Inside the 'rewilding' movement

In places where human beings have done everything they can to pave and plow over nature, what might happen if we just left the land alone?

"The plants are reproducing. They’re filling in the spaces where we didn’t plant," Joey Algiers, restoration ecologist, says. "They’re transforming the soils beneath them that have been damaged for decades and decades."

It's called rewilding. But people have different visions in mind of what "wild" actually means.

Is it trying to get the land back to what's essentially a lost wilderness — repopulated with long lost indigenous flora and fauna?

Or is it leaving wilderness at is, even if we don't like how it looks, or what it contains?

Today, On Point: Inside the 'rewilding' movement.

Isabella Tree, British author and conservationist. She and her husband live on the 3,500-acre Knepp Estate, which they started rewilding in 2002. Co-author of “The Book of Wilding: A Practical Guide to Rewilding, Big and Small."

Joey Algiers, restoration ecologist with the National Park Service for the Santa Monica Mountains National Recreation Area.

Emily Iskin, postdoctoral research fellow at Boise State University.

Part I

MEGHNA CHAKRABARTI: Isabella Tree joins us today. She's a British author and conservationist. She and her husband live on the 3,500-acre Knepp Estate. And in 2002, they decided to make a major change to their land. And Isabella joins us today from the Knapp Estate in West Sussex in England.

Isabella, welcome to On Point.

ISABELLA TREE: Thank you. Nice to be here.

CHAKRABARTI: If I were to have the delightful chance to walk across or walk around your 35 acres right now since this is radio, first of all, I'd like to ask you, what would I hear?

TREE: You might hear a roaring stag. It's the end of the rut season, but we still have a few mighty male stags out there who are still roaring a little bit towards the end of the season.

You might hear some bill clattering of our white storks, and I've literally just seen about a dozen of them fly past the window. And this for us is one of the most exciting things because we haven't seen white storks in Britain for 600 years. And we've reintroduced them, they're nesting here for the first time since 1416.

So that's really exciting. We've got lots of autumn migrants field fairs, Red Wing coming to feed up on the seeds of our thistles before they head off for migration down to Europe. It feels like the year is coming to a close, but it's in its last throes.

We've got all the migrants and the geese and the ducks. And yeah, it's a lovely time of year.

CHAKRABARTI: It sounds like you can hear almost nature preparing herself for the slow slumber of winter time. Yeah. It sounds gorgeous, actually. Now take me back to the late '90s, early 2000's.

What would have I heard then?

TREE: Ah, you would have heard probably a lot of farm machinery, you wouldn't have heard many birds. It would have been yeah, in many ways, it was a biological desert, there was a bit of life coming into the lake here. But otherwise, and the hedgerows, but we cut the hedgerows every autumn, depriving the birds of berries for winter.

So we had no autumn migrants coming in to feed themselves up or anything. It was a very conventional, micromanaged industrial farming landscape.

CHAKRABARTI: And how long had it been that way?

TREE: Since the second world war, really, since our Dig for Victory campaign, the country was in crisis and we were facing starvation.

And everyone in Britain was encouraged to plow up every available inch of land. So everything, including cricket pitches, floodplains, flower meadows, the chalk grass downlands that I'm looking out my window at now, everything that had been really sacrosanct during the first world war was plowed up.

And really we continued on down that vein, really thanks largely to big farming subsidies that paid farmers to continue to produce food, even from land that was unsuitable for it.

CHAKRABARTI: I see. Yeah. Okay. So in just comparing the sounds that you created in my mind in describing essentially, as you call it, the biological desert of pre 2002 Knepp Estate, I hear silence or machinery.

And then the estate as you describe it now, my mind hears this lush cacophony of wilderness, essentially.

TREE: Yes, that's exactly right. And I think that was one of the first things that struck us. We embarked on this sort of adventure really completely unaware of what was going to happen.

But I remember that first summer when we had stopped farming, stopped plowing, we had reseeded the plowed land with wildflowers and native grasses. And that summer, the sound of insects was completely overwhelming, and you'd walk through the grass kicking up common blue butterflies and crickets and grasshoppers.

And as farmers, we hadn't even realized we were missing that sound of insects. That's what's so extraordinary.

CHAKRABARTI: Yeah. Oh my gosh. The unappreciated insect, it's a major story in the loss of biodiversity on planet earth, actually. So it's very, it seems totally appropriate that the insects would be the first thing that caught your attention now.

So we should say clearly that obviously you and your husband launched a rewilding project of your estate, and the efforts and the results of that are categorized or discussed in a book, Isabella, that you have co-authored. It's called “The Book of Wilding: A Practical Guide to Rewilding, Big and Small."

So that's why we're delighted to have you on the show today, Isabella. So tell me. Just prior to 2002, what was it that made you and your husband decide, no, we're not going to continue this tradition of very humanized, a very human, humanized is not the right word, but human controlled landscape and we're going to do something different.

Why'd you do that?

TREE: I'm afraid to say it's nothing incredibly romantic or altruistic. It's not because we felt that we were going to do something for the planet. It was actually money. We were making a huge loss farming this land. We sit on incredibly heavy clay. 320 meters of it. I think there's something like 35 words for mud in the old Sussex dialect.

That's how much mud governs our lives. We just simply couldn't compete with farms on lovely loamy soils that were really productive. We would in, over a wet winter, we couldn't get farm machinery onto the land at all. So we couldn't sow spring crops. We just couldn't be competitive.

And by 1999, we were 1.5 million pounds in debt. And so that's really when my husband said, "Look, we just can't go on like this. We've got to find an alternative way of managing our land." Selling for us was out of the question because the land has been in Charlie's family for over 200 years.

And so we knew we had to stop farming. We sold our dairy herds. We sold our farm machinery. We sold our milk quota that cleared our debts. And really just being free of that burden of a failing business meant that we could think outside the box. We could be much more imaginative and creative than when we were trying just to keep the business going.

And that's when we came across this really extraordinary Dutch ecologist called Frans Vera, who has really changed the way I think that conservationists think about nature restoration. What he's saying is that the big drivers of habitat creation, the way you can bring nature back, is by using the large free roaming animals that would have been here in the past.

So aurochs, tarpan, the ancient ox, the ancient horse that we used to have in Europe, wild boar, beavers by the millions, we would have had elk, reindeer, bison, we even had a European water buffalo. And all these animals would have been generating habitats, just their disturbance, the way they rootled, they trampled the soil, they transported seeds around the landscape, they kept waterways open, and they kept much more open, diverse, complex landscapes than we're used to thinking of today.

So we thought, "Wouldn't it be interesting to try and experiment?" We, both in a very amateurish way, Charlie and I love nature. Could we bring life back onto this very depleted, polluted, chemically soaked land by using large free roaming animals to help us do that?

CHAKRABARTI: And which animals did you first then introduce back onto the estate?

TREE: Obviously, we've hunted to extinction in Europe, many of our large herbivores. So the aurochs is gone but we do have its descendants' cows, cattle. So we chose old English longhorns. They're a very old breed. They look a little bit aurochs, like they've got fantastic sweeping horns.

They're very sturdy, so they can live outside all year round. We're not supplementary feeding them. So they've just got a forage for whatever they can find in the landscape. And they really fit that profile. Their dung restores the soil with the nutrients. They transport seeds around the landscape.

And they generally trash the vegetation, which is actually creating new niches for other life. And then because we've also lost the tarpa and the original European horse, we've introduced Exmoor ponies, which are wonderful old breed of, they look wild.

They've got these amazing thick coats in winter. Again, very resilient, very able to live outside all year round there. Those instincts for survival are still very much with them. They've got this amazing eye called an ice eye, which kind of is a sort of like a skin that goes over their eye to protect them from hail and snow.

So they're amazing species and we just, now we watch them galloping around, around what was once a farm.

CHAKRABARTI: Wow. Isabella, we told our listeners that we were going to be talking about rewilding today and we got just an avalanche of responses. So throughout the hour, we're going to hear from some of our listeners.

For example, here's Barbara Bobo from Champaign County, Ohio, and she says she's got about three acres and decided to let half of it go natural.

BARBARA BOBO: I've seen an increase in butterflies, bees, ants, and more importantly, birds. And there was a fox in my backyard at one point. I have a pine windbreak, west of my house. And there are a very small heard of deer, down to about three now, I think, since there's a lot of neighbors shooting guns these days. But they sometimes take a nap, overnight, in my windbreak, too.

CHAKRABARTI: I love the idea of napping animals.

TREE: So lovely.

CHAKRABARTI: This is Jeff Mavis. He's another one. This will sound familiar to you, because he and his son are farmers. They farm about 900 acres of corn and soybean in Fayette County, Ohio. They switched about 80 acres to grassland through a government initiative called the Conservation Reserve Program.

And here is what he sees on his land now.

JEFF MAVIS: We have seen a return of pheasants over the last few years, we have a new kind of quail population. We hadn't heard quail for years until about 5 years ago, and we have more predators, foxes and coyotes. I feel like we've seen more lightning bugs. Honeybees, a lot of the natural forms like aster in the fall.

And even Goldenrod, they're getting honey when all the other flowers are gone, still in September.

Part II

CHAKRABARTI: Now, Isabella, over the course of the hour I want to talk to you about the differences of the types of rewilding big and small, but in order to set up the small part of our conversation, let's hear from another listener, because you can imagine that a lot of folks in the United States, they don't have 3,500 acre estates, but they have smaller acreage, or even just their backyard. So in that sort of smaller acreage realm, Rachel Balkcom, she talked to us. She lives in Erie, Colorado. It's about 30 minutes outside of Denver. And one of the first things she and her husband did when they moved onto their about two-acre property six years ago was just, Let the grass die. They did not want a lawn.

RACHEL BALKCOM: We allowed the natural ecosystem to come in and do what it does, which it will do of its own accord, of course. Anyway, right away, got mustard greens and other wild plants. So sunflowers, thistles, there are plants that came in that naturally regenerate the land, because they shade the land and they allow permeability of the soil.

CHAKRABARTI: So they were seeing some quick successes with the species springing back, but Rachel says, at the same time, at first the yard was not exactly nice to look at.

BALKCOM: It also absolutely looked terrible for about two years, which I think a lot of people don't realize and you just have to grin and bear that. As it's regenerating, it just looks like dead grass.

CHAKRABARTI: Gradually, Rachel says things did shift. Blue jays appeared in the locust and oak trees and started spreading the seeds around the property. Rachel planted wildflowers and vegetables among the plants that had popped up on their own. And now, six years later, it's a whole new landscape.

BALKCOM: It's a wild, stunning.

It's green, it's purple, it's yellow. We have finches everywhere. We have morning glories. A lot of what grows indigenous here are herbs. And so we have these smells of particularly mint and sage. And of course, sage is in the mint family as well. That will walk through the property really consistently. And the sounds are different too.

Just an absolute cacophony of bird sound most of the time. We do have red tailed hawks out here, but since we now have so many jays. And the jays imitate the hawks in order to keep predators away from them. It sounds like we have a thousand red tailed hawks all the time. And we don't. We have a few.

CHAKRABARTI: I love those jays.

Jays get a bad rap a lot, but they are fabulous. Now, Rachel says she and her husband do intervene sometimes. They harvest herbs and vegetables. They cut back some plants to keep them from completely taking over. But Rachel says that is a part of her role and responsibility as a steward of the land, because she is part of nature, too.

BALKCOM: It feels like at least once a month, there's a new sound, there's a new bird, and we'll come inside and say, "Oh, I heard this, or I saw this, and we'll look it up and edit the list and find out who's there, and often we'll find out why." And so it allows us really consistently to have demonstrated for us, the symbioses that exist and the interconnections and again, to understand ourselves as part of that.

CHAKRABARTI: That's On Point listener, Rachel Balcom in Erie, Colorado. Now, Isabella, the reason why we wanted to share Rachel's story is because when it comes to this concept of rewilding, it can mean many different things to different people. One can be a rewilding purist. Maybe I'll count myself among those folks who say you just let everything go and you don't touch it.

But then there's also other forms, restoring, things like that. How do you view what rewilding is?

TREE: I think it's an amazing word, isn't it? Rewilding. Because it's so difficult to pin down. It's almost like it rewilds itself every time you try and contain it. And I think the best way to think of it, and it's how we've tried to portray it in our book, is that rewilding is a spectrum and it's all to do with size.

So if you're at the kind of Yellowstone end of the spectrum, where you've got apex predators, you've got the whole kind of fully functioning ecosystem, then human beings don't have to play a part at all. But if you are at a much smaller level, so say you're at the 3,500-acre size that Knepp is, then we don't have apex predators.

So we stand in for the apex predator and we control the numbers of herbivores so that we can reduce that impact on the environment as an apex predator would. The smaller you go, actually, the more interventions you need to do. You become the keystone species that is missing. You become the beaver, you become the wild boar.

So it's a question of thinking in terms of how the natural processes act in the landscape and replicating those, you become the browsing and grazing animal, if you like.

CHAKRABARTI: I see. I just want to repeat again the name of the book because the book is very good and actually quite useful.

It's called “The Book of Wilding: A Practical Guide to Rewilding, Big and Small." And I really love that the analogy that you used, Isabella, about human beings. I suppose this is actually true anywhere, right? Because no matter what we do, we are in control of this planet, right? Even if we leave things alone, there are processes, human based processes going on around a landscape that will have an impact on it.

But I'd love to get, I was going to say, we're supposed to get down in the dirt with you, as a terrible analogy.

TREE: (LAUGHS) I liked it.

CHAKRABARTI: To talk about some specific aspects of rewilding, right? Because you said you had introduced the larger scale herbivores first to Krepp estate. Thereafter, what did you do regarding, you know, plants and trees. And you talked about birds so beautifully at the beginning of the show.

Did the birds mostly just come back on their own? Tell me a little bit more about the process.

TREE: No, exactly. So after the last harvest of the fields, we simply left them open. And so the wind dispersed the seeds, the birds came in and they brought seeds with them. Nature can grow trees.

It knows how to do it. So what we were seeing was just spontaneously colonizing scrub, thorny scrub, brambles, dog rose, hawthorn, bramble. The perfect kind of scrub that provides food for small mammals and insects and birds, but also provides them with protection from predation.

So instantly you're getting this habitat evolving by doing absolutely nothing by sitting on your hands. And then in come the trees, we have jays that plant trees, a single jay can plant 6,000 acorns in an autumn.

So we were seeing all these oak trees popping up all over the place, but obviously if we just left it to the vegetation, eventually, just as in your garden, you would have got closed canopy woodland shading out the light and actually biodiversity would have fallen. So what you need is that kind of endless disturbance that these free roaming animals cause to keep open this kind of matrix, this kaleidoscope of more open habitats that all species can enjoy.

And so that's really what happens, I think, in a garden, if you just close the garden gate and just leave it to its own devices. It will turn into a very shady, very species poor space very quickly. So you have to be that proxy of all those other influences that happen in the bigger landscapes.

CHAKRABARTI: So smaller gardens are the focus of a lot of our listeners, because that's the land that they have. And let me just share a couple more stories of things they've done. This is Sandy Martin in Seattle, Washington, and she says she's not letting her entire yard sort of get rewilded, but she does a few things to support the wildlife in her backyard.

SANDY MARTIN: I put zero fertilizer on my lawn. I also do not rake up leaves, but I mulch them. I have been planting pollinator plants that are more native to the northwest, so that I attract birds, bees, and hummingbirds.

CHAKRABARTI: So that's Sandy in Seattle, and this is Emily Spilker in Lafayette, Indiana. She says she has about a third of an acre, and she's on a multi-year journey to get rid of her grass.

EMILY SPILKER: I've done, very cheaply, just free mulch, cardboard, discounted perennials, and seed packets that are native to Indiana. And then the difference that I've noticed is huge. I've gotten into birdwatching. I have so many more visitors in my yard, be that birds or pollinators. I am a huge proponent of rewilding, and I can't wait to get rid of all my grass.

CHAKRABARTI: Now, Isabella, if I think there's one thing that Americans, and the English in particular, still have in common, it's love of a perfectly manicured lawn.

TREE: It's the lawn. Oh my god.

CHAKRABARTI: We had a lot of people calling and saying --

TREE: It's a tyranny.

CHAKRABARTI: Yeah, the first thing they want to do is get rid of their grass.

Not just because it's doing all the things that you said earlier. It's taking up land, it's preventing the return of natural species or native species, but also all the millions and millions of pounds of fertilizer that people put on their lawns. And that has a lot of long term effect, not just on that land in particular, but chemical transport through groundwater.

Talk about grass for a little bit. And then I do want to explore the chapter that you have in the book about rewilding water, which is so interesting.

TREE: Yeah. It is extraordinary, isn't it? Our obsession with these kind of billiard table lawns, like we all want to play on the center court of Wimbledon or something.

And really they are biological deserts. It is possible to have a much, if you want to have a lawn, of course, a garden is for your own pleasure. And if you've got kids or grandchildren who want to be playing ball games, you'll want a closely cropped lawn, but how about a wonderful chamomile lawn, a wildflower lawn where their lovely bare feet can crush the wildflowers, and you can let this wonderful scent as you play.

I think it's really about talking thinking in terms of, what would there be out there in the landscape? So certainly, you get animal lawns in the landscape. You think of kind of Serengeti, for example. But you also get mixed in with that much longer grass. So places where small mammals, insects, birds can take cover. Having that sort of, there's a wonderful organization here called plant life and they call it giving your lawn a Mohican.

So you allow some of it to grow much longer, and you get this much more interesting vegetation complexity, these staggered layers of lawn. But getting rid of a lawn altogether, I think is really exciting. We had in our walled garden here at Knepp, my husband's beloved croquet lawn.

And you can imagine the kind of the TLC or over attention that went into that. Fertilizer, insecticides, everything, herbicides to keep it just that monoculture clipped lawn. And so what I've done with the help of a wonderful landscape gardener called Tom Stuart-Smith and James Hitchmough, we've dumped 400 tons of crushed brick and concrete onto that croquet lawn.

CHAKRABARTI: Wow.

TREE: and it's never felt so liberating.

And so what we've done is out of that sort of monoculture 2D landscape. We've created a sort of 3D landscape of humps and bumps and hollows. And the substrate, the concrete and crushed brick is very poor, which a lot of wildflowers absolutely love and it's free draining. So all the plants that we've planted in there now, over a hundred species, some of them, from the States, wonderful kind of prairie grassland species are very dry loving and very hardy.

So we don't have to water that area at all anymore. So we've completely dropped our inputs of fertilizer and water. But created this incredible mosaic of plant communities, because you've got different plants that like the north facing slopes. This isn't a big slope, they're almost like large termite mounds, but softer.

And then where you've got the hollows, you've got much wetter ground. So different plants are liking that.

CHAKRABARTI: Oh, I'd also say that. Yeah, I'm sorry to interrupt there, but you can still play croquet there. It just makes for a much more challenging game.

TREE: (LAUGHS) It's more like crazy golf, yeah.

CHAKRABARTI: So go ahead and finish your thought, because you said after introducing more hardy, dry, thriving plants the whole landscape changed. I just want to hear the rest of that story. I'm sorry for having to interrupt.

TREE: Yeah no, it's just that having different areas of richer soil in one patch or a soil, sandy soil, you can create many plant communities in a much smaller space.

And that means that instantly your biodiversity is going to increase. You've got many more insects. Insects often have very complex life cycles. So sometimes they're like a damp patch in one part of their life cycle, but need dry conditions in another. So without knowing it, you're triggering all these sort of amazing trophic cascades.

We now think about planting not just for the pollinating insects, but for their predators too. If you're growing vegetables, for example, obviously you will be putting inputs on to grow your veg. But wat about thinking of the natural predators that will be eating the aphids, the green fly, the caterpillars and allow them to build up to sit back and let those boom-and-bust cycles of nature play out, instead of reaching for the pesticide or a quick fix.

CHAKRABARTI: Now, we have about two minutes before our next break, Isabella. I am fascinated by the chapter about rewilding water, because I think a lot of that you've described so far, beautiful, but also maybe familiar to some people who are undergoing the same process. But what about water systems themselves?

TREE: That's another amazing dynamic system. And it's a once only intervention and you've done some amazing things in the states with this new technology of restoring river systems and using a kind of technique of getting a braided river back, which responds to its floodplain, which is dynamic, which holds back water during floods.

And we're beginning to learn that from you, I think, over here in Europe. That giving space to rivers not only creates wonderful conditions for biodiversity, but it also creates much safer landscapes for us. So yeah. Restoring natural water systems is a kind of one-off intervention that you can then completely sit back on your hands and let that water continue doing what it wants to do.

CHAKRABARTI: Did you do that at Knepp Estate?

TREE: Yeah, so we've let, just on our heavy clay, when you just let the water sit where it wants to sit, you get instant ponds. That's one thing our land is good at. But we also restored about a mile and a half of river. So we took put the river back onto its floodplain from a kind of canal where it had been forced in Victorian times.

And now we have a very dynamic, wonderful floodplain with all sorts of incredibly rare species, including the scarce chaser dragonfly, which only occurs in six places in Britain, but somehow, it's found us. So yeah, it's amazing, exciting thing to do.

Part III

CHAKRABARTI: Now, Isabella, again, as you can tell, we got a lot of response from our listeners, and they brought such wonderful stories, many of which brought up benefits to rewilding that I had not thought of myself. And here's a couple. This is listener Susan Burkholder. She lives on about a half-acre in Greensboro, North Carolina, and she says her property, over time, she loved to garden and do all that work outside, but it's become harder to manage, actually, and by somewhat rewilding her land, she's welcomed having less to do.

SUSAN BURKHOLDER: It just got to be more and more work for me as I was getting older. At some point, probably about 10 years ago, I remember there was an area in this on our side yard where I just decided, "Oh, this is just going to be my volunteer plot and I'm just going to just leave it be and see who shows up there and say, 'Howdy.'" Fast forward to today, I have continued to let more and more of the yard go quote-unquote.

CHAKRABARTI: So that's Susan, who lives in Greensboro, North Carolina. Now Patty, in Portland, Oregon, is 77, and she's taking this analysis even further.

PATTY: As friends my age are considering possible retirement accommodations, because they can't keep up with yard chores, I've decided no retirement home for me.

I feel like I've got a win situation. Less work, more wildlife.

CHAKRABARTI: That's Patty in PDX in Oregon. Now Isabella, tell me, did the rewilding of the land at Knepp Estate, clearly you've described in detail how it's returned a health and vitality to the land, did you feel a sort of an impact on you and your well being in return?

TREE: That was probably one of the most extraordinary and unexpected things, I think. We suddenly, we relaxed, we'd been working, my husband had been working so hard running this failing business and running the farm. And it was just amazing. As we saw the land relax around us, it felt like it was breathing a sigh of relief and so were we.

And I think just allowing things to just stepping back a little and not trying to micromanage is a huge relief. When we look at what we do in our gardens we really slave drive ourselves, but if we can allow ourselves to get a bit messier, to allow dead wood to fall and stay there, knowing that it's fantastic habitat, allowing a pile of leaves to stick around in a corner that brambles to come up every now and again.

It's not only hugely relaxing, but it's incredibly rewarding. And I think psychologically you learn not to be a control freak. You learn to trust in nature a bit and to trust in life. I think we all perhaps need to learn how to accept the way the dice rolls and what happens.

And nature can teach us that. So it's been a very interesting experiment in psychology on top of everything, I think. And you had used such a perfect phrase earlier about basically, biodiversity deserts that can be highly managed lands. And I'm just thinking that it's probably also just good, almost, it's physically good to be reconnected to a more complex web of nature when there's more just natural space around you versus farmland, for example.

CHAKRABARTI: Isn't that one of the reasons why forest bathing got started in Japan, for example?

TREE: Totally. And we all, I think, appreciated that during lockdown, didn't we? Those of us who were lucky enough to have nature on our doorstep, but even those of us who didn't, that need, that real hunger for wild spaces became very apparent. And we know how important it is, to not just our physical health to be out in nature, and to breathe clean air. But our mental health too. It's no good. I don't think, just saying green space is enough. Green space can also be a desert.

We've got to look at what that green space could be. And can we hear noise? Nature is noisy. Is it full of life? I think the wonderful American biologist E.O. Wilson called it biophilia. It's that innate feeling all of us really have deep inside of us to connect with living things.

And if it's not a really living landscape, then it's not really going to be doing the job. So I think we have to learn to look at our landscapes again, afresh, without any of the sort of cultural baggage we've grown up with and really think, is that a functioning ecosystem? Is there life in that landscape or should we be asking for more?

CHAKRABARTI: You mentioned E.O. Wilson. I had the privilege of interviewing him several times before his death and he's one of the --

TREE: Oh, such a hero.

CHAKRABARTI: Most remarkable minds I've ever had the joy of being in conversation with. We wanted to take a minute to talk about the efforts on public lands here in the United States, because that can often be a complex thing.

The politics around public lands in America are quite contentious. Let's just put it that way. But that does not mean that there haven't been extensive efforts to either restore or rewild lots of acreage in this country. So we talked to Joey Algiers. He's a restoration ecologist with the National Park Service for the Santa Monica Mountains National Recreation Area.

It's just outside of Los Angeles. The park recently took on its biggest restoration project ever. Beginning in October of 2021, Algiers says he, his staff, and volunteers planted some 100,000 trees and plants.

JOEY ALGIERS: So we were planting our iconic oak trees, coast live oaks and valley oak trees, and then we focused heavily, not just on planting the trees, but putting in the supporting species as well.

So our native grasses and native herbs to try to create a whole community.

CHAKRABARTI: Algiers says the project focused on mountainous areas that had been depleted and degraded both by ranching and wildfire.

ALGIERS: They were dominated by invasive species, primarily annual grasses with non-native forbs like mustards and thistles.

And those grasses are very aggressive. They spread very quickly. They move into natural areas. They dry up quicker than our native plants, and so they pose a huge fire hazard.

CHAKRABARTI: Now the truth is that naturally occurring wildfire can be beneficial and oftentimes is essential to rejuvenate some ecosystems.

But in the Santa Monica Mountains, he says fire is happening too often.

ALGIERS: Like our mountains, for example, could burn once every 50 to 150 years. And that would be fine, they would rebound, they'd have enough time in between fires to grow, to mature, to replenish the soil with seeds, but we have areas that have burned 12 times in the last 100 years, and so that's a fire like once every 10 years or less, and that's just not enough time for our natural systems to recover.

CHAKRABARTI: Now, increased wildfire frequency in the United States is caused by many factors. Climate change, historic forest management practices that have deliberately suppressed fire in order to save trees as an agricultural resource and of course, fire suppression to protect homes.

And now that one is still important. That need has not gone away for people who live nearby. Algiers says this restoration project will take decades to reach its full potential. The willows and oaks they planted are growing as are stands of perennial purple needle grass, California's state grass. They are thriving.

He says by removing the invasives, he's even seen some species come back.

ALGIERS: We're seeing native rushes come back and even a creek monkey flower. We still have a ways to go as far as keeping those areas maintained, but our survivorship's been really high. We're seeing, in some cases, our trees are up to 85% survivorship.

We spent a lot of time caring for these plants and caging them and keeping them protected from herbivores. And then our grasses and our shrubs are doing really well too.

CHAKRABARTI: So we're going to come back to what the rest of Algiers had to say about their efforts in California. But Isabella, I wanted to jump in here because this is a huge issue about what is wild right now.

And in fact, my staff and I have been debating this for several days. Because regardless of human influence or not, nature changes, species move. What was supposedly native once or native now wasn't native before. So how do you think through this invasive species, natural species?

TREE: It's so interesting. Because we've just, Charlie and I have just been on a book tour in the States and the first question anyone in the audience asks is, "What about nonnative invasive species?"

And I think that's looking completely at the wrong problem, the wrong thing. In the UK and Europe, we don't tend to think that way. Because we've been, I suppose our ecosystems have been so messed up for so long. We no longer know what a non-native is. We were outraged when the American signal crayfish came into the UK.

And started killing off existing crayfish in the UK. But actually, we didn't have any crayfish until the French monks brought them over in the 12th century. We really don't know what's native and what isn't. We know we have rabbits and hares, which are now part of our ecosystem. Hares have their own biodiversity action plan, so they're protected.

I think when you're looking at an invasive species you have to ask yourself, I think, "Why is it invading?" And chances are that it's just walking through an open door into a dysfunctional landscape that is no longer able to resist it. If you've got a very, a full functioning ecosystem.

It's much harder for an invasive species to come in and get a foothold. It may arrive, but it won't become the invasive that we think of. So I think the emphasis really should be on how an ecosystem functions. We're never going to be able to get rid of non-native invasives. I think the U.S. spends $3 billion a year trying to get rid of non-natives and hasn't had a single success.

You can work and work to try and get rid of these species, but unless you're getting a functioning ecosystem back, you're not going to, you're not going to achieve anything. And that money would be much better spent on restoring those natural processes in the first place.

And I think this is where free roaming animals come in actually, because a lot of free roaming animals will eat those invasives.

It's always a question of numbers. You don't want too many to prevent other plants coming back. But equally, you want that kind of, we're missing that process of animals controlling vegetation for us. And if we can allow them to do their thing, they can be a really big ally in both restoring soils with their dung and also transporting the natural seeds, the native seeds around the landscape.

CHAKRABARTI: Can I just jump in here because the point that you were making about organized attempts to rewild with lost, quote-unquote, indigenous species, we got a call about that or a comment. This is Campbell Vaughn in Augusta, Georgia. He's an extension agent for the University of Georgia, and he wanted to let us know that letting the land go completely untouched. Because of this native versus non-native issue, he thinks it may not always be good.

CAMPBELL VAUGHN: We're seeing so much of this fallow space being taken over by invasive species in my area in Augusta, Georgia. It's Chinese privet, sometimes it's kudzu the other one is the escaped Bradford pears, which have really taken over. You would hope that the natives and stuff would come back. But it seems like the invasives are the first ones to jump.

CHAKRABARTI: I hear the tone of regret in Campbell's voice there, but he seems to be making your point about the land as it is, is better suited now. Or because it's been so damaged, better suited for the invasives. I want to just finish up what Joey Algiers told us about the project in California.

And about the trying, they're still actively trying to reintroduce native species that have been pulled out, or so outcompeted by those invasives, and part of the story is because those native species are actually hardier when it comes to fire, which is really interesting. But he told us that he worries that without humans, to actually use your language Isabella, to be the alpha species to keep those native species alive, that the California species they're working on could totally disappear.

ALGIERS: For myself and for many resource managers and conservationists, the fact that these species are rare and unique, and they have been evolving since the beginning of life. They have this evolutionary, incredible evolutionary history. They are special in their own right. They have a right to be there, they have a right to persist, and the fact that they are being displaced because of human activity is why I think that's worthy enough for us to intervene.

It'd be like removing a book from a library. You'd never have the chance to read that book or to know it. And even if you never did know it, there's just something, some intrinsic value about having that art there.

CHAKRABARTI: So that's Joey Algiers, restoration ecologist with the National Park Service.

Oh, Isabella, we only have two minutes left.

TREE: No! (LAUGHS)

CHAKRABARTI: I have so many more questions for you. Because we got calls from people who say, "I've been trying to rewild my yard, but the city's making me cut all that grass down."

TREE: Oh, I know.

CHAKRABARTI: Yeah. So I don't know how to respond to that. I guess you'd have to negotiate.

TREE: I rebel, rebel. We've just been in Chicago, and somebody told me there that they weren't allowed to grow a plant above about a foot high. And you're just thinking, "This is crazy." And we were walking around the field museum. It's amazing what they've done to that space around the field museum, it's full of American, native plants and full of migrating birds. When we were there, I couldn't get over it.

And we could learn a lot from that in London. But I think, we've just got to, we got to stand up to these councils that really, you know the institutions that tell us what they think is right. I think we instinctively know what nature wants and we've got to get nature back in every inch that we possibly can, not just for biodiversity but for climate, change too.

CHAKRABARTI: I agree with that. I definitely agree with that. But to be fair, a lot of these regulations in U.S. towns and cities are for safety purposes. And so I think that's a tough mountain to climb.

Probably worth another show for us. But Isabella, do you happen to be sitting next to a window right now or no?

TREE: I am. I'm in front of a window. Yeah.

CHAKRABARTI: In 10 seconds, can you tell me what --

TREE: I've just seen another dozen white storks fly past, and we had a sparrowhawk in the oak tree just about five minutes ago prospecting and there's a matriarch cow leading her herd, bellowing off into the woods.

CHAKRABARTI: Oh, one day I will call you up and ask if I can visit.

TREE: Please do, we'd love that.