Monitoring and Understanding Forest/Atmosphere Carbon Dioxide Exchange: the NRS Flux Tower Network

Research Issue

The exchange of carbon dioxide (CO₂) between the land and the atmosphere is one of the most important indicators of ecosystem productivity. The eddy-flux measurement approach, involving the short-term measurement of flux densities (vertical transport of mass, momentum and energy per unit area and time), has become a standard approach to continuously monitor the effects of climate variability and other causal factors on carbon sequestration or release from ecosystems. Net ecosystem CO₂ exchange is presently measured at more than 30 sites in North America. Many of these research and monitoring sites are part of the AmeriFlux network. Flux towers are an integral part of the North American Carbon Program, a multi-agency effort to measure and understand the sources and sinks of CO₂, Methane (CH₄), and Carbon Monoxide (CO) in North America and in adjacent ocean regions.

Summed over the course of a month, season or year, data from these sites provide accurate measures of ecosystem CO2 source or sink strengths. The flux towers provide information specific to one ecosystem type or condition. Increasingly, multiple flux towers are located in contrasting conditions to increase understanding of the effects of different treatments (e.g., harvesting), gradients of vegetation composition, or age chronosequences. 

Data from flux sites help test physiological models of C exchange and are critical to relating fluxes and remote sensing data. Companion physiological and ecological measurements enable partitioning carbon fluxes into plant and soil components and reveal mechanisms responsible for these fluxes. At some sites, biomass-based estimates of C storage have validated C budgets from direct flux data, and vice-versa. Data from the flux sites have been applied in ecology, weather forecasting, and climate studies, especially for sites with several years of data to quantify inter-annual flux variations. 

Our Research

The Northern Research Station has several operating flux towers located at:

1. The Howland Research Forest
2. The Bartlett Experimental Forest
3. The Silas Little Experimental Forest
4. The Marcell Experimental Forest
5. The Baltimore Long Term Ecological Research Site

The Northern Research Station has a long-term study sponsored by NASA and the Forest Service under the North American Carbon Program, to develop a landscape-scale monitoring tier that links the intensive measurements of the flux tower sites with the extensive monitoring by FIA and remote sensing.

Expected Outcomes

• Develop quantitative scientific knowledge about changes in carbon stocks, and the factors regulating these changes, to support sustainable forest management for North America.
• Develop the scientific basis required to monitor and verify the results of managing forests for increasing carbon sequestration.
• To develop forecasts for future trends that will guide policies for protecting forests under climate variability and change.

Research Results

Scientific papers, models, data assimilation tools, large datasets for modeling and synthesis activities (available through AmeriFlux and the NRS website), general technical reports, methods manuals, books. 

• Howland data 
• Howland site info and papers

Research Participants

Principal Investigator

• David Hollinger, Plant Physiologist, USDA-Forest Service – NRS
• Kenneth Clark, Research Forester, USDA-Forest Service – NRS
• John Hom, Biological Scientist, , USDA-Forest Service – NRS
• Randy Kolka, Research Hydrologist, USDA-Forest Service- NRS

Research Partners

• Bryan Dail, University of Maine
• Andrew Richardson, University of New Hampshire
• Eric Davidson, Woods Hole Research Center
• Ming Xu, Rutgers University
• University of Maryland Baltimore County

For further details log on website :
https://www.nrs.fs.fed.us/disturbance/climate_change/flux_towers/