Dave Taft Thick, twining and handsome, Oriental bittersweet (Celastrus orbiculata) has been introduced into countless gardens since the mid-19th century. In the wet dark weather of fall, the vine covers itself with orange and yellow berries. Some sources claim it is these strongly contrasting berries from which bittersweet derives its name. Whatever the source, every autumn I find myself lamenting that “bittersweet†more perfectly describes the ecological havoc that this beautiful nonnative plant wreaks upon habitats so far from its home in China, Japan and Korea.
You have to admire a plant that can make itself at home in so many places, through so many means, under so many conditions. Bittersweet is comfortable gracing the fancy, fall-inspired table settings and centerpieces of florists and caterers; it is the perfect complement to pumpkins, autumn leaves, gourds and grapes. It is equally at home in our local woodlands. I would be hard-pressed to find a grassy verge, a forest, a fence line or a meadow in any of New York City’s five boroughs without it.
Oriental bittersweet does its worst in a blaze of autumn glory.
The mechanism is fairly simple. Bittersweet is spread by the many birds that eat its berries and distribute them wherever they perch. The thick, leafy vines rapidly overtake trees, shrubs, even grasses, outcompeting and eventually smothering them. Supporting plants break under the weight or die from excessive shading. During Hurricane Sandy, woodlands with large amounts of bittersweet seemed to suffer more downed trees, as the vines produced additional drag during the storm’s intense winds. Especially in coastal areas where sandy soils cause trees to grow shallow surface roots, the vines can topple trees.
Another rather specific threat posed by the explosion of Oriental bittersweet is its gradual displacement of Celastrus scandens, our closely related native bittersweet. With flowers and berries growing only at the tips of its new growths (Oriental bittersweet grows berries from leaf axils along the length of its stems), American bittersweet has become quite rare. With similar flowering periods and overlapping habitats, Oriental bittersweet outcompetes its American counterpart and, more insidiously, often hybridizes with it. The offspring are often intergrades between the two species, displaying aspects of each parent.
In a few short weeks, the woods will be alive with bittersweet’s yellow and orange berries. Gathering the vines’ long, twisted strands for holiday wreaths has become a useful and popular public program in parks and other sites plagued by masses of the plant. The best time for these activities is now, just before the orange centers of the berries are exposed. But be sure you are actually making a wreath from the nonnative plant, because American bittersweet has become a threatened plant in our area. Perhaps more important, be sure to remove and destroy the berries on your wreath before disposing of it, lest you spread more of this beautiful problem to places not yet graced by its bittersweet beauty.
