The hemlock wooly adelgid could completely change the ecology of the Southern Appalachians
by Joe Tarr
Every other weekend, Will Blozan goes hunting in the backwoods of the Southern Appalachians. He's not looking for exotic animals or birds, but for something most of us take for granted or have little understanding of—hemlock trees.
Blozan searches for the largest and oldest of the Eastern hemlocks and documents them.
Co-founder of the Eastern Native Tree Society, Blozan found many record-breaking trees in the Smokies and elsewhere. The tallest reached 169 feet, 10 inches, which he measured by climbing and dropping a tape from the top. The tree with the largest girth he's found was 6 feet. The largest in terms of mass was 1,506 cubic feet. The oldest he's found was over 500 years old, a small tree he wrapped his arms around in an understory near Russell Field.
But these dimensions don't really measure what hemlocks mean to Blozan or how much they shape the forest ecosystem of East Tennessee.
"They're ancient. They epitomize patience to me because they're so old," Blozan says. "They're in one place for 400 or 500 years, they're just doing their thing. Something about that tree is very calming."
There is a good chance that calming presence will be lost in the next couple of decades from the Smokies and most of the Southern Appalachians. A tiny insect known as the hemlock wooly adelgid has been spreading south, wiping them out along the way.
It's hard to measure how great a loss the hemlocks will be to the Smokies and the Southern Appalachians. You can talk about it in the cold scientific terms about species loss or the warming of streams, but for anyone who has spent any time in the forest, the change will be a lot more profound and hard to comprehend.
Called by some the redwoods of the East, the hemlocks form towering canopies that create dark, damp and cool habitats that will disappear without the trees. The woods will be sunnier. Many bird, animal and insect species will die off or their numbers cut back. The loss of the hemlocks would be comparable to the American chestnut blight early in the 20th century. Some say it'll be worse.
In the next few years, when you are out in the woods, take a good look around. There's a good chance these woods will never again in our lifetime or our children's or grandchildren's lifetimes look the way they do today.
"It's going to be heartbreaking because I love the tree," Blozan says. "And it's going to happen, unfortunately."
A relative of the balsam wooly adelgid—which decimated Fraser firs in the Smokies between the '60s and the '90s—the hemlock wooly adelgid is native to Asia. It was accidentally introduced to this country and first found in California and Oregon in the early 1930s. The Western hemlocks are resistant to wooly adelgids, but Eastern hemlocks are not. In 1951, the bug was discovered in Virginia and it's been spreading slowly throughout the Eastern United States ever since. It's killed nearly all the hemlock stands in New Jersey, about 26,000 acres.
The wooly adelgid is so small that it's difficult to see. But, the bug secrets a white waxy substance that protects it from elements while it feeds. It is active during the fall, winter and spring, becoming dormant for a short time in the summer.
The bug is dispersed by the wind and on birds. It travels longer distances in trees from nurseries and soil.
With its long beak, the adelgid punctures the hemlock needle near the branch and sucks the nutrients out of the tree. An infested tree can die within a year, although usually it takes two or three.
The adelgids were first found in Shenandoah National Park, in the Blue Ridge Mountains of Virginia, in 1984. It took a while for the insects to take hold, but once they did the effect was devastating. A survey of the hemlock stands in 1990 and '91 found that about 70 percent of them were in good health. In 1993, less than 12 percent were in good health. Today, the tree has been essentially wiped out there, says Shenandoah forester James Akerson.
There are still some uninfected trees and some small stands remain, but there are no more hemlock forests, he says. Less than 1 percent of Shenandoah was hemlock dominated, but their loss has had a huge effect.
"To us, it was a big deal when we began losing them because they were focused along streams and our trails and it was there where we had our highest biodiversity," Akerson says.
Without the hemlocks, much of the forest is open to sunlight, particularly during the winter months, he says. "There's sun on the floor of the forest. You used to have a mossy floor, now you don't have that. You'd have what you'd see in a typical hardwood stand."
The hemlock's downfall here was aided by several years of drought (which put more stress on the trees) and mild winters (which allowed the bugs to reproduce more prolifically).
The adelgids have been moving relatively slowly, so the scientists in the Great Smoky Mountains expected them to arrive there in about 10 years. They were disheartened when they discovered them last spring in the Twentymile area. By the end of last year, they were found in about 40 other sites in the park.
In Tennessee right now, the adelgids are mostly on federal lands, says Bruce Kauffman, forest health specialist with the state's Department of Agriculture. The adelgids have been found on one piece of private property in Sevier County, but that's it, he says. The U.S. Forest Service reports the bugs have been found in Blount, Sevier, and Carter counties.
The Smokies have about 5,000 acres that are primarily hemlock, although the trees are scattered throughout the rest of the forest. "It doesn't sound like a lot, but it is," says Kristine Johnson, supervisory forester in the park. "There's not likely to be another evergreen to take its place."
The trees are among the oldest in the east, with some documented as old as 900 years. There are several in the Smokies 400 years or older. Blozan has documented the oldest current tree in the Smokies at more than 500 years. "I know there's trees over 600 years old. They're either too big to core or they're rotten inside," he says.
So these hemlock forests have taken hundreds of years to develop. Their loss will have a spiraling effect on many other plant, animal, and inspect species, as well as how the park looks and feels.
According to a report by the National Park Service, "Continued decline of eastern hemlock forests associated with infestations of hemlock woolly adelgid will bring about major ecological changes. The plant species most likely to expand in declining hemlock stands are mainly hardwoods and invasive alien species that will not provide habitat or ecological functions anything like those of eastern hemlock."
This would mean the decline of several species. The golden-crowned and ruby-crowned kinglets reside in the hemlocks in the winter; Blackburnian and black-throated green warblers use them in the summer. There are some 27 insect families represented in old growth hemlocks and 63 in secondary growth, several of which would likely be affected. A number of plants that thrive in the understory, including moss, would decline.
Streams would be less stable—warmer and more likely to dry out in the summer; colder in the winter. Brook trout and aquatic insects would decline. Soil leaching would also increase.
For many, the threat is eerily similar to something that wiped out another dominant tree in the Eastern United States. Ranging from Maine to Georgia and west to Michigan, the American chestnut was the most economically valuable of the hardwoods. A hearty tree, it grew fast and was one of the tallest in the forest, stretching over 100 feet. In open areas, they were great shade trees, with crowns that spanned 100 feet.
But around 1900, a fungus from Asian nursery stock was introduced and quickly spread. By 1940, 3.5 billion chestnut trees had died from the blight. (The Chestnut tree still exists as small saplings, but the disease kills them before they reach a significant height. Two foundations are now breeding the chestnuts for blight resistance and there are active programs to reestablish it.)
Many people think the loss of the hemlocks would be more significant than the chestnut blight. The chestnuts didn't dominate sections of a forest the way hemlocks do and after their demise other hardwoods took their place.
"It's a very unique ecosystem that won't be replaced by anything else out there," says Rusty Rhea, a forester with the U.S. Forest Service. "When the chestnut went away, the oaks came in and took hold.... There's nothing else out there that would come close to mimicking hemlocks. That's going to have impacts on an untold number of species."
"We haven't lost chestnuts, the genetic material still there," Rhea adds. "Unfortunately, without any type of management, we could probably lose hemlock. [The adelgid] preys on all lifestyles of the tree, so there's no room for escape there."
In their demise, hemlocks are likely to be replaced by oaks, black birch, red maple and white pine, which would create a very different environment.
"The Hemlocks are by themselves. They're a forest type, they're not a component of a forest," Blozan says.
There's still hope that a significant number of hemlocks can be saved. It comes in the form of another insect from Japan. Known officially as Pseudoscymnus tsugae, it's a tiny ladybug beetle. In Asia, wooly adelgids have been kept in check in part because the trees are resistant and in part because there are predators like the ladybug who feed on them.
About the size of a pinhead, the ladybug follows the same breeding and feeding cycles as the adelgid. In fact, the only thing it can eat is the hemlock wooly adelgid.
Unfortunately, the beetles are in some ways much more delicate than the adelgids. "Often, what they've done with insects is rear them on an artificial diet," says Ernest Bernard, research nematologist at the University of Tennessee. "Unfortunately, this beetle can only be raised on hemlocks infested with wooly adelgids."
So, to rear the ladybug, workers must collected infested hemlock branches in the wild and bring them back to a lab. As the beetles grow, they're moved into different rooms with different environmental settings.
As a result, they're expensive. The Smoky Mountains National Park pays $1.25 to $2 for each beetle.
It released about 20,000 into the wild last year and it's not known how well they've survived. Releasing them is also a tedious process. The ladybugs arrive on hemlock branches, which are carried out into infected areas. "We went to the most heavily infected limbs and we flicked the beetles—where we could see them—onto the branches," Johnson says.
Bernard is trying to start a rearing lab at UT, which would be convenient to the Smokies. "We would have liked to have been open by spring but we don't have a facility and we don't have funding," Bernard says. Now, they're shooting to be open in the fall, perhaps using a trailer for the lab. He estimates they could have beetles ready for release about three months after opening.
The university estimates it'll cost $180,000 a year to produce 100,000 beetles a year.
The park has applied for a $396,000 grant for 2004, '05 and '06 to help fund the lab. But, so far, a determination hasn't been made yet. The park also applied for a grant from the Forest Service. In the meantime, Friends of the Smokies and the Great Smoky Mountains Natural History Association donated $42,000 to the park to help keep the beetles in check.
The state isn't likely to offer much help. "There's not been a real strong amount of funding available for that," Kauffman says. "We're in a 9 percent budget cut situation here and this isn't a time when money comes available, unless it's from the federal budget. We're not in a mode where controls are going to be practiced."
There are other control measures that can be used temporarily. Park employees have sprayed infected trees with a soap solution that washes away the adelgids' protective cover and kills it. They've also injected the soil around trees with a nicotine solution that gets into the tree and poisons the insects. It works on trees up to 70 feet tall, but it is unknown how effective it is on trees taller than that. Because these efforts have to be done repeatedly, they're not practical as a long-term solution.
Some fear the beetles are too little too late to save the hemlocks. "I think the lagtime for the beetle to make an impact is going to be too long," Blozan says.
But Bernard says that the ladybugs have helped in other areas. In a section of Connecticut, the ladybugs saved about 90 percent of the hemlocks.
"We do know it's the only possible answer we have right now. The beetles are quite voracious. They can eat hundreds of adelgid eggs in their lifetime," Bernard says.
Other predator beetles are being studied for possible release in the states, including several species from China and one found in British Columbia. Their release has not yet been approved.
There are many other factors that could doom the hemlocks. In many places, the trees are already stressed from drought and other ailments. A lack of funding could stall whatever adelgid controls might work. And, the adelgid might prove too prolific and potent.
"I try to be optimistic. But I have to say the time to have done something was in the '50s when we found out about it. It's very difficult to control an adelgid in a forest environment," Johnson says. "Having said that, I'm cautiously optimistic. It's almost unthinkable to us to lose our hemlock forests. We're going to do everything we can do."
Rhea was more optimistic. "It might be too late in some areas, but I don't think it's too late in the Southern Appalachians."
Up in Shenandoah, where the adelgids are now dying out because they have no more food, Akerson was perhaps the most hopeful. "A lot has happened in a decade," he says. "The problems started quite a while ago and there weren't as many tools as there are now.... Our message is that you've got time on your side."
But, just in case, you might want to pay a little more attention to the hemlocks next time you take a walk in the woods. Enjoy those shaded coves they form around streams and at higher elevations, places filled with plants, birds and insects not found in any other forest. You may not have much time left to savor them.
March 6, 2003 * Vol. 13, No. 10
© 2003 Metro Pulse
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