Appalachian Trail Conservancy: http://www.appalachiantrail.org/site/c.mqLTIYOwGlF/b.4805859/k.BFA3/Home.htm
National Park Service: http://www.nps.gov/appa/
National Parks Conservation Association: http://www.npca.org/
In a report released Wednesday, the association said threats also include quarries, wind farms, racetracks, illegal all-terrain vehicle use and mountain bikes. All along the 2,178-mile trail, the report says, decisions about projects must consider "the special and fragile character" of the trail, its resources and its landscapes.
But the West Virginia-based group that helps manage and maintain the trail says that's a daily challenge.
"When you run north-south in the eastern U.S. for almost 2,200 miles, you're kind of in everybody's way," said David Startzell, executive director of the Appalachian Trail Conservancy in Harpers Ferry.
"Our objective is not to be the Great Wall of China to everything that might be proposed," he said, "but we do try to influence the siting and design of projects."
The Appalachian Trail stretches through 14 states, from Springer Mountain in Georgia to Mount Katahdin in Maine, and encompasses more than 250,000 acres. Yet the average width of the protected area around it is just 1,000 feet, making it vulnerable to pollution, invasive plant species and projects that can compromise both habitat and the wilderness experience.
The NPCA, which is pushing to have the trail listed on the National Register of Historic Places or labeled a National Historic Landmark, says development also increases access for illegal motorized vehicle use, which can damage the trail and encourage both poaching and vandalism.
"There is good physical protection in both the Deep South and New England," says Ron Tipton, the association's senior vice president for policy. "In the middle, the threats are very intense."
Subdivisions are probably the single greatest threat, Tipton said, particularly in high-density population areas such as Maryland, Virginia and New Jersey.
In 2008, Pennsylvania passed legislation requiring some counties and townships to pass zoning ordinances aimed at protecting the trail from incompatible uses. Tipton would like to see similar action in at-risk areas.
"It's not as important when you go through one national forest after another in the South," he said.
The association wants more money to pursue protective designations, to continue studying the health of the trail's natural resources and to buy more high-priority adjacent lands.
Only about 10 miles of the trail are still privately owned, and the association wants to acquire about 150 properties to make it entirely public property.
Buying adjacent lands as well would ensure people feel like they're in the wilderness, not just next to a subdivision, Tipton said.
Though best known as a hiking path used by about 2 million people a year, the trail also is a living laboratory that could help warn the Eastern Seaboard of looming environmental problems.
In 2006, a diverse group of organizations began long-term monitoring of the trail's environmental health, relying on volunteers to collect data about plants and animals, air and water quality, visibility and migration patterns.
The Appalachian Mountains are home to one of the richest collections of temperate zone species in the world, and the trail has a natural diversity nearly unsurpassed in the national park system. It also has different ecosystems that blend into one another - hardwood forests next to softwood forests next to alpine forests.
An inventory completed in 2001 identified more than 2,200 rare plant and animal species, including six that were threatened or endangered and 360 considered rare in their states.
But a 2005 survey documented invasive, nonnative plants at 250 locations between North Carolina and Maine, with the highest percentages in Virginia, West Virginia, Maryland, and Pennsylvania.
The Appalachian Trail Conservancy says threats to the trail generally fall into three categories, including those that occur on trail lands, such as ATV use, illegal dumping and the theft of timber.
Then there are major development projects such as power lines, highway expansions and wind farms that cross the trail or would sit on adjacent lands.
Finally, there are long-term threats including air pollution, acid rain deposition and global climate change.
"At any one time," Startzell said, "there are probably 30 to 40 issues we're dealing with."