Take Me Outside: Beware the beautiful, but invasive Oriental bittersweet

"Bittersweet — it's the perfect name for a plant that has some lovely qualities but is also a terrible menace. Many people are familiar with this plant because it has been used for autumn decorations. It grows as a vine with an orange-red berry enclosed in a bright yellow casing.

The supple twisting stem and colorful berries make the bittersweet ideal for creating a fall wreath to hang on your door. But don't be tempted to do this. If you do, you might be inadvertently contributing to the destruction of your local forest.

How can something so pretty jeopardize an entire ecosystem? Well, not all bittersweet is to blame. There are two species of bittersweet which grow in the eastern United States. One is a native, the American bittersweet, the other is the introduced Asiatic or Oriental bittersweet. It is the latter that causes the problems.

Oriental bittersweet was brought to the United State from China around 1860 and was planted along railroad beds to reduce soil erosion. Gardeners also cultivated it and trained it to grow on trellises. As plants do, it branched out from its original locations.

Like most exotic invasive species, it has not evolved alongside natural predators in this area so its growth is not limited. It is able to outcompete the native species and thus take over a territory. Being a vine, it can grow quickly because it doesn't need to put energy into strong supportive woody tissue. It uses local trees and shrubs to support itself as it twists around them and winds toward the sunlight.

The rapidly climbing vine will wrap around a tree, reaching as much as 40-60' high, strangling it so water and nutrients can no longer flow up and down through the trunk. Girdled like this, a tree will soon die. Other impacts occur when the vines envelope higher tree branches. The additional weight of the vines may cause the branches to break or the entire top of a tree to snap off. A vine infested tree is also more susceptible to snow and ice damage from additional weight. Sometimes the vines are so thick that sunlight cannot penetrate to the leaves of the host plant, inhibiting its ability to photosynthesize. The vines can get so thick, they can literally bring down a forest.

It's best to remove the bittersweet before it gets to that stage. Once it has penetrated an area, it is very difficult to control. Cutting the vine only encourages further sprouts from the roots. It is best to pull up the roots when the plant is young. Kill the plant by hanging it to dry or burning it. Do not compost fresh roots as they will sprout where they are laid and infest a new area.

To be sure that you are pulling out the invasive species and not the native one, notice the leaves. The American bittersweet has oval leaves. The leaves of Oriental bittersweet are nearly round. The other difference is the placement of the berries. The native version grows clusters of berries on the ends of branches while the exotic species has berries all along the stem. Unfortunately, the two plants hybridize and thus it may be difficult to distinguish them. This may also lead to the demise of the native species.

The berries are arguably the most attractive part of the plant. They are not highly sought after by wildlife but may be eaten by songbirds and game birds such as ruffed grouse or pheasant. The birds are one of the vectors for spreading the seeds. They ingest the berries where they are growing and then deposit the seeds in their droppings quite a distance away. The berries are found only on the female plants, as this species is dioecious — having male and female flowers on different plants.

Because the Oriental bittersweet is such a threat to our forests, in 2009 it was placed on a list of regulated plants in Massachusetts. It cannot be sold, transplanted, distributed, propagated or transported.

To help the forests and stay on the right side of the law, hanging colorful corn on your door is a much sweeter choice than the bittersweet wreaths of the past."

Article Credit: Ruth Smith, Berkshires Week, The Shires of Vermont

Photo Credit: M. Williamson, Asiatic Bittersweet cover, CC by 3.0 US, http://www.ipmimages.org/browse/detail.cfm?imgnum=1509001