration portal to support global carbon-flux analysis. Concurrency and Computation: Practice and Experience, 22(17): 2323-2334.
- Baldocchi, D.D. et al., 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(11): 2415-2434.
- Baldocchi, D.D., R.Valentini, Running, S.R., Oechel, W. and Dahlman, R., 1996. Strategies for measuring and modelling CO2 and water vapor fluxes over terrestrial ecosystems. Global Change Biology., 2: 159-168..
- Boden, T.A., Krassovski, M. and Yang, B., 2013. The AmeriFlux data activity and data system: an evolving collection of data management techniques, tools, products and services. Geosci. Instrum. Method. Data Syst. Discuss., 3(1): 59-85.
- Falge, E. et al., 2002. Seasonality of ecosystem respiration and gross primary production as derived from FLUXNET measurements. Agricultural and Forest Meteorology, 113(1-4): 53-74.
- Gu, L. and Baldocchi, D., 2002. Foreword. Agricultural and Forest Meteorology, 113(1-4): 1-2.
- Law, B.E. et al., 2002. Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation. Agricultural and Forest Meteorology, 113(1-4): 97-120.
- Lee, X., Massman, W.J. and Law, B. (Editors), 2004. Handbook of Micrometeorology: a guide for surface flux measurements and analysis. Kluwer Academic Press, 250 pp.
- Massman, W.J. and Lee, X., 2002. Eddy covariance flux corrections and uncertainties in long-term studies of carbon and energy exchanges. Agricultural and Forest Meteorology, 113(1-4): 121-144.
- Running, S. et al., 2004. A continuous satellite-derived measure of global terrestrial primary production. BioScience, 54: 547-560.
- Running, S.W. et al., 1999. A global terrestrial monitoring network, scaling tower fluxes with ecosystem modeling and EOS satellite data. Remote Sensing of the Environment., 70: 108-127.
- Schaefer, K. et al., 2012. A model-data comparison of gross primary productivity: Results from the North American Carbon Program site synthesis. Journal of Geophysical Research, 117(G3).
- Schmid, H.P., 2002. Footprint modeling for vegetation atmosphere exchange studies: a review and perspective. Agricultural and Forest Meteorology, 113(1-4): 159-183.
- Schmidt, A., Hanson, C., Chan, W.S. and Law, B.E., 2012. Empirical assessment of uncertainties of meteorological parameters and turbulent fluxes in the AmeriFlux network. Journal of Geophysical Research, 117(G4).
- Schwalm, C.R. et al., 2010. A model-data intercomparison of CO2 exchange across North America: Results from the North American Carbon Program site synthesis. Journal of Geophysical Research, 115.
- Sims, D. et al., 2008. A new model of gross primary productivity for North American ecosystems based solely on the enhanced vegetation index and land surface temperature from MODIS. Remote Sensing of Environment, 112(4): 1633-1646.
Posted May 2014