Search the Site

Episode Transcript

My guest today, Suzanne Simard is a professor in the Department of Forest and Conservation Studies at the University of British Columbia. Combining breakthrough research and public facing activism, she’s transforming our understanding of and our public policy towards the forest.

SIMARD: Relationships are complex, and it seems shortsighted to think that relationships between trees that spend their entire lives beside each other wouldn’t be more complex than just being competitors.

Welcome to People I (Mostly) Admire, with Steve Levitt.

Growing up in Minnesota, I spent a fair amount of time in the forest, and it’s always been pretty obvious to me that the forest functions a lot like a modern capitalist economy, with trees and plants locked in fierce competition over scarce resources like sunlight, water, and nutrients in the soil. But Suzanne Simard’s research shows that everything I’ve ever thought I understood about forests and probably everything you’ve ever thought you understood about forests is completely wrong.

*      *      *

LEVITT: Let’s go back to say the year 1980. Can you paint a picture of what logging practices looked like at that time with respect to cutting down trees and replanting the parts of the forest that had been cut?

SIMARD: It was a major transition period between logging operations where there were small companies or local communities that were logging their forests on a very small scale; supporting small local mills. In the case of my grandparents and my dad, they were logging just to feed the family. And just taking the smaller cedars out of these old growth forests. So it was all very selective logging at the time. But that changed in the ‘70s and ‘80 where the larger multinational corporate companies move in and were awarded tenures to have large licenses to do large-scale logging. And it switched to clearcut logging. And so in 1980, when I became a forester — I was a student at the time, and I got a job in one of those corporate logging companies. And all they did was clear cut. The modus operandi was to make money, and so these companies were given the license to make as much money as possible; to practice forestry as cheaply as possible for making sure the bottom line or the profits were as great as possible for the company. Keeping in mind that in Canada, and where I’m from British Columbia, that the forests are what we called crown land or land that was really appropriated from the early people, the First Nations people, but then put under the jurisdiction of the province or you might think of the federal government. And so the way the government made money from the forest on the crown land is awarding these licenses to corporations who then paid royalties back to the government, which the government then used that money to pay for social services and education and healthcare and so on. Canada is now a very wealthy country. And that is basically from the logging and the resource extraction from the land. 

LEVITT: So these companies have strong incentives to cut down all the trees and the public policy supports it. So after these companies clearcut the land, they’re obligated then to replant them. What did that look like?

SIMARD: Yeah, the land was replanted after clear cutting to ensure that there was a quick repopulation of that forest with trees. And the sooner you re-established these young seedlings, the faster they grow then the sooner that they can harvest them in the future. And you also can control what species are coming back. And so thinking of the marketplace, if Douglas fir is really lucrative, which it has been, then there’s a tendency to grow back that Douglas fir. So a lot of the species that are planted are commercially valuable species, and some species that are not considered valuable — deciduous trees here in Western Canada, they’re not planted. In fact, they’re discouraged from growing back at all.

LEVITT: Okay, so to my economist way of thinking, that seems really logical. It seems sensible that when you want to grow a particular species, you’d want to clear out all the other competition from it, and it sounds like a very effective, efficient, technocratic kind of approach to doing logging.

SIMARD: It’s a faulty model. Until recently, that is how we saw forests. It’s the Eurocentric view of a forest; post-colonial North America counts into there as well. The forest is a bunch of trees that compete with each other. They compete for light ‘cause they shade each other, and deprive each other of carbohydrates. They compete for water; whatever I get, you don’t get. And it like becomes this zero-sum game where I’m the winner, you’re the loser and nothing else really matters.

LEVITT: Okay. But all that in the background, you, Suzanne, are an undergraduate in 1980, you’re studying forestry. You’re being taught these best practices in school. But when you land that summer internship, you start to have doubts. How come?

SIMARD: I’d grown up in these rainforests where my grandfather and all my uncles and my dad — they’d logged in this very sensitive, selective way and the forest just bounced back. It thrived under this very hands-on, careful tending of the forest. And what became my summer job was not that at all. It was this massive clear cutting and opening up these huge spaces. And at that time as well, there was a mountain pine beetle outbreak that emerged around 1980. It was infesting vast areas of land that I was working in, and I saw my company just chase after those trees as they were dying, and I thought, this is probably going to make the problem worse. It’s creating more extensive areas that are more cleared and then we’re replanting them to the same species that this beetle has been infesting, which was lodgepole pine at the time. As a young student, my job was to go and how the plantations were doing. And I was just seeing these ceilings suffering under these conditions. They often were yellow and there was mortality. A lot of them did live too though. And I saw these new forests grow up and become completely different than what was cut down before them. So what was a highly variable, old multi-species forest with lots of complexity, became more uniform, all the trees, were basically behaving and growing at the same rate. And I thought, this does not feel right. The old trees that my grandfather left behind were all gone. There was a lot of mortality. And so I just thought, we can do better than this.

LEVITT: So what’s interesting, you already, in your early twenties, you had some intuition for much of what you were going to do in your life’s work; for why the replanting was failing. And these were intuitions that flew directly in the face of what almost everyone else in forestry believed to be true.

SIMARD: If you spent time in a forest, in an old forest or a wild forest, you would know intuitively that it’s not just a dog-eat-dog world. That these plants are together, you know that they work together. That the health of this tree is interdependent with the health of its neighbors. That if you have part of your community that is removed or sick or dying, it affects all the other members of that community. Let’s say you’re going to grow a lodgepole pine forest or a pine forest. And one of the early successional plants is alder. And that was part of my master’s study. Alder is a nitrogen-fixing plant. In other words, it has in its roots these little bacteria that are in nodules that take nitrogen gas from the air and they fix it or they convert it into usable forms of ammonium that the plant can use, the alder can use. Lodgepole pine can’t do that. There’s only a very small suite of plants, nitrogen-fixing plants that can do that. If you take the alder out of this ecosystem, what I found is that eventually the lodgepole pine also declines. The productivity of that forest actually goes down because nitrogen is not continuing to be added to that ecosystem. The alder is gone. And so the pine is really dependent on the alder to maintain or increase the productivity or nutrient content of that ecosystem. And at the same time, the alder is dependent on pine to make a more diverse forest. If you have only alder generation after generation, it actually starts to acidify the site because there’s so much nitrogen being added that the soils become very acid and low productivity. And so then the forest, it’s not just adding alder and pine in a pie and saying, “If I take away more alder I’ll have more pine.” It’s actually that the pie grows when you have the two of them together. And so there’s this cooperation going on between these two plant species that is actually making the ecosystem emerge into a more productive place.

LEVITT: So here’s what’s confusing to me. You said, “Anyone who’s been in an old-growth forest and spent time there can see and understand the cooperative nature of it.” But your forestry professors, didn’t they spend time in the old-growth forest? And yet the conventional wisdom you were being taught in school completely ignored that.

SIMARD: I think certain foresters would’ve seen it. And of course the Indigenous people that have lived here for thousands of years, they knew that — they’ve known it forever that it’s a cooperative place. And foresters that were building the forest industry through the 1900s, they didn’t spend as much time in the forest. They spent more time, with their textbooks and their computers trying to model out how to make the perfect forest that’s going to produce the most money. And that has gotten more and more acute over time. There’s fewer and fewer people in the forest actually observing what’s going on, and more stuck behind their desks trying to figure out how can we grow a better forest from this computer. And so I think that real sensibility about forests from observation, you need to go out and observe and see how it works. And I think now we’re seeing the consequences of this with climate change and other things, it’s just becoming more obvious that not understanding the forest in that really intimate way leads to all kinds of mistakes.

We’ll be right back with more of my conversation with Suzanne Simard.

*      *      *

LEVITT: So let’s go to your Ph.D. thesis, where at least I see this first glimmer of amazing originality in the way that you’re going to approach your research. Can you describe what question you were asking, and then what your research design looked like to try to answer that question?

SIMARD: I was really interested in how these elements like nitrogen and carbon and water move from plant to plant. And I was coming at it from just a place of curiosity. Where did these things — how did they move around below ground? I was especially interested in soil because I’m a person of the dirt.

LEVITT: What do you mean by that? “Person of the dirt?”

SIMARD: Well, when you’re born to this world, you’re presented with something that is your specialty. And mine was about the dirt. I started eating dirt as soon as I was born. And I just was always fascinated by what was going on in the soil. I played in it constantly. And then when I went to university, I found out that there was actually a course called “Soils” and I was, like, amazed, like, I belong there.  

LEVITT: So when you say you ate dirt, did you have a favorite flavor of dirt or were you, a generalist when it came to eating dirt?

SIMARD: I was a specialist when I was a little kid because my mom would put me in the dirt pile and then would just start eating the dirt. As I grew older, you know, I was more eating dirt when my brother would throw a dirt lump in my face. And then later, when I became interested in soils and to understand the texture and to know more about soil processes, soil scientists actually put dirt in their mouth — is there silt in it? Is there sand? Is there clay? And so I thought that was the best ever. And I especially love the dirt under forests that had birch and fir and cedar. I thought that was the sweetest dirt in the world.

LEVITT: Okay. So go back, you were talking about your question in your research design. 

SIMARD: Yeah, so I was interested in how these elements would move around, and I was contacted by someone that was working with me who said, “There’s been this study done by David Read,” who is a scientist in the U.K., “where he took seedlings ⁠— they were pine seedlings ⁠— in the lab, and he grew them together and he inoculated them with a fungus.” And the fungus is mycorrhizal fungus. And mycorrhizal fungi are, helper fungi, generally, meaning that these fungi colonize the roots of plants, trees, most plants in the world form these associations with these fungi. The purpose of it is that the fungi will gather nutrients and water from the soil and bring it back to the plant, and they trade with the plant for photosynthate because the fungi can’t photosynthesize. And the plants benefit from this because it doesn’t take as much energy to feed a fungus to gather up these nutrients than to build more roots to get into these little crevices in the soil. So they form partnerships with these fungi, and the fungi gather up these essential nutrients and water.

LEVITT: So you’re describing a well-known symbiotic relationship between the fungi and the trees. And that’s something people are well aware of.

SIMARD: People have been aware of this since the 1800s. And so the novel part of David Read’s study is that he grew these pine seedlings in a common garden, in a root box, and inoculated them with a fungus. And that fungus actually linked the two seedlings together. And then he took some radioactive carbon, and he added it to the atmosphere of one of the seedlings. It was taking that CO2 that had four carbon-14 on it; it was photosynthesizing it. And then that radioactivity got absorbed in the needles and the carbohydrates and sugars of that plant. And then he was able to observe this radioactivity actually moving from that seedling that was given that C-14 CO2. It actually traced the C-14 into the other plant directly through this network of fungi that we’re linking the two plants together.

LEVITT: So the thing that’s surprising about that — it’s not just that the tree and the fungus are in a relationship. Via the fungus, these trees are now passing things back and forth to one another.

SIMARD: That’s exactly right. These trees were in relationship with each other, through this fungus. And it was David — he just did this little experiment. It threw out this tantalizing tidbit of new knowledge in the scientific world. And this was in the 1980s. And people didn’t know what to do with it. And, it created a lot of controversy. In the U.K., there was, like, a bunch of researchers that were really, suspicious of this, that it didn’t fit the model of how these communities were constructing themselves. It’s all about competition. And here these two trees are seem to be collaborating or at least, they’re in some kind of communion with each other.

LEVITT: But the obvious criticism is, this is seedlings he planted and then put the fungus with them. This is not a natural environment at all. This is a concocted environment. 

SIMARD: It was totally artificial. So, I thought, I wonder if this happens in forests. ‘Cause here I was observing at that time as a young forester in these wild woods of Western Canada, these plantations that were starting to cover our landscape, and I was thinking we’re killing these ecosystems. I was observing that forests were becoming more and more unhealthy and I thought, I wonder if this kind of movement of nutrient, in this case carbon, happens between the plants we’re seeing as enemies of each other. And so I set up this experiment to test that in the forest. The main experiment was that I grew Douglas fir, which was what we were trying to grow commercially. And keep in mind this was in a new clearcut, which had been planted to Douglas fir, already, to grow more Doug fir. And it had been weeded out of birch, because birch was considered a weed. And I thought, I wonder if Douglas fir is somehow linked together with birch. And one of the reasons I thought that they could be helping each other is that when birch was weeded out of these Douglas fir plantations, there was a lot more root disease in the Douglas fir. So they were getting infected by a root disease called armillaria. But when the birch was left there, they didn’t become infected, in fact the firs thrived. They were healthy, they were growing well. And so I thought these two trees need each other. And then I did another little experiment in the lab and I discovered by looking through the microscope a lot, that the fungi on the birch and the fir were the same. And so I thought, “Ah, if they’re the same species morphologically, they might be linked together.” I didn’t know for sure if they were, but I thought, this is a good hypothesis. And I’m going to test this hypothesis by growing them together and then labeling the Douglas fir and the paper birch with carbon isotopes. What this entailed is that, I went to a nursery and I got some Douglas fir, I got some paper birch seedlings, and then I got some cedar seedlings as well. The cedars, I called it a control, because they didn’t form the same mycorrhizal fungi as the birch and the fir. It’s very different in that it doesn’t hook into the same fungal networks; it’s got its own suite of fungi that are completely separate. So there was no way that the cedar could be connected to birch and fir.  

LEVITT: So you’re looking in books and under a microscope and learning about these different fungi. And you now have your own hypothesis, which you’re making up based on intuition, that you think that the fir and the birch are going to pass resources back and forth, but you can’t see any way that cedar roots would ever attach. So you don’t think they’re going to be part of the trade.

SIMARD: That’s right. I was so interested in birch and fir because this management practice was treating birch as though it was the devil, that we had to get rid of it. And I saw it as an important part of succession. So I needed to know, if birch and fir were passing any of this carbon or other nutrients back and forth, was it just through the soil, or could it be through the fungi that might be linking them together? And I use the cedar as an indicator. If it were to pick up any isotope that I had labeled on birch or fir — if that cedar picked up any of those isotopes, I knew that it would’ve had to come to the cedar through the soil, not through mycorrhizal fungi that might be connecting it. So it served as an indicator of how much carbon or other nutrients would be moving through the soil.

LEVITT: And how long do you wait before you go back to see where the connections are made?

SIMARD: I let them grow for a year by themselves out there in the forest. They lived through the winter. They grew the next summer. And then a year later, and they were probably about knee height at that time, I went back out to the field and I set up my experiment with these plants. What I would do is I would cover with plastic bags, one over the paper birch, one over the Douglas fir and no bag on the cedar, ‘cause it was my indicator of what might be moving through the soil. And I inject in the bag of the Douglas fir, carbon 14. So carbon 14 basically forms CO2 inside the bag, and then the fir is taking up that CO2 that’s labeled with C-14, just like David Read did.

LEVITT: And so in your wildest dreams, what’s going to happen?

SIMARD: Well, I was interested to see where it went. Would it go to birch? Would it just disappear? Would some of it end up in cedar? Would it end up in the fireweed nearby? I really didn’t know, but I thought, well, if David Read saw this in the laboratory, maybe I’ll see this in the field. And, you know what, I did.

LEVITT: And so your results turned out to be amazing — an amazing confirmation of your intuition. The carbon was moving from the fir to the birch. You put your Geiger counter that detected radio activity on the fir and it would light up and you’d put it on the birch and it would light up. And when you put it onto the cedar, nothing.

SIMARD: The cedar picked up a little bit but only a small fraction of what the other two were receiving from each other. And so that told me that most of this conversation between the birch and fir — this passing back and forth of these carbon isotopes — that most of it must be going through mycorrhizal connections. And very little was moving through the soil as was indicated by what was taken up by the cedar.  

LEVITT: And it’s hard to believe that the birch and the fir should be friends. They’re not even the same species.

SIMARD: Yeah. Or that their relationship is more complicated than just being enemies. I mean, relationships are complex and it seems shortsighted to think that relationships between trees that spend their entire lives beside each other wouldn’t be more complex than just being competitors. Maybe they’ve got like really complex relationships that allow nuances in how they behave and so that they can actually adjust and adapt and change their behaviors as they’re growing up together to enhance the whole community. That’s what I was interested in. I wasn’t necessarily thinking, oh, that they’re just cooperative. I was interested in knowing the complexity of these interactions. 

LEVITT: These results flew in the face of conventional wisdom. And if I understand it, they had immediate and straightforward implications for the commercial loggers and for government policy. That getting rid of the birch was just a really bad idea. Am I right in saying that?

SIMARD: Well, it was certainly how I interpreted it and I spoke about that, but that was not what happened.

LEVITT: So did you get the chance to present your findings to the decision makers?

SIMARD: I never got invited to present my results to the decision makers. It’s not that I wasn’t willing to go talk to the decision makers, they just weren’t interested. instead I published my work in this journal, Nature, and it got international attention. And then the policymakers started to pay attention to me, because I was actually getting a few interviews in the media as happens when you publish in Nature. And I was saying that birch and fir are in a relationship that is complex, it’s collaborative and it’s also competitive at the same time, but it’s far more complex than how we’re treating them, which is to get rid of the birch. And in one particular interview I said, to a newspaper reporter, I said, “For all the good they’re doing to get rid of the birch, they might as well go paint rocks.” That almost got me fired because it was questioning their policy, which is still in place today and these are still going on. So that just goes to show you even 25 years later that they still have not changed. 

LEVITT: Yeah, I’m not surprised. One thing I’ve learned over the course of my career is just how hard it is to change policy via academic research. My own first experiences in the policy realm were, at least superficially, much more successful than yours. My story is that as a graduate student, I had done some research — I’d written a paper that suggested that police were quite effective at lowering crime. And interestingly, it was more or less the only academic paper at that time that came to that conclusion. All the research, mostly really poorly done correlational studies from the 1970s, found, surprisingly, that the number of police either had no impact on crime or even increased crime. Okay, so just by pure chance, it turned out that Bill Clinton became president and he made one of his top priorities to hire an extra 100,000 police officers. And it turns out my paper, believe it or not, makes it to Bill Clinton himself. And I’m told that his copy of the paper was heavily underlined and had really good questions written in the margin. And then Janet Reno, who was the attorney general at the time, she carried copies of it in her briefcase and she was handing them out to senators and congresspeople trying to win their votes. Well, the bill passes and a hundred thousand police get hired. And I thought, “Wow, this policy stuff is easy. You know, you write a good paper and a few years later it’s put into action at the national level.” But that’s all I knew ‘cause it’s the first time I’d ever interacted with it. And I realized, of course, eventually how completely confused I was about how policy was made. The Clinton Administration, they didn’t care in the slightest whether my research was high quality or even true. They wanted to hire police and they wanted to wave around some academic papers for credibility. And it just so happened my research was the only thing that supported them. But with or without my research, that same bill would’ve passed. The policy outcome would’ve been the same. Thirty years later, I can honestly say that as many papers that I’ve written, that have policy implications, I can very precisely estimate the total sum impact that my research and Freakonomics books and podcasting has had on policy. And that is a big fat zero. In my whole career, I don’t think I’ve materially affected a single public policy. 

SIMARD: I think it’s true for me too.

LEVITT: So, I don’t know. Well, let’s get to that because, you didn’t stop there. So you have this result that flies in the face of conventional wisdom, but you’ve delivered over and over these results; which are just really mind-blowing. They’re shocking. So just quickly, can you just rattle off the three or four really fundamental insights that you feel like you’ve had through your research on how forests work?

SIMARD: Well, you know, my research was a path of discovery. I’d established that birch and fir were sharing carbon in that early Ph.D. research. I became a professor and a big debate in the literature at the time is that, okay, so if carbon is moving back and forth below ground between species, does it really matter? Is it really helping these species survive and grow? And so I set out to try and see if it did; and the gold standard was if it affects the survival of the recipients or the growth of the recipients, then it’s enough to actually matter to plant ecologists and fungal ecologists. And so I got a student who went and planted seeds around older trees, where they could connect to these older trees or not. His name was François, and he grew them in little mesh bags that he buried in the ground, that allowed the older trees to form mycorrhizal connections with the emerging seedlings or in bags that had smaller pores that they couldn’t form these connections. And we followed the establishment and survival of those seedlings that are growing in these bags. 

LEVITT: So again, a randomized experiment, where you’re either allowing the mycorrhizal network to develop, or you’re precluding it through these artificial bags that are stopping it.

SIMARD: Yes. And so what he found is that, yes, that the establishment and survival of the seedlings where they could be connected to the old trees was higher than it was where they couldn’t be connected. And so to me, we were answering that question: yes, it matters to the establishing seedlings. The next thing that we wanted to ask — the next groundbreaking thing — was if these networks exist in these forests and it’s helping the regeneration of seedlings, what does the network look like in a complex forest below ground and how might it affect the dynamics of a complex forest? And so we went out with another graduate student, Kevin Beiler, to fir forest that was what we call uneven-aged. It had trees of many ages from two- or 300-year-old trees down to seedlings that were growing in their understory and all ages in between. And what Kevin did with my colleague Dan Durall, is that we mapped what that network looked like. So he sampled the roots of all these trees in plots that were 30-by-30 meters. And he did this in six different plots in this forest. And he gathered up all of the root tips and the rhizomes or the fungal strands that were between the trees. And he did D.N.A. analysis on them. He used a special technique called microsatellite analysis. And what that analysis allows you to do is to determine whether a fungus that is colonizing the root of one tree, and if that same fungus is on its neighbor, that these two trees would be connected together. Okay. So what emerged from that map was that the younger trees were connected to the older trees and that the most highly connected, of the members in that community were the oldest and largest trees in the forest. 

LEVITT: And these are the trees that you’ve come to call the mother trees.

SIMARD: These are the mother trees. So they’re just the biggest oldest trees. Okay, so I’m going to go one step further and say, “Okay, so this forest then is a highly connected place that the younger trees are connected into the networks of the older trees.” So then the next question, which I asked with my graduate student, Amanda Asay, was, do these older trees actually favor or recognize the seedlings that are of their own seed? So, their kin. And so we asked is there kin selection in Douglas fir?

LEVITT: Okay. Can I tell you? This seems totally impossible. Okay, but what do you find?

SIMARD: Well, and so we were building on the research of Susan Dudley. And she had been doing kin recognition research in plants in eastern Canada. And we used her techniques, basically, her methodologies to uncover whether or not different Douglas firs could recognize each other if they were related or not. So we grew Douglas fir that were full siblings. And we grew them next to seedlings that were strangers, complete strangers. And we looked at how they behaved relative to those two different kinds of relations. They’re relatives or strangers. And we found that Douglas fir, it preferentially will provide carbon to kin seedlings that are their neighbors versus strangers that are growing next to them. 

LEVITT: So somehow this big tree is able to figure out in the root structure whether the new seedling is actually related to it, genetically, and delivers more help to the ones that are related than other members of the species which are unrelated.

SIMARD: Yes, that’s correct. It’s far more complex than we just talked about. And I have to say one of the reasons that we haven’t published all the papers is that Amanda Asay, my student, actually passed away in the middle of trying to get her papers published last year in a skiing accident. And so it’s been a difficult journey for me to get this out there.

LEVITT: So I don’t know how much you know about game theory, but situations in which the participants are simultaneously in competition, but also benefit from cooperation, that falls into this class of games that’s known as the prisoner’s dilemma. So in these situations, if you only play the game once, then the only equilibrium is to compete, not to cooperate. But if you play the game over and over against the same opponent, and you’re sufficiently patient, then cooperation becomes an equilibrium. It’s interesting ‘cause when you’re describing the forest, you’re describing a situation which has at least some of the precursors that would support this cooperative equilibrium in the prisoner’s dilemma, which is that the same trees do indeed play against the other trees over and over. What do you think of a cooperative equilibrium in a prisoner’s dilemma as an analogy for what’s happening in the forest?

SIMARD: Yeah, I think it’s a good analogy. I actually use that analogy when I’m trying to describe in my book how this competitive cooperative relationship carries out in a community. There is competition, there’s no doubt. In a simple community or a simple situation competing, yeah, it can get you so far. But, in a plant community, if you become the only one or the dominant one, community actually starts to decline. That’s when cooperation becomes more imperative because you need things from your neighbors: you need nutrients, you need uplifted water, you need filtered light. So if you continue to out compete your neighbors, you lose those benefits. And so that game theory that’s in the prisoner’s dilemma actually plays out beautifully in a natural plant community.  

LEVITT: So the one piece that doesn’t fit for me though, in this analogy about the prisoner’s dilemma is that in order to support that cooperative equilibrium, you need the players to be able to punish the other players if they cheat, right? So if we’re in a cooperative equilibrium and all of a sudden you cheat me, I have to have a way to punish you. And, at least in my limited view of what trees do, I don’t really see how they would have power to punish another particular tree. But of course, you’ve surprised me before with the evidence about what trees can do. So maybe I’m just not thinking deeply enough about the talents that trees have.

SIMARD: Actually, the trees have many opportunities and tools to punish each other. Even at the root level, like, if we’re talking about like movement of carbon back and forth between trees, if your neighbor cheats by say, taking more than it needs or robbing you or stealing your carbon from you, how can it regulate that? How can it punish its neighbor and cut it off from that cheating? Well, there’s been some really great research by other mycorrhizal scientists. I’m thinking of Toby Cures, for example, who showed that there’s actually this tit-for-tat exchange going on between the fungi and the plants. So if, let’s say, paper birch is supplying carbon to Douglas fir, and the Douglas fir’s taking and taking to the point of where it’s going to starve the paper birch — if there isn’t enough of a market exchange for what the birch is providing in return from the Doug fir, which could be, you know, nutrients, then those mycorrhizas will work together with the trees and can actually sever those connections. So the connections between trees are very dynamic. They’re constantly regressing and reforming and being severed. There’s a lot of avenues for regulating that movement, just through the mycorrhizal dynamic itself. The other thing that trees can do even in the above ground world is that they can grow taller and shade out their neighbors. That’s the easiest thing that they can do. They can change their root crowns and their above ground crowns in amazing ways to get what they need the most. So they’re very plastic, they have a lot of agency, above and below ground to regulate and really shape where the resources are going and who gets what.

LEVITT: Is it possible that the lowly fungi are in some way the puppet masters who are truly in control? We’re talking about the trees, but could one imagine that the fungi have in some vague sense domesticated the trees? And they’re managing the forest to maximize what’s best for the fungi and not for the trees?

SIMARD: I always try to not go into these sort of simple either-or situations. To me, the whole system is working together. But it’s an interesting thought experiment to think that one could be in control. So how could the fungus be in control? Well, the fungus, what it needs the most is carbohydrate, right? It can get all the nutrients and water it wants. It’s got this incredible mycelium that’s able to access, all throughout the soil. Its limiting resource though is photosynthate. And so it needs partners to provide that, and if that fungus has got many partners, it’s very resilient. It’s got this diverse portfolio of partners that if one dies or senescences or goes dormant for a season, it’s got other partners that can provide that photosynthate. And so, yes, the fungus has this incredible ability to have agency over its environment and which hosts it’s providing to and which ones it might want to cut off. But I think we have to be careful not to go into the trap that it’s either one or the other, the plant or the host, or any of the creatures in the forest. They’re all working together to make this balanced complex system.

You’re listening to People I (Mostly) Admire with Steve Levitt and his conversation with Suzanne Simard. After this short break, they’ll return to talk about how a life threatening illness changed Suzanne’s perspective.

*      *      *

Within academic economics, there’s a general belief that it’s a bad idea to mix scholarship and advocacy. Science should be objective and unbiased, and that runs into conflict with advocacy, which plays by a different set of rules. An advocate knows what they want, and they’ll do more or less whatever it takes to make change happen. I’ve observed, however, that this separation of scholarship and advocacy is not the norm in other areas of research. Climate science is probably the best example. Suzanne Simard is both a scientist and an outspoken advocate for the forest. I’m curious to hear how she handles that dual role.

LEVITT: In your academic papers, you write like a scientist; you’re measured, precise, full of caveats. In your writing for a broader audience, in your TED Talks, maybe less so here today in our conversation, you adopt a very different voice. It’s a powerful storytelling voice. You ascribe motives and meanings to trees, and even the word choices you make, like the phrase “mother tree.” It shifts the discussion out of a purely factual realm into a more emotional space. Now, I assume this is your conscious choice on your part. You’re not only a scientist, you are a believer in the immense value and the beauty of the forest, and this more evocative way of speaking and writing is far more persuasive and furthering your cause. Is that an accurate characterization of your dual roles as a scientist and an advocate? 

SIMARD: Yeah, I think it’s a really tough line to be walking. I can think of my life in these phases, right? I grew up in the forest. I’m a creature of the forest myself. And then I became a scientist and I learned the ways of the scientific realm but I was also undergoing this great shock of what was happening in our forests and our landscapes. And I’m worried about the next generations. I’m worried about my kids. I’m worried about the human race and all our relations. And, as you so accurately earlier said that it’s really hard to affect policy if you ever do at all with science or scientific papers. And so I thought to myself, there’s something really important here that I think the public needs to know. We are taking this very simplistic approach to forests. And you could think of agriculture or any way that we manage ecosystems in our current era. And it’s so destructive because it’s basically, so reductionist and it’s dissembling these highly complex systems to make them look like systems that we want to reap benefits from. And I thought, “I need to tell the world that this is not working, and in fact, it’s destroying us.” What we’re doing in forests it’s contributing to climate change. It’s contributing to biodiversity loss, it’s contributing to changes in our hydrologic cycles because forests are vast over the world and they have this outsized role in all of our biogeochemical cycles. And I need to tell people, I need to tell them what I know. And I can’t reach them with my scientific papers. I knew that already. I published my Ph.D. work in 1997, it’s almost 30 years later; it would still be unknown unless I spoke out. And so I thought it’s my responsibility as a scientist to actually speak out. And I don’t say that’s true for every scientist. Like some scientists would never want to do this, they feel very uncomfortable or they think it’s wrong; that I’m not as accurate as the scientific experiments show because I’m telling it as a story. But I try to adhere as much as I can to the science itself. But at some point, you have to make it into a story so people will listen. And yeah, it hasn’t been an easy path, because I do get a lot of backlash from my scientific colleagues. It’s not much fun, but, but I feel like I have a bigger responsibility here.

LEVITT: People hearing you talking today, they’re hearing a powerful voice. One that’s full of confidence with a strong vision of how the world should be. But reading how you describe yourself when you were younger, it sounds like you’re describing a totally different person, terrified of public speaking, bullied by the powerful people in your profession. You never even imagined that you’d be considered for a tenure track research appointment. Are you able to see and feel the transformation in yourself, or has it been so slow and organic that it’s invisible to you?

SIMARD: Yeah, it’s been a huge transformation and I still am that shy little kid. But I’ve made myself grow out of it. ‘Cause I felt like even, to survive, I had to become more than that. And I still cry sometimes, because I’m sensitive still. But I’ve managed to learn enough about how to take criticism and make it work for me and make things better. And still stand up at the end of the day and move on.

LEVITT: You had a very difficult and scary fight with cancer. Did that play a role in this transformation?

SIMARD: It did. Anybody who gets cancer — it’s a really terrifying experience. You feel like, “Oh, this could be the end of my life.” And, probably 50 years ago, it would’ve been the end of my life except for that I got all these incredible treatments. I have two daughters. They were, at the time, 12 and 14. And I thought if I survive this, I’m going to do everything I can to make sure that my kids thrive. Not that I didn’t think that before, but now it was just like, okay, I’m going to just forget about trying to go to conferences in some far-off land to experience this thing. No, I’m going to stay home and do my job, which is to look after my kids and my family and my community. And then I also thought I’ve got to get rid of the fears of retribution, of criticism, and I’ve got to move forward, because I’ve been given this chance to do that. I survived this. I’m going to do everything I can to use this time that might be borrowed time to make sure that I do what I think is worthwhile for this world, which is what I’m doing now. I figured out too is that I really wanted to give back to the forest for what it gave me to heal during that period. I spent a lot of time in my forests when I was going through chemotherapy and afterwards, anytime I could get out there. And in my forest there’s the yew tree that provides the medicine for taxol, which saved my life. And I thought, I’m going to do research on yew trees. And about the community of yew, not just the chemical that’s in it, but what does community do for the ability of yew to produce medicine? And so I have a grad student now, Eva Snyder, who is working on that very question. So I would say that my life did really change, and I’m just going forward in as gutsy as I can with my goal of helping make the world a better place for our next generations.

LEVITT: I wanted to highlight your transformation because a lot of young people listen to this podcast, and I worry they get the wrong idea about the world. ‘Cause my guests, you included, they’re amazing. You’ve done incredible things. And my guests, they speak with confidence in poise and polish. But like you, most of my guests, they’ve learned those trades, right? They were awkward 16-year-olds, they were confused 20-somethings. And I think you’re more open and honest about your transformation than most are. And I think it’s so valuable for people who are struggling or intimidated or ignored to hear stories like yours about possibility.

SIMARD: I look back and I’m amazed at what I have been able to do. I’m a prof. I teach 18 year-olds to 40 year-olds all the time. I have two daughters, 22 and 24. And I feel like I was just that age myself. I know the struggles it’s very intimidating. But, you know what, I came from nowhere, right? I grew up under a log for Pete sakes. I sucked my thumb till I was 12. I ate dirt. I was beaten down in so many ways, but I just kept getting back up and never forgetting what drove me; that I had this love for forest that transcended everything. It was always my beacon. And I thought as long as I keep my focus on what matters to me, which is about the health of the forest and the health of our communities, then I’m okay. And would say to young people out there everything you do, keep your vision of what’s so important to you. What drives you, what’s your higher purpose? Because we all have that, we all have a higher purpose. Sometimes it’s not clear to us, but you just going to find it and do that thing. Maybe it takes 10 years to figure that out or 20 or 30. But it’s okay, ‘cause you’ll figure it out. And you’ll make mistakes and the mistakes actually make you stronger. And it’s the same in a forest. Like the forest is constantly adjusting and changing and moving and reforming its networks. That adaptability is absolutely imperative to our own successes as human beings that we’re able to adjust and change and accept our failures and use them to move on, but also striving for that thing that makes you tick. In my case it was forests in others it’ll be something different.

As I reflect on my conversation with Suzanne Simard, the thing I just can’t get out of my head is how remarkable it is that the conventional wisdom on forests was just so completely wrong 30 years ago. It wasn’t like nobody was thinking about these issues. There was a massive industry with huge amounts of money at stake, and an army of academics studying forests. And the older I get, the more I’ve come to believe that in many issues, the conventional wisdom is dead wrong. How does that happen? Well, I think it’s because for almost every question we ask, there are a set of basic assumptions that are taken for granted that are never challenged. And if it turns out that one of those fundamental assumptions is wrong, you’re almost certain to come to the wrong conclusion. And since no one ever thinks to challenge these basic assumptions, these mistakes can persist for a long time. Back in the day when I was consulting with big firms trying to make them better, I had a very simple strategy: I would try to understand what the company’s most basic beliefs were about what made the firm special and how their markets worked. And I discovered three things: First, these beliefs were typically formed very early. A company like Wal-Mart still operates using rules of thumb and pearls of wisdom Sam Walton came up with 50 years ago. Second, it was almost impossible for people within these firms to see that these basic beliefs might be wrong, even though to an outsider like me it often seemed pretty obvious they were wrong. And third, when you challenged these beliefs as an outsider, the only thing you accomplished was to get yourself fired as a consultant. Which is why my career as a management consultant was both short and unsuccessful. If you want to learn more about how Suzanne Simard, much more successfully than me, took on the flawed conventional wisdom of forestry, check out her fascinating book entitled Finding the Mother Tree. And now to our listener question.

LEVEY: Hi Steve. So our last episode was with mathematician, Steven Strogatz, and we had a huge number of listener emails. Hundreds of people wrote in and they were really excited about an idea that you and Steven Strogatz talked about towards the end of the show. It was about a class called Math 101, a course in high school that teaches students what math really is; like music appreciation — it would be math appreciation. So just to give people a taste of all the positive feedback. Here’s an email from a listener named Heidi. “Hi, Steve and Morgan. I am a total disciple of this podcast, and I’m usually moved to some action after each episode. This usually means that I read the latest book written by the guest, or I make my 13- and almost 16-year-olds engage in a discussion about the new thing I learn from your interview while I drive them to school. This time was different. I actually got chills of excitement thinking about a Levitt and Strogatz model of teaching high school math that completely transforms generations of American students and leads to so many more people loving math and using it to change the world in countless positive waves. I’m cheering for you in your quest to improve math education, and I really believe you will do it. With gratitude, Heidi.” Wasn’t it wild how much feedback we got from our listeners?

LEVITT: Well, listening to you read Heidi’s email gives me chills of excitement. How amazing was it? What did we get? Twenty times as many emails as we usually get? And they just keep coming and they’re all favorable. And what was interesting about them is that maybe one in three of the emails we got on the subject ended with, “So tell me how I can sign up to do some work on this, how I can contribute.” Which was really amazing. I’ve heard from potential funders. We’ve heard from of educators who are in charge of the math program at charter schools. We’ve even been in touch with a handful of the state math leads, the people in charge of math policy for the entire state who are really energized by this idea. I had no expectation that this would be the response.

LEVEY: So, do you two have any plans for moving forward with this idea? 

LEVITT: Well, plans would be too strong a word. So I did talk to Steven Strogatz and he was, I think, even more surprised by the response than I was. We certainly have hopes and ideas, but we’re way too early to have any real sense of what we’d want to do. What I often do when I approach a big hard problem like this is I just try to imagine a world without any constraints and I ask myself, “If nothing was stopping me, what would I actually want to do?” And in this particular case, I have a real vision of what I’d like math to look like. I’d love kids to get really good at arithmetic through say sixth, seventh or eighth grade. And then I would love this, to be determined, but amazing math appreciation course to be the next course they take in eighth or ninth grade. And then I would like to scrap everything we do in math after ninth grade and reorganize it in the form of electives. So not force everyone onto the same set of courses, but to open it up to different kinds of courses. So some of them would look familiar. You’d still have a calculus course if people wanted to take calculus and an algebra course if people wanted to take algebra. But I would also have very different courses. Courses we don’t have right now. Like I would like to see math-for social scientists course. Do kids know if they want to be a social scientist when they’re in high school? No, not really. But maybe by taking a course and seeing the kinds of math that are used in the social sciences would help kids say, “Hey, that’s the kind of math I like,” or “the kind of math I don’t like.” And of course I’d love to see data science classes offered. And I’d offer a class called proofs. I think one of the most powerful things in math, for me at least, was learning how to prove things; how to think about the world through the lens of starting with assumptions and working your way to conclusions. The way we do proofs right now in high school math, I don’t think kids take the right message away from the proofs that they learn.

LEVEY: So Steve, this might be too negative, but I’m wondering right off the bat what barriers you see to this concept.

LEVITT: Oh, yeah. What I just described was this utopian world. The reality is it is almost impossible to change what happens in the classroom. I’ve been struggling with that on data science for years now. So I think our first approach would not be to try to create a full-blown course and to imagine that it’s going to suddenly be adopted in many, many schools. Rather, the short-term goal might be to, where possible, get teachers giving 10-minute bite size segments where they talk about something wondrous in math before they go into what they’re already teaching on some particular subject. And, honestly, the biggest puzzle that Steven Strogatz and I see now is if you go online, say to YouTube, there’s amazing mathematical content. Just to give one example, the YouTuber 3Blue1Brown does really great math content. He’s got 5-million subscribers, and yet, as far as I know, it’s almost never used in the classroom. And my hypothesis is that the people who are producing content, that’s being consumed, say on YouTube. They have a different market. They’re not thinking about how to do it in a way that makes it turnkey, trivial, simple for teachers to go and use that in the classroom. And so maybe one of the things that Steven Strogatz and I can do is either to create material that could go into what teachers are already doing or more likely, I suspect that kind of awesome content is already out there and it’s just not as widely publicized as it should be. So actually, let me take this opportunity: we’ve got so many listeners, if you know of anyone who’s creating content that is simple and easy for teachers without any work to be able to put right into their classrooms to help kids really appreciate math, we would love to hear about that. That I think is the first big win we could hope to have, would be to make those kinds of materials much more available to teachers than they currently are.

LEVEY: Thanks to everyone who wrote in with their stories of math anxiety, or their willingness to help Steve and Steven with their Math 101 crusade. If you have a question for us, our email is That’s It’s an acronym for our show. Steve and I read every email that’s sent and we look forward to reading yours.

And in two weeks we’ll be back with a brand new episode featuring paleontologist and bestselling author Neil Shubin.

SHUBIN: So if you drive across Route 80 in Pennsylvania, you’ll see red rocks along the road — those are Devonian age rocks. Those are rocks 365-million-years-old that were formed in ancient rivers and streams. And guess what? If you look carefully at those rocks, which we did, you start to find fossils, you know, of some of the earliest fish to walk on land.

LEVITT: You stand on the shoulder of the highway?

SHUBIN: Yes, we did stand on the shoulders of the highway.  

*      *      *

People I (Mostly) Admire is part of the Freakonomics Radio Network, which also includes Freakonomics Radio, No Stupid Questions, and Freakonomics M.D. All our shows are produced by Stitcher and Renbud Radio. This episode was produced by Morgan Levey and mixed by Jasmin Klinger. Lyric Bowditch is our production associate. Our executive team is Neal Carruth, Gabriel Roth, and Stephen Dubner. Our theme music was composed by Luis Guerra. To listen ad-free, subscribe to Stitcher Premium. We can be reached at, that’s Thanks for listening.

LEVITT: Mycorrhizal. Mycorrhizal fungi. Mycorrhizal fungi. Mycorrhizal fungi.

Read full Transcript


  • Suzanne Simard, professor of forest and conservation studies at the University of British Columbia.



Episode Video