Kill the Buckthorn, Save the Frogs

The new issue of Chicagoland Gardening magazine has an article that provides more evidence that European Buckthorn (Rhamnus cathartica) is an evil plant, at least in those areas where it is invasive.

Western Chorus Frog
Western Chorus Frog. Cute little guy, isn’t he? Photo from herpnet.net

Most objections to European buckthorn are based on its impact on native plants. In much of North America, this shrubby small tree is a menace. It generates innumerable seedlings, and forms thickets that can squeeze out every other plant.

In the Chicago area alone, there are 26 million stems of buckthorn, and buckthorn removal is a constant challenge for those who seek to protect and restore natural areas.

Now it turns out that European buckthorn is a menace to frogs as well as to native plants. Buckthorn contains a chemical called emodin. Researchers from Northern Illinois University and Chicago’s Lincoln Park Zoo found emodin in ephemeral breeding pools in suburban Chicago woodlands. More buckthorn meant more emodin in the water and soil.

die buckthorn scum
A T-Shirt available from Wild Ones, an organization of native plant enthusiasts. Photo: wildones.org.

The researchers tested the effects of emodin on the tadpoles of western chorus frogs. The results: emodin caused deformities and death.

The authors of the study, which will be published in The Journal of Herpatology, hypothesize that emodin has the same impact on the tadpoles of other American frogs. Western chorus frogs are just one of several amphibian species that have low hatching rates in woods infested with European buckthorn. These species reproduce at the time of year when the concentration of emodin is highest.

Amphibians in general are facing an alarming decline. According to the conservation group Amphibian Ark, 30% of the world’s amphibian species are threatened with extinction.

european buckthorn
European Buckthorn leaves and berries. Photo from UWGB.edu.

I like to garden with plants native to the midwest region of North America, but I am no purist. However, when it comes to European buckthorn I have a zero tolerance policy. It’s hard to believe that these trees were once sold in nurseries. Unfortunately, it took years for people to realize the environmental impact.

After we moved into our current house I personally took down two buckthorns growing in the back garden, and I regularly pull up buckthorn seedlings.

So if you have amphibians on your property, you have another good reason to get rid of buckthorn. Do you have European buckthorn in your garden, and have you tried to remove it?

41 Comments on “Kill the Buckthorn, Save the Frogs

  1. As the founder and first president of Northern Kane County Wild Ones, thank you for spreading the word. Buckthorn rapidly will become the exclusive understory in a woodland or savanna. It leafs out early and loses it leaves late, thereby keeping sunlight from reaching the ground during growing season. This dense shade keeps oaks from reproducing, guaranteeing their demise. The dense cover also keeps native wildflowers from sprouting and growing on the woodland floor. Without an herbaceous carpet, the soil will soon erode away. In addition, trees rely on the deep fibrous roots of native sedges to keep them adequately hydrated.

    • Good explanation of how buckthorn suppresses native plants. I have also read that it is allelopathic and secretes toxins into the soil.

  2. As far as I know there is no buckthorn near us Jason, but I’ll be keeping my eyes peeled! This is interesting as we often judge plants’ invasiveness on simply how much ground they take over – the effects on wildlife could be far more serious than we at first see. Thanks – I’m going to try and find out more now. 😀

    • As you are in Europe, I suppose the European buckthorn doesn’t do the same damage where you are. Maybe there are American plants that are just as destructive in Europe, though.

      • I’ve been looking at pictures and we do have something down near the canal that looks similar, I just never noticed the thorns! I’ll take a closer look next time I’m out. We have problems with Canadian Golden Rod here.

  3. No buckthorn here but there are plenty of other invasives. This sounds almost like the buckthorn is intentionally trying to damage the environment! Who knows what else is going on.

  4. When I lived in southern Ontario, I walked to work on a community trail and at least 50% of the plants were buckthorns. You could see how invasive it was (together with garlic mustard that was growing at its base). Fortunately, neither of these are here. I keep an eye open though as you can import them unknowingly with plants you buy.

  5. European buckthorn is a prohibited noxious weed in Alberta, but I can’t say that I’ve ever noticed it in any of my wanderings. I was not aware of the amphibian connection. Good to put the word out.

    • Maybe buckthorn is not adapted to the conditions in the Canadian Rockies. You’re not missing anything good. Though you probably have a different array of invasives to deal with.

  6. I’m with you on the buckthorn. I knew it was invasive and all the forest preserves and Arboretums have been trying to control it for years. It is such a pest, even in my own yard. My nature loving neighbor has a lot growing in her backyard, and they hang over into my yard. I keep cutting them back, and trying to get rid of all those pesky shoots that come up everywhere. Hopefully the new neighbor will be more receptive to getting rid of it. I didn’t know about the toxicity to the Western Chorus Frog, but just another reason to keep up the fight against this invasive species. Thanks for letting us know about the Wild Ones organization

    • The Wild Ones have several chapters in the Chicago area and do a variety of programs. It’s maddening that someone thinks he is being good to nature by allowing their yard to be full of buckthorn. My neighbors were not thrilled when I removed my buckthorns, because they were part of the hedge that separated our back yards. But they were polite about it.

      • Around me, it’s the main “wild” hedge plant. As homeowners put in more structured yard plantings, they come out, but there’s still plenty around. Even when I start looking at the natural roadside hedges, it’s unfortunately mostly buckthorn.

  7. Much Buckthorn is in the Niagara area, but it is news to me on affecting frog tadpoles. It really seems no end to what species a plant can help to those it hurts. Birds like it here for a late season berry. I have heard birds spread it, but can tell you it is prolific as it seeds, it does not need the birds help. The Parks department culls it yearly, but never gets it under control.

    • I don’t think you can ever eliminate buckthorn, all you can do is push it back. It has been mostly removed from much of the Cook County Forest Preserves. I know the birds like the berries, I think they do help it spread over a wider area.

  8. i don’t have it in my garden but it’s everywhere you look here and the chances of ever eradicating it are slim at best. But still, the U.S., in the 4 years between 2005 and 2009, imported 667,000 live plants-from just China alone. We have nobody else to blame but ourselves.

  9. What’s good in one place is a problem in another; it is so important that we gardeners are responsible with the plants we choose and a native should always take precedence over a foreign introduction!

    • Sadly many invasives here were first planted as ornamentals: purple loosestrife, porcelainberry, even kudzu and creeping charlie. All pretty plants, even beautiful, but disastrous for the ecology.

  10. It’s an endless problem the world over isn’t it, people bring in non native species that do untold damage and then of course it’s too late. I haven’t any of it so maybe that’s why I have so many frogs.xxxx

  11. Rhamnus caroliniana is a native plant in the eastern and central U.S.. It does not have thorns, as do its european cousins. It does contain emodin in its bark, but I wonder if the effect is the same as the non-native species? I haven’t seen any in my own woods, but I would like to know!

    • I kind of doubt if anyone has researched that yet. I think the buckthorn/frog study just done in this area was a sort of first of its kind. I’ve gotta think thought that it is unlikely a native species would be the same kind of problem. Does it tend to dominate the understory the way the European buckthorn does?

  12. This came up in our master naturalist classes, and I was very concerned that we might have lots of Buckthorn in our woods. Turns out, we didn’t. But many of the nature centers and state parks do. Sad to see the amphibian numbers declining.

  13. Thankyou for your post, we had been supplied some in with plants for a mixed native hedge, I have just researched this and yes although good for bees and brimstone butterflies,in the UK, I think we will choose something else and consign the buckthorn to the shredder. We want to encourage frogs here. Just shows how important choosing the right plant is, wherever you are in the world. And how valuable sharing research from other parts of the world is too.

      • I couldn’t find any research on UK effects on amphibians, but better safe than sorry, there seems to be far more research articles on the net in the USA. Not sure what that tells me but I could not see a reason why our frogs should be immune. Thankyou again, I really like the depth and variety of your posts. Best wishes.

  14. Thanks so much for posting this. I don’t have any buckthorn in my yard but I suspect it’s only because I’m too far away from the forest preserves where volunteers regularly try to eradicate it. Or maybe the invasive white mulberry I’ve been trying to control and get rid of forever won’t let it grab hold.

      • The berries themselves were purple and the starlings used to…well…it was a mess. I think the name of the tree is White Mulberry, it’s of Chinese origin and the leaves are weird, two different kinds, like the tree couldn’t make it’s mind. Wonder if it’s a hybrid altogether.

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