06-26-2001 Agenda Packet - Laserfiche WebLink

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ALIEN ALLELOPATHS by Mary Maguire Lerman Mpls. Park and Recreation Board Have you heard that woodlands and wetlands in Minneapolis- and for that matter- throughout Minnesota are 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 direct or indirect effect of one plant on another through production and release of natural compounds. These compounds prevent nearby plants from thriving. You have probably heard gardeners talk about black walnut and sunflowers causing this to occur. Here in Minnesota though, the woody plant that has earned the title of "Alien Allelopath" is buckthorn. And boy do we have it. Right here in the City of Lakes. In fact, we have more than one type of buckthorn that is now a concern for our native landscapes. Look around your yard and neighborhood. Many of you have Common Buckthorn (Rhamnus cathartica) growing in your yard. It was probably planted as a hedge-likely 70 or more years ago. Native to Europe, it was imported to North America in the late 1700's and widely planted as hedging material until 1930. In St. Paul and Minneapolis, the number of buckthorn hedges is astounding. It has been out of the nursery 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. You will find buckthorn growing up through fences, under roof/gutter lines and among other fruiting shrubs. Unfortunately, the birds forget to limit their landscaping to private residences and businesses. You will find buckthorn growing in woodlands. The birds perch in trees on the edge of woods. Once the seeds in their droppings get established on the edge of native plant communities (where no one mows!), the buckthorn multiply, form"buckthorn brigades" and begin the invasion to the interior of these communities. The woodlands in the metropolitan area are infested with common buckthorn. Here in Minneapolis, you only have to drive along Lake Harriet Parkway, Minnehaha Parkway, the River Parkways and through Theodore Wirth Park 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, you will notice shrubs that have green leaves that often persist on the plant into December. That green mass is Common Buckthorn.