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