National Invasive Species Awareness Week runs February 22-28, 2021. But what does that mean? What are invasive species and how do they impact our local habitats? In this post, we’ll explore an invasive plant species. You can learn more about the definition of invasive species here. You can also learn about how we combat some of those species here.
Exotic, or non-native, buckthorn plants native to Europe and Asia were first brought to the United States as a decorative plant in the late 1800s. It was appealing as it grew easily in almost any habitat and produced shrubby bright leaves and clusters of berries. It became widespread in New England and the Great Lakes region in the early 1900s. These days you might hear the name not in gardening magazines but in invasive species conservation projects. Because buckthorn can grow so easily and so quickly, it crowds out almost all other plants, especially ones that need more time to grow, certain soils, light or shade or even different water levels.
There are three species of non-native species of buckthorn: Common or European buckthorn (Rhamnus cathartica), glossy buckthorn (Rhamnus frangula), and Dahurian buckthorn (Rhamnus davurica). European and glossy buckthorn, in particular, are proving to be a considerable problem in the Chicagoland region. These introduced species have become invasive — they grow very quickly, crowding out native plant species. They compete with native buckthorns, dwarf birch, and highbush blueberry. In wetland areas, they have been found to disrupt amphibian development, posing another hurdle for many species already facing reduced populations. Their berries are eaten by birds, but as they are a bit of a laxative, the birds spread the seeds across the landscape, causing the plant to spread even further.
Check out these images from Cranberry Slough Nature Preserve, Forest Preserves of Cook County. Notice how on the left side of the path buckthorn has grown in every available space? On the right hand side of the path the forest floor has plenty of room for diverse plants and animals to grow or roam.
Local habitat restoration activities incorporate removing invasive plant species, such as the European buckthorn. But if a landscape is heavily altered by invasive species, how do we know what it should look like?
Natural history museum collections can provide information about the plants and animals present in the area. From studying and gathering samples from local areas over the years, we know what plant species are native and what kind of ecosystem they are part of. Historic photographs and naturalists’ field notes can provide a first-hand account of what an area looked like, too. Here are images taken by Academy staff during field surveys they conducted in the Skokie Marsh in the early 1900s, now known as Skokie Lagoons. These glass plate negatives show what the area looked like before the invasive buckthorn species was present. The base of the trees is clear of the shrubbery choking the understory that is present now. Compare these images with the one above from the Forest Preserve District.
Dr. Allison Sacerdote-Velat, curator of herpetology at the Nature Museum, has conducted research into the detrimental effects of invasive buckthorn species in local wetlands. In her research, published in the Journal of Herpetology, Dr. Sacerdote-Velat found that European and glossy buckthorn grow aggressively in wet soils, including those around amphibian breeding ponds. This was found to have negative effects, both directly and indirectly, on amphibian survival and ecological interactions. These invasive buckthorns produce a substance called emodin, which has been found to disrupt frog embryo development. It is part of young plants’ defensive mechanism, produced through the plant’s metabolic processes, and helps prevent young sprouts from being eaten by animals. It has been found in higher concentrations around buckthorn sprouts that are trying to grow and in the spring when plants are producing their leaves and berries. Additionally, invasive buckthorns also use more water than native plant species, pulling it from temporary wetlands and soils and depleting important habitat for tadpole development, resulting in reduced frog populations.
Removal of invasive species, like European buckthorn, helps protect the native plants and animals growing in an area. How can you stop buckthorn from crowding out native species of Illinois? Join a local habitat restoration project to help remove invasive plants and plant native species. If you’ve been hiking or walking in parks or natural spaces with buckthorn, check the bottoms of your shoes and remove any debris that might be carrying buckthorn berries and seeds and dispose of them. Stopping the spread of buckthorn seeds can help contain this voracious plant and protect the space native species need to grow!
“What is Restoration?” Forest Preserves of Cook County. https://fpdcc.com/nature/restoration/
“Ecological Restoration.” Friends of the Forest Preserves. https://www.fotfp.org/volunteer/ecological-restoration/
“Exotic Buckthorns.” Vegetation Management Guideline. Illinois Natural History Survey. https://www.inhs.illinois.edu/research/vmg/buckthorn/
“Common buckthorn.” Trees and Plants. The Morton Arboretum. https://www.mortonarb.org/trees-plants/tree-plant-descriptions/common-buckthorn-illegal-sell-illinois#:~:text=Common%20buckthorn%20is%20an%20invasive,and%20should%20not%20be%20planted.&text=Buckthorn%20is%20a%20large%20shrub,cannot%20be%20sold%20in%20Illinois.