A Multi-decade Analysis of Carbon and Energy Fluxes Over a Broadleaf Forest in the Southeast U. S.: Preliminary Results

Forests cover 30% of the Earth’s land surface and store 45% of total terrestrial carbon, while serving as an important sink for anthropogenic carbon dioxide (CO₂) emissions. Questions have been raised recently about what effect a warming climate may have on the continued capability of global forests to remain a significant CO₂ sink. In this work, a nearly three-decade record of carbon, water and energy fluxes over a temperate broadleaf forest are analyzed to begin to assess trends in ecosystem functioning under a changing climate. The data record used is a combination of measurements from two close-proximity AmeriFlux sites in East Tennessee on the Oak Ridge National Laboratory reserve. The tower at Walker Branch Watershed was operated from 1995 through 2007, while observations from the Chestnut Ridge site began in 2005 and continue to the present. At each of these sites, eddy covariance fluxes of CO₂, water vapor, energy and momentum along with other turbulence statistics were measured continuously above the forest canopy, along with meteorological variables and soil moisture and temperature. An analysis is presented to justify the merging of these two datasets into a nearly three-decade record for a forest in East Tennessee that is considered very representative of broadleaf forests in the Southeast. Preliminary trends in fluxes, meteorological variables and net ecosystem exchange are examined to begin assessing how the broadleaf forest ecosystem is responding to rising ambient CO₂ levels and a changing climate. Future work will attempt predictions on how the forest ecosystem may respond to expected environmental changes over the next several decades.