Spread of Oriental bittersweet not so sweet for Vermont forests

What does our invasive plant highlight this month have in common with a tangled mass of twine? More than you would think. Known as Asiatic or Oriental bittersweet, Celastrus orbiculatus is a woody vine that can wrap around trees and cover the forest in a hopeless tangle.

This species was brought to the United States from China in the 1860's as an ornamental plant. You can see these vines and their berries formed into holiday wreaths occasionally on doors and mantles this time of the year. However, you do not need to look at pictures nor holiday decorations to see this plant right now.

If you look outside, you can identify this plant with ease by recognizing a few of its key features which are visible into the winter season.

First, this plant is a woody vine. This vine can be spotted from afar when the trees have dropped their leaves to reveal bittersweet's twisting tendrils. The vine has grey to light brown bark with parallel grooves or lines running up and down it. Grape vines look similar; however, they can be differentiated by grapes' dark brown, shaggy bark that peels away in thin strips.

Bittersweet vines can reach a width of four inches in diameter. The smaller vines appear to have a smooth bark with small, white to yellow speckles scattered along them. Second, this invader has characteristic fruit that stays on the plant into the winter. Invasive bittersweet has clusters of berries that hang along its branches. These fruits have a yellow outer layer that pops open to show scarlet berries beneath. The spherical fruits appear to be divided in three.

The third identifier is the aggressive nature in which it grows. Thick mats of vegetation and total coverage of trees and fences are typical growth formations of this invader.

Still, why should we care about this plant? Pieter van Loon, the director of forest stewardship for Vermont Land Trust tells us, "many values, including timber, wildlife, biodiversity, and recreation are compromised when bittersweet moves into the neighborhood."

Mike White, forester with Calfee Woodland Management in Dorset, explains how Oriental bittersweet "can girdle (strangle) trees and the extra weight and surface area can make trees more susceptible to wind and ice damage." White adds that this plant is unique among other invasives because "it is the only non-native, invasive plant in our region that can have direct effects on full-sized trees, impacting trees with potential timber or aesthetic value."

"Both these situations [girdling and extra weight on the tree] mean a significant increase in the chance of branches or tree sections falling on trails and, in the worst case scenario, on people or dogs using trails," van Loon adds. However, this plant has the potential to do more damage to sugarbushes and impact those individuals whose livelihoods depend on their trees.

"There is a conserved property in Southern Vermont where the vines grow up and along the trees and the tubing and cause tremendous maintenance problems for the landowners," van Loon tells us. He warns that bittersweet "is a serious threat to the long-term viability of sugar maples in the bush."

There are a few easy steps that you can take right now to help stop further spread of this invasive plant:

- Do not buy decorations with bittersweet. Birds eat and transport the berries, but we can be spreading the seeds, too, by this simple action.

- If you see the berries in your yard, collect them in a plastic bag, seal it tightly, and dispose in the trash. Do not compost the berries.

- Cut the larger vines to halt the further growth and production of berries for next year.

- Contact a local forester to discuss what actions you should take this upcoming spring, summer, and fall if you recognize bittersweet growing on your property.

Farrah Ashe is the Batten Kill Watershed CISMA Habitat Steward for the Vermont Department of Environmental Conservation. Contact the author at Ashe.bkcisma@gmail.com with any additional questions you may have on Oriental bittersweet.


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