Help Remove Invasive Species: Buckthorn

How can a shrub be harmful?

 

European buckthorn (also called common buckthorn or buckthorn) is a tall, understory shrub introduced to North America in the early 19th century. as an ornamental shrub, primarily to serve as hedges. This woody shrub is extremely hardy and able to thrive in a variety of soil and light conditions. It is able to outcompete native plant species with its fast growth rate and distinctive phenology; buckthorn leafs out earlier in the spring and holds its leaves later in the fall, allowing it to continue to grow when most native species are dormant.

Buckthorn also has few predators. If you look closely at a buckthorn leaf, you'll rarely see any spots or small holes; that's because European buckthorn has no specific insect predators in North America. Deer also avoid eating buckthorn, instead munching on native species and furthering buckthorn’s competitive edge. Combine these characteristics with its plentiful seed production, and it's not hard to see how it can very quickly establish itself and come to dominate forest, oak savannas and other natural areas. However, where we see a lush-looking sea of bright green leaves, butterflies, bees and insect-eating birds see the equivalent of a barren desert.

While birds (and sometimes mice) do eat the berries of buckthorn, it's often because buckthorn is the only available seed source for much of the year. However, buckthorn berries are not a good food source. The berries are low in protein and high in carbohydrates, and produce a severe laxative effect. For smaller birds, the laxative effect can be strong enough to result in death. Adding insult to injury, the excreting birds end up distributing the buckthorn seeds over long distances.

Other negative effects stem from buckthorn’s leaves. Buckthorn leaves are high in nitrogen and calcium, making them very palatable for decomposers like earthworms. Once they fall to the ground, they alter the decomposition regime, decomposing very quickly and creating boom and bust cycles for microbes and other decomposers. They also alter soli chemistry; soil under buckthorn has higher nitrogen, which can encourage the growth of disturbance loving, weedy species suc as the invasive garlic mustard plantBuckthorn may even have a facilitative relationship with invasive European earthworms. Buckthorn prefers to germinate on bare soil, and as earthworms rapidly consume the leaf litter layer in forests, this provides a preferential germination environment for buckthorn and reinforces its invasion. Earthworms also likely benefit from buckthorn’s high-nutrient littler, allowing them to increase their population size in invaded areas.

Finally, because buckthorn shades out and outcompetes native groundcover plants, it's bad for water quality. Allow us to explain... Native groundcover helps stabilize soil and retain and absorb rainwater. Without them, rain will quickly wash over exposed, bare soil (like that under buckthorn bushes) and into nearby water bodies. This increases erosion of the River Gorge, lakeshores and streambanks. In many cases, as the rainwater travels it picks up pollutants: bits of asphalt shingles from our roofs, fertilizer from our yards, oil from the street etc, and then dumps it all, unfiltered(!), into the Mississippi River.

    The MN DNR provides more detailed information on buckthorn here.

    Removing buckthorn at an event

    That's a big buckthorn!

    Volunteers do not need to learn about removing this invasive before helping with a buckthorn removal event. Event staff will provide a complete overview and brief training, as well as all tools. Most event listings will specify whether volunteers will be pulling seedlings, using loppers or weed wrenches, or hauling pre-cut buckthorn. Some events are a mix of these activities and event staff will make sure each person has a task they are comfortable with. Also, when tool use or terrain make the event unsuitable for young children, this will be noted in the description on the events calendar

    The information below is intended to provide an overview for those who enjoy learning about local ecology or who are wondering if they or someone they know has buckthorn in their yard and, if so, what they can do about it.

     

    Identifying features

    The first step to successful buckthorn removal: Know your enemy! While not incredibly remarkable in any of its physical features, buckthorn is the only tree with all of the following characteristics:

    • It is a tall, understory shrub, or small tree, reaching up to 20' in its maturity. 
    • The base of the shrub often contains multiple stems and its bark is extremely flaky. 
    • Nicking the bark will reveal an orange cambium, or inner tissue, distinctive to this species.
    • The leaves are arranged alternately, though sometimes oppositely, bearing a broadly elliptical shape and tipped at the end. The sides are finely serrated, or small toothed, and the texture is waxy. Because buckthorn leaves remain green even into late autumn, they are perhaps most easily recognizable at this time.

    The City of Burnsville has an excellent buckthorn identification page, along with removal tips. Additionally, FMR ecologist Alex Roth has written an intersting article regarding buckthorn's distinct phenology.

    Removing smaller plants

    For removing seedlings and smaller, younger buckthorn plants, simple hand removal works quite well. The use of pliers, or a small shovel may also be used. With immature seedlings, roots are not yet deep, so it should be fairly easy to get the job done. Remember to shake the soil free from the roots so smaller plants can detach and decompose.

    If you have both large and small shrubs, start with the larger ones as they will produce seed-bearing berries.

    Removing larger shrubs

    For larger shrubs, simple hand removal techniques will not suffice. Weed wrenches are used for plants with a "trunk" 0.5-2.5 inches in diameter (depending upon conditions).

    The Weed Wrench tool is easy to use: it is clamped tightly to the exposed stump and pulled back from the top, which rips the stump and roots from the ground.
    • A youtube video of Russ Henry of Giving Tree Gardens in Minneapolis is available here.
    • Last we checked, you could rent one in the Twin Cities area from Crown Rental, Reddy Rents, Hejny and Highway 55 Rental. There are probably many other rental places out there, and you may also try your local community group or city forester to see if they have a loaner program.

    When soil disturbance is an issue — in areas with loose soil, slopes and native plants — FMR's project manager will work with professional crews to use other control methods.

    Destroying the evidence/getting away "clean"

    Stacked buckthorn from invasives removal event

    The disposal of buckthorn brush can be a tricky task.

    At volunteer events, volunteers will help collect the branches for removal. Once taken away, the branches must be destroyed. This is particularly important when the branches contain seed-bearing berries. The best way to ensure the destruction of the seeds is with fire. (FMR volunteers will not be asked to burn anything, of course.) If you are removing buckthorn on your own property, contact the city you live in for details about burning permits or get in touch with your waste hauler and inquire about woody brush pickup processes.

    Followup

    If the steps listed above are properly followed, the chances for success are rather high. However, because each buckthorn berry contains up to four seeds, seedlings may reappear despite your vigilance. It's best to revisit the site to check for new seedlings.

    With persistent efforts we can triumph over the threat of buckthorn invasion. Many of our restoration sites, including the beautiful oak savanna in South Minneapolis, were once buckthorn thickets and now provide excellent habitat and help improve water quality throughout the watershed! 

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    For further information on how to tackle the issue of buckthorn invasion within your own yard, visit the Minnesota DNR.

    You may also want to check in with your community organization, neighborhood group or local watershed district about the possibility of assistance or matching grants to replace the invasives with watershed-friendly native species. Some cost-sharing programs are listed in FMR's Landscape for the River guide.