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Species Abstracts of Highly Disruptive Exotic Plants

at Effigy Mounds National Monument

Rhamnus cathartica


Park: Effigy Mounds National Monument (EFMO)
Species: Rhamnus cathartica L.
Common Name: Common buckthorn
Urgency Ranking: High
Overall Ranking: 2
Significance of Impact: 74
A. Current impact: 33
B. Ability to be a pest: 41
Feasibility of Control: 31

Taxonomic Description:
Common buckthorn is a deciduous, polygamodioecious, spiniferous, small tree or profusely branched shrub (1-5 m tall). Leaves are mostly opposite, simple, broadly elliptic, and oval or obovate (2.5-7 cm long and 2.5-5.5 cm wide) with two to three main lateral veins. Leaves are glabrous with the tips abruptly acuminate, the base is rounded to cuneate, and the margins are irregularly serrate with six to eight teeth per centimeter. Petioles are grooved (3-5 cm long), slightly pubescent above, and glabrous below. Stipules are often persistent, linear (3-5 mm long), and glandularly toothed. Staminate inflorescences are axillary clusters of two to eight flowers on current year's spurs. The calyx is green, expanded into a campanulate hypanthium (1.5-2.5 mm long and up to 2 mm wide), and four-lobed. Lobes are 2-3 mm long. The corolla consists of four petals. Petals are lanceolate (1-1.3 mm long) and yellowish-brown. Each of the four stamens (2 mm long) is attached below the hypanthium. Pistillate inflorescences are in axillary clusters of two to 15 flowers on current year's spurs. The pistillate calyx is similar to the staminate calyx. Petals are usually absent. If present, they have four linear yellowish-brown lobes (about 0.75 mm long). The ovary is globose (1 mm wide and high), green, and attached at the base to the hypanthium. The fruit is a drupe (6-8 mm in diameter) and is black, smooth, juicy, and found singly or clustered at the base of new growth. Each drupe contains four seeds. Seeds are gray, ovoid (4-5 mm long), and pointed. The inner surface is prominently ridged, and the outer surface is grooved. The twigs are spine-tipped, slightly flattened, yellowish-brown to gray, smooth, and glabrous. Lenticels occur as narrow vertical slits. The bark of the trunk is slightly scaly and light to dark gray in color with horizontal lenticels.

Biology/Ecology:
Common buckthorn is a native to Europe and is now naturalized in most of northeastern North America. It was probably introduced to North America in the 1800s for use as hedges, shelter belts, and wildlife habitat. The naturalized habitat includes pastures, fence rows, roadsides, and ravines. Common buckthorn invades logged or grazed woodlands, disturbed forest edges or openings, prairie thickets, and open oak woodlands. It grows in neutral to alkaline, well-drained, sandy or clayey soils and in poorly drained calcarious soils. Common buckthorn will tolerate a small amount of shade but grows most vigorously along the edges of woodlands and on sunny exposures of southern or western slopes.

Common buckthorn will quickly reach reproductive age. It flowers from May through June, and the fruits ripen from August through September. It is a prolific seed producer. Seeds are efficiently distributed by many wildlife species including blackbirds, starlings, cedar waxwings, robins, bluejays, wood ducks, and mice. Seeds can also be dispersed by water.

Common buckthorn has a long growing season and a rapid growth rate. It vigorously sprouts from buds below the soil surface. Leaves appear in late April to mid-May and are retained until late October or early November. It forms thick, dense, virtually impenetrable, even-aged stands. If growing in an open area, the crown will expand until it touches the surrounding vegetation. Seedling establishment under the canopy and into other shaded areas is limited.

Distribution:
An intermediate number of common buckthorn plants occur at Effigy Mounds National Monument (EFMO) combining to cover an area of less than 5 hectares. These plants are found in mid-successional sites disturbed between 11 and 50 years ago. Common buckthorn was found in the forested areas of the South Unit. Although the effects of common buckthorn on native herbaceous vegetation is not well known, it is apparent that it will readily invade and replace the native plant communities in areas where light is not a limiting factor. It poses a threat to the areas' primary successional resources. The plants have a significant visual impact on the vegetation of EFMO.

Control:
Common buckthorn is susceptible to several methods of control. However, most methods will require repeated treatment because of common buckthorn's resprouting ability. Information on the seed bank ecology of this species is not available.

An important consideration prior to applying any control measure is to determine if enough desirable plants are present under the canopy of common buckthorn to replace the eradicated plants. If desired vegetation is scarce or absent, response of the desired vegetation will be slow. Most control methods harm other plants and may result in disturbances that favor reinvasion by common buckthorn or other exotic species.

Cultural controls for common buckthorn are typically ineffective and may encourage resprouting or seedling establishment. Prescribed burning may furnish limited control. Rarely enough fuel is present to carry an adequate fire near the target buckthorn because it shades out understory species. Some studies have suggested that a late April or late May prescribed burn may top kill small plants. Root reserves will be low at this time and resprouting may be reduced. It has been shown that burning at an incorrect time may stimulate resprouting. Annual prescribed burning to maintain the vigor of the native vegetation is one approach to control. Burning may result in seedling invasion on the newly exposed soils. Grazing may reduce the vigor of preferred vegetation and result in the invasion and expansion of this species.

Mechanical control methods of common buckthorn have the potential to reduce plant vigor and numbers, but may stimulate resprouting. Early June and late August cuttings or mowings applied for 2 or 3 successive years has been shown to reduce stem heights and numbers. Girdling has been shown to be an effective control measure and does not appear to encourage resprouting. A 2 to 3 cm wide cut into the phloem during the winter will effectively kill the above ground portion of the plants. Hand pulling or grubbing of seedlings or small plants may be effective, but the resulting soil disturbance may encourage new seedling establishment. Underplanting with native woody species to prevent invasion by common buckthorn has resulted in limited success.

Chemical control appears to be the best method available for control of common buckthorn. Many herbicides are not specific to common buckthorn or may not be specifically licensed for this use. It is important to read and follow all label directions.

Stump application of a 20% solution of Roundup (glyphosate) applied after cutting in August or September, or wick application of a 2-3% solution in May, has successfully controlled common buckthorn. A September mist application of Krenite S (fosamine) has been reported to provide control. Basal application of a 2-4% solution of 2,4-D or 12.5% 2,4-D in diesel fuel during the early part of the growing season has been effective. Basal application or a broadcast spray of Tordon (picloram) or Velpar (hexazinone) have provided control of common buckthorn.

Little work has been done on the biological control of common buckthorn. It serves as an intermediate host for oat rust (Puccina coronata) but does not appear to be significantly effected by it. Some work has been done in Canada on the ability of the insects Scotosia vetulata Schiff. and Triphos dubiata L. to control common buckthorn.

References:

Converse, C.K.  1985.  Element stewardship abstracts for Rhamnus cathartica and
     Rhamnus frangula.  The Nature Conservancy, Minneapolis.  20 p. 

Foster, R., E. Knake, R.H. McCarty, J.J. Mortvedt, and L. Murphy (eds.).  1994.
     Weed control manual. Meister Publishing Company, Willoughby, Ohio.  362 p.

Great Plains Flora Association.  1986.  Flora of the Great Plains.  University 
     of Kansas Press, Lawrence. 1392 p.

Malicky, H., R. Sobhian, and H. Zwolfer.  1970.  Investigations on the 
     possibilities of a biological control of Rhamnus cathartica L. in Canada:
     Host ranges, feeding sites, and phenology of insects associated with European
     Rhamnaceae.  Zeitschrift fur Angewandte Entomologie  65:77-97.

Stephens, H.A.  1973.  Woody plants of the North Central Plains.  University Press
     of Kansas, Lawrence. 530 p.


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