Buckthorn Taking Over

by Mary Maguire Lerman

Woodlands and wetlands in Minneapolis may soon be pleading for their lives. An alien has invaded and threatens their very survival. This invader’s arsenal includes a vigorous root system, mycorrhizal root fungi, a long growing season, hungry birds, the advantage of no natural predators and an allelopathic effect on other plants. Say what?
Allelopathy is the suppressive effect of one plant on another through production and release of natural compounds. These compounds prevent nearby plants from thriving. You might have heard gardeners talk about black walnut and sunflowers causing this problem. In Minnesota, though, the woody plant that has earned the title of “Alien Allelopath” is buckthorn.
We have more than one type of buckthorn that is now a concern for Minnesota native landscapes. Look around your yard and neighborhood. Many homes have common buckthorn growing in their yards. It was most likely planted as a hedge 70 or more years ago. Native to Europe, it was imported to North America in the late 1700s and widely planted as hedging material until 1930. It has been out of the nursery plant trade since 1930 when research showed that it was the alternate host of crown rust of oats. However, someone forgot to instruct the songbirds that it should not be planted.
As a result, the songbirds have spread this plant so that it can now be found in every county in the state. Birds have limited landscaping skills, so they plant it wherever they stop to perch or feed. Buckthorn creeps up through fences, under roof/gutter lines and among other fruiting shrubs. Unfortunately, the birds forget limit their landscaping to private residences and businesses. Buckthorn grows commonly in woodlands and wetlands.
The woodlands and wetlands in Minneapolis are infested with common buckthorn. One only need to drive along Minnehaha Parkway, the River Road Parkways, through Theodore Wirth Park and along Diamond Lake to see its devastation. It is easiest to spot in late fall when our native trees and shrubs have dropped their leaves. At that time, the only shrubs left with green leaves are the common buckthorn.
The Minneapolis Park and Recreation Board is working with affected neighborhoods in the city to remove buckthorn in the woods and wetlands. Some say if it isn’t removed soon, future generations will not have the opportunity to enjoy the flora and fauna of woodlands and wetlands. The buckthorn suppress the native plants so that replacement native trees and shrubs are not developing in these areas. When a severe windstorm or other disaster destroys the mature trees in these areas, all that will remain is buckthorn thickets. It is not only the issue of buckthorn destroying native plant communities, it is also a park safety/visibility issue. Buckthorn thickets are so dense that many park users do not feel comfortable walking in areas infested with these shrubs.