Christopher Mattrick is worried. The plant ecologist for the 800,000-acre White Mountain National Forest (WMNF), Mattrick is rightly proud of the area’s diverse plant and animal populations. Certainly, a big draw for many of the forest’s six-million-plus annual visitors is the chance to see native species synonymous with New England, like the sugar maple, so brilliant in the autumn. “You travel here and think, ‘What a beautiful place, nature in its pristine glory,’ ” he says. “Many people think it’s a primeval woodland and it is, to a great degree, just that.” But the question that keeps the scientist up at night is just how long will it stay this way?

Mattricks’s main concern is invasive species: the hundreds of non-native insects, earthworms, and plants that are threatening the forest’s natural biodiversity. “We are on the cusp of invasion,” he says. “I can see a trend moving in that direction.” In fact, what’s bugging Mattrick is that he’s done more than simply observe the influx of exotic plants originally from faraway places-like Japanese knotweed and the Norway maple; he’s also helped chronicle it. And the news isn’t good.

Since 2001 scientists from the WMNF and the New England Wildflower Society have been inventorying invasive plants within the forest’s borders, as well as in adjoining areas. What they’ve found, says Mattrick, are about 2,000 infestations, most of them occurring in the disturbed areas that are prime breeding ground for all types of invasivesÑtrailheads, road edges, and power line corridors. Mattrick’s personal estimate is that the actual number of cases is 20 times greater.

The WMNF is hardly the only place struggling with the impact of proliferating invasive species. Across much of New England, and the rest of the country, native plants and animals are literally fighting for their lives against species originally specific to Asia, Europe, and other parts of the world. Spurred by globalization and the easy international movement of people and products-the New Zealand mudsnail recently discovered in the Great Lakes is believed to have been imported via ships’ ballast water-invasives, once introduced to a new ecosystem, lack natural predators. Because of this, they flourish.

While there are plenty of non-native species or “aliens” that enter new ecosystems with little impact, invasives also can have a devastating effect. The chestnut blight, caused by an Asian fungus, essentially wiped out the American chestnut, a tree that had been both an important part of the ecosystem and the economy. Dutch Elm disease, West Nile virus, and Hoof-and-Mouth disease are other high-profile examples of havoc that can be wreaked when invasives aren’t controlled.

The changes to the landscape are unmistakable. In Virginia, for example, The Nature Conservancy’s Brad Kreps says, “You could potentially, 10 to 15 years from now, be walking through a monoculture of garlic mustard.” Kreps, who works at the 7,000-acre Warm Springs Mountain Preserve and directs the conservancy’s Allegheny Highlands Program, adds, “If it’s left unchecked, it will spread-and it will out-compete natives for light and moisture.”

According to The Nature Conservancy, invasives are at least partly responsible for the decline of nearly half of the threatened and endangered species in the U.S. By the organization’s calculations, only habitat loss poses a bigger threat to endangered plants and animals.

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