Scourge of the forest: Oriental Bittersweet

For years now, I have periodically engaged in a bitter personal vendetta, directed toward the invasive species that have confidently taken up residence on my property of mixed hardwoods and grassy meadows.

Over the past few centuries thousands of exotic species have left their ancestral homes for distant shores and, like many an immigrant, found there a better life. Freed of the diseases and predations of their native range, they often find it possible to establish themselves in a stronger position than their situation at home would have permitted. While opportunity is a positive thing for the opportunist, it also brings disruption and displacement to the host. The ecosystems of our planet were already diverse and thriving, and none of these species were actively seeking to improve their lot by wholesale migration, when we humans decided to improve our own lots by inviting them along on our travels. Today, it is as if we are living in our own fractured fairy tale, where Jack has gone to seek his fortune, and invited Henny Penny, Turkey Lurkey, and Ducky Daddles along for the trip — and now, the sky is falling.

The usual suspects

Thus a group of shrubby, exotic species have spent more than a decade building a claim of adverse possession to key areas of my domain. The doctrine of adverse possession applies when one’s usage of another’s property is hostile, actual, open, notorious, exclusive, and continuous. All of these elements are embodied in the growth habits of Autumn Olive, Buckthorn, Amur Honeysuckle, Tree of Heaven, Multiflora Rose, and Oriental bittersweet, which round out a list of some of the most aggressive and unwelcome invaders in eastern North America.

First, my attention was focused on autumn olive. I spent several years with loppers and chainsaw trying to eradicate this shrub, where it had already taken over a large part of the meadow, which had formerly hosted a hay pasture. Autumn olive was also infesting much of the woods, choking out understory plants and changing the chemistry of the soil with its nitrogen-fixing properties. Its sage-to-silver leaves and speckled red berries, perhaps quite attractive and appealing in its native context, became embedded in my mind as symbols of dread. My eye has become so attuned to this stimulus that I can even spot Autumn olive saplings when driving down the freeway.

Sage-green saplings of Autumn olive, on a yellow carpet of another invasive, Cypress spurge.

Later, I discovered its primary partners in vice: Amur honeysuckle and common buckthorn. World travelers alike, they were overstaying their layover on my small farm, and completed the triumvirate of terror that characterized my first few years of shepherding this property back to its native form. Armed again with loppers and herbicide, I added these invasive shrubs to my own bitter itinerary.

At that point, I felt confident that my list of intruders that deserved termination with extreme prejudice was complete. And for a time it seemed to be so. I did remember at one point noticing a twisty vine that seemed to be threatening to girdle a tree — but there was only one instance that I could see, so I dismissed it as an odd fluke of forest growth.

But last fall, I decided to cut a hiking trail through the woods — partly for recreation during the pandemic, but also to gain better access to the honeysuckle, autumn olive, and buckthorn that I had not been able to remove previously. That was when I became fully acquainted with the real scourge of the midwest forest — Oriental Bittersweet.

Oriental bittersweet, in the first stage of its evil plan.

Here comes top critter

Oriental bittersweet, Celastrus orbiculatus, is a tree that acts like a vine, beginning life with a flexible, almost rubbery stem that needs the support of other trees in order to grow upwards and receive enough light to survive. In a forest, it can grow just high enough to lean toward a tree, and once in contact, will wind around it multiple times as it grows, achieving a berth from which it can wind upward to infinity. Because it does not physically attach itself to the tree, like Boston ivy or poison ivy would, it relies on close contact to stay in place. There is only one problem with this plan. As time passes, both the host tree and the vine will grow in thickness. At some point, they begin to interfere, as the vine grows into the tree, and the tree grows outward into the vine. The vine always wins the battle, because its outer side remains intact while the tree is completely surrounded by the vine. Thus it is only a matter of time before the tree is strangled and killed.

Oriental bittersweet, girdling and killing a young tree.

Among bittersweets, there are multiple varieties, including an American bittersweet, Celastrus scandens, that is native to North America. But for some reason, someone, somewhere, felt that C. scandens was not enough to satisfy their gardening interests. Thus another variety, C. orbiculatus or Oriental bittersweet, was brought to North America from its native range in Eastern Asia, probably in the late 1800s. Today, it is endemic throughout many parts of the midwest. In fact, it appears to be spreading more rapidly of late, if my experience with it is indicative. I am quite certain that ten years ago, there was little to no bittersweet on this property, but today it is rampant. In some spots, it has already killed and then toppled mature trees, leaving in their place a mound of dead branches covered by a mat of its own vegetation. By all signs, it is gearing up to decimate this forest, and it would, if left undisturbed for only a few more years.


So if you see a vine winding its way up a tree, how do you know if it’s Oriental bittersweet, or the native variety, which does much less damage?

First, there are indeed other types of woody vines that climb trees, and many of them are relatively innocent. Poison ivy is one. It may not be innocent of mischief, but it is native, and it is relatively innocent of injuring the trees that host it. Poison ivy has a vine that goes more or less straight up the tree, attaching itself to the bark by means of thousands of sticker-like tendrils that make the vine look somewhat wooly or hairy where it meets the bark. Although it does cause skin rashes if you come in contact with it, poison ivy is actually an important food source for birds, due to its white berries that stay on the vine well into the winter. If you’re in no danger of brushing against it on a regular basis, it’s a sign of good stewardship to simply let it play its part in the ecosystem.

Another widespread vine, also native, is the wild grape. In my low-lying, historically marshy region, I believe it is Vitis riparia that is the dominant species. These vines have a shaggy bark, and do not loop around the trunk of the tree they climb. Much like a squash vine, they climb primarily by smooth spiral tendrils that grab onto branches and twigs during the summer months, when the vine is leafy and putting out clusters of grapes. It is a benign and beneficial native that is a sign of a healthy forest.

By contrast, the bark of Oriental bittersweet is relatively smooth and sleek, especially when young. Telling the difference between it and the native bittersweet can be difficult, but if the berries are on the vine (in fall to mid winter), it becomes much easier.

On close inspection, I was able to find a single example of the native American bittersweet amid the invaders. It was gently trailing up into the canopy, terminating in a blush of red berries, and much less aggressive in its growth habit, with no instances of tight looping that would have girdled the tree. As you can see below, except for the red berries, its presence can hardly be distinguished from the trees that support it, since it isn’t actively killing the tree it’s climbing. The bark of the vine that bore the berries was also a bit darker and earthier, looking much less like a coiling snake, as it rose into the sky.

Its berries were a little different from those on the other, larger, tree-strangling vines I was removing. This allowed me to make a direct comparison between the berries of each variety, and confirm that what I had here was indeed the native variety, and not the invasive. When berries are on the plant, American bittersweet can be distinguished from the invasive variety by looking at the capsules that surround the red berries, and how the berries grow on the twigs.

On the left, the native American bittersweet. On the right, invasive Oriental bittersweet.

As seen above on the right, Oriental bittersweet — the evil invader — has yellow capsules around the berries, while the American bittersweet, on the left, has capsules of a richer orange, sometimes even approaching the color of the red berries themselves.

Another more subtle sign is how the berries grow on the twig. The berries of American bittersweet appear in a single cluster at the terminal end of a long twig, whereas Oriental bittersweet has many shorter stems coming off a central twig, each of which contains its own cluster of berries. This can also be seen in the photo above. I suspect that this gives Oriental bittersweet an advantage in terms of sheer volume of berry production. Even after the berries are gone, you can sometimes detect an Oriental bittersweet by looking at the ground below the vine, after the capsules have fallen off in early winter. The berries may have already disappeared in the bellies of birds, but so many berries have shed their yellow capsules in the process that they may litter the forest floor in spots — often near the trunk of the tree that hosts the vine, which I imagine is where birds like to roost while picking apart the clusters.

Adding to its bad behavior, Oriental bittersweet can hybridize with American bittersweet, meaning that the vine you see might resemble American bittersweet, but have some of the invasive characteristics of the invader. If you permit an infestation of the foreign variety to continue, it will rapidly outnumber any natives that you might happen to have, and pollute their gene pool for good measure.


My approach to killing Oriental bittersweet was simple: use loppers to cut the vine near the ground, and paint the cut end with 41% glyphosate, using a one-inch paint brush. This minimizes over-application of this herbicide, which I don’t completely trust despite its widespread use. While I prefer to avoid herbicides entirely, it is simply not a viable option when dealing with many invasive species, which will resprout even if cut off at the ground. I feel that man-made problems have man-made solutions. While I do not agree with the indiscriminate, gratuitous spraying of glyphosate over an entire crop field as a routine practice of farming, I am fully in support of its targeted use to help reverse the other misjudgments our species has committed.

To give an idea of how aggressive Oriental bittersweet really is, consider this piece of debris salvaged from the brush pile that resulted from one of my vendettas. The main part of the vine is more than 2 inches in thickness, and had already found a good solid berth in the upper part of the tree it was climbing, when a skinny branch from the same vine decided to try the same thing, and girdled its own parent.

Depending on your inclination, this may resemble the beginnings of a natural harp, or a natural bow and arrow (sans arrow). But after a winter of cutting, piling, and burning this aggressive and snaky vine, I see it as divine justice.

In another manifestation of justice, in many cases, the trees that I found being killed by this indiscriminate climber were the very autumn olives, buckthorns, and honeysuckles that were in line for eradication by me. This forest had become so weedy with invaders that they were taking part in their own parallel cycle of unnatural succession — a battle among compatriots, which the bittersweet is strongly favored to win.

As human activity continues to include the unregulated propagation, sales, and purchase of exotic species at home improvement chains and nurseries across the country and across the world, what will become the next top critter? We should shudder to think.

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