Meet the invasive buckthorns near you
By Abraham Stone and Dr. Sigrid Resh
Soon enough, we will be reminded of the life that has lain dormant while snow blanketed the UP. Trees will begin producing leaves, the trilliums and trout lilies will bloom, and morels will pop out in our backyards (if you’re lucky)!
The Keweenaw Invasive Species Management Area (KISMA) will soon begin the process of invasive species management and ecosystem restoration. Two of our highest priority and most abundant woody invaders are common buckthorn (Rhamnus cathartica) and glossy buckthorn (Frangula alnus). Their leaves will appear late-May, and, if you have them in your yard, you will want to remove them for aesthetics, native birds and other animals, and to stop their spread.
What do the buckthorns look like?
Buckthorn trees can be common around the landscape. We see them next to walking trails, integrated into many (but not all!) forests, and in our yards-out of place from their Eurasian homelands.
The bark on common buckthorn looks dark and metallic, and the branches and stem are covered with occasional sharp thorns. Glossy buckthorn’s bark is a dark burgundy, has no spikes, and, when young, is covered with lenticels (small growths on the trunk; the trees use these to respire!). Both species have dark green oval leaves with clear venation and either toothed (common buckthorn) or smooth (glossy buckthorn) edges – the leaves are hairless. They are among the first understory trees to leaf out in the spring and some of the last to lose their leaves; if you see green leaves coated with snow in December, it’s probably buckthorn!
It can be easy to misidentify buckthorn trees with our welcomed cherry (toothed leaves like common buckthorn but many more vein pairs), serviceberry, and apple trees, but the more familiar you become with them the easier it is to decipher what you’re looking at. If you’re confused, take a little bit of the bark off a twig and see what color lies underneath; if it’s a bright orange, you’ve found a common buckthorn. If you can see any of the roots, a blood-red color will indicate glossy buckthorn. If any other color, it’s a local friend!
Why is buckthorn
a big deal?
Buckthorn represents the kind of invasive species that changes the forest around it in a very tangible way. Because it stays leafed out longer than most natives, it often can block out the sun for any plants under it. Growth is fast in the spring, so areas of small foot-high sprouts can quickly become four foot bushes in the right conditions.
Buckthorn is prolific summer fruiter, and the fruit contain highly germinant seeds – often, these fruits will linger with the leaves when the first snows hit! The fruit land below the buckthorn trees, contributing to a seedbank of potential buckthorn regeneration. Once these seeds germinate and grow, they eliminate the native tree seedlings that cannot grow as fast, so forests that have spent some time cultivating a buckthorn understory often eventually lead to the elimination of nearly all native trees in the area. The fruit can also be eaten by birds, which poop out the seeds, spreading the trees to new areas.
Furthermore, many of our native insects do not eat them, which means they are not a good habitat for birds to rear their young. In 2017, research in Washington D.C. published in Biological Conservation and conducted by Desiree Narango and others showed that yards with native plants used for landscaping had higher native caterpillar populations and more breeding chickadees compared with yards that had more non-native plants (https://doi.org/10.1016/j.biocon.2017.06.029)
How to remove
Buckthorn can be controlled but you need to know two important traits. They resprout with many stems when cut or injured, and they have a seedbank in the soil that will vigorously germinate for many years, so management is not a one-time effort. Steps to managing smallish buckthorn infestations for KISMA https://www.mtu.edu/kisma/terrestrial-invasive-species/common-buckthorn/:
1. Hand-pull small seedlings and saplings.
2. For stems too large to hand-pull, use a weed wrench to loosen the roots. You can borrow a weed wrench from KISMA to save your back when pulling them out.
3. If the tree is too large for the weed wrench, cut the tree a few inches above the ground and cover with a double layer of thick plastic (we use thick bags), secure bag to stump with zip tie, spread bag edges over soil around stump, and weigh bag down with rocks or wood. Leave bag in place for two growing seasons. This smothering technique will prevent stump sprout regeneration and kill the root mass. Check to make sure sprouting doesn’t occur-cut a reposition plastic if necessary.
Dispose of small seedlings and sapling by hanging in trees so roots cannot touch the soil and continue to grow. Wood can be chipped or burned. Best to manage before the trees develop fruit; however, if fruit is present, collect as much as you can and burn or bag and send to landfill. Never compost fruit.
These documents provide identification and additional management options: https://mnfi.anr.msu.edu/invasive-species/CommonBuckthornBCP.pdf and https://mnfi.anr.msu.edu/invasive-species/GlossyBuckthornBCP.pdf.
At Michigan Tech, we are exploring the application of a native fungus specifically for treating buckthorn regeneration, so stay tuned for any updates!
Great native alternatives to common buckthorn are the native cherries like pin cherry (Prunus pensylvanica) and choke cherry (Prunus virginiana), serviceberry (Amelanchier sp.), and highbush cranberry (Viburnum trilobum), which provide a needed food source to native wildlife. Native alternatives to glossy buckthorn are native dogwoods like red-osier dogwood (Cornus sericea) and flowering dogwood (Cornus florida) and our native willow like pussy willow (Salix discolor) and a variety of others.
KISMA can help
If you need help with identification of buckthorn in your yard or any other invasive species concerns, contact us at firstname.lastname@example.org or visit our website at https://www.mtu.edu/kisma/. KISMA can also provide a list of native species to replace your buckthorn. Another good source of native species to plant in the UP is: https://www.canr.msu.edu/nativeplants/plant_facts/local_info/upper_peninsula#tr
Research compiled by Abraham Stone, email@example.com, undergraduate in Ecology; Dr. Sigrid Resh, firstname.lastname@example.org, coordinator, Keweenaw Invasive Species Management Area (KISMA) and Research Assistant Professor, Michigan Technological University