Native plants give way to European and Asian 'invaders'

Oriental bittersweet was an exotic foreigner still found mostly in East Asia when the New York Botanical Garden planted its first specimen in 1897, although it had been growing elsewhere in the United States since the 1860s.

Today, it is everywhere. The shrubby vine is common in woodlands and fields in 21 states, ranging from North Carolina to Maine to Illinois.

The American bittersweet, meanwhile, has been in a slow decline.

Once common across the eastern two-thirds of the US, the native version of the plant still is around, but it has vanished from many areas now dominated by its hardier, faster-breeding Asian cousin.

"We go entire seasons now without seeing it," says Gerry Moore, director of the science department at the Brooklyn Botanic Garden.

The rise and fall of the two plants has been chronicled by the botanic garden as part of a 20-year study that offers a dispiriting outlook on the future of some native flora.

So far, the project has identified 50 native species that have disappeared from metropolitan New York during the last 100 years, and others that have become far less abundant due to factors including the destruction of their habitat, pollution, and competition from foreign interlopers.

In some areas, the landscape is also becoming less biologically diverse.

"While you used to have a marsh of 50 or 60 species, you might now have an entire marsh of phragmites, the common reed," Moore says.

The study focused on counties within 50 miles of New York City, but experts say other scientists have made similar findings nationwide.

The problem is nationwide

In the West, sagebrush has been giving way to cheatgrass, which found its way to the US in packing materials and ship ballast in the late 1800s.

Nature lovers strolling through wooded glades, thinking they are among trees that have stood since the Revolution, are actually looking at Norway maples, native to Europe.

Kudzu, which hails from Japan and China, infested the South after farmers in the 1930s through the 1950s were encouraged to use it to stop soil erosion.

Even the pristine open spaces of Grand Teton National Park in Wyoming are now populated with houndstongue and yellow toadflax, both from Europe.

Bit by bit, scientists say, the American landscape is becoming less American.

"We are going to our national parks now and seeing Europe," says Tom Stohlgren, a research ecologist for the US Geological Survey. "We are homogenizing the globe at a very fast rate."

The problem's causes

Experts say the trend has many causes, but the biggest one may turn out to be globalization.

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