December Weed of the Month: Managing Invasive Plants in a Forest

department of agriculture

December 6, 2018

December Weed of the Month: Managing Invasive Plants in a Forest

Mari Hardel, Minnesota Department of Agriculture

This forest has the invasive shrub common buckthorn invading the understory

Minnesota is well loved for forested areas – from expansive tree covered landscapes to wooded city lots. While not all forests in Minnesota have invasive species, they are all susceptible. Invasive plant management tactics may look different depending on the infestation size, location and other factors. We have the opportunity to contribute to invasive species control & protection of our forested landscapes.

Invasive plants commonly found in Minnesota forests vary by region – based on differences in climate throughout the state, the level of forest fragmentation and, largely, the influence that humans have on that particular landscape. Some forest invasive plants grow successfully in shade and can tolerate or thrive in a canopy cover of trees. Other forest invasive plants are quick to invade clearings and forest edges where more sunlight is available. Therefore, you’ll be looking for woody vines or woody shrubs like buckthorn and also herbaceous plants like garlic mustard.

Examples of commonly found invasive plants you may find in your forest:

  • Twin Cities: Common buckthorn, garlic mustard and Asian bush honeysuckles
  • Duluth area: Common buckthorn and Asian bush honeysuckles
  • Southeast: Oriental bittersweet, common buckthorn, Japanese barberry and Asian bush honeysuckles
  • Southwest: Common buckthorn and garlic mustard
  • Northeast: Common buckthorn and Asian bush honeysuckles
  • Northwest: Common buckthorn

Creating a management plan for your forest:

  1. Determine the area you would like to manage:
    • Size: Understanding the scope and limitations (or lack thereof) within your management area can help when piecing together the rest of your plan. Size can determine what management strategies are most appropriate. Do you have the capacity to manage this area?
    • Survey the area: What is already there, native and invasive? Look high (for vines) and low (for small seedlings).
  2. Do your research:
    • Do LOCAL research. For example, buckthorn is incredibly commonplace in St. Paul’s forested areas and might be managed reactively by controlling spread. In northern Minnesota (outside of Duluth) buckthorn is considered early detection and can feasibly be eradicated with proactive management. Invasive plant species distribution maps can be found at
    • Beyond any invasive plants have you already found, what might you be likely to find in your forest?
    • What native species are common or rare in your region, and what native species would you like to see in your forest?
  3. Talk to your community:
    • If you all work together on a project, your time and resources will go further. Consider if the neighboring property has invasive plants, there’s a good chance your property will have those plants in the future.
  4. Draft a plan based on gathered information plus these considerations:
    • What is your desired outcome?
    • How much time, money, and energy do you have to spend on managing your forest?
    • What time of year will you be controlling invasive species and what will your methods of management be? Some plants respond to treatment best at certain times of the year, and there are often treatment options to choose from (chemical, mechanical, biological, etc.).
    • What will you do once invasives are removed? Planting with native species afterward is a great option and will provide competition for the invasive seeds still in the soil.
    • Planning tools are available at:
  5. Implement your plan:
    • Are you doing the work yourself or hiring a contractor?
  6. Monitor:
    • It is likely you will see results within the first year of management. However, even if you were successful one year you still have work to do. Seeds sprout and new weeds can move into opened areas. Adjust your management plan depending on your outcomes and keep at it!

Whether you’re managing a wooded backyard or hundreds of forested acres, you’re not simply controlling invasive plants – you’re helping to restore the native ecosystem and providing increased biodiversity and habitat. Consider creating a larger forest stewardship plan with invasive species management as a component to the larger picture.

Additional Resources:

U of M Forestry Extension’s My Minnesota Woods

DNR foresters for woodland assistance

MDA Noxious and Invasive Weed Program

Buckthorn ID – Steps for reducing soybean aphid host

How to manage buckthorn


Photo 1: This forest has the invasive shrub common buckthorn invading the understory and would be a good candidate for invasive plant management.

Photo 2: This forest has been managed for invasive species and shows success on the path to restoring the ecosystem.

Photo 3: Garlic mustard is an example of a herbaceous invasive plant that can invade Minnesota forests.

Photo 4: Fall is a good time to treat woody invasive plants such as the Oriental bittersweet at this forest location.


MEDIA: For more information on Weed of the Month, contact Allen Sommerfeld, MDA Communications, at or 651-201-6185

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