Cover it up! Using plants to control buckthorn

Background

Common buckthorn (Rhamnus cathartica) is an invasive shrub that outcompetes native plants and degrades Minnesota forests. Minnesotans spend millions each year removing buckthorn from their properties, yet they find the invasive shrub returning to the same spots again and again. Removal of buckthorn is a common forest management activity, but may only provide short-lived benefits since buckthorn has been known to rapidly regrow.

In grasslands, heavily seeding native species can restore native communities and inhibit invasion, but this approach is rarely used in forest management (Schuster et al. 2018). 

This research team investigates whether they could similarly establish enough native plants in forest settings to prevent buckthorn from re-establishing.

Outcomes

Reich and team developed strategies to improve and diversify the native plant community while discouraging buckthorn reestablishment. 

They defined buckthorn shade tolerance, and found that dense plantings of native grasses, wildflowers, sedges, ferns, shrubs, and juvenile trees (specifically those that provide heavy shade in spring and fall) can provide enough shade to suppress new buckthorn growth. Seeding woody species was more effective at creating rapid shade cover than bare root planting of the same species.

The team made a significant discovery regarding buckthorn seed viability. They overturned long-held conventional wisdom that buckthorn seeds can persist in the soil for up to 6 years. Instead, they found that seeds survive in the soil for 1 to 2 years. This may decrease the resources needed to maintain a site after buckthorn has been removed.

This project team established a citizen science network to contribute to the research. Volunteer participants established 600 plots throughout Minnesota to evaluate how native seeding works to suppress buckthorn.

In the last phase of this project which ended in 2024, researchers found that the abundance of native tree and shrub stems is a more important factor in suppressing buckthorn re-establishment than were the identity of the woody stems. In their experiments, areas that had more native trees and shrubs (including volunteers) had fewer buckthorn. Researchers recommend that land managers focus on establishing the greatest number of native stems as possible and to take advantage of naturally establishing species for the area. Choose species which work best for the site conditions and management goals rather than using prescribed species based on this project. Researchers produced a management guide on revegetation after buckthorn removal.

This project illustrates the value of adaptive management that leverages natural tree regeneration and augments native stem densities through strategic planting.

For related research, see: Making revegetation as part of buckthorn management feasible in Minnesota.

Publications

• Revegetation of Elymus grasses suppresses invasive Rhamnus cathartica in deciduous forest understories (Ecological Engineering, 2024)
• Understory revegetation enhances efficacy of prescribed burning after common buckthorn (Rhamnus cathartica) management (Natural Areas Journal, 2024)
• A guide to forest understory revegetation: To help manage buckthorn and other invasive plants (2024)
• No evidence of a long-lived seedbank in common buckthorn, Rhamnus cathartica L., within Minnesota deciduous forests (Biological Invasions, 2023)
• Using plants to control buckthorn (Rhamnus cathartica): Improved biotic resistance of forests through revegetation (Ecological Engineering, 2022)
• Managing Invasive Buckthorn, white paper (College of Food, Agricultural and Natural Resource Sciences, 2022)
• Revegetation to slow buckthorn reinvasion: strengths and limits of evaluating management techniques retrospectively (Restoration Ecology, 2021)
• Phenological niche overlap between invasive buckthorn (Rhamnus cathartica) and native woody species (Forest Ecology and Management, 2021)
• Fosamine ammonium impacts on the targeted invasive shrub Rhamnus cathartica and non-target herbs (Invasive Plant Science and Management, 2020)
• Increased light availability due to forestry mowing promotes regeneration of invasive European buckthorn (Restoration Ecology, 2020)
• Phenology matters: extended spring and autumn canopy cover increases biotic resistance of forests to invasion by common buckthorn (Rhamnus cathartica) (Forest Ecology and Management, 2020)
• Using revegetation to suppress invasive plants in grasslands and forests (Journal of Applied Ecology, 2018)

Outreach and presentations

• North Dakota State University and University of Minnesota Extension Sheep/Goat Webinar, 2024
• Weed Inspectors of Hennepin County, 2024
• Maple Grove Rotary, 2024
• Wisconsin Woodland Owners Association, 2024
• Prairie Enthusiasts St Croix Valley Chapter, 2024
• Prairie Enthusiasts Conference, 2024
• Friends of Eden Prairie Parks, 2023
• Using Plants to Control Common Buckthorn, webinar hosted by the Invasive Species Centre (2023, video)
• Woody Invasive Species Advisory Panel, 2023
• Upper Midwest Invasive Species Conference, 2016, 2018, 2020, 2022
• Legislative Citizen Commission on Minnesota Resources, 2022
• ​​Minnesota Department of Natural Resources, 2021
• CitSciVirtual Conference, 2021
• Ecological Society of America, 2020
• Minnesota Noxious Weed Advisory Board, 2020
• Gathering Partners Conference, 2019
• Duluth Cooperative Invasive Species Management Area, 2019
• Duluth Invaders R2ED Team, 2019
• UMN Undergraduate Research Symposium, 2018
• St. Croix Research Rendezvous, 2018
• Legislative-Citizen Committee on Minnesota Resources, 2018
• Metropolitan State University Natural Sciences Seminar, 2018
• MITPPC Buckthorn Symposium, 2017
• Floodplain Forests Group, 2017

News and media

• The secret to fighting invasive buckthorn is native Minnesota plants (MSN, 2025)
• Ep. 509 - The Power of Biotic Resistance (In Defense of Plants podcast, 2025)
• New research shows grasses can fortify forests against buckthorn invasion (UMN Twin Cities News, 2024)
• Beating the buckthorn blues (University of Minnesota, 2024)
• In the battle against buckthorn, patience and plants are winning strategies (East Metro Water, 2024)
• A Thorny Problem: Invasive buckthorn is damaging to landscapes and notoriously hard to control (Minnesota Conservation Volunteer, 2024)
• Meet the researcher: Mike Schuster and the quest to outstep buckthorn (MITPPC, 2023)
• Scientists think a fungus could conquer invasive buckthorn (Star Tribune, 2023)
• Researchers say seeds from invasive buckthorn don’t live as long as previously thought (St. Croix 360, 2023)
• U of M Research Project Reveals New Information on Buckthorn (WJON, 2023)
• Uprooting decades of buckthorn management practices: no long-lived seedbank (UMN News, 2023)
• Talking invasive buckthorn management with U of M (UMN News, 2022)
• Why is buckthorn a problem? (video, Fox 9, 2022) 
• In retirement, Minneapolis man takes on stubborn foe: Buckthorn (Star Tribune, 2021)
• Buckthorn Phenology and Possible Management Strategies with Mike J. Schuster (Podcast To Know the Land)
• FMR's ecologists investigate how to suppress buckthorn (Friends of the Mississippi River blog)
• Forests 'can take cover to resist alien invaders' (BBC, 2020)
• Cover it Up!: Buckthorn Control with Native Plants (MITPPC, 2019)
• U of M Center battles hungry invasives (Pioneer Press, 2019)
• Grow with Kare: Be a citizen scientist and fight buckthorn! (Kare 11, 2019)
• Battling buckthorn to restore natural resistance (Science Museum of Minnesota, 2017)
• “U faculty among global list of highly cited researchers” (UMN Office of the Vice President for Research
• Annual Facebook outreach from Great Lakes Research and Education Center, National Park Service