Buckthorn: There is Light at the End of the Tunnel

As one of the most aggressive and invasive plants threatening Minnesota, buckthorn is a major problem in urban and rural forest alike. Managing a buckthorn infestation can make many go from pulling plants to pulling out their own hair, as the plant appears never stops growing and popping up in new places. However, Mike Schuster and Lee Frelich, buckthorn experts, join this episode of the podcast to make the seemingly impossible, possible. Listen in to learn tips and tricks for successfully managing buckthorn, get details on the Cover It Up! Project, and find out where to start to manage buckthorn on your property. 

Smarty Plants is a podcast of the Minnesota Department of Agriculture. Visit www.mda.state.mn.us/plants-insects/smarty-plants for more episodes. Look for a new episode of Smarty Plants every month.

Transcript

Jennifer Burington: 0:19

Hello everyone. I am Jennifer Burington, and welcome to Smarty Plants, a Minnesota Department of Agriculture podcast, informing the public about invasive species that affect our environment and agricultural resources. Common buckthorn may look like just another shrub or small tree in the woods, but it's one of the most aggressive, invasive plants threatening Minnesota's forest today. It was introduced to North America as an ornamental plant and for use in hedgerows and wildlife habitat. Since then, it has spread across much of the northeast and upper Midwest and is now found throughout Minnesota, especially in the southern half of the state. buckthorn is listed as a restricted noxious weed in Minnesota, meaning it is illegal to import, sell, or transport buckthorn in Minnesota. In this episode, we'll talk about why buckthorn is so invasive, the damage it causes, and an approach to management that uses plants to help control buckthorn and restore native forest understory. Joining us today to discuss buckthorn are Mike Schuster and Lee Frelich. Mike Schuster is an assistant professor at Hamlin University and a researcher with the Minnesota Invasive Terrestrial Plants and Pests Center at the University of Minnesota. His research focuses on the process of exotic plant invasions, their effects on ecosystem function, and strategies for biodiversity management. Since 2016, Mike has led the cover it UP project, which evaluates innovative revegetation approaches for forest stories. The project aims to increase biotic resistance and reduce invasion by buckthorn and other exotic woody species. Lee Frelich is director of the University of Minnesota Center for Forest Ecology. He earned a PhD in Forest Ecology from the University of Wisconsin Madison in 8 19 86 and has authored or co-authored 241 publications. His research has been featured more than 600 times in news media outlets, including the New York Times, Newsweek, and the Washington Post. His research interests include large scale fire and wind disturbance, earthworm invasion, and climate change, and temperate and boreal forests. Mike and Lee, thank you for making the time to speak with us.

Mike Schuster: 2:45

Thanks for having me.

Lee Freilich: 2:46

Yeah, nice to be with you.

Jennifer Burington: 2:49

Okay. So to get started, for listeners who may have heard the name Buckthorn but aren't sure how to identify it, what are some of the key, uh, characteristics of, let's start with common buckthorn. If you wanna start.

Lee Freilich: 3:08

Well, it's a shrub and it gets to be maybe an inch or inch and a half in diameter in 10 years or so. Um, it can get to be a small tree actually if you let it go, but it's in forest under stories. It has round green, round dark green leaves, um, that are. A little more than an inch in diameter. It does have some thorns on the stem. They're not really obvious. They kind of look like the stubs have broken off twigs, but they actually are thorns and they get berries. Um, a little maybe quarter inch diameter berries that are almost black in color that birds like to eat and spread all over the place.

Jennifer Burington: 3:56

Yes, they do.

Mike Schuster: 3:58

Yeah. And those, those berries are one of the really key features, uh, especially in the winter and late fall, that, uh, the female trees will produce these thick, heavy laying branches full of those fruit. And that makes it very obvious when you have a buckthorn invasion on your property, you can see those fruit very easily in the wintertime. The other thing about buckthorn, uh, part of how it got its name is that the, uh. The terminal buds actually branch, uh, or, or Nestle up next to a, a terminal thorn. And if you look at it, it kind of looks like a, uh, deer's footprint. So buck, and then there's a little thorn in the middle. So Buck thorn, you put those together and that's. Buckthorn.

Jennifer Burington: 4:38

Mm-hmm. So we started out talking about common buckthorn. Um, can you, Mike, explain the difference between common buckthorn and glossy buckthorn and kind of if they're managed differently a little bit?

Mike Schuster: 4:51

Absolutely. So the difference between glossy buckthorn and common buckthorn is. Well, of course that glossy buckthorn is glossy, so the leaves have a bit of a shine to them. Uh, but the margins of the leaf are also much smoother. And so we see some similarities between glossy buckthorn and common buckthorn. But, uh, they're pretty easy to distinguish just based on that leaf margin. We also see glossy buckthorn showing up in places where common buckthorn generally doesn't do as well. So particularly in those wetter environments, uh, and especially in northern portions of the state, we see that being a place where glossy buckthorn is a little bit more at home compared to common buckthorn. And the differences in management then are largely associated, not necessarily with the physiology or the biology of these particular plant species, but much more a consequence of the environments in which they invade. So there are different management approaches that we can take in more wetland areas compared to. Uh, more upland or dryland places. You know, there are different considerations that we have to make based on the types of plants and exposure to water and things like that. So, uh, different strategies including things like herbicide use or access, uh, to heavy equipment are things that make management of glossy buckthorn and common buckthorn pretty different in practice.

Jennifer Burington: 6:12

Perfect. And so kind of, um, kinda going along with that, what is why is common? Buckthorn, um, such a problem in forests and then also in residential areas. Um, 'cause it sounds like it does great everywhere. Uh, so Lee, if you wanna kinda start us off with that one.

Lee Freilich: 6:34

Oh boy. Is that ever a question? Um, well they fill the understory of forests crowding out. Many, many native species of shrubs, tree ceilings, native forest plants. So if you have the upper canopy of the forest and then you have a buckthorn layer underneath, you've got like two canopies and hardly any light gets through to the ground and the native. Plants that are lower down just don't get the light and they die off as a result. Um, in addition to that, the deer don't like to eat the buckthorn, so they'll eat the native plants even more than they normally do. Um, and it's such an expansive problem in Minnesota, like most of our oak forests have buckthorn in the understory in southern Minnesota. I mean, fortunately. Forest at our pier, sugar maple. The maple itself casts a pretty dense shade, and the buckthorn doesn't do as well, but the conservation of oak forests, um. He is threatened by buckthorn being everywhere in Oak Forest, and there's no way oak seedlings are generally gonna get through a buckthorn cover. Uh, and the whole suite of native species that goes with it. The structure of the habitat for wildlife species that use the understory of the forest is all different, including birds that live in the understory or on the forest floor. So, yeah, it's um. Really one of the major conservation problems for forests in southern Minnesota.

Mike Schuster: 8:15

Yeah. I would add to the, the, you know, litany of things that Lee brought up was that, you know, buckthorn really fundamentally changes the way that our functions are built in the way that they function, the. Consequences of that mean that everyone's affected by buckthorn invasion, whether you know it or not, right? If you enjoy being outdoors, if you enjoy having clean water, if you enjoy having wildlife and all the services that those things provide to us, whether we are people that take a hike every day or you know, never leave our house, those are all things that we all benefit from having in nature and buck Thorney roads, those services.

Jennifer Burington: 8:53

Yeah. And in residential areas too, like it's the same thing you want, um. You don't wanna have all the same monoculture of just, just buckthorn in a residential area. Um, they used to make great hedges, but it, they're a big problem in all their areas. So, um, yeah, and every, a lot of people have them in their residential areas. There's some probably throughout every city I know every manage city. Public works and parks managers knows that there are buckthorn in all of their parks. Um, so it is, it's not just a forest, it's also residential. Um, birds, like we mentioned, they love those seeds and they can just drop 'em anywhere and you can sprout, sprout, new little buckthorn, um, that are really easy to pull out. But we'll talk about that later.

Mike Schuster: 9:38

Absolutely. So the, one of the interesting things about the patterns of buckthorn innovation is that they often co-occur with residential development, right? That, you know, buckthorn was brought in as this hedge plan, and it's fantastic at being a hedge, right? It grows quickly, it withstands browsing and damage really well, produces tons of fruit, has really dense leaves. All these things make buckthorn an amazing hedge. The problem is that it doesn't stop being hedge as soon as it gets into. Anywhere else.

Jennifer Burington: 10:04

Yep.

Mike Schuster: 10:05

And so we have, uh, perpetual buckthorn hedge throughout the state, uh, as a consequence of us planting it and then it being moved by, um, birds and other animals to new places.

Jennifer Burington: 10:16

Mm-hmm. So, perfect. All right. So we talked a little bit about, um. Crowding out native plants. Um, are there chemical impacts from buckthorn that affect the soil or wildlife? Lee, if you wanna start us.

Lee Freilich: 10:31

Sure. Um, yeah, there's a chemical called emodin, which is a secondary compound, which secondary compounds are other things that plants make in addition to, um, the carbohydrates that they make to build their own structure. So, and um. It's pretty toxic for a lot of things. I was just reading an article, um, in preparation for this podcast that emodin has native Im impacts on the development of frogs, for example. So if you have a whole ecosystem of a small pond. The whole watershed is filled with buckthorn and the water is full of emodin. You know, it could be a major problem for, um, those wildlife species that. Have kind of mucus membrane like skin, you know, and might absorb these toxic, um, chemicals that buckthorn makes. It varies a lot among bird species. Some bird species are actually fine with eating buckthorn berries and other bird species will avoid buckthorn. So, um, apparently they can sense, sense it, you know, and there's a lot of variability among bird species. Um, and their response to emodin and, and there could be numerous things we haven't even thought of. I mean, I didn't see any studies on emodin impact on. mycorrhizal Fungi, for example, that have relationships with the roots of trees and all of our species of trees are microrisal. Does it affect that? Does it affect the microbiome? Um, does it differentially affect the growth of different native plant species? Those are all things we need a lot more research on.

Jennifer Burington: 12:25

Mm-hmm.

Mike Schuster: 12:26

Buckthorn has a bunch of other chemical, uh, impacts in addition to the Frelich and what we would call allopathic impacts that Lee was mentioning. So, um, one of the things that buckthorn does is, you know, pretty drastically change the nutrient profile of, uh, the soils that it invades. And this is part of a positive feedback loop that it shares with invasive European earthworms. Something that a lot of, uh, people are surprised to know is that Minnesota doesn't have any native earthworms. The earthworms that we do have are all from Europe, with the exception of some more recent Yeah.

Lee Freilich: 12:59

We, we, we do have one native species of earthworm we just discovered recently, but it's not very common. It's only in special habitats, like under logs. So yeah. The, the huge majority of earthworms you see out there are European and, and now the Asian ones, the, the so-called jumping worms mm-hmm. Are becoming common in the metro area at this point.

Mike Schuster: 13:26

Absolutely. And so those, those relationships that buckthorn shares with the European earthworms, uh. Transform the soils in a way that makes, uh, the soils more hospitable to earthworms and the earthworms make the soil more hospitable to buckthorn. And you get this, uh, invasion meltdown process that perpetuates more invasion and less native biodiversity.

Jennifer Burington: 13:49

But, uh, buckthorn has spread across Minnesota and. What makes it so difficult to manage and why do we so often see it return after control efforts? I know from myself, I have some in my backyard and it's been a few years that we've been pulling on it. So, um, it's not a, it wasn't a, a summer project and then done, and all of a sudden it never comes back again. So, if Mike, you wanna kind of start us off with this one?

Mike Schuster: 14:16

Yeah. Buckthorn removal is never a, uh, one and done process, unfortunately. And a lot of those traits that we were discussing a moment ago about buckthorn making a really good hedge are the same reasons why buckthorn perpetuates itself, uh, in our, um, managed and unmanaged landscapes. So the ability to tolerate damage and regrow and produce lots of, uh, seeds, those are all things that contribute to an, uh, an inertia in our. Systems where buckthorn is managed but then comes back again pretty readily. Mm. Part of that is that, uh, we kind of have three different modes that buckthorn uses to keep itself lodged in our systems. One is that there are gonna be plants that just aren't treated fully, right? It's pretty robust, pretty resistant, and whatever management we do, whether that's, you know, cutting down the trees, spraying it with chemicals, using fire, or whatever it is, there are gonna be some plants that persist, right? So not everyone's gonna get killed by whatever management we do. Then we have another layer of plants that, uh, are intentionally or unintentionally excluded from the management. So, in particular, these are things like small buckthorn that maybe we go out in the woods and we're like, we're gonna take care of all the large buckthorn, and we just don't even see the little guys that are hanging out on the forest floor. Right. Those are still buckthorn. They're still there. Um, and they will grow up, uh, pretty quickly once we remove their big, uh, brothers and sisters, moms and dads. Then the third, uh, pathway that they use are seeds. So buckthorn produces tons of seeds, especially in highlight areas like forest edges or, uh, in parks, especially under maybe those, those oak canopies that are a little bit more open, especially now with things like oak quilt spreading those. Plants produce so many seeds that, uh, will germinate very quickly. Uh, you know, within the first couple years of, of dispersal, uh, most of them will, will pop up and they create these chia pets, these carpets of buckthorn seedlings. And, uh, it's very challenging with those three things, whether we're talking about those resprout or the missed individuals or the new seedlings for anything to compete. Um. And oftentimes there isn't much there to compete against buckthorn in the first place. So we have like overwhelming pressure from these buckthorn that are already on site and then very little to compete against it.

Lee Freilich: 16:44

Yeah, and I would add to that, that we have so many forests where the understory is essentially an empty niche because. We, when we fragmented the forest, when European settlers came, we created a lot of edge deer love edges. The deer population exploded, and at the same time, the European earthworms invaded. So the European earthworms. Ate the forest floor, the organic horizon, or what people call the duff. And a lot of the plants and tree ceilings were rooted in that. So the standing crop was destroyed. And after that happened, the deer ate all the remaining plants.'cause the deer to plant ratio was way higher when 90% of the plants are wiped out by the earthworms. And then you have this empty niche. There's no standing crop of plants to reseed the area. So we had a lot of forests that just had empty underst stories, nothing that would compete with buckthorn. And that's very widespread. And I think that's one of the reasons that buckthorn has invaded so many areas and has become so high in density. I mean, when you look in. In forests in southern Minnesota and you have like a thousand to 10,000 of them per acre. And then you go to Europe where buckthorn is native and you see like one per acre. You know, because the mechanisms that control it there are, are in play and they are not here nothing to compete with it. And there are probably other ways that they are controlled by, by insects and herbivorous insects and. Who knows what kind of chemical warfare between other plants in Europe and their native habitat is keeping buckthorn under control. And that's all absent here.

Jennifer Burington: 18:43

So talking a little bit more about herbicides have kind of mentioned, um, chemical control a little bit. Uh, herbicides are often used in managing buckthorn. Um, how effective are they and where do they fall short? Mike, if you wanna start us.

Mike Schuster: 19:00

Yeah, so herbicides are a highly effective tool, right? We, we have them because they work. Um, but the challenge with buckthorn management is not killing a single tree. It is killing, uh, a population, um, or rather controlling a population would be the, probably the better way of phrasing that. Um, and, and so herbicides are really effective. Um, and we have lots of different ways that we can use herbicides, whether that's a cut stump treatment or a basal bark or a foliar. All of those are highly effective, um, at killing individuals. Um, your mileage will vary depending on the chemical and the environmental factors, but in general, they are pretty good. Um, places where they. Fall short are in those kind of ecosystem or community level impacts, right? Where we have potential non-target impacts, uh, where, you know, an an herbicide that we use is gonna have some detrimental impact on some other species that maybe we're trying to either propagate or is already on site, uh, or. Where we're just missing individuals and having some of that detection error play out in a way that, uh, doesn't result in, in a, uh, high level of stand control.

Jennifer Burington: 20:15

Yeah, I know they have a lot of, um, you can buy like the bingo dabbers that have the herbicide, um, kind of in them already for buckthorn. So you can go through and do the cut, cut the, the larger you're, you're talking like earlier about the, the larger couple inch, an inch or two inch mm-hmm. Um, trees when the buckthorn get very, uh, a little bit larger and then using that, doing the cut and then the treat right after it. Um, and I know they have a lot of those available, but. Uh, yeah. And that you, you're not gonna treat a teeny tiny little seedling that's just a couple inches off the ground. You're gonna have to pull that one out, but, yeah.

Mike Schuster: 20:52

Yeah. I mean, you could, you could treat that little guy. You could. I mean, I, I, I've done that at times. Um, but, but certainly most land owners. Property managers are gonna want to use, you know, the cut stump treatment for the larger individuals and then uproot things, uh, as they see feasible or, or, you know, as, as practical, one of the things with uprooting, uh, even though it's the guaranteed way to kill a plant, right? The, the only surefire way, uh, to. To control a single buckthorn stem is to pull it outta the ground no matter what other treatment you use. There's always a chance of failure except if you pull it out of the ground. Um, but that can be fairly labor intensive, especially given the number of stems that we see in these stands. And, um, it also has, you know, impacts on soil disturbance, um, because of these relationships with buckthorn, excluding native ground cover. And the earthworm invasions means that these, these soils are pretty. Fragile. Um, and so uprooting plants, uh, on top of that can, you know, make issues of erosion or, or other, uh, kind of stand level impacts, um, much worse. So it's, it's a balancing act about finding what tool is gonna work best in each situation and have the best ratio of, uh, benefit and cost.

Jennifer Burington: 22:12

So talking a little bit more about the cost and benefit and the different strategies, uh, which strategies have proven to be the most effective for achieving long-term control of Buckthorn Lee, if you wanna start us.

Lee Freilich: 22:28

Um, yeah. The most effective method is to. Fill that empty niche after you do the initial removal of buckthorn with the native plants in order to create a bottleneck in the lifecycle of the buckthorn, which is dense shade at the soil level when the ceilings are fo first, um, germinating. So creating that shade, I think is the, is the most important thing for long term as well as. Keeping your eye on surrounding seed sources because your neighbor's land might still have seed sources.

Mike Schuster: 23:08

The, the lifecycle of buckthorn is really interesting in the way that, uh, it is a quantity over quality strategy and, um. And oftentimes we, we set buckthorn up for a win in a way that, uh, the quantity is also quality, unfortunately. So, uh, what happens is that buckthorn produces all these seeds, and as we talked about a moment ago, uh, there's all this empty niche space. There's no competition from native plants or. You know, heck, it could even be other invasive plants. Um, but there's no competition. It's, it's just buckthorn. And that allows these little seedlings to thrive and turn into big buckthorn very quickly. Um, what we find, if we look at the year over year survival rates of any given buckthorn, is that they're most vulnerable to competition. In the first couple years of their life, once they get to be two, three years old, then they start to be much more robust and established and tolerant of any type of competition. But when they're little, when they are, you know, in their first, second summer growing, that's when they're vulnerable. That's when we can actually compete against them. And that's fortuitous for us because that's also when they're smallest. Um, and. We have the greatest number of plant species that are gonna be taller than them and be able to actually produce leaves that will shade them out, right? If, if buckthorn was, you know, three feet tall in its first year, that wouldn't be the case. But fortunately, seedlings are a couple inches tall, and so we can effectively generate plant cover in a way that pushes them out and reduces the total number of plants that we have to deal with going forward. I'll also add that. Management isn't a silver bullet, right? There is no silver bullet in management, and that establishing dense native plant cover is a promising and data-driven tool for reducing buckthorn invasion over the long time, over the long term. But the strategies that we see working are not just one thing. It's many different things, many different approaches. To create a, a mosaic of, uh, management tools and outcomes that overlap in a way that in gives us the best opportunity for success at the community level. Um, there might be some tools that are gonna work better in certain portions of your property and other tools that are gonna work better in others. And so utilizing multiple different things, whether that's mechanical removal, uprooting chemical treatment, fire, whatever you have, um, doing those things. Over, um, a, a management regime and not just a single touch is a important component of having long-term control.

Jennifer Burington: 25:56

So there is light at the end of the tunnel for buckthorn control. Yes. So Mike, if you wanna keep talking here for a little bit, can you tell listeners about your specific project, your cover it up project, and what have you learned about using native species, uh, to prevent buckthorn from returning? And where can this approach be most effective? We've kind of talked a little bit about forests and we've talked about residential buckthorn. Or on residential properties and forest land. Um, so if you wanna kind of explain your research a little bit more.

Mike Schuster: 26:29

Cover it up is a project that started in, in 2016 and the idea was, you know, just can we get native plants to compete against buckthorn? And when we started that, it was actually a pretty big question. Um, you know, the, you might look at native plant systems or, or just, you know, natural areas and, uh, say the proof is in the pudding that no. Native plants can't compete against buckthorn because if they could, what's buckthorn doing here in the first place? Um, and so we started off kind of with a shotgun approach, looking at a bunch of different, um, a bunch of different species and a bunch of different contexts, uh, varying from relatively uh. Resource, uh, intensive approaches like planting trees, uh, like balsam, fur and sugar, maple, and these really dense kind of, uh, patches, uh, all the way just to kind of more, uh, accessible forms of management like, uh, herbaceous seeding. And through that process, we identify that, yeah, native plants can, uh, can win if you give them. The chance if you kind of put your thumb on the scale of competition and give them. The first crack at things. If they can establish quickly before the little buckthorn turn into big buckthorn, then they can interrupt the cycle and push buckthorn, uh, out of the system. At least to an extent, that makes further management much more practical. And in the years since that we've. Started to develop more nuanced understanding of, you know, what makes this strategy work and what its limitations are, what types of species work best in which scenarios. And this has taken the form of many different experiments at this point, um, throughout the state of Minnesota and beyond looking at different management approaches and pairing them with, you know, herbaceous, seeding, um, different compositions of seeding different seed rates. And we see that often, um, often. Getting plants in the fight fortifying for, uh, forests right away after management or simultaneously with some sort of mechanical removal of buckthorn really is the strategy. This isn't something where you do your management, remove the buckthorn, and then wait five years to put native seed down. The battle's already lost at that point. This is something where we need to be proactive and, uh, preempt the buckthorn with our native. Uh, plant species and allow them to, um, soak up the resources that would otherwise be exploited by the buckthorn that remain after our management.

Jennifer Burington: 29:01

So that sounds like a big project, and you probably have a lot of species that you're looking at, um, for native species. So can you name some of the native plants, uh, homeowners can use to replace, um, buckthorn or to cover up, uh, their forest floor so that buckthorn can't come through?

Mike Schuster: 29:18

We have looked at a large variety of plants. Uh, certainly not all the plants. That's impossible. Um, certainly not the majority of plants, right? There are tons and tons of native plants out there that we could look at that I encourage people to explore and potentially utilize in this approach. What we've demonstrated is, uh, a concept, right, is a, a general idea of how you might be able to do this and identified some key. You know, features of different plant species that seem to be important in that, and those broadly fall into two categories. One is rapid establishment, so they have to be things that grow really quickly. Um, and they also have to be things that, uh, hold their leaves or shade buckthorn, particularly in the fall. So. One of the things that makes Buckthorn special is that it holds its leaves late into the fall that allows buckthorn to photosynthesize to create sugars that it relies on to survive and grow, uh, at a time when pretty much other, any other understory species is going to be dormant for the season. Uh, and that's a huge leg up. That's a bunch of sugar that other species just don't have access to, but buckthorn does. And if we can turn that superpower into a weakness. Well, that's how we win. So, native plant species that either hold their leaves into that, uh, critical fall window or at least produce, you know, some thatch, some, some dead material that can still shade even if it itself isn't green and photosynthesizing. Those are the things that are gonna do well. We see examples of that in things like, uh, elderberry species. So elderberry is a shrub and, uh. It grows pretty quickly. Um, of course it is a favorite of deer, so it needs to be protected. Um, but it grows quickly enough and holds its leaves late enough that it can shade out. Buckthorn effectively. We've observed that, uh, elderberry leaves, even though they senesce, even though they turn brown, uh, they're still on the shrub late into fall, early winter, just like buckthorn. And so they can shade out those little guys, uh, when they're most vulnerable. Other things like, um, evergreen species, so like fir, uh, is a, is another option that you can use. Uh, of course many land managers don't want to transition like an oak woodland into a fur plantation. So, you know, again, your mileage will vary. I. On the herbaceous side of things, we see things like wild rye grasses being a very accessible, very, um, reasonable tool because of this as well. So, wild rye grasses are relatively cheap to acquire. They're easy to seed and they establish densely in a pretty wide range of environmental context. Uh, basically anything more than about. Seven, 8% light availability. Uh, so canopy openness, if you look up at the sky, how much actual sky you see, as long as that's, you know, seven, 8% or more, you're gonna start to get these wild ryes really starting to pop up. And those are places, uh, or those are species that, um, produce these thatchy grass layers in the fall and mitigate that advantage that buckthorn would otherwise have. So those are all things that are really important. Um, and so we see those species being. Useful tools in this approach that many, um, many land managers can access. We also see species that, um, maybe don't have as much benefit right away. So buckthorn seeds germinate very quickly, you know, with the first couple years of management. And so the key really is to have those plants established in that, you know, one to two year window. But. That doesn't mean that's the end of the story, right? buckthorn is still gonna show up in, in your stand because there's buckthorn out in the world that's gonna disperse in. And so we need to build these long-term resistance, uh, into these communities. And the way to do that is not through monoculture, not through just wild, dry grasses, because they actually thin out after about three to five years. And so then we have to look at other species things like, uh, Virginia water leaf or um, uh, white snake root. These are species that, uh, maybe take a little bit longer to establish in the site, but going forward, as the wild rise wane out of the system, they can take the reins, they can establish this dense layer that will then compete against the smaller but continual stream of buckthorn that comes in the future.

Lee Freilich: 33:57

Yeah. And I would add to that some of my favorite, um, understory herbaceous species, namely the ones that form pretty dense colonies that cover the ground. And some of them aren't even very tall, but they're very good at excluding just about everything else, and that those are species like wild ginger, woodland flox, wood nettle, and enchanter's nightshade. So in my own gardens, they've been able to exclude everything else and I'm just managing the competition among them and nothing else can get in there. So, um, there are a lot of species left to try in future research, um, for the purpose of competing with buckthorn, and they do have to be there to compete. So, um. I've tried a lot of these and they do get along with the European earthworms and the jumping worms, which is another thing they have to be able to do because the invasive worms are out there and not all native species will grow well in the earthworms presence, whereas the ones that I just mentioned do. And then for Shrubs, green and Dogwood, um, I don't know if you've tried that in the cover it Up project, but. It's also called, called Round leaf Dogwood. And they have these nice big four or five inch diameter leaves, which seem to me would be really good at casting shade. And they're kind of moderately shade tolerant, so they should grow in, in Oak Forest under stories. Um, but yeah, it's um, very important to. To fill that empty niche with something.

Jennifer Burington: 35:44

Yes, before you get, uh, some of the other, uh, noxious weeds, um, garlic, uh, mustard and honeysuckles and other, other ones like that.'cause as soon as you open everything up, all those other ones wanna come right back into.

Mike Schuster: 36:01

One of the other things Lee mentioned was, uh, dogwood and Dogwood is something that we've, we've explored in a few of our experiments trying to, uh, plant it in as a bare root, uh, but also seed it, seed it in. And, uh, that's something where. You know, it, one of the challenges that we have with this type of approach is just getting access to propag, getting access to plants, right? You can buy a bare root stock of, of these shrubs, but at a management scale, that's pretty impractical to create a, a whole forest full of shrubs, uh, by planting bare root. Looking at seed sources though, uh, that's something that is. Much more practical in many contexts because, you know, it's a lot easier to seed something in than it is to plant something in and get a similar density. But of course you're dealing with this reality of, of deer populations and browsing and everything like that. But it does seem like there is a way that we can, you know, kind of mix and match these strategies in a way that you have targeted planting. Amongst seed in a way that can, you know, have isolated impacts of planting and then the more kind of widespread impacts of seeding. And, you know, what do you know, after a few years we have this, uh, succession and, and development of these natural communities that are more robust to invasion and more functional in a way that, uh, benefits not only native plants and wildlife, but also us.

Jennifer Burington: 37:31

Yeah. Lots of tools in the toolbox to use and using them. All, some, a little bit more than others, um, makes it actually a feasible project to, to do and then it can be a success. Um. So kind of going Lee a little bit more with the relationship between buckthorn, buckthorn and earthworms, um, how do earthworms help buckthorn spread? We kind of talked about they have both invaded kind of here at the same time. Um, if you wanna kind of explain that a little bit.

Lee Freilich: 38:01

Sure. Yeah. The buckthorn and earthworms are co-evolved with each other on their home continent. Um, so, and there's actually a symbiotic relationship between the night crawler, which is our invasive earthworm species with by far the largest biomass. I mean, we have eight or 10 invasive European earthworm species in most forests, but the night crawler is. By far the, the highest amount of biomass and night crawlers create a perfect seed bed for buckthorn seeds to germinate. And the buckthorn leaf litter is a perfect food source for the earthworms. I mean, earthworms eat dead leaves for a living, right? Um, that's what they do. And buckthorn leaves have just the right composition. That they're absolutely the favorite of earthworms. They have high amounts of nitrogen and calcium, for example, and the earthworms can tell that when they touch the leaf. As we did an experiment where we had leaves of different species, dead leaves, um, and when the earthworms woke up in late April, they sorted the leaves in the vicinity of their burrow by species of tree from which they came, and they brought the species like basswood. That have more calcium and nitrogen closest to their burrow and ate all of those. And then the maple leaves. And then the oak leaves in August. Um, but buckthorn leaves are the most perfect food there is. So if you have a thicket of buckthorn, night, crawlers can live anywhere, and they only have to go a few inches to get a perfect source of food. I mean, it's like having a grocery store in your house for every or your living quarters, for every, um. Night crawler. So the earthworms also by removing the thick organic horizon. You know, I said they make a perfect seed bed. Well, the, the seed doesn't have to spend a lot of energy sending its root system through the organic layer to get down to mineral soil. The earthworms get rid of the organic horizon. They eat all the new leaves that fall every year. So you don't get a buildup of, of, uh, forest floor material like there used to be before earthworm invasion. And that facilitates not only buckthorn, but garlic mustard and honeysuckle and Japanese barberry and all sorts of, of, um, invasive plant species that really do well on that type of a bare mineral soil seed bed. So very strong symbiotic relationship there.

Jennifer Burington: 41:03

So we've talked a lot about how bad buckthorn is, and for listeners who may have, may be feeling overwhelmed, we have, we, there is hope at the end, um, about managing buckthorn. Where do you suggest. They start, um, their control efforts. Lee, if you wanna start us off.

Lee Freilich: 41:22

Yeah. Well, what I really like is what I call the rolling restoration. Like if you have acres and acres of land, clear out the buckthorn in one small area, get the native plants established, and then every year move the front. You know, another 10 or 20 feet or 50 feet how, however much you can do with a physical removal by cutting the buck, cutting and pulling the buckthorn. And once you get the native plants established solidly, you have an automatic seed source there so they can keep moving as you push the restoration forward across the property. So if you basically look at it as doing a little bit every year. And running the process backwards. So it took the buckthorn like several decades to invade. You're just gonna run that backwards for the next few decades and don't get overwhelmed that you can't do it all at once.

Mike Schuster: 42:24

Lee's idea of a rolling restoration also really fits well with some of the, the work that we've done where we've seen some of the biggest. Challenges are those small buckthorn, right? And so it's better to do a small area well than a large area poorly. Um, having a rolling restoration allows you to really focus on, um, on, you know, community level management, so you're not just getting the big buckthorn, even though those are the ones that are, you know, drawing your attention right away. They, you know, when you, when you, when you walk out to the woods, you're like, oh, I, I gotta get that one, right? Yes. But. Probably more important is making sure we have good control of all the other ones, uh, as well. So, uh, those are the things that, that are, are gonna make your, uh, work more challenging in the long run. And so a rolling restoration where you're really focusing on. The, uh, on the community piece by piece is gonna be something that, uh, I think is emboldening for a lot of managers because you can see the impact in a small area and it makes things much more feasible, uh, than trying to do everything all at once, everywhere.

Jennifer Burington: 43:36

Perfect. And then just to give listeners a little bit more information about, um, buckthorn management, uh, do you guys have any resources that you would like to share? One that, um, I know of is on our own website, on the Department of Agriculture website, which is www.mda.state.mn.us and we have, um, a noxious weed list and you can go and see, um, buckthorn is on there, or you could just search for buckthorn and help identify if you have glossy buckthorn, common buckthorn. Um, and then we have links to the Minnesota DNR also has, um, kind of a, a brochure on different management approaches, especially like the herbicide management, when to do application, how much and, and the types. So Mike, if you have some resources that you'd like to share.

Mike Schuster: 44:26

So a lot of our work is detailed on, uh, the covered up website, which is cover it up dot um, dot edu. Um, but. That has things like, uh, you know, our results, our seed mixes that we use, um, links to suppliers for, for different, uh, seed mixes and all that sort of thing. So, um, I think that's a fairly reasonable resource for people that are starting to explore the idea of revegetation seeding. Um, but more generally, uh, you know, there are tons of resources, especially in our state, uh, about how to. Deal with buckthorn, uh, whether that's the MDA website or, um, the DNR website. Uh, university of Minnesota Extension also has a ton of really good resources for people about how to deal with buckthorn and other invasives.

Jennifer Burington: 45:17

And along with the University of Minnesota extension too, there's the master gardener groups, um, that people can contact for their counties. Um, that'll probably off be able to offer, um, some suggestions and if not, um, maybe sharing some of the native plants that they have had success with, um, in, in their buckthorn management, uh, projects. Uh, so yeah. Well, thank you guys. I appreciate you having me here. Uh, thank you so much for coming. Um, appreciate your time. And it has truly been, uh, a joy talking about, uh, buckthorn and I certainly learned a lot and I'm sure our listeners did too.

Lee Freilich: 45:54

Yeah, it was fun. Thanks for having me on the podcast.

Mike Schuster: 45:58

Yeah, thanks for having me. I'm always happy to talk about buckthorn.

Jennifer Burington: 46:01

Perfect. This has been Smarty Plants, a podcast from the Minnesota Department of Agriculture. Our producer is Brittany Raveill. Our editor is Larry Schumacher, and I have been your host. You can learn more about pests and other invasive species that affect our environment at www.mda.state.mn.us and while you head to our website, we'll be working on the next episode of Smarty Plants. See you there.