Understanding the Hemlock Woolly Adelgid Issue
(Written by Mark Warren)
The eastern hemlock (Tsuga canadensis) - that riverine evergreen - favorite tree to many - is vanishing. It is likely to be the most devastating environmental loss of our lifetime.
Hemlocks around you may appear healthy, but the picture is changing. The trees in north Georgia lie at the end of a long arc of destruction that began in mid-Atlantic states where adelgids, aphid-like insects, were unknowingly introduced on plants from the Orient half a century ago. When they multiplied to sufficient numbers, the infestation traveled quickly north and has now swung south down the Appalachians. Adelgids are here and, sad to say, spreading quickly. Once in place on a new tree, these aphids suck the life out of every needle and the tree dies - its skeleton standing as a monument to how quickly catastrophes brought on by exotic species can sweep through a forest, or a continent.
In addition to the aesthetic loss of this beautiful tree, resultant events will likely occur - not fully predictable but certain to affect our streams and wildlife. If you have ever fished or canoed a mountain stream you know that no tree excels the hemlock in creating deep shadow. Unlike white pine, which sheds lower branches as it matures, the hemlock stretches thick-laced boughs low over the water, providing cold "holes" and eddies that are instrumental in maintaining the cooler water temperature needed for high oxygen content. With hemlocks absent from the banks, change of a few degrees could mark the end of certain aquatic species - possibly trout, crayfish and salamanders, for examples.
We don't yet know how far-reaching the ill effects will creep into the ecosystem. As is often the case in history, the big picture becomes clear too late. We do know that if we do nothing, hemlock trees are virtually doomed. So what can we do?
It is not feasible to save every hemlock; adelgids are spreading rapidly. Two weapons are available: beetles and insecticide - both expensive.
The savior beetles, from Japan and China, dedicate their entire lives to devouring the aphids. Raising these beetles into adelgid-eating armies requires development of breeding laboratories. The vast areas in need of the beetles overwhelm the few laboratories that exist. An effort is being made to establish and maintain a laboratory in Georgia.
Inoculation with insecticide effectively kills adelgids but remains a potent deterrent for only two years, and the potential for poisoning nearby streams is disturbing.
The hemlock woolly adelgid has already invaded the watersheds of the Chattooga, Tallulah, Hiawassee, and Toccoa Rivers and Brasstown and Coopers Creek.
It is predicted that by the year 2015 approximately 90% of our hemlocks will be lost. If we do nothing virtually all will be lost. Please provide your support so that in just a few years we will not be describing to our grandchildren the majestic evergreen called hemlock that once towered over our creeks and rivers and gave our Appalachian valleys their dark and beckoning mystery.