|Seedlings of Common Buckthorn rise from the seedbank after an area is cleared of larger plants. Suppressing reinvasion |
is a major challenge of Buckthorn management.
Researchers at the University of Minnesota rank Buckthorn high on their list of problem invaders. They’ve been studying Common Buckthorn, Rhamnus cathartica, and Glossy Buckthorn, Frangula alnus, for years, and last summer they shared some of their findings.
Their white paper, Managing Invasive Buckthorn, focuses on two areas of research: goat browsing to manage Buckthorn growth and native plant cover to suppress reinvasion. Here are highlights from their work.
Goat Browsing Has Potential – and Pitfalls
On steep hillsides or other inaccessible places, goats are an alternative for removing buckthorn. Their browsing and trampling can reduce Buckhorn abundance and open the canopy, allowing more light to reach other plants.
Goats are most effective on small Buckthorn within the animals’ reach. To limit damage to other plants, fall is the best time to release the animals, but that’s also when they’re most at risk of acquiring meningeal worms. These brain parasites can infest snails and slugs that the goats also consume while browsing. Co-grazing ducks and geese with goats can lessen the risk, as waterfowl can eat infested snails and reduce their numbers but not get sick.
Goats don’t eat just Buckthorn; they’ll eat other plants, too, including desirable ones. Some plants may rebound the following year, but they’ll be competing with Buckthorn that also resurges under the newly opened canopy. As explained in the next section, that’s why establishing cover is important after Buckthorn is removed, whether by goats or other means. A good way to suppress Buckthorn’s return, the researchers found, is to increase competition.
Part of this Buckthorn thicket was cleared with a forestry mower. Just a few
years later, it has regrown to become as dense as the unmowed portion.
Native Cover Suppresses Reinvasion and Rebuilds Communities
Buckthorn management doesn’t end when the plants are cleared from an area. Reinvasion and a return to dominance are common, because Buckthorn can regrow from the seed bank or from cut stumps that weren’t treated with herbicide.
Fortunately, the researchers discovered a way to suppress reinvasion. They experimented with dense plantings or seedings of trees, shrubs, grasses and forbs and found that if light availability under plant cover drops below 3-4%, Buckthorn regrowth is limited. In closed forests with less light, planted trees and shrubs worked best to establish that cover. In more open areas, such as oak woods, both planted stock and seeded grasses and wildflowers were effective. The scientists are now experimenting with less dense planting and seeding.
Even after plant cover is introduced, it is important to monitor a site for germinating or sprouting Buckthorn. As the native planting matures and casts more shade, removing Buckthorn should become easier as fewer plants survive. It’s a years-long effort, but with the right combination of techniques, Buckthorn should recede as the native plant community returns.
For help identifying Buckthorn in winter, see this updated post from January 2021 or download this free, two-page guide. Additional Buckthorn information is available from the Minnesota Department of Natural Resources and the Minnesota Department of Agriculture.
Bernhardt, C., et al. 2022. Managing Invasive Buckthorn. University of Minnesota College of Food, Agricultural and Natural Resource Sciences and the Minnesota Invasive Terrestrial Plants and Pests Center. CFANS-Buckthorn-White-Paper-June-2022.pdf (umn.edu)