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United States Department of Agriculture

Agricultural Research Service

Title: Regional Implications of the Throughfall Displacement Experiment on Forest Productivity

Author
item Hunt, Earle

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 29, 2002
Publication Date: June 9, 2003
Citation: Hunt, E. 2003. Regional implications of the throughfall displacement experiment on forest productivity. In: Hanson, J., Wullschleger, S.D., editors. North American Temperate Deciduous Forest Responses to Changing Precipitation Regimes, Ecological Studies. New York, NY: Springer, p. 447-460.

Interpretive Summary: Global climate models generally indicate that the southeastern region of the United States should become wetter on average during the next century because of global climatic change. However, the frequency of drought and wet years is also expected to increase. In order to study the effects of changing precipitation regimes on temperate deciduous oak forests, Oak Ridge National Laboratory set up the Walker Branch Throughfall Displacemen Experiment (TDE), in which about one-third of the precipitation is caught under the canopy (throughfall) at a "dry plot" and used to irrigate a "wet plot, thus manipulating the water supply. Data from this experiment was used to test a computer simulation model of the carbon, water, and nitrogen cycles, called BGC++. Then, the model was used to simulate changes in forest productivity over the southeastern United States for changes in precipitation amount and frequency of extreme precipitation. Generally, forest productivity increases in many areas with increasing precipitation, but at some locations sunlight is the limiting factor, so an increase in rainfall decreases the amount of sunlight for growth. Similarly, forest productivity decreases with decreasing precipitation, but at some locations cold temperature limits forest productivity so the warmer temperatures associated with drought causes a net increase in forest production. These multiple interactions can be teased apart with computer simulation modeling, allowing the results of the Walker Branch TDE to be extrapolated regionally.

Technical Abstract: Global climate models generally indicate that the southeastern region of the United States should become wetter on average during the next century because of global climatic change. However, the frequency of drought and wet years is also expected to increase. In order to study the effects of changing precipitation regimes on temperate deciduous oak forests, Oak Ridge National Laboratory set up the Walker Branch Throughfall Displacemen Experiment (TDE), in which about one-third of the precipitation is caught under the canopy (throughfall) at a "dry plot" and used to irrigate a "wet plot, thus manipulating the water supply. Data from this experiment was used to test a computer simulation model of the carbon, water, and nitrogen cycles, called BGC++. Then, the model was used to simulate changes in forest productivity over the southeastern United States for changes in precipitation amount and frequency of extreme precipitation. Generally, forest productivity increases in many areas with increasing precipitation, but at some locations sunlight is the limiting factor, so an increase in rainfall decreases the amount of sunlight for growth. Similarly, forest productivity decreases with decreasing precipitation, but at some locations cold temperature limits forest productivity so the warmer temperatures associated with drought causes a net increase in forest production. These multiple interactions can be teased apart with computer simulation modeling, allowing the results of the Walker Branch TDE to be extrapolated regionally.

Last Modified: 12/18/2014
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