An insect infestation that is killing hemlock trees in New England forests is having a significant impact on the water resources of forested ecosystems that provide essential water supplies to one of the nation’s most populous regions, according to research by Indiana University geographers and colleagues at three universities in Massachusetts.
The study is the first to show an increase in water yield—the amount of water reaching streams and rivers—resulting from forest damage caused by an insect pest called the hemlock woolly adelgid. Insect-damaged trees use less rainfall and allow more water to reach the ground and run off into waterways. With less foliage, the trees return less moisture to the atmosphere via transpiration and evaporation.
“We observed a 15 percent increase in annual water yield,” said Taehee Hwang, an assistant professor in the Department of Geography in the IU Bloomington College of Arts and Sciences. “But there are a lot of issues involved with this subject. Water quality may suffer as rainfall runs off more quickly from forested areas and carries higher concentrations of nutrients. The long-term picture may change as hemlocks are replaced with broad-leaved trees that have a different impact on water resources.”