Alien Intruders Threaten Smokies’ Native Species

Published: August 8, 2009

CHARLOTTE, N.C. — Like an island, the leafy wilds of Great Smoky Mountains National Park lie anchored in a sea of tourist kitsch, power-plant pollution and vacation homes. And, oh, what the waves wash ashore.

From wild hogs to hemlock-killing insects to city lights polluting the night sky, the park’s worst environmental problems invade from outside its borders.

That locks park managers in a never-ending fight to protect and restore native species while fending off intruders. Now celebrating its 75th year, the park covers a half-million acres in North Carolina and Tennessee and is worldrenowned for its diversity of plants and animals.

“My primary challenge is to preserve the park ‘unimpaired’ for future generations, and that’s a pretty big word,” says Superintendent Dale Ditmanson.

When air pollution from far-flung smokestacks smothers mountain views, he adds, “I can’t send a ranger out to fix that.”

Nor can supervisory forester Kristine Johnson stop the devastation of Eastern hemlocks, the Smokies’ towering sentinel trees. The hemlock woolly adelgid, an Asian bug the size of one letter in this sentence, is killing trees 500 years old.

Johnson’s crews save some infested trees with insecticides and release beetles that prey on the adelgid, but the park holds far too many hemlocks to treat. While trees at higher altitudes are showing surprising resilience, the stands on mid-mountain slopes turn steadily grayer.

If most die, as appears likely, it will become the Smokies’ second epic disaster from an exotic source in recent decades. Until the 1940s, the white flowers of American chestnut trees covered the park’s slopes like snow. An imported fungus killed them all. Hemlocks are now only the highest-profile casualties. Of the 1,663 flowering plant species in the park, 380 don’t belong there. Fifty — multiflora rose, privet, Japanese honeysuckle, Oriental bittersweet — are aggressive enough to choke out native plants.

Park staffers inspect sources of gravel and topsoil, in which exotic plants might hitch rides into the park. They urge campers not to bring firewood into the park from 12 states where tree-killing insects are at work.

They can’t, however, make each hiker wipe his feet before entering. Muddy boots carry the seeds of invasive garlic mustard and coltsfoot up the Smokies’ slopes.

But every war has its victories. A little jewel of a fish, the brook trout, gave the Smokies a triumph of the natives.

Brookies’ story, like that of many species in the park, goes back 10,000 years to the last ice age. Trout were among the plants and animals that moved south as glaciers advanced, then were left stranded in the highlands when the ice receded.

Heavy logging early in the last century ruined many trout streams. By the 1970s, park biologists realized that air pollution was turning high-altitude water acidic. Non-native rainbow trout — the park had stocked 1.8 million over the years — were moving up streams.

Squeezed from above and below, brook trout had lost 70 percent of their range.

Now years of hard, expensive restoration work are paying off.

Park crews use chemicals to kill rainbows in streams. Then they capture brook trout, sometimes hiking miles across steep slopes with the fish in water-filled backpacks, and release them in the newly cleared streams.

The park now has 120 miles of brook trout water and plans to restore an additional 20 to 25 miles. In 2007, for the first time in three decades, the park allowed anglers to once again fish for brook trout.

There’s a reason so many non-native plants thrive in the Smokies: It feels like home.

The park’s diverse terrain, from river bottoms to some of the highest peaks in the East, mirrors the native habitats of many of the invaders. Most of them were brought to the United States as ornamental plants.

“We have places that are like South Africa, like Canada, like Europe, and many places that are like China,” Johnson says.

The Southern Appalachians’ frequent rains and many streams provide niches where non-natives can survive, adds Gary Kauffman, a U.S. Forest Service botanist in Asheville, N.C.

The moist conditions make it more likely seeds will germinate when soil is disturbed by logging, road construction or falling trees, he said. Non-native plants spread especially quickly along streams, which can carry seeds, stems and roots long distances.

Once established, exotic plants often don’t face the diseases, parasites or harsh climates that keep them in check at home, and they can choke out natives.

Their nationwide impact, in reduced crop yields, lost livestock range and extra lawn and garden maintenance, is an estimated $50 billion a year. When the invaders weigh as much as a grown man and wear long, curved tusks, the park turns to more assertive control techniques.

European wild hogs, covered in coarse hair, escaped from a North Carolina hunting preserve in the 1920s and spread into the Smokies. Consummate survivors, the hogs rototill the ground with their tusks as they grub for food, trampling rare plants, gobbling salamanders and fouling streams.

A heavy crop of nuts last fall only magnified their prolific reproduction. So far this year, park crews have trapped and killed more than 500 hogs, the biggest number since 1987.

“We know that, like the hemlock woolly adelgid, we’re never going to get rid of them,” said park spokesman Nancy Gray. “But we’re trying to keep their population stable.”

Last year’s bumper crops of nuts, berries and cicadas also gave a boost to a Smokies native species: the park’s 1,500 black bears. Sows that normally give birth to two or three cubs were spotted with four to five this spring.

The park had to close five backcountry campsites where hungry bears ripped into tents. They twice closed a trail near popular Cades Cove after a bear threatened hikers. The most-visited national park even guards its dark nights and serene quiet.

Development nibbles at the park’s edges. By 2002, the little town of Gatlinburg, Tenn., housed 407 stores, hotels and motels, restaurants, real estate offices and entertainment venues, one for about every 10 residents.

Two years ago technicians installed high-resolution cameras atop the tower of 6,643-foot Clingmans Dome, the park’s highest point, and began recording background brightness levels in the night sky. Monitoring of soundscapes, separating the rush of waterfalls from the honk of car horns, also began.

The work will serve as a baseline for future comparisons.

Animals, such as night-hunting owls, need darkness and quiet as they do food, water and shelter, said Jim Renfro, a park air-quality specialist. So do people.

Look up on a clear night, he said, and it’s still possible to see the Milky Way and stars. But the horizon glows, high into the sky, with the earthly light of the Tennessee Valley, Asheville and Atlanta.

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