Throughfall Displacement Experiment (TDE)
1993-2006
Understanding Forest Responses to Environmental Change
As global temperatures and precipitation patterns shift, forests in the southeastern United States can face growing risks from increased drought and water stress. Recognizing these challenges, researchers at Oak Ridge National Laboratory led a long-term study to investigate how these forests respond to changing water availability.
Funded by the U.S. Department of Energy’s Office of Science through the Biological and Environmental Research program, the Throughfall Displacement Experiment (TDE) was a large-scale field experiment that involved manipulating precipitation levels in a mature hardwood forest. Spanning multiple years, the project generated critical insights into how forest ecosystems may adapt — or decline — under various drought conditions.
The Walker Branch Watershed in Tennessee was selected as the site for the TDE. The area contained nearly 20 tree species and uniform environmental conditions, allowing for precise comparisons across treatments. In addition, over two decades of baseline ecological data from the site provided a unique opportunity to assess long-term responses in a well-characterized forest ecosystem.
The TDE simulated various precipitation scenarios by intercepting one-third of natural rainfall on an 80 x 80 meter “dry” plot and redistributing it to a nearby “wet” plot. To achieve this, scientists used 2,000 suspended subcanopy troughs, designed to reduce soil moisture to levels comparable to historic drought conditions observed in the 1980s. The treatments resulted in a 33% decrease in precipitation reaching the forest floor on the “dry” plot and a corresponding increase in precipitation on the “wet” plot.
Data from the TDE continues to inform Earth-system models, guide forest management strategies, and inform national policies focused on ecosystem resilience.
Projects and Findings
- Investigators
- Funded Projects
- Research Findings (Updated April 2002)
- TDE Publications (updated March 2010)
- TDE Synthesis Volume