Oak Ridge Experiment on CO2 Enrichment of Sweetgum



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The response of natural ecosystems to an increasing concentration of carbon dioxide in the atmosphere is a key component of analyses of the current and potential impact of global change. Efforts to understand how eastern deciduous forests will be affected by carbon dioxide enrichment of the atmosphere have heretofore been addressed by studying components of the forest system (individual small trees, specific processes), but it is now time to take the critical leap to measuring the integrated response of an intact forest with a focus on stand-level mechanisms.

To understand how the eastern deciduous forest will be affected by CO2 enrichment of the atmosphere, and what are the feedbacks from the forest to the atmosphere.  This goal is being approached by measuring the integrated response of an intact forest ecosystem, with a focus on stand-level mechanisms.

A free-air CO2 enrichment (FACE) facility, comprising five 25-m plots was constructed in a deciduous forest on the Oak Ridge National Environmental Research Park. The study site is a sweetgum (Liquidambar styraciflua) monoculture planted in 1988. This closed-canopy, 18-m tall stand offers the opportunity for rigorous tests of hypotheses that address the essential features of a forest stand and how they could influence the responses to CO2. These features include:

  • the closed canopy, which constrains growth responses
  • full occupancy of the soil by the root system, which constrains the nutrient cycle
  • the larger scale of the trees compared to saplings in open-top chambers, which changes the functional relationships of carbon cycling
  • and the longer time scale that can be addressed, permitting studies of soil carbon changes.
A User Facility
The Oak Ridge FACE facility is a user facility operated by the Environmental Sciences Division of the Oak Ridge National Laboratory (ORNL). It is open to researchers from universities and other research laboratories who are interested in pursuing other questions relevant to forest response to elevated CO2. There are no fees charged for using this facility. However, all research conducted at the site must be approved by the Principal Investigator, and users must agree to abide by the saftey and access requirements of ORNL and DOE. Contact Rich Norby for more information about using this facility.

The facility was established with support from the ORNL Director's R&D Fund and the Biological and Environmental Research program of the U. S. Department of Energy Office of Science. Additional support was provided by the Terrestrial Ecology and Global Change (TECO) program through the National Science Foundation.

A Network of CO2 Enrichment Experiments
This project was part of the CO2 research network fostered by the Global Change and Terrestrial Ecosystems core project of the International Geosphere-Biosphere Programme. Results from the experiment contributed to the Terrestrial Ecosystem Response to Atmospheric and Climatic Change (TERACC) project, a 5-year initiative integrating experimental data and global change modeling. Data from the ORNL FACE experiment are being used in an model benchmarking activity at the National Center for Ecological Analysis and Synthesis. In support of data synthesis and modeling activities, site and ecosystem response data are freely available through the the Carbon Dioxide Information and Analysis Center ( CDIAC).

A description of FACE technology, site characteristics of FACE experiments worldwide, and links to other sites and resources also are available at CDIAC).

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Last revised: June 28, 2009