Native plants give way to European and Asian 'invaders'

The American landscape is becoming less American as plants from Europe and Asia invade open spaces, crowding out native species and lessening the nation's biological diversity.

Invasive plants, such as the Brazilian pepper – seen here in Florida – are spreading throughout the United States at an alarming rate and forcing native species to extinction.
Brooklyn Botanic Garden/AP
Once prevalent throughout the eastern two-thirds of the US, American bittersweet has been largely replaced by its more aggressive cousin, the Oriental bittersweet.

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.

European traders and settlers have been bringing Old World plants to the Americas since colonization, but the process has accelerated with every advance in travel.

Now, foreign species arrive so frequently aboard planes, trucks, and cargo ships that the odds of the next Oriental bittersweet arriving are exponentially greater.

"That's the scary part, and the $64,000 question," Stohlgren says. "What we have had is an explosion in trade and transportation, and we have yet to see the full effect of that."

"It took 170 million years for the continents to drift apart, but only 400 years to move them all back together," he said. "I describe this as Darwin on steroids, and we are going to see extremely fast changes because of it."

Climate change and pollution may only worsen the problem, as they make the habitat of many native plants less hospitable, said Peter Raven, president of the Missouri Botanical Garden in St. Louis.

"Obviously the loss of wild areas and their reduction in size makes it harder for natives to persist. As global warming proceeds, it will get worse," he said.

The problem is one that has attracted attention both in the US and globally.

What's being done

The Nature Conservancy, a leading environmental group, has persuaded some major home and garden retailers to stop selling invasive trees like the Norway maple and Lombardy poplar in different regions.

It also has been working with researchers and government regulators on developing models that might predict when a nonnative plant could have the potential to become dangerously invasive, if imported into the US.

Several states have established advisory committees on invasive species and a few have banned the sale of plants like purple loosestrife and Japanese barberry, both of which came over the late 1800s and are now out-competing native flora.

The US Coast Guard has been working on draft regulations for ballast water, aimed at preventing ships from picking up invasive aquatic organisms on foreign coasts and bringing them into North American waters.

Too late for some plants

Any changes will come too late to prevent some of the native losses identified by Brooklyn Botanic Garden researchers.

Their comprehensive and ongoing survey has found that wildflowers such as the scarlet Indian paintbrush, pennywort, Sidebells wintergreen, and the Sundial lupine have all seriously declined in the region

At the same time, camphor weed, once found only in the South, has become common throughout the metropolitan area.

"There is still a lot of native diversity out there, but this is an alarm," says Troy Weldy, director of ecological management for the Eastern New York chapter of the Nature Conservancy, and co-author of the New York Flora Atlas.

Species shift due to globalization, he said, "could turn out to be much more of a threat than climate change."


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