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An Unwanted Guest Hiding Among Our Fall Colors?

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Few sights are more breathtaking than October fall colors in the Southern Appalachian Mountains. When precipitation and temperature occur in optimal sequence during the months leading up to October, this color is simply spectacular. Driving along roads and highways can actually be pleasant, rather than stressful, such is the therapeutic effect in nature’s autumnal gift of color.


The color yellow stands out particularly well among tulip poplar, hickory, and striped maple trees. But even red maples share their scarlet tints with bright yellow patterns amid their foliage. And, the leafy vines of native poison ivy also advertise their presence with this color, offering at least one redeeming feature to us humans. Perhaps the species is apologizing for causing our itching misery when accidentally brushing against it in greener times.


But, among those golden leaves seen growing along roads and trails at this time of year, there is one showy plant snaking its way up the tree trunks that is an uninvited guest. Its most notable feature is seen in the form of one or many of its vines wrapping around each other and the trees it climbs. And, along with its bright yellow changing leaves, this unwelcome intruder also exhibits showy orange-red berries once it reaches a mature stage. The name of this plant is Oriental Bittersweet (Celastrus orbiculatus).


Why is it unwelcome? The vine shares many undesirable characteristics with other non-native invasive plants (NNIP). It competes with native species for space, water, sunlight and nutrients, interferes with natural succession, and reduces biodiversity. In addition, bittersweet strangles young trees, killing them before they can reach maturity. It also produces numerous berries which easily germinate and then the vines spread quickly.

It's interesting that many or most people are familiar with kudzu, another NNIP whose above ground vines spread quickly, but are unaware that oriental bittersweet is a far greater threat to forest ecosystems. Kudzu only grows in full sun and partially sunlit forest edges, and it mainly appears where it was originally planted for erosion control along highways. Bittersweet will grow in the sunlight or under deep shade in the middle of a remote forest canopy. Kudzu produces a few seeds within pods, like other members of the bean family, but has a poor method of spreading its seeds (few native birds and mammals recognize it as food) Instead, it spreads mainly underground from a relatively slow-growing network of roots and root crowns. But bittersweet produces a fecundity of berries that are widely consumed by birds. They then spread the seeds far and wide, unfortunately reaching into interior forest stands. Besides strangling saplings, bittersweet will climb mature trees and eventually cover the canopy with its branching vines and leaves, shading the native canopy from life-giving sunlight. Without a sufficient amount of foliage to photosynthesize sugars for their trunks and roots, trees cannot survive.


Oriental bittersweet was first introduced into the United States in 1874 by Thomas Hogg, Jr., who served first as a U.S. Marshall assigned to the Japanese Consulate (1862-1869) and later as an advisor with the Japanese Customs Service (1873-1875). He was also an avid gardener and plant collector who brought a number of Japanese native plants to the U.S. on his return trips and, during his latter term, he brought bittersweet to his family’s nursery in New York. He distributed it to other horticulturists and it became listed in the first nursery sales catalog by 1887. It was highly praised as a showy ornamental vine by a number of plant nurseries and Harvard's Arnold Arboretum Horticulturist, Donald Wyman, promoted it in numerous articles beginning in 1939. Curiously, he was still praising it in 1964 while also noting that its "vines are vigorous twiners and can become vicious pests." It was not until 1973, when Duke University doctoral student, David Patterson, described bittersweet's harmful impacts in his thesis, that alarm became widespread about the species' aggressive and invasive habits. Since that time numerous studies have increased this concern and efforts were begun to control its spread.


Though bittersweet had appeared in North Carolina by the end of the 19th century, it is interesting to note that the Biltmore Nursery was selling bittersweet plants up to two feet tall in 1907 for 15 cents each, $1.50/dozen, and $10.00/100. That was 116 years ago. This likely explains why the Asheville area and immediate adjacent counties are so densely infested with the plant today.


For more information on non-native invasive plants, NNIP removal, and replacement with native insect and wildlife attractive plants, visit "Services" at www.restoraflora.com.


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