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Oak Ridge National Laboratory (ORNL) FACE

The Oak Ridge Experiment on CO2 Enrichment of Sweetgum is a Free-Air CO2 Enrichment (FACE) experiment at the Oak Ridge National Laboratory in Tennessee, USA. We are testing critical hypotheses about the responses of a closed-canopy deciduous forest to the atmospheric CO2 concentrations of future decades. The research is sponsored by the U.S. Department of Energy.

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.