Invasion of The Habitat

By MICHAEL D. LEMONICK

By the end of the year, well over 10 million people will have traveled to America's national parks to see the few tiny patches of land that are still as pristine as they were before Columbus landed, or so most believe. In fact, the National Park Service is coping with a growing problem that is partly nature's doing but largely the result of civilization's subtle intrusions. Far from being islands of primeval beauty, parks from Hawaii to North Carolina are being overrun with nonnative plants and animals, virtually all of them introduced, inadvertently or on purpose, by man. These "exotic threats" have become, officials say, the most serious danger facing the 323,750 sq. km (125,000 sq. mi.) national park system.

The most dramatic threats are in Hawaii, where the 900 indigenous plant species -- some found nowhere else in the world -- face new competition from another 900 species of nonnative plants, including banana poka and ornamental ginger. The banana poka was imported in the 1950s by a Japanese gardener, and has since spread its vines over 16,200 hectares (40,000 acres). Other exotics were introduced in the 1930s in an attempt to conserve water and stem soil erosion. Now biologists fear a time when the native plants will be completely gone from places like Haleakala National Park.

Invading animals are also a difficult problem. Rats have been hitching rides to the islands on ships for centuries, then escaping into the forests where they feast on nesting birds and their eggs. Local authorities imported mongooses to hunt the rats in 1883. But no one considered that mongooses hunt in the early morning and early evening, when the rats are not out. So the mongooses switched to birds, compounding the problem.

In Great Smoky Mountains National Park, the main culprits are wild boars, descendants of animals imported to North Carolina in 1912 for hunting. The boars weigh as much as 136 kg (300 lbs.), and, says park official Joe Abrell, "tear up most everything in their paths." Man is responsible as well for oriental bittersweet, a vine imported to control erosion. It is strangling trees. Says park resource specialist Keith Langdon: "Once it gets a grasp on the land, it doesn't relinquish it."

Another plant is overrunning parts of the Southwest, including the Grand Canyon. Introduced about 70 years ago to act as an erosion fighter and windbreak, the tamarisk tree has taken over about 81,000 hectares (200,000 acres), pushing out native trees and threatening eight species of birds that nest in them. The Grand Canyon's major animal offenders are burros; turned loose by prospectors generations ago, they have grown into vegetation- devouring herds.

Large animals can be either killed or removed, but that sometimes causes problems of another sort: a burro-shooting program at the Grand Canyon had to be halted after a public outcry. In Hawaii Volcanoes National Park, though, a population of 15,000 or so feral goats was reduced to only 4, and in the Smokies the wild boar population has been pared. Smaller animals are much harder to fight, and plants harder still. Herbicides kill too indiscriminately, and bringing in new exotic species to control the old is demonstrably dangerous. Rangers often have to resort to chopping down or uprooting invading plants one by one, a holding action at best. In the end, park officials -- and visitors -- will have to accept that the nation's wild lands will never return to their original state. The best that can be done is to work hard to keep new exotic threats from following on the heels of the old.

With reporting by Scott Brown/Hilo and Michael Mason/Atlanta