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Tiny insects threaten mountain forests

Published July 16, 2006

CHIMNEY ROCK, N.C. - Within the serene forests that draw hundreds of thousands of visitors to southern Appalachia every year, a quiet massacre is under way.

A tiny pest small enough to float on the breeze - a bug called the hemlock woolly adelgid - is slowly poisoning the majestic hemlock trees that make up much of the green canopy in the rugged region, threatening the scenery that visitors admire from the overlooks of the Blue Ridge Parkway and the cliffs of Chimney Rock Park.

"They may never have noticed the hemlocks when they were alive, but they sure notice them when they're dead," Chimney Rock naturalist Ron Lance said during a recent hike to check on adelgid damage.

There are weapons to fight the adelgids, including chemicals and other insects, but using them is expensive and labor-intensive.

Adelgids measure just 1/32 of an inch long, small enough to be carried by the wind or to stow away on birds, landscapers' tools or backpackers' gear.

The aphid-like insects are thought to have arrived on ornamental plants imported from Japan in the 1920s. They showed up in urban landscaping in Virginia in the 1950s and spread into the wild. Their population exploded in the 1980s, and by the 1990s they had devastated Virginia's Shenandoah National Park and spread to the Northeast.

In the past decade, they've moved south into areas of Tennessee and the Carolinas. And in many parts of western North Carolina, hemlocks are "often the only tree there," said Chris Ulrey, plant ecologist for the Blue Ridge Parkway.

Adelgids (pronounced "uh-DEL-jid") can take as long as two years to kill major limbs, but they also severely weaken a tree, making it more susceptible to disease, wood-boring insects and severe weather.

They inject toxic saliva while sucking sap from a hemlock. Needles on infested branches go from a deep, rich green to a sickly green-gray, then dry up and fall off. Most new branch buds die. The "woolly" in the adelgids' name refers to the cottony masses that surround their eggs; an infested tree is easy to spot because it looks as if it has been dusted with the sort of white flocking used to simulate snow on Christmas trees.

Kristine Johnson, supervisory forester at Great Smoky Mountains National Park, which straddles the North Carolina-Tennessee line and is the nation's most visited national park, said the damage to hemlocks on ridges overlooking U.S. 441 between Cherokee, N.C., and Gatlinburg, Tenn., was obvious this spring.

"They're very large, old trees and they're on such steep slopes that we haven't been able to treat most of them," she said.

Ulrey has tracked the adelgids' progress along the 469-mile Blue Ridge Parkway, which runs from near Waynesboro, Va., to near Cherokee.

"Nearly all of the hemlock in Virginia on the parkway is dead or will soon be dead, in the next year or so," Ulrey said.

South of Boone, N.C., however, there is still some hope of saving trees.

Adelgids can be killed off, at least temporarily, by injecting insecticides into the trees or the surrounding soil, by spraying trees with an insecticide or soap solution, or by releasing beetles that feed on the adelgids.

But there are limits to money and manpower, and soil injections are believed to provide only about five years of protection.

At Great Smoky Mountains National Park, Johnson and forester Tom Remaley have targeted 24 backcountry areas with insecticide and beetles.

Park officials are focusing on campgrounds, visitor centers and areas near roads and trails - anywhere that hemlocks are highly visible to the public or where a dying tree could spread adelgids.

On the Blue Ridge Parkway, Ulrey said, all trees along the parkway itself are being treated, as well as those along the trails that extend from the road.

"We're getting as far off the trail as we can," he said. "We can't get too, too far off, but with our crew we've been averaging about 1,000 trees" a year for three years.

Once the current infestation has run its course, the adelgid population will crash and achieve a rough equilibrium with the now outnumbered beetle population. The beetles should then be able to hold the adelgids in check, allowing the hemlocks to grow back.

"I like to tell people that in 200 to 300 years, things should be back to normal," he said with a laugh.

[Last modified July 16, 2006, 02:21:40]

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