Water is constantly moving throughout the natural environment. Some scientists study the flow of water into, out of, and held within particular natural areas. Trees play a role in the flow of water by absorbing groundwater, releasing water as water vapor through its leaves, and slowing down runoff. In the forests of the southern Appalachian mountains, eastern hemlock trees make up about half the living plant material along mountain streams. However, these trees are being attacked by an invasive Topics: Active Forest Management, Insects, Water, Coweeta Hydrologic Laboratory, Eastern Hemlock, Experimental Forests, Hemlock Woolly Adelgid, Humidity.