Time To Stop Picking on Weeds and Non-Natives? People may think of invasive species and weeds as pests, or invaders that don't belong. But biologist Mark Davis and author Richard Mabey say non-native species and weeds don't deserve their bad rap, and discuss how these 'invaders' can benefit both humans and the environment.

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Time To Stop Picking on Weeds and Non-Natives?

Time To Stop Picking on Weeds and Non-Natives?

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People may think of invasive species and weeds as pests, or invaders that don't belong. But biologist Mark Davis and author Richard Mabey say non-native species and weeds don't deserve their bad rap, and discuss how these 'invaders' can benefit both humans and the environment.

IRA FLATOW, host: Next up, weeds. Anyone who's been out in the garden this summer knows the troubles the simple dandelion can cause - they choke out your tomatoes, that basil that you've been trying to nurse back to health for that pesto you're waiting for. But weeds aren't all bad, according to my next guests. They help keep your garden soil healthy. And what we call a weed today may have been a food or a medicine just a couple of generations ago. Look at those dandelions - the greens are a trendy salad ingredient.

But there's that other environmental demon, too, non-native species like the Asian carp clogging up the Mississippi River, or the famous kudzu suffocating American forests. Invasive species can run rampant. They can wreck ecosystems. But just like weeds, many invasives just quietly make themselves at home. They provide food, some shelter for local species, and become just as important to the environment as species that settled in the area a long time ago.

Most of the time, we can't eradicate invasive species anyway. And if you can't beat them, is it time to - well, maybe not join them, but at least learn to live with them? What do you think? If a species comes from someplace else, is that really such a bad thing? And what about weeds - you have some favorite weeds of yours that really are more like plants and pets to you? Give us a call. Our number: 1-800-989-8255, 1-800-989-TALK. You can tweet us: @scifri. Or go to our Facebook page at scifri, or go to our website at sciencefriday.com, and talk to the folks there.

Mark Davis is the DeWitt Wallace Professor of Biology in McAllister College, in St. Paul. He joins us from Minnesota Public Radio. Welcome to SCIENCE FRIDAY, Dr. Davis.

Dr. MARK DAVIS: Hello, Ira. It's a pleasure to be a guest on your show.

FLATOW: You're welcome. Richard Mabey is the author of "Weeds: In Defense of Nature's Most Unloved Plants." He joins us by phone from England. Welcome to SCIENCE FRIDAY, Mr. Mabey.

RICHARD MABEY: Hello. I'm very happy to be with you.

FLATOW: Do we know, Richard, what a weed is defined as?

MABEY: Well, people have had all kinds of attempts at defining them. Ralph Waldo Emerson - one of your countrymen - said a weed is simply a plant whose virtues have not yet been discovered. The most common definition of a weed is a plant in the wrong place. But that, of course, begs what is the right place and who makes the decisions about the right place? So really, if you look at the 10,000 years in which humans have been deciding which plants they want around them and which plants they don't, it's all entirely subjective. A weed is a plant that gets in the way of your plants.

FLATOW: There you go. This is SCIENCE FRIDAY from NPR. I'm Ira Flatow, talking with Richard Mabey and also with Mark Davis. What about invasive species, Mark. Do we have a definition, a concrete definition, or does that need to be changed now?

DAVIS: Well, that's a good question. Currently, in the United States and in most parts of the world, the term invasive is supposed to be used - or is typically used to refer to a non-native species that is causing harm of some sort. And that could be human health harm, it could be economic harm, it could be ecological harm. The catch is, is that the term invasive is often used not too discriminately.

Certainly, historically, over the last couple of decades, in the '80s and '90s, in the scientific community, non-native species in general were typically referred to as invaders. And there really was very little discrimination between non-native species that caused the problem, and non-native species that were relatively benign or perhaps even helpful.

FLATOW: But there must be plants around that we think of as being American, that started out as invasive species. And we just didn't know it.

DAVIS: Well, certainly there's non-native species. I mean, it's interesting, if you look at the state flowers or state insects, a good number of them are not native species, which actually illustrates one of Richard's points in his book, which is that, yeah, non-native species or if we're talking about plants - weeds actually are part of the heritage of an area. So for example, the state flower of Vermont is a purple clover and the state insect, as it is for about, oh, nearly a third of the states in the United States, is the honey bee. Of course, neither of those are introduced, but for all the people currently alive...

FLATOW: Are we talking about - I'm sorry, go ahead.

DAVIS: Well, I was going to say, for all the people currently alive, they were - when they born, the honey bee and the purple clover were already present. And so, you know, for an awful lot of people, non-native species have always been part of their life, and they don't really regard them as an invader.

FLATOW: Richard, but we talk about weeds - do weeds actually have any benefit to them?

MABEY: Well, yes. I mean, there are all kinds of - I should call human benefits that you can list. I mean, there wouldn't be crop plants. We wouldn't have had the ability to grow plants in agriculture if there weren't certain species that showed themselves very adaptable to human presence. And indeed almost all crop plants, from the emmer - wild emmer that became the first wheat, through to the very first leaf plants - members of the (unintelligible) family - they're all weeds. And if you can say that that's one of the characteristics of weeds - is that they thrive in human composting, they exploit the disturbance of the ground - then we wouldn't be here if it wasn't for weeds.

DAVIS: But the need, the essential importance of weeds at the moment - and it's the question we simply don't ask. We have a kind of knee-jerk reflex to both invasive plants and the more humdrum garden weeds. We do not ask why they are there. We assume that they're some kind of invasion from beyond, and we fail to take responsibility for our part in creating conditions which are right for them. And all they are trying to do is to green over, basically, empty ground. And for that, I think, perhaps we should give them a second chance.

FLATOW: Yeah, I agree. Richard Mabey is author of "Weeds: In Defense of Nature's Most Unloved Plants." Mark Davis, DeWitt Wallace professor of biology in Macalester College in St. Paul. We're going to take a break, come back and take more of your calls about weeds. Stay with us. We'll be right back.

I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.


FLATOW: You're listening to SCIENCE FRIDAY. I'm Ira Flatow.

We're talking this hour about weeds and invasive species, and why they may not be as bad as you think - with my guests Mark Davis, DeWitt Wallace professor of biology at Macalester College in St. Paul; Richard Mabey, author of "Weeds: In Defense of Nature's Most Unloved Plants." Our number: 1-800-989-8255. Let's get a phone call or two, if we can. Kara in Louisville, Kentucky. Hi, Kara.

KARA: Hello.

FLATOW: Hi there. Go ahead, please.

KARA: I'm a professional organic gardener in Louisville, and I am very interested in this topic, of course. And there are a lot of native species here that are dangerous as well as invasive, like poison ivy and the trumpet vine, which is sometimes called cow itch. And also, there's a plant - I can't remember its name, but it's responsible for the death of Abraham Lincoln's mother by milk sickness. It's blooming right now, and I've pulled a lot of it.


KARA: It's very common. So I'd like to hear your guests' remarks on those kinds of plants.

FLATOW: OK. Thanks for calling. Richard or Mark, do you know what plant she was talking about with Abraham Lincoln's mother?

MABEY: I don't know the plant responsible for Abraham Lincoln's mother, but I'm disturbed that there is such a human-centered view of these plants. I mean, we live on a planet where there are enormous numbers of organisms that have to make a living as well as us. And poison ivy, for instance - the berries of poison ivy are the most important food of the chickadee in your country. And are we condemning the chickadee to a diet because we actually get inconvenienced by poison ivy? I really think that when - you know, in the middle of the 21st century, we start to take a planet-centered view of these plants, and think not just in terms of the occasional inconvenience they cause to us, but how do they fit into the whole ecosystem?


MABEY: And if you start to do that, you begin to find that things that we call weeds are absolutely crucial in the lives of enormous numbers of other organisms.

FLATOW: Interesting. Richard, would you agree?

DAVIS: Mark. Yes.

FLATOW: I'm sorry. Mark, would you agree?

DAVIS: I really appreciate the caller's point. Species are just species. Some of them are, from the human perspective, are desirable, and some of them are not desirable. So we have some native species that we like. There are native species that are problems. There are recently introduced species that we like. There are recently introduced species that are problems.

I think the perspective that Richard and I are both trying to get out is just a simple, more sensible view that we shouldn't embrace this native versus non-native perspective, which really has been embraced - particularly in the United States - by a lot of people over the last couple of decades, which is an interesting point in itself.

I suspect we may get some other calls quite critical of what Richard and I are saying. This is an exceedingly emotional topic for a lot of people. They have really - they really like to dislike certain species. Ultimately, I think that that's maybe an inherent human characteristic. That's what the anthropologists would say. It's what some evolutionary biologists are saying now. That - for example, when altruism evolved, along with that was a distrust of people outside your group. So, in other words, maybe humans are predisposed to have an us-versus-them viewpoint on the world. And we just - for that, we just fall into this trap when it comes to species. We want to embrace the natives and actually, we love to hate the non-natives.

FLATOW: Isn't this - I had heard that Kentucky bluegrass is a weed in Great Britain. Is that right?

MABEY: Yes, it is. I mean, I don't think anyone would actually call it a weed because it's a component of natural pasturelands in this country. But of course, it went over to the United - America with the first settlers, probably in the hooves, in the forage they took over with them. And it very rapidly became established, because it was a grass that had evolved in company with the heavy hooves and intensive grazing of European stock. And the native grasses east of the Mississippi, in America, were simply no match for the batch. And so what with - our meadow grass conquered your indigenous area grasses, and then got rebranded as Kentucky bluegrass.


MABEY: And it's a very, kind of ironic example because it was both an invasive weed when it got to you, which actually drove out your indigenous native species - which, of course, was an enormous boon to ranchers, because the grass is vigorous and it survived the trampling of cattle and was extremely nutritious. So how do you weigh that in the balance? It became, in a sense, a crop plant.

FLATOW: Exactly. We have a tweet in. Here's - I knew our listeners would come through - from Zolofa(ph), who says, Lincoln's mother that we referred to - that Lincoln's mother was poisoned by eupatorium rugosum, the white snakeroot. Cattle that eat this plant could pass a toxin to humans. And that's...

DAVIS: Sure. That's a common plant around the - in Minnesota.

FLATOW: Yeah. And that's how that happened; 1-800-989-8255 is our number. What can we do with kudzu? A lot of people have been asking about this, you know? You see it everywhere. Could we make something? I mean, could we just, you know, maybe make alcohol out of it, ferment it somehow? And then it wouldn't be a weed anymore. It'd be a cash crop.


DAVIS: Well, people certainly have been making - using it for baskets and other things. I think some scientists are investigating it for some medicinal uses. So there are people that look at some of these introductions, even ones that have caused great problems, asalso possibly providing some opportunities. I know there are people already harvesting some of the Asian carp, and actually shipping them back to Asia because there's a big market for them there. That's the kind of - I suppose, speaking as an American - that's the American way, to look at opportunities that some of these might provide.

Now, I do want to make clear - and Richard makes very clear in his book as well - neither of us is saying that some of these newly introduced species are not causing very severe problems. We're just trying to make the point that in fact, most of the species aren't - the new species aren't. And we're living in an increasingly globalized world. And having this distinction between native, non-native, good versus bad, is - it's a 20th century concept, really, sort of like wilderness.

I mean, wilderness doesn't really make that much sense anymore. And the native versus non-native is going to progressively make less and less sense as the 21st century proceeds.

FLATOW: Let's go to Alan in Houston. Hi, Alan.

ALAN: Hello. I want to give a shout-out to - I'm 65 years old. And in my lifetime, we've seen the invasion of fire ants, which are killing off other species of ants besides being a nuisance. And also, we've seen the invasion from the south of the so-called killer bees, the more aggressive honeybees. But what I want to talk about - I grew up in San Joaquin Valley of Central California and was introduced at an early age to the tumbleweed.

And it's been accepted into our culture and folklore, and we hardly think about cowboys on the range without seeing tumbleweed. But in fact - is it true there were no tumbleweeds around back in the 1800s, that they're invading Russian thistle?

DAVIS: You're exactly right. And whether the term, you know, the appropriate term is invading or not, I mean, they were introduced, and you're right. Any of us that grew up watching Westerns, tumbleweeds were part of the - what we felt was the native landscape. And in fact, yeah, they weren't. They were - they're an introduced plant.

ALAN: A lot of plants will distribute themselves in the wind by shedding their seeds, and this plant uniquely dies in a ball shape. And the whole plant comes loose and rolls along the ground in the plains with the wind, while it distributes it seeds. It's just bouncing along. Thank you very much.

FLATOW: Thank you. That's informative. I always thought they were dead plants, you know, that the sticks were just left over, and they were tumbling around. But that's how they distribute their seeds.

DAVIS: That's a wonderful example of evolution - evolutionary adaptations.

FLATOW: Wow. Let me ask you this, Richard: Where do most of the plants we think of as weeds come from? Are they native, or do they come from other places?

MABEY: Well, it's not so much where they come from as the kind of place they come from. We're talking about weeds and invasive plants as if they were completely different kinds of categories. But in fact, all weeds are invasive plants, and it could be reasonably said that all plants are invasive plants. Because certainly, in the temperate zones - we were ravaged by glaciers during the end of the Ice Age, and the landscape was completely bare. So the plants had to come back from other places.

And the very first plants to come back were the highly adaptable, flexible, fast-moving mobile species that we have come to call weeds. They are ones who have - whose evolution have adapted them to disturbed conditions: the edge of the volcanoes, scree on mountains, floodplains by rivers. And as soon as human beings started creating the same kind of disturbed landscape that existed - that still exists in a lot of natural areas on the planet, then these species were able to move out of their original environments and actually take roots in our landscapes - you know, in cultivated fields, in battlefields, in building sites - where we were creating precisely the same kind of conditions that they grew in naturally.

FLATOW: Mm-hmm. Richard, in writing "Weeds," I know you asked, you know - ask authors about their favorite things is like asking them about their favorite children, but I'll ask anyhow. Did you have a favorite weed?

MABEY: Do I have a favorite weed? I think my favorite weed would be the one that causes the most trouble...


MABEY: ...whichever that is to any person. Because the great paradox about weeds, for me - and I'm kind of speaking culturally here rather than as a gardener or anything - is that even though they depend absolutely on human activity to prosper - they need that chaos that we create on the planet to survive - they won't do things our way. They are the cussed outlaws. And to me, that makes them the absolute epitome of wildness. And so the - for me, the best weed is the wildest, most cussed weed.

And let me think of one that we both share. I think you've got a giant hogweed, (unintelligible) a massive, 18-foot tall umbellifer that causes skin rashes on people if they don't respect it. It came from the Caucasus, and it got caught up in the kind of paranoia about the Cold War. And there are some good science fiction stories...

FLATOW: I'll bet.

MABEY: So I would say giant hogweed is my favorite weed because it causes the most trouble.

FLATOW: This is SCIENCE FRIDAY from NPR. I'm Ira Flatow, talking with weeds with Mark Davis and Richard Mabey. That was one heck of a weed - the size of that plant. Our prairie, though, back in the 19th century, were covered with all the different kinds of weeds and plants and things, were they not, Richard? You know - and Mark, I mean, there were all kinds of things there; did people go out and start identifying what the weeds were, what the invasive species were? Or did they just set out - wherever they put their roots down, they decided this is a weed and this is something good?

DAVIS: Well, it depends, I guess, who the person was. North American botanists certainly were recognizing that some of the plants that they were seeing had come from Europe. I mean, botanists were recognizing that from the beginning. The typical citizen, unless they had a special interest and hobby in botany, you know, it's unlikely - no. They wouldn't distinguish between a native species and a non-native species. What they would distinguish between would be species that were, for whatever their interests were, were helpful, and species that were problems for them.

And that's really, I think - at least, speaking for myself and my colleagues; a number of colleagues that share my view - is really, what we're arguing is that we should focus more on what the species' current role or function is and less - care less about if it's been here for 10,000 years, or if it's been here for 200 years, or if it's been here for five years.

FLATOW: So if it gets - if it's happy and it's getting - if it's happy in its niche, it's doing, you know, filling up that niche and doing, I guess, good things for us, we shouldn't care where it came from.

DAVIS: Exactly.

FLATOW: I guess just like people.

DAVIS: It's very much like people. Many of your listeners may have seen the article in the paper this morning that illustrates one of the problems of kind of vilifying and demonizing non-native species. I mean, once you really vilify something, it sort of justifies almost any kind of control measure. And so, you know, the front page of the New York Times - and probably other papers - the recent realization that a new herbicide that supposedly was supposed to be environmentally friendly, that's being used to kill things like dandelions and clovers, native in the U.S., ends up also killing or at least - yeah, I think, actually what the article says, killing trees.

FLATOW: Yeah. Yeah.

DAVIS: Well, this is - and there's a growing resentment among the public. I get letters all the time thanking me for some of my writings because they're upset with this continued effort to spread more chemicals, to try to get rid of these supposed terrible plant species out there.

FLATOW: All right. We're going to have to...

DAVIS: And there...

FLATOW: We're going to have to end it there. Mark and Richard, thank you...

DAVIS: Sure.

FLATOW: ...for taking time. We've run out of time. Mark Davis is the DeWitt Wallace Professor of Biology at Macalester College, in St. Paul. Richard Mabey, author of "Weeds: In Defense of Nature's Most Unloved Plants." Interesting read. I suggest you go out in the backyard and have a read for yourself. Thank you both for joining us today. Have a good weekend.

DAVIS: Well, certainly my pleasure.

FLATOW: You're welcome.

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