Cover it up! Using plants to control buckthorn

photograph of researchers observing a ground plot in a forest
Researchers monitor a forest floor plot as they study using native plants to suppress buckthorn

Project phases

Phase 1 (complete)

Project information

Research project title: Cover it Up! Using plant to control buckthorn
Taxa: Plant
Species: Common buckthorn (Rhamnus cathartica)
Project status: Completed in 2019
Funding: $327,000


Buckthorn is an invasive shrub that outcompetes native plants and degrades Minnesota forests. Minnesotans spend millions each year removing buckthorn from their properties, yet owners find the invasive shrub returning to the same spots again and again. Removal of buckthorn is a common management activity, but often only provides short-lived benefits since buckthorn rapidly re-establishes.

In grasslands, heavily seeding native species can often restore native communities and inhibit invasion, but this approach is rarely used in forest management (Schuster et al. 2018). This research team investigated whether they could similarly establish enough native plants to prevent buckthorn from re-establishing in forests.

Research questions

  • What native planting techniques can reduce the recurrence of buckthorn after removal?
  • How much shade is needed to prevent buckthorn from thriving

Practical implications

This work could change the way we think about buckthorn management, helping Minnesota land managers save significant time and money in their long-term restoration efforts.

Phase 2 (in progress)

Project information

Research project title: Cover it Up! Phase 2
Taxa: Plant
Species: Common buckthorn (Rhamnus cathartica)
Project status: In progress
Funding: $560,000


Minnesotans spend millions each year removing common buckthorn, yet the invasive shrub often returns to the same spots again and again. This vicious cycle happens because buckthorn is better at filling empty spaces in an ecosystem than most other native plants.

The first phase of this work, led by MITPPC-funded ecologist Peter Reich, developed strategies to improve and diversify the native plant community while keeping buckthorn away for good. The team established that dense revegetation through native shrubs can reduce buckthorn recolonization by blocking at least 96% of incoming light. 

For phase 2, Reich’s team will expand their study from the Twin Cities metro into Greater Minnesota and explore how managers throughout the state can suppress buckthorn for the longest time and at the lowest cost. A network of citizen scientists will help carry out experiments in woodland areas across Minnesota. 

Research questions

  • What is the ability of slow-growing native perennial plants to suppress buckthorn?
  • How do deer and fire management interact with revegetation to strengthen buckthorn suppression?
  • What are the best methods to cost-effectively establish dense, suppressive shrub cover from seed?
  • Working with citizen scientists, what is the performance of revegetation seed mixtures in diverse environments across Minnesota?

Practical implications

The revegetation treatments designed and tested may serve as a template for managers throughout Minnesota. This could result in significant cost and labor savings and improve the health of woodlands by excluding invaders, reducing herbicide applications, and increasing forest understory plant diversity.

Phase 3 (in progress)

Project information

Research project title: Managing buckthorn with trees: diversity, density, and practicality
Taxa: Plant
Species: Common buckthorn (Rhamnus cathartica)
Project status: In progress
Funding: $499,734


Through MITPPC-funded research, Reich’s team has established that densely revegetating woodlands can suppress buckthorn reestablishment by blocking a large majority of incoming light. Whether this can be done operationally and cost-effectively at the scale of management remains unknown.

The research team will carry out large-scale experiments with native tree, shrub, and herbaceous species to determine the degree of revegetation necessary to block out buckthorn reestablishment and determine the associated costs of this strategy.

Research questions

  • What density of trees, shrubs, and herbaceous species is most effective at suppressing buckthorn regeneration?
  • What is the response of buckthorn of both buckthorn and native vegetation to these treatments?
  • What are the most cost-effective and practical methods for revegetation?

Practical implications

The outcomes of this research may provide affordable and practical solutions for land managers to establish native plant communities after buckthorn removal.


During phase 1 of this project, the research team developed strategies to improve and diversify the native plant community while keeping buckthorn away for good. Together with more than 12 local partner organizations, they found that native grasses, wildflowers, sedges, ferns, and juvenile trees can provide enough shade to prevent new buckthorn growth. 

The project illustrates that it is possible to curate native plant communities in a way that makes them resistant to buckthorn invasion. In general, they recommend that forests be managed to promote the establishment of shrubs and trees that provide heavy shade in the spring and fall. Their findings suggest that by doing so, managers can simultaneously increase forest health, inhibit invasion, and reduce the need for investment in future buckthorn removals. 

Phases 2 and 3 are currently in progress.


News and media

Outreach and presentations

  • 2019 Gathering Partners Conference
  • 2019 Duluth Cooperative Invasive Species Management Area
  • 2019 Duluth Invaders R2ED Team
  • 2018 UMN Undergraduate Research Symposium
  • 2018 Upper Midwest Invasive Species Conference 
  • 2018 St. Croix Research Rendezvous
  • 2018 Legislative-Citizen Committee on Minnesota Resources
  • 2018 Metropolitan State University Natural Sciences Seminar
  • 2017 MITPPC Buckthorn Symposium
  • 2017 Floodplain Forests Group
  • 2016 Upper Midwest Invasive Species Conference 

Project team

Peter Reich | principal investigator

Lee Frelich | co-principal investigator

Peter Wragg | post-doctoral associate

Michael Schuster | post-doctoral associate

Abbie Anderson | citizen science coordinator

Kirsten Granstrom-Arndt | researcher

Artur Stefanski | researcher

Raimundo Bermudez Villanueva | researcher


Lab or other website

The Cover It Up Project 


Collaborating organizations

Minnesota Department of Natural Resources

Friends of the Mississippi River

St. Croix Watershed Research Station


UMN Extensions

Three Rivers Park District

Ramsey County

Washington County