Alien invader in Minneapolis: buckthorn

You may have noticed in wooded areas throughout the Metro area the small shrubby trees whose green leaves linger into early winter after other leaves have dropped. These are buckthorn shrubs.

Buckthorn is a European shrub that was brought into Minnesota in the 1800s as a hedge plant.

Like purple loosestrife and Eurasian watermilfoil, these non-native plants are strong competitors in our native ecosystems. Free from the natural enemies (predators, diseases, parasites) of their homeland, non-native plant species can out-compete native species and cause harm to ecologically diverse native plant communities.

While Minnesota has recently banned the nursery production and sale of buckthorn, many hedges still exist in Minneapolis' neighborhoods, including Southwest.

Once you get acquainted with buckthorn you will be surprised how prevalent it is.

Buckthorn is a shrub or small tree that reaches a height of 15-20 feet with a trunk diameter of up to 10 inches. Buckthorn leaves are generally round, pointed at the tip and have toothed edges.

Buckthorn can be easily confused with native cherry trees, which have similar looking bark and purplish berries for fruit.

Birds easily spread buckthorn by feeding on the seeds and "depositing" them as they fly to other areas. Buckthorn shrubs are very aggressive and completely replace native shrubs, wildflowers and grasses.

A buckthorn-dominated woodland typically has taller canopy tree species such as oaks, maples, basswood and ash with a solid stand of buckthorn shrubs growing beneath the taller trees. This type of woodland with little plant diversity does not provide good habitat for wildlife and threatens native plant communities by eliminating them from their natural range.

The Minneapolis Park and Recreation Board has been working for years on buckthorn control in Minneapolis Parks. Working with neighborhood organizations, volunteers and staff the Park Board has removed buckthorn from many park areas, most notably: Robert's Bird Sanctuary near Lake Harriet, the Mississippi River Road and Cedar, Harriet and Calhoun Parkways.

Buckthorn is a very persistent pest. Removal efforts consist of cutting down and treating stumps with herbicides and hand pulling of the many small seedlings each tree produces. It is a laborious task that will continue for many years to come.

For more information on buckthorn, go to the following Websites: University of Minnesota Extension Service, www. extension. umn.edu; Minnesota Department of Natural Resources, www.dnr.state.mn.us and Minneapolis Park and Recreation Board, www. minneapolisparks.org.