12th Annual Finalist – Environment. Eastern hemlock trees are some of the largest and most common trees in the Great Smoky Mountains. They play an ecologically vital role in cooling mountain streams and providing habitat for many other species.Unfortunately, they are under attack from a non-native insect called the hemlock woolly adelgid (Adelges tsugae). Without successful intervention, the hemlock woolly adelgid is likely to kill most of the hemlock trees in the park. Photograph Copyright Kathryn Greven, All Rights Reserved.