Beating the buckthorn blues

In the mid-19th century, North America imported two species of Eurasian buckthorn—common and glossy—because they made lovely ornamental hedges.

Big mistake.

Today, its dense foliage and rapid growth help buckthorn, especially the common variety, crowd out native plants. The tall shrub has spread through forests, savannas, and towns in much of Minnesota and other states.

But it’s up against formidable foes like Mike Schuster, a researcher in the Department of Forest Resources. With his colleagues, he has opened up new avenues to controlling the green invader—and found some good news about its vulnerabilities.

For example, it had been thought since the 1990s that buckthorn seeds survived in soil for five or six years.

“We provided strong evidence that that was not based on data,” Schuster says. “We planted common buckthorn and observed it for up to four years. Across the 13,232 buckthorn seeds planted, germination occurred almost entirely in the first two years after planting. Therefore, the idea of a long-lived buckthorn seed bank was not realistic.”

Schuster’s work also showed that if buckthorn is replaced with fast-growing native species such as wild rye grasses, those plants will cover up and “shade out” much of the new buckthorn growth. Volunteers and professionals are putting this finding to use in many areas of the state through the U of M's Minnesota Invasive Terrestrial Plants and Pests Center’s Cover It Up project.

And to keep buckthorn stumps from resprouting, “We found that a herbicide not widely used, called fosamine, is really effective,” Schuster adds.

Horned heroes?

There’s one group that loves buckthorn: goats.

A recent study led by Tiffany Wolf, an assistant professor in the Department of Veterinary Population Medicine, and Daniel Larkin, an associate professor in the Department of Fisheries, Wildlife and Conservation Biology, probed the benefits of using goats to control buckthorn.

Goats readily graze on it, and work by Wolf’s former postdoctoral researcher Katie Marchetto showed that the animals didn’t spread the seeds. Marchetto discovered this by outfitting goats with diapers, feeding them buckthorn, and testing “what made it through.”

“Very few seeds—less than one percent—turned up in goat pellets,” Wolf says.

Goats browsing in wooded areas are at risk of being infected, often fatally, by a brainworm carried by snails and slugs. But the three researchers were also part of a study showing that if waterfowl graze along with goats, they eat the snails and slugs and may lessen the risk to goats.

Unfortunately, goats also eat native plants. However, “Native and invasive species come back after grazing,” Wolf says.

"The bottom line is that while goats can play a role as part of a sustained, multi-pronged strategy for buckthorn control, they’re not a panacea," Larkin says.