Is That an Exotic Invasive Species in Your Holiday Decoration?

The following article is reprinted from the (Andover, MA) Eagle-Tribune and may be accessed online by clicking here.

Andover, MA — December 4, 2009 — As you drive along New England roadways this time of year you can frequently spot tangles of long vines adorned with bright yellowish-red berries. Many people don’t realize these plants, which are commonly used in Thanksgiving wreaths and decorations, are actually an exotic invasive species known as oriental bittersweet (Celastrus orbiculatus).

Native to China, Japan, and Korea, oriental bittersweet was introduced into the United States in the late 1800s as an ornamental plant. It has since spread throughout much of the eastern and midwestern United States and Canada. Like many exotic invasive species, oriental bittersweet is wreaking havoc with the environment.

“The oriental bittersweet is the number one invasive alien plant problem in Massachusetts,” according to naturalist and author Peter Alden. “Each fruit is an ecological time bomb.”

The fruit Alden is referring to are those colorful berries. A single oriental bittersweet plant can produce hundreds of fruits, and each fruit contains from two to four seeds. Birds such as robins, mockingbirds, and starlings feed on the fruits and then disperse the seeds in their droppings. People can inadvertently act as dispersal agents for bittersweet seeds as well, by casually discarding their Thanksgiving decorations outdoors where the seeds can then germinate.

Being a vine, oriental bittersweet tends to grow on trees and shrubs, which it uses for support. Once established, bittersweet grows rapidly and can literally engulf its host plants, eventually killing them by outcompeting them for sunlight and nutrients. According to the U.S Department of Agriculture, oriental bittersweet can grow 10 to 12 feet per year, overtopping trees and shrubs up to seven feet tall in a single growing season.

In addition to the host trees and shrubs that are killed, another apparent victim of the oriental bittersweet invasion may be the native American bittersweet, Celastrus scandens. Keith Killingbeck, a plant ecologist and biology professor at the University of Rhode Island says he used to see American bittersweet quite frequently in the early 1980s while teaching his field botany courses.

“I have not seen American bittersweet in Rhode Island in quite a while,” says Killingbeck, “and do not believe it has appeared on one of my course plant lists for at least 5-10 years.”

Speculation is that oriental bittersweet may have cross bred with American bittersweet, producing hybrids.

“Some experts say that the immense amount of pollen from the suddenly everywhere oriental bittersweet has overwhelmed any native American bittersweet,” says Alden, who also fears that American bittersweet may be “biologically dead in Massachusetts.”

“An exotic plant invasion can move through an area with the speed of an epidemic,” according to the Worcester Land Trust’s invasive plant publication. “Plants introduced from somewhere else leave behind the diseases and herbivores that kept them under control in their native habitats. This provides them with an advantage that allows them to crowd out native species.” Biologists call this process “ecological release.”

The grasses that now cover the “golden hills” of California, for example, are mostly Mediterranean grasses introduced as forage for cattle, the native bunch grasses having been outcompeted and driven to extinction in most parts of the state.

And it’s not just limited to plants. The familiar house sparrows and starlings of cities and suburbs were originally introduced from Europe and have now spread across North America, often outcompeting and sometimes literally evicting native bird species from nest holes and bird houses by killing nestlings and destroying eggs.

Fire ants have spread throughout the South, killing off native ant species and often attacking native wildlife and even people, following an initial invasion from cargo ships from South America into Mobile, Alabama, in the 1940s. The Texas horned lizard, an emblematic species of the Southwest, has declined across much of its range, and researchers now believe its disappearance could be due in part to the fire ant.

Burmese pythons are now established in south Florida where they have been observed preying on native wildlife, including alligators. It’s believed the pythons began breeding in the wild in Florida after being released by pet owners when the snakes became too big to handle.

And on it goes. From plants and insects, to birds, reptiles, and other organisms, thousands of exotic invasive species have become established in the United States and elsewhere with the potential to cause serious ecological problems. Whole ecosystems could be disrupted by exotics as the delicate balance between species that has evolved over millennia is disturbed. Native plants that may have provided food and shelter for native animal species could disappear, or have their populations severely reduced, resulting in extinctions.

For example, another invasive plant, Phragmites, also known as the giant reed, has disrupted many wetland ecosystems in Massachusetts.

“It shades out everything,” Alden says. “You do not see a single plant. If we were to walk into the middle of a bed of Phragmites there will be no native tree or shrub or vine or wildflower. Nothing grows under the dense shade and the dense root mass of the Phragmites. It becomes a sterile monoculture of no use to anybody.”

Lots of other exotic plant species besides oriental bittersweet have become established in Massachusetts as well. Japanese knotweed, purple loosestrife, Ailanthus, buckthorn, garlic mustard, and Eurasian water-milfoil are but a few of the exotic plant species that are now common throughout our state and region.

Many states, including Massachusetts, have passed laws recently outlawing the importation and sale of exotic species.

“The state banned import and sale of oriental bittersweet in January 2007,” says Alden. But, enforcement of the laws have been a problem, he notes, adding that many stores still sell wreaths made of oriental bittersweet.

Biologists are also looking at ways to control exotic species, ranging from outright destruction of invasive plants and animals, to importation of the exotic species’ natural enemies, such as phorid flies which are being used to control fire ants in the South to beetles which have been brought in to feed on purple loosestrife here in New England.

The U.S. Department of Agriculture has recommended a variety of approaches for dealing with oriental bittersweet, including cutting, uprooting, and using herbicides.

MassWildlife recommends planting native species in your yard or garden, as opposed to exotics that could spread into wild areas and cause problems. They also recommend not disposing of decorations containing the fruits and seeds of exotic species outside.

“We’re in a sea of invasive aliens here in Massachusetts,” says Alden. “We’ve got to get the resolve to do something about it or its going to eat all of our species of native plants over the next hundred years with probably very few survivors.”

View this article on the Eagle-Tribune website by clicking here.

1 comment

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