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Common Buckthorn
(Rhamnus cathartica)

by Rick Meader

Buckthorn is so common in southern Michigan and regions of the United States and Canada that most casual observers aren’t aware they are relatively new to those areas. In fact, its densities are such that in some places its complete removal would make a significant change to the look of those areas.

IDENTIFICATION: It’s a coarse shrub or small tree with many low branches that support a rounded, bushy crown of crooked, stout branches. The small trees may reach a height of about 6m and have blackish bark which peels away as the tree gets older. Some of its branchlets end in short, conspicuous spines. The leaves are simple and range from alternate to subopposite to opposite in arrangement. The blade is 4-9cm long, ovate to elliptic in shape, with finely serrated margins, 3-5 pairs of noticeable, arcuate veins, an acute tip, and a short petiole. The winter buds are black to dark brown, almost claw-shaped against the twig.

FRUIT: The fruits are a multiple of purplish-black, round drupes that are about 6mm in diameter and contain 2-3 nut-like pits, each enclosing a seed. They mature in August-September and are persistent throughout the winter. The seeds are excreted by birds (which is the primary method of dispersal), and young buckthorn seedlings are often found beneath bird perching trees.

SITE: It is fairly shade-tolerant and grows on a variety of sites, but favors moist, well-drained calcareous soils near streams or riverbeds, open woodlands, fencerows and woods edges. It does not do as well in very dry sites.

ORIGINS: Common buckthorn is a native of England, eastward through Scandinavia and Russia, and on into western Asia. It is also found at lower elevations as far south as Morocco and Algeria. It was introduced to North America by people living in the eastern United States in the second half of the 19th century, apparently for use as edging (introduction in eastern Canadian cities soon followed). The plant’s tolerance of a wide variety of soils and sites, its hardiness, and its dense growth and persistent greenery made it ideal for widespread use in tall hedges.

NORTH AMERICAN RANGE: Once the plants became adapted to the conditions in North America, they soon spread out from their planted sites. Human plantings, large numbers of seeds, high seed vitality and rapid germination gave them a strong competitive edge versus native species. Their tolerance to a variety of site and light conditions have helped them expand widely. Currently, the range of R. cathartica in North America is an area bounded by Saskatchewan, Canada, in the northwest, Nova Scotia in the east, North Carolina in the southeast, and northeastern Kansas in the southwest.

MEANS OF COMPETITION: The prolific nature of buckthorn makes it invasive in the worst sense of the word. Once established in an area, it quickly becomes the dominant midstory or understory shrub or tree in areas with conditions favorable for its development, outcompeting many native species. Its heavy seed production and strong vitality shut out other plants from growing beneath its dense canopy.

ERADICATION: In order to restore natural areas to a more natural condition, a variety of methods have been used. Girdling, cutting, cutting and painting the stumps with a Garlon 4 and oil mixture, or cutting and painting the stumps with a Roundup solution and prescribed burning have all been used with varying effectiveness.

The most recommended and effective method of eradicating buckthorn is a multistep process. First, in fall or winter when surrounding plants are dormant, cut the trees and paint the stumps within minutes of cutting with a 10-20% solution of Roundup. Second, use repeated prescribed burns to knock back any resprouts from the root collar, as well as to kill off the hundreds of seedlings that suddenly have lots of sunlight with the demise of their parent. Of course, you must establish a healthy population of replacement plants (preferably native) to prevent the buckthorn from being reestablished following the cuts and burns. One team in Wisconsin found that when a seeding of native grasses and forbs was added, resprouting of buckthorn seedlings was limited by the sod created by the native plants, and the fire continued to knock back the buckthorn seedlings that did sprout (Scriver and Leach, 1998). Buckthorn is a tough customer, so be prepared to do some consistent, engaged action against the intruder, and with continued effort you can get your land back for more desirable native plants.

Bibliography

The Canadian Field Naturalist III(4), Archibold, O.W., D. Brooks and L. Delanoy, 1997.

Michigan Trees, Barnes, B.V. and W.H. Wagner, Jr., 1996.

Restoration and Management Notes 16(1), Scriver, B. and M. Leach, 1998.

Article reprinted from the Spring 1999 issue of the Ann Arbor Wild Ones Newsletter.
Copyright © 1999 Wild Ones–Natural Landscapers, Ltd.

 

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