AmeriFlux Network


Nations of the world face challenges in developing sound policies and directions for addressing global change. The scientific community has the responsibility to provide the scientific basis for those policies. This includes developing the understanding of the influence of land, ocean and atmospheric processes in climate change. The goal of AmeriFlux is to develop a coordinated research network of long-term flux sites in the Americas for quantifying and understanding the role of the terrestrial biosphere in global climate change. Specifically, the network aims to provide reliable estimates of carbon stocks in plants and soil, biological and environmental controls on carbon dioxide and water vapor exchange between the land and atmosphere, and improve our description and understanding of variation from ecosystems to continents and from seasons to decades. The network provides quantitative information to adequately predict large-scale long-term responses to changing environmental conditions. This is accomplished using micrometeorological and biological measurements at intensive sites coupled with extensive measurements (e.g. surveys and remote sensing) and modeling. For ecotype and instrumentation details for all AmeriFlux research sites nationwide, visit the AmeriFlux website.

Key science questions of AmeriFlux are:

  • What are the magnitudes of carbon storage and the exchanges of energy, CO2 and water vapor in terrestrial systems? What is the spatial and temporal variability?
  • How is this variability influenced by vegetation type, phenology, changes in land use, management, and disturbance history, and what is the relative effect of these factors?
  • What is the causal link between climate and the exchanges of energy, CO2 and water vapor for major vegetation types, and how does seasonal and inter-annual climate variability and anomalies influence fluxes?
  • What is the spatial and temporal variation of boundary layer CO2 concentrations, and how does this vary with topography, climatic zone and vegetation?


  • As of January 2011, the AmeriFlux data archive contains 787 site-years of data from 140 sites. Of these 140 sites, 92 are still active and 48 are inactive. 90 sites are in the United States, 1 in Brazil, and 1 in Mexico.
  • Across sites, an average of 83% of the total amount of carbon taken up by the terrestrial systems in photosynthesis was respired back to the atmosphere.
  • Volcanic aerosols from the 1991 Mt. Pinatubo eruption greatly increased diffuse radiation worldwide for the following two years.
  • AmeriFlux sites bolster progress towards verifiable regional carbon cycle flux estimates.
  • Validation of the satellite remote sensing MOD17 algorithm (GPP and NPP) is on-going (Running & Heinsch)
  • A preliminary study on how representative AmeriFlux sites are of the ecoregions in the coterminous US showed that southern, southwestern, and Pacific Northwest environments are less well represented by the existing tower sites (Hargrove et al. 2003). Further analysis will be conducted over the next three years.
  • Integrating flux tower methods with ground-based biometry reveals the importance of disturbance dynamics in controlling large-scale carbon balance in the Amazon of Brazil.
  • AmeriFlux data were used to demonstrate the importance of phenology to seasonal and interannual variation in NEE (Gu et al. 2003b).
  • AmeriFlux tower flux data were used to examine the role of climate on soil C decomposition rates.
  • Several studies in seasonally drought affected or well-drained sites have observed large soil respiration responses to pulse rain events.
  • Flux tower data analysis methods continue to be developed and explored to produce quality data for synthesis activities and reduce uncertainty in flux estimates.

Build a cohesive network of research sites to quantify and understand carbon sources and sinks and the response of terrestrial ecosystems to climate and disturbance.

Research involves analysis and field direction of AmeriFlux operations, and the PI provides scientific leadership of the AmeriFlux network. Activities include the coordination and quality assurance of measurements across AmeriFlux network sites, synthesis of results across the network, organizing and supporting the annual Science Team Meeting, and communicating AmeriFlux results to the scientific community and other users. Objectives of measurement research include (i) coordination of flux and biometric measurement protocols (ii) timely data delivery to the Carbon Dioxide Information and Analysis Center (CDIAC); and (iii) assurance of data quality of flux and ecosystem measurements contributed by AmeriFlux sites. Objectives of integration and synthesis activities include (i) integration of site data into network-wide synthesis products; and (ii) participation in the analysis, modeling and interpretation of network data products. Communications objectives include (i) organizing an annual meeting of AmeriFlux investigators for reporting annual flux measurements and exchanging scientific information on ecosystem carbon budgets; (ii) developing focused topics for analysis and publication; and (iii) developing data reporting protocols in support of AmeriFlux network goals.

A strategic plan guides AmeriFlux research, and the PI is responsible for coordinating priority activities across the network. The approaches to these investigations include the following: Integrating micrometeorological and biological measurements to quantify and understand the carbon balance of terrestrial ecosystems; reduce uncertainties in flux measurements, improve data QA/QC and archiving standards, and require AmeriFlux sites to adhere to consistent measurement and data delivery standards; continue cross-site calibration of measurements using the "gold standard" roving instruments and software; conduct multiple measurements at AmeriFlux sites on CO2 flux variation, biometrics and carbon storage; measure atmospheric CO2 concentrations at selected sites, and use of the data for modeling atmospheric CO2 exchange; conduct intensive measurements of CO2 exchange and biomass carbon along with physiological parameters for use in calculating NEP and NPP at AmeriFlux sites; improve knowledge of how processes regulate CO2 and water vapor exchange, and improve the representations of respiration, phenology and disturbance in ecosystem carbon models; encourage expansion of flux sites as needed to fill critical gaps in biomes, disturbance gradients and climate space; conduct collaborative studies of scaling and integration of AmeriFlux results that include combinations of flux site data, cluster sites, remote sensing and modeling; organize the annual AmeriFlux Science Team meeting.

Results to date
National Research Council Committee on Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements (2009-10). A key recommendation relevant to AmeriFlux is: ‘An interagency group, with broad participation from the research community, should undertake a comprehensive review of existing information and design a research program to improve and, where appropriate, implement U.S. estimates of AFOLU emissions of CO2, N2O, and CH4. Key elements are likely to include continued research on the biogeochemical cycles of these gases, supported by observations from eddy covariance towers, other flux measurements for N2O and CH4, and ecosystem inventories of all of the major carbon pools and their trends in the United States. These observation systems will be necessary in a modeling framework (e.g., ecosystem biogeochemistry process modeling) to provide the accuracy needed for annual, spatially explicit assessments within countries.

Dr. Law contributed to the GEO-Carbon Report and presented an overview at the ministry level meeting of the Group on Earth Observations (Washington, DC, 2009). The strategy in the report is integrated observation systems that include flux networks for model and remote sensing calibrations.

To ensure international consistency of methods and integration of results, Dr. Law serves on: (1) The Global Terrestrial Observing System – Terrestrial Carbon Observtions (GTOS-TCO panel chair); (2) The Advisory Panel for the Integrated Carbon Observation System (ICOS) of Europe (2009-); (3) the Advisory Board of Carbon and Greenhouse Gas management in Europe (GHG-Europe, 2009-). Law also testified before the House on AmeriFlux measurements (2009).

Data management and FLUXNET synthesis – Law continues to serve on the steering group of FLUXNET, which determined Fair Use Policies for open access to all FLUXNET data for modelers and the greater scientific community, and reviews individual proposals for using the data to minimize redundant analyses. The data of interest are the Level 4 data that are gap-filled and quantities are computed (gross photosynthesis, ecosystem respiration). These data are on the AmeriFlux website, but we still rely on Europeans to process the Level 4 data. FLUXNET is a Research Coordination Network project funded by NSF; it ends in 2012 and there are no plans to continue processing AmeriFlux data beyond that point. Dr. Law encouraged AmeriFlux sites to submit the next round of data for the past year to be processed by the Europeans. She continues to work with CDIAC in discussing improvements to the AmeriFlux web site and data issues.

Research Synthesis Results
Nitrogen deposition reduces forest soil respiration. A synthesis of data from NitroEurope and flux data from AmeriFlux, CarboEurope, and ChinaFlux found that low to moderate levels of nitrogen deposition to terrestrial ecosystems lead to enhanced uptake of CO2 from the atmosphere and reduced organic matter decomposition. In an earlier study, we found increased net uptake across a set of sites, but the mechanisms were unclear. Here, we had ancillary data on soil processes to find that soil respiration was reduced with N deposition. The results were published in Nature Geoscience (Janssens et al. 2010), and the results were highlighted on Nature’s home page.

Forestry, including afforestation, reforestation, and avoided deforestation can sequester atmospheric carbon dioxide and, hence, has been proposed as a strategy to mitigate climate change. However, forest management practices also influence land surface properties, including albedo (the amount of sunlight reflected back to space), surface roughness, and evapotranspiration, all of which affect the amount and forms of energy transfer to the atmosphere. In some circumstances, these biophysical feedbacks can warm the climate locally, counteracting the effects of carbon sequestration on global mean temperature and reducing the net value of climate change mitigation projects. In Anderson et al. (2010), we reviewed published and emerging research that suggests ways in which forestry projects can reduce unintended consequences associated with biophysical interactions, and highlighted knowledge gaps in managing forests for climate protection. We suggested ways to incorporate biophysical effects into frameworks that use forests as a climate protection strategy.

New methods are recommended for computing photosynthesis parameters for model inputs. Gu et al. (2010) compiled A-Ci (assimilation) curves from AmeriFlux sites and used the data to develop and demonstrate a model for computing Vcmax and Jmax from the data in a consistent manner. The paper also recommends methods for improved measurements of assimilation rates. The code for processing the A-ci curves is posted on the AmeriFlux web site.


Invited Presentations (2009-2010):

  • Law, B.E. The Role of Forests and Forestry in the Terrestrial Carbon Cycle: Considerations for a Changing Climate. Forests and the Environment. Apr 18-20, 2011. Bologna, Italy.
  • Law, B.E., A. Linn. Verifying Greenhouse Gas Emissions. American Geophysical Union. Dec 11-17, 2010. San Francisco, CA.
  • Law, B.E. Enhancing Global Forest Observations in a Changing Climate. Global Climate Observation System Panel, COP 16, United Nations Framework Convention on Climate Change. November 30, 2010, Cancun, MX.
  • Law, B.E. Integration of observations and modeling to quantify forest carbon stocks and fluxes. IPCC Expert Meeting on Uncertainty and Validation of Emission Inventories. March 23-25, 2010. Utrecht, The Netherlands.
  • Law, B.E. 2009, Testimony before the U.S. Senate Committee on Energy and Natural Resources Subcommittee on Public Lands and Forests. “Managing Federal Forests in Response to Climate Change, Including for Natural Resource Adaptation and Carbon Sequestration.”
  • Law, B.E. 2009. Testimony before the U.S. House of Representatives, Committee on Energy & Environment on “Monitoring, Measurement, and Verification of Greenhouse Gas Emissions: The Role of Federal and Academic Research and Monitoring Programs.”
  • Law, B.E. A Global Carbon Observation System. Group on Earth Observations (GOP VI) Carbon Community of Practice. November 19, 2009. Washington, DC.
  • Law, B.E. Can tower flux measurements constrain forest uptake of CO2? American Association for the Advancement of Science. February 13-15, 2009. Chicago, IL.

Click on publications in the menu for a complete list of publications.

Student Training:
Four post-doctoral research associates: Ajit Govind, Tom O'Halloran, and James Kathilankal.