A new article from the University of Minnesota refutes a long-standing belief about the noxious plant common buckthorn, with implications for eradication efforts. Research at several sites, including in the St. Croix Valley, has indicated that the plant’s seeds only live for a couple years in soil, not the five to six years that had been accepted wisdom.

The scientists from the Minnesota Invasive Terrestrial Plants and Pests Center say the mistaken belief in buckthorn seeds’ longevity has given the plant an advantage by overestimating it.

“This should be good news for folks looking to remove buckthorn: you can cut down all the fruit-bearing trees and be confident that what remains after a year or two really is the extent of the problem. If we are more aggressive in those early interventions, we will likely have better outcomes compared to more selective approaches,” said lead author Michael Schuster, a researcher in the ​​Department of Forest Resources.

The idea that buckthorn seeds live in soil for up to six years has persisted over the past several decades. The scientists traced it back to a 1997 newspaper article about glossy buckthorn, a separate but related species, which introduced the concept and was then repeated in governments reports and other sources until it was considered accepted knowledge.

The new research was developed based on several study sites around central Minnesota, including two sites in Marine on St. Croix, where buckthorn had recently been removed. The scientists planted common buckthorn seeds in areas to provide consistent information. During subsequent years, they counted the number of seedlings growing at each location.

What they found was that 99.8 percent of all buckthorn seedlings emerged in the first two years after a mature stand of buckthorn was removed. Only one or two seedlings were seen after those first two years.

“Buckthorn forms these extremely dense carpets of seedlings — think of a massive Chia Pet on the forest floor — but that only happens in the first year after the mature trees have been cut down,” Schuster said. “So we were confused why we kept seeing this discussed as something that can happen over a six-year window.”

Buckthorn is native to Europe and was introduced in North America as a decorative or hedge plant. It has since spread widely, dominating the forest understory in many places. It pushes out native plants and has other harmful ecological effects, including causing increased soil erosion and runoff into streams.

Because buckthorn fighters have for a long time believed that the plant’s seeds can persist for so long in the soil, they have developed removal methods that let buckthorn regrow to some extent before a second treatment is needed. This has actually let the plant become a bigger problem, the scientists say.

“Prevailing buckthorn management strategies focus on repeated chemical and mechanical control of buckthorn over five or more years,” the new article concludes. “Our findings suggest that a shorter period of intense follow-up management may suffice if management criteria are broadened to incorporate smaller stems, since management during these initial years is likely to affect a much greater proportion of propugale pressure than previously thought.”

The research was conducted by a group examining the potential of using native plants to suppress buckthorn growth. The studies have been funded by the Minnesota Environment and Natural Resources Trust Fund, which receives revenue from the state lottery, as recommended by the Legislative-Citizen Commission on Minnesota Resources.

Reference:

Schuster, M.J., Wragg, P.D., Roth, A.M. et al. No evidence of a long-lived seedbank in common buckthorn, Rhamnus cathartica L., within Minnesota deciduous forests. Biol Invasions (2023). https://doi.org/10.1007/s10530-023-03113-4

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