De-Vining New Haven

My introduction to de-vining started last summer, when I was a Greenspace intern with URI. On my first day, Chris Ozyck gave us a tour of New Haven, where we learned about ongoing projects and the flora we’d be working with throughout the summer. As we walked through Beaver Ponds Park, he pointed out a large willow tree he had planted some years ago and the beautiful gathering space he helped create under a catalpa tree’s canopy. Chris also showed us a plant that had been on his mind for a long time—the wretched Oriental bittersweet (Celastrus orbiculatus). Bittersweet is an invasive vine that is ubiquitous in Connecticut, especially in urban forests. Chris taught us to recognize bittersweet quickly and to share the importance of its removal.

He explained that vines like Oriental bittersweet endanger our urban forest by killing native trees that provide valuable community and ecosystem benefits. Invasive vines like bittersweet are masters at preserving energy. They use a tree’s structure to reach up into the canopy instead of making their own upright trunk. And bittersweet vines can get really big. David Shimchick of Friends of East Rock Park notes that, “Some of the bittersweet has the diameter of an anaconda—they literally strangle the tree and weaken it.” David is right. Gone unchecked, a bittersweet vine will coil around a tree and thicken over time, squeezing the trunk like a giant snake. The squeezing can become so tight that girdling occurs, where water and nutrient flow are restricted, resulting in the tree’s death. While bittersweet will thrive in a tree’s sunny canopy, it will also do well in a shady ground story. Its shade tolerance and horizontal root structure make it a resilient (and difficult to manage) plant. For humans, that means this plant is a severe threat. As Stephanie FitzGerald of Edgewood Park explains, “We have adult trees and tiny trees, and the tiny trees don’t make it because of the bittersweet vines. As a result, we don’t have many teenage trees.” Which makes a lot of sense; invasive vines like bittersweet can take over understories and suppress native-tree regeneration, resulting in less diversity in forest stratification. We haven’t even mentioned how easily bittersweet spreads either. Its bright red/ orange berries attract birds, making it an easy target for extensive bird dissemination.

While birds are the predominant medium of bittersweet dispersal, how did it get here in the first place? Like many invasive plant species in the United States, bittersweet is native to Southeast Asia and was introduced in the 1860s as an ornamental and erosion-control plant. By 1940, it had spread to Connecticut, Massachusetts, and New Hampshire. In 1974, bittersweet’s reach encompassed over 33 states. Today, its greatest concentrations can be found in New York and coastal Connecticut— that’s us, New Haven! So what are we doing about it?

My Greenspace intern cohort wasn’t the only group learning about invasive vines. Chris collaborates with groups all over New Haven, including youth groups like the Common Ground & Wilbur Cross Climate Action group, Greenspace groups (Mill River, Beaver Ponds, and East Rock, among many), and anyone who’s interested in joining. He first started the de-vining initiative in 2020 when COVID-19 was in full force. De-vining turned out to be a safe way of socializing, getting outside, and protecting our urban canopy. For Joan Hilliard of Beaver Ponds Park, “De-vining allows me to get outside and move, instead of sitting all day.” Movement for the mind and body is crucial, and Stephanie noticed the benefits among her Edgewood group, too, “I love the camaraderie of the people, I love the fresh air, and my mood is always better after doing this work.”

From releasing strangled oak saplings to mature hickories, de-vining isn’t just satisfying, it has a positive impact on urban-forest health and community resilience. First, freeing a native tree from bittersweet’s death grip supports biodiversity and urban-ecosystem health.

A rescued native tree can contribute to bird and mammal food sources (via insects laying eggs on native trees and an increase in hard mast, like acorns and hickory nuts). The tree will also serve as another seed source for native- tree regeneration. Second, a healthier, bittersweet-less urban forest is better equipped to collect stormwater runoff and reduce flooding. It also means that we have more trees photosynthesizing, converting CO2 into O2, and providing cleaner air for New Haven. Lastly, de-vining brings people together. It’s a collective effort that has community-wide impact, and building community is at the core of URI’s work.

If you join a community group as a volunteer, you will get trained to ID many plants, including invasive vines. Once you’ve learned how to ID bittersweet, it’s hard to miss, with its gray bark and X-shaped ridges and lenticels. You can find it coiling around anything it can latch onto, including itself. When you come across a bittersweet vine, the protocol is to cut it down low, as low as you can go, and at eye level, too. Loppers are the tool of choice, but a pair of pruning shears works fine with some twisting and turning. If the vine is very large, a pruning saw will do.

Removing bittersweet can sometimes mean going into bushy areas where a trail hasn’t been cleared. As you traverse through forests or parks, keep an eye out for poison ivy. As the old adage goes, “Leaves of three, let it be.” The stem where the three leaves meet is red. In the winter, you can ID it by its brown, naked buds (no scales) and fuzzy-like vine. In general, leave all fuzzy vines alone (poison ivy and Virginia creeper) and remove hairless vines like bittersweet and porcelain berry (which has purple, blue, and pink berries).

Now that you know how important it is to remove invasive vines like bittersweet, what are you waiting for? Come help us de-vine New Haven! And don’t forget your loppers!

Photo credit: Anna Ruth Pickett (New Haven Climate Movement volunteers “de-vining” with Chris Ozyck in East Rock Park.)