The (Hemlock) - Northern Hardwood Forests Ecological System in Harpers Ferry National Historical Park (NHP) is not common. The only natural community in this ecological system in Harpers Ferry NHP is the Eastern Hemlock - Hardwood Forest. Any other natural communities in this ecological system are beyond the borders of the park. There is a small example on the Blue Trail on Loudoun Heights. American beech and chestnut oak grow on steep north-facing slopes overlooking the Potomac River. Notice the dead eastern hemlock trees, killed by the invasive hemlock woolly adelgid. Ecobit: Hemlock Woolly Adelgid