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Throughfall Displacement Experiment



Models of global climate change predict that increasing levels of greenhouse gases in the atmosphere will (1) cause an increase in average global temperatures and (2) alter regional levels of precipitation. It is also predicted that the incidence of drought will increase with a warming global climate. Forests throughout the southeastern United States, where evapotranspiration demand is high and is predicted to increase as temperatures rise, would be particularly vulnerable to declines in annual precipitation. Experimental manipulation of hydrologic inputs at the TDE is accomplished by intercepting throughfall in approximately 2000 subcanopy troughs (0.3 x 5 m) suspended above the forest floor on a "dry" treatment plot and transferring the throughfall across a control plot for distribution onto a "wet" treatment plot. Each plot is 80 x 80 m in size. The treatments result in a 33% decrease in precipitation reaching the forest floor on the dry plot and a corresponding increase in precipitation on the wet plot. Reductions in soil moisture on the dry plot are expected to be equivalent to the driest growing seasons of the 1980's drought which resulted in reduced tree growth of some species. The site was chosen because of its uniform slope, consistent soils, and a reasonably uniform distribution of vegetation. The forest community is dominated by white oak, chestnut oak and red maple, but it contains just under 20 tree species. The past 25 years of research on the Walker Branch Watershed provide an important reference data base against which to judge the outcomes of this large-scale field experiment.


Environmental and biological data for an upland oak forest in eastern Tennessee.


Throughfall Displacement Experiment
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