From the Viette's Views Gardening Blog
The Southern Appalachian spruce-fir forest, is a unique ecosystem which is now limited to the highest mountaintops (above 5,500 ft) of the Southern Appalachian range. The forest, a relict of the last Ice Age, is dominated by red spruce and Fraser fir. During the Pleistocene when much of North America was covered by ice, this spruce-fir forest was widespread in the Southeastern United States. As temperatures warmed, these trees disappeared from the lower elevations and the high mountaintops of the Southern Appalachian chain became refugia for this forest ecosystem where small island populations of the spruce-fir forest have survived.
Unfortunately, over the last 50 years about 95% of the mature Fraser firs in the southern spruce-fir forest have been killed by the balsam woolly adelgid (Adelges piceae), a small insect that was accidentally introduced from Europe in the early 1900’s. This pest initially decimated populations of balsam fir in the Northern Appalachians and has since moved south to the Smokies.
If you drive down the Blue Ridge Parkway, you will notice lots of dead fir trees scattered along the high ridges but up on Clingmans Dome in Great Smoky Mountains National Park at the southern end of the parkway, the devastation is extensive. Because the adelgids don’t usually attack the trees until they are about 15-20 years old, there are many young firs growing below the dead trees. Sadly, these will undoubtedly become infested once they get older.
The balsam woolly adelgid is related to the hemlock woolly adelgid (Adelges tsugae) which has been devastating populations of hemlocks throughout much of eastern North America including the northern part of the Blue Ridge Mountains. The hemlock woolly adelgid has recently been discovered in the Smoky Mountains and now the beautiful hemlocks which grow at the lower elevations in the park are threatened.
The problem with these and other non-native pests is that the trees and plants that they attack have no natural defenses against them. The balsam woolly adelgid has attacked and killed the majority of the mature Fraser firs in the Southern Appalachians and most of those that remain are infested and will soon succumb to this pest. It’s very sad. Clingmans Dome looks like a Fraser fir graveyard with just the graying skeletons of these once magnificent firs still standing.
The beautiful red spruce trees which grow along side the Fraser firs in this forest ecosystem, though not attacked by the balsam woolly adelgid, are indirectly affected by the loss of these trees. Without the protection of the sturdier firs, the red spruce are more prone to wind damage and blowdowns.
On top of all this, air pollution in the Southern Appalachians which leads to the formation of acid rain and acid mist is thought to be slowing the growth rate and weakening the red spruce and remaining Fraser firs leaving them more susceptible to disease and insect damage.
Research is ongoing to try to determine ways to save these last remaining populations of the southern spruce-fir forest and perhaps over time, the trees will develop their own defenses against the adelgids and the effects of pollution.