Air pollution, destructive invasive pests and a surplus of people all threaten the park's future.

President Bush might discuss air pollution and haze, and how to reduce it, during a park visit today to mark Earth Day. Environmental groups from Western North Carolina and Eastern Tennessee plan to demonstrate against the administration's air proposals, which they say would hinder efforts to reduce pollution.

Air monitors in the park record high levels of ozone, particularly at higher elevations. In the upper atmosphere, ozone protects the Earth from harmful rays. But ground-level ozone is a gaseous pollutant formed when emissions from power plants, factories and automobiles react in sunlight. It's harmful to breathe, particularly for the young, the elderly and people with respiratory problems.

The Environmental Protection Agency put the park on its bad air list last year at the same time it added nearly a third of North Carolina counties, including the Triangle. Areas on the list must reduce ozone pollution before the end of the decade.

Among exhibits on flowers and wildlife in the park's Sugarlands Visitor Center near Gatlinburg, Tenn., is a display on air quality showing daily ozone levels.

Jim Renfro, air quality manager at the park, said the park has some of the highest air pollution levels of any national park. Renfro said several years of wetter, cooler weather and the Tennessee Valley Authority's installation of pollution controls on two power plants have lowered pollution, which peaked in 1999 with 52 bad air days. By comparison, the Triangle had 29 that year.

"Five years of data, I would not call a trend, but it is a signal that things are starting to improve," Renfro said. "There are no measures that are getting worse. They are either remaining stable or improving. That is good news."

Too much ozone, pests

Still, ozone levels doubled in the park between 1988 and 1999 during years of record heat, and they remain high.

"It's still way above what it was in 1988," said Howard Neufeld, a plant ecologist at Appalachian State University in Boone and principal researcher on Environmental Protection Agency and park service studies of air pollution in the Smokies.

Neufeld documented 90 species of plants and trees in the park that have shown leaf damage, lower seed production or slower growth because of pollution.

"The major difficulty for the park is a lot of pollution is coming from the Midwest," Neufeld said.

Dick and Judy Nielsen, a retired couple from Saginaw, Mich., have been visiting the Smokies periodically for 25 years for its natural beauty. They climbed to the top of Clingmans Dome, the highest point in the park, to admire the view Wednesday, a day when ozone reached unhealthy levels. The view was disappointing. Haze reduced the rows of distant peaks to dim outlines.

"It seems especially bad today," Judy Nielsen said. "I had an asthma episode halfway to the top."

Nowhere is environmental change more evident than atop Clingmans Dome, where dead gray trunks of Fraser firs create a ghost forest. People visiting the area often blame air pollution for killing the firs. Pollution might weaken the trees, but scientists say a tiny insect from Europe -- the balsam woolly adelgid -- is killing them.

Since being detected in the park in the 1960s, the adelgid has killed 70 percent of the mature Fraser firs that grow in the upper elevations. When the trees die, plants that thrived in their shade are overtaken by sun-loving plants that crowd them out.

"You're seeing a total breakdown of the ecosystem," Park Ranger Tim Cruze said.

In 2002, the hemlock woolly adelgid was discovered in the park; it is threatening the park's hemlock forests. Park rangers are spraying selected trees with soapicide to kill the pest and are releasing predatory beetles that eat the adelgid.

While air pollution poses a long-term threat, the invasive pests threaten more immediate and dramatic change.

Too many people

The park is visited by more than 9 million people a year. Not all observe the adage to leave no trace.

Backpacker Elizabeth Hobday, 26, a Raleigh musician who began hiking the Appalachian Trail in late March, paused at Newfound Gap, near Clingmans Dome, the trail's midpoint in the Smokies. Hobday said she had seen a lot of wildlife but also disturbing signs of people.

"Very few of the shelters have privies," Hobday said. "You'll go down below the shelter and see toilet paper everywhere."

Some trails are so heavily used, such as the spectacular trail to Laurel Falls, that the park service has paved them.

Some sections of the park, such as the 11-mile loop through Cades Cove, have bumper-to-bumper traffic during peak season. To address the congestion, park officials are studying the idea of requiring visitors to Cades Cove to park their cars and take shuttles.

"There are so many environmental issues that face this park," said Cruze, the park ranger. "It's not all gloom and doom. But everything is not all right either."

Staff writer Wade Rawlins can be reached at 829-4528 or wrawlins@newsobserver.com.