"Not just sticks of carbon" - how growing trees for the climate must also benefit biodiversity

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Thomas Crowther, professor, Department of Environmental Systems Science, ETH Zurich: It's important to remember that a forest is not just a load of sticks of trees. They're not just sticks of carbon. These are diverse, thriving ecosystems, and it's the biodiversity within them that allows them to capture and store all of that carbon.

Robin Pomeroy, host, Radio Davos: Welcome to Radio Davos, the podcast from the World Economic Forum that looks at the biggest challenges and how we might solve them.

This week: trees - they're a big part of our effort to fight climate change - but only if we get it right.

Thomas Crowther: These ecosystems are fundamental to our survival on the planet. Yes, they contribute to our fight against climate change. But if carbon is the only thing we're aiming for, we'll probably do more harm than good.

Robin Pomeroy: This scientist’s work on the carbon storage potential of trees helped spark a global movement into the planting, conservation and restoration of forests. But he tells Radio Davos that vast tree plantations are not the answer.

Thomas Crowther: A trillion trees, to me, means millions of local communities being economically empowered by the biodiversity they depend on.

Robin Pomeroy: As he publishes updated research that shows trees have the potential to meet a third of humanity’s carbon goals, Tom Crowther says that does not mean we can slow down efforts to cut emissions.

Thomas Crowther: Nature is not an excuse to avoid cutting greenhouse gas emissions. We can't offset those emissions with nature. What we need is to move continuously towards our climate and biodiversity targets together.

Robin Pomeroy: Subscribe to Radio Davos wherever you get your podcasts, or visit wef.ch/podcasts. I’m Robin Pomeroy at the World Economic Forum, and with this look at the right way to use forests to capture carbon

Thomas Crowther: A revolution of people being empowered by nature.

Robin Pomeroy: This is Radio Davos

Robin Pomeroy: So we're going to talk about trees and who better than Thomas Crowther, who's an ecologist, who's an expert on biodiversity and climate change and how the two things interact. Hi, Tom. Well, how are you? What, where where do we find you today?

Thomas Crowther: I'm very good. I'm in Zurich.

Robin Pomeroy: Okay, so tell us about the work you do. I mean, how do you describe to people who've not come across it before the work you've done on trees and nature and the relation between that and climate change?

Thomas Crowther: Our research is essentially aiming to generate a holistic perspective of what nature is. In academia, it's and often a tendency to really focus in on individual parts, but we tend to try to step back and see the bigger picture to study how microbes, plants and animals vary across the planet. And by having that global perspective, it can be really useful in understanding how these ecosystems lock away things like carbon.

And that makes it very relevant for the climate conversation because we can see where ecosystems are now. We can also see how they might potentially exist in their natural state, or if we could manage them in certain ways, how that might be able to increase or decrease carbon storage on the planet.

And as a result, that means we can figure out the synergies, the ways that we can move towards our combined biodiversity and climate targets together.

Robin Pomeroy: So you've just published new research on the potential of trees to absorb huge amounts of carbon. This is a follow up paper to research published in 2019. Can you give us a bit of the history of what that paper was and kind of what that led to?

Thomas Crowther: Yes, I guess the only thing I'd correct is that the study is showing the potential of forest ecosystems to capture carbon.

Again, it's important to remember that a forest is not just a load of sticks of trees. They're not just sticks of carbon. These are diverse, thriving ecosystems, and it's the biodiversity within them that allows them to capture and store all of that carbon in the long term as a wonderful by-product.

But yeah, our research on forests, I'll put it lightly, it's been a rollercoaster ride. So about four and a half years ago we published a paper in the journal Science showing that the restoration of Earth's forests could capture around 200 gigatons of carbon. That's 200 billion tonnes of carbon, which would make it a really useful contribution in the fight against climate change. It's about a third of our climate change carbon drawdown goals.

And when that paper came out, it went absolutely viral. It was headlines in every media. It inspired the launch of the UN's Trillion Tree Campaign. WEF launched their 1t.org The UN Decade on Ecosystem Restoration was initiated. This was a time when nature was really heavily in the conversation.

But it also came with downsides because it was also a moment where greenwashing exploded. This idea that you could just plant a few trees and ignore the very real and urgent challenges of cutting emissions and conserving the ecosystems we have.

And this idea of mass tree planting really just exploded. And it led to a huge amount of controversy because obviously academics and scientists and NGOs all across the planet, were outraged: mass tree planting has nothing to do with global restoration and the recovery of ecosystems. And yet there's this really dangerous idea that companies are just going to go, okay, we'll carry on emitting our carbon, bang a few trees in the ground and everything's done. Not only would that probably damage the ecosystems that they're planting in, it would be devastating because ongoing greenhouse gas emissions would continue to limit the sustainability of those ecosystems in the long term.

So it was a moment where nature came to the fore, but also greenwashing came to the fore. And so it's been a really turbulent time for the last few years. This threat of greenwashing is an insidious threat, and it has undermined the entire environmental movement.

Robin Pomeroy: Well, that's that's quite a statement.

Thomas Crowther: Yeah, it's been an intense time, and I've obviously experienced the intensity of that conversation from within. It's been a pretty brutal time. It's been a horrible four years of my life, particularly as an ecologist who loves the complexity of nature, to be linked with this message about mass planting of trees is devastating.

Robin Pomeroy: So this new research now, I guess this gives you a second opportunity to talk about the message you're really putting out the last time. Tell us something about what else do we learn from this new paper that's that's being published, in which journal?

Thomas Crowther: So this paper is coming out in the journal Nature this week.

The first step is we needed to move the academic community beyond this sort of controversy.

So we've built this collaboration with hundreds of forest scientists across the planet.

The other nice thing is most of these papers on the topic of all focussed on an individual scientific approach to evaluate restoration. Some people said that our previous estimate was was in line with expectations. Others found that it might have been four or five times too high. So we needed a comprehensive range of people and a comprehensive range of approaches so that we could study this global forest system in every way possible.

So we did that. We had millions of ground source datasets, we had satellite observations, and by pooling all of that data together, we could see that there is, outside of urban and agricultural areas, there's room for forests to capture about 226 gigatons of carbon, which is a huge contribution to the climate fight.

But what's really exciting is that we could also show how and where that carbon gets captured. So it's not just about mass plantations of trees. 61% of that potential can be achieved by conserving the ecosystems that we still have. Most of the forests on our planet are only at 30% of their full maturity. If we can serve those ecosystems and allow them to grow to maturity, we could capture, as I say, 61% of that potential.

So that is a huge change in the conversation from last year.

Robin Pomeroy: I think a lot of people, you know, who are not specialised in this, they're aware that trees, plants, suck in carbon from the atmosphere. But there's this notion that a mature forest with big trees in it, they've already sucked up the carbon, they're not really going to suck up any more. Is that true? I'm sure there are nuances I'm missing by stating that. How can a forest continue to keep pulling carbon out of the air?

Thomas Crowther: So there's two parts to this.

First, most of the world's forests are nowhere near that full, mature state. You know, most of us have never even been in an old growth forest where there's huge trees that you couldn't put your arms around. We need to be conserving the ecosystems that we have to allow them to reach that maturity. And that's a huge amount of carbon drawdown.

But in addition to that, you're right, once they've reached full maturity, then they're in a steady state. Then they're absorbing as much carbon as they released. They're not taking up additional carbon. They're just storing. But it's that storage that is the biggest challenge in the climate movement. Storing billions of tonnes of carbon is an incredibly important role of forests, so we desperately need to conserve those ecosystems when they're at maturity.

Robin Pomeroy: You've talked about your work monitoring around the world. Tell us something about how that's possible, because a tree, seen from space is - you can see them, but there's a lot of them. They're relatively small. How can you know precisely the data we need to know in terms of where forests are growing, where they're shrinking, deforestation, and if we can calculate the carbon uptake of those forests. How do you do it and how do you present that data that once you've brought it in?

Thomas Crowther: There's a general rule in academia, particularly in these global scale studies, that any individual measurement gives you one bit of inference, but you want to combine it with as many different measurement styles as you can to sort of see how they align with one another.

And so what we always do is, in the last 20 years there's been this revolution of satellite data, which is incredible, brings global perspective. You can see every tree everywhere, but it doesn't tell you the data that's going on below the surface.

And what's been wonderful is that, during that same time, there's also been a revolution of big data with people on the ground sharing all of their measurements.

And so when you've got measurements from the ground and you've got measurements from satellites, you can compare them with one another and sort of benchmark those estimates so that you can build models that can really accurately predict variation across the space.

Robin Pomeroy: What do you hope will be the reaction to this new research? What are the things that you hope people will understand better perhaps than they did last time?

Thomas Crowther: I hope that people recognise the value of forests for what they truly bring.

These ecosystems are fundamental to our survival on the planet. Yes, they contribute to our fight against climate change. But if carbon is the only thing we're aiming for, we'll probably do more harm than good.

Carbon is not the only goal if instead our goal is to promote biodiversity and the well-being of people who depend on it. You'll get wonderful carbon as a by-product.

But if instead you focus just on how do I maximise carbon capture in a place you could incentivise really damaging solutions like these mass plantations that have caused so much damage.

So I think we need to recognise the immense value of nature, but that we can only achieve that potential if we do it alongside other actions like emissions cuts and promoting healthy biodiversity for the well-being of people who depend on it.

Robin Pomeroy: Trees is one of those things, it used to strike me anyway that everyone could agree on. My first World Economic Forum Annual Meeting in Davos was in 2020 when President Donald Trump came. No great supporter of climate change action, I think is fair to say. But he did sign up or he did back the Trillion Trees project because it's nature. It's trees. Who doesn't love a tree? So it was able to bridge a kind of a political divide where sometimes climate change action is wrongly seen as kind of left of centre.

But then there has been this kind of backlash in some ways that the trees have become far more political than they were perhaps five years ago. What's happened there and how can we change that again?

Thomas Crowther: No, you're exactly right. It's been a really unusual phase.

Nature has this incredible power because it is supported by both sides. It's a bipartisan solution. Everybody wants nature to thrive because we all fundamentally know that we depend on it. 100% of the economy is 100% dependent on nature. We couldn't survive without the biodiversity on our planet. So I think it does bring people together.

But there has been this danger, and that Donald Trump announcement was part of the backlash to the paper that I mentioned in 2019.

When people misuse nature, it can be dragged into a really dangerous place because if companies are going to just plant a few trees and then don't worry about cutting emissions, they're going to do a lot more harm than good. And at the same time, we've seen these vast plantations of trees to capture carbon that don't respect the rights of the indigenous populations that live on that land. That is devastating human rights issues.

All of these things can be overcome if we refocus our goals again away from just carbon and towards biodiversity and the wellbeing of people who depend on it.

Every time you find a local solution that makes nature the economic choice for people, that is when nature thrives across landscapes and you can't stop it from growing in the right way.

Robin Pomeroy: Remind us what the Trillion Tree initiative is. What was it aiming to do and what is it aiming to do?

Thomas Crowther: So the Trillion Trees initiative was launched following academic research that showed that our Earth is home to 3 trillion trees and that there's room for a third more. So if we conserved a third of the land that is currently degraded, that a third of those trees could come, that amounts to a trillion new trees.

The alliteration was unbelievably catchy. The whole world heard about a trillion trees, but the whole world also had the misconception that this was about planting a trillion trees. And it has nothing to do with mass tree planting, at least from the scientific perspective. A trillion trees, to me, means millions of local communities being economically empowered by the biodiversity they depend on. That could be agroforestry. It could be ecotourism and conservation. It could be sustainable silviculture or rewilding programs. There's a thousand ways in which nature can recover. But mass planting of trees has nothing to do with it, and that needs to be removed from any national or international nature based solution.

Robin Pomeroy: Could you explain a couple of those terms? Agroforestry and silviculture to people have not come across them before. What are those?

Thomas Crowther: Yeah, there's thousands of technical words about how we can work with nature, but these are essentially examples of sustainable ecosystem management.

And what I mean by that is any system where nature can improve the livelihoods of people.

I'll give you an example. There's one coffee farmer we work with in Ethiopia who has an amazing farm. He's in the Kaffa region of Ethiopia. There's large scale coffee production and what happens is they remove the forests so that they can grow coffee.

But this particular farm, Desta's, actually keeps the forest intact and they plant local coffee plants in amongst the sunny patches. And because the forest traps water and nutrients, those trees grow without the need for fertilisers or irrigation. As a result, the productivity of his coffee is actually better than the surrounding area. That means nature is making his farm more productive.

This is an agroforestry system where nature is increasing the productivity of his farm and because of that, lots of the other farmers in the area are starting to do the same thing. And that is what restoration means. It's when nature is the economic choice for people.

Robin Pomeroy: Stories like that I think would really resonate with people, particularly city dwellers, who they don't run a farm. They're consuming products all the time like coffee, and they have no idea really where it comes from. I would love to think my coffee is grown in a forest among the trees, but is there a risk that some of these solutions are a bit small scale, perhaps a little bit quaint? Can we do this at a scale that can prevent deforestation and enhance people's livelihoods? That isn't just the odd initiative here or there are these ideas that could be properly global and scaled up.

Thomas Crowther: That's such a big question. I've got to answer this in three parts.

The first is that this topic of scale is actually underpinning a lot of the political debate and the controversy around nature. Because whenever people try to fix nature at scale, that is when dangerous decisions happen.

Nature is inherently a local issue. What we need to restore nature is have millions, hundreds of millions of local communities being empowered by the nature they depend on. We need hundreds of millions of Desta's.

And so that is scale. Scale is not ten massive plantations or 100 massive plantations here or there. That is not a global restoration movement. Global restoration means millions. It's a revolution of people being empowered by nature. And there are the seeds of that potential.

I work in affiliation with an organisation called Restor. You can go on to Restor and see hundreds of thousands of local farmers, indigenous populations, local communities who are working with nature at scale.

Robin Pomeroy: I've seen it. It's kind of a Google map. It is a Google map, right where you can drill down into where you live or place in the world you're interested in and actually see. I mean, one I went to, it was a school somewhere in England, I think, and it was their school field where they were restoring a patch of nature, you know, half a hectare or something.

So it's that micr, but when you zoom out, you've got the whole world of these things going on. That's exactly what you're talking about, isn't it?

Thomas Crowther: That is exactly. Hundreds of millions of these local initiatives makes for a global impact. So that's the first part my answer.

The second part, my answer about doing it at scale is that if an organisation does really want to commit to nature at scale, I'm all for that. But the best place for them to look is at their own supply chains first.

Everything you buy in the supermarket has a footprint on deforestation. Most of the things that we're buying, primary rainforest are being lost because of those products.

Now if organisations, particularly the large ones, can look at their own supply chains and take steps to end deforestation there, that is by far the biggest environmental footprint they'll have. And only after that do they want to invest in equitable development for these millions of local projects across the planet.

That is how we get large scale restoration. It is not by planting trees at scale.

But I would also say that efforts to promote nature outside of your supply chain are also wonderful. But don't do it by just paying for one large scale tree planting effort. The way to engage in nature beyond your supply chain is to try to invest or donate to portfolios of thousands and thousands of local community projects.

No one ever greenwashes their back garden. It's a quote I've started saying every now and again, but it's true. The local initiatives are never greenwashing. No one's planting seven apple trees to greenwash. They're doing it because the local community wants it. No one's rewilding, you know, animals across a landscape to greenwash. They're doing it because of the ecological integrity and the value it brings to the people who depend on it. Those are the projects we need to be investing in.

Robin Pomeroy: It's the conundrum that faces all of us with climate change. And there's this cliché, do people still say this? 'Think global act local'. But the thing with climate change is we all contribute to the problem, but it's very hard to see how we can contribute to the solution as individuals. I don't feel I could stop deforestation somewhere in the world. I really can't on my own.

But you're suggesting that there is a way. I mean, how can we stimulate the companies, particularly, I think, this being the World Economic Forum, to do that? Is it declarations at a conference of the parties at the COP that's coming up? Is it meeting in Davos? Where will this progress happen, do you think? Or is it already happening? And it's just a matter of pushing for ever more progress?

Thomas Crowther: I think there is ever growing progress. And while I think most of us are frustrated by the apparent emptiness of pledges, they are at least showing that sustainability is becoming a key part in every organisation, and that is only going to grow as we continue to face the threats of climate change and biodiversity loss.

So I'm not worried about the momentum that's building. What I think people need to be making sure is that those pledges are socially and ecologically responsible.

Pledge to end deforestation in your supply chain, pledge to distribute wealth to a million local communities. These are not dangerous pledges. The danger is when those pledges are based around the number of trees, the amount of carbon and the amount of emissions that you don't need to cut anymore.

We cannot be engaging in nature as an excuse to avoid emissions cuts. There's no contest between nature and emissions cuts. We categorically need both. You can't achieve one without the other.

There's one bit that is relevant about the upcoming paper because while the previous paper showed there's this huge potential for forests, the dataset that we've used shows statistically that if you were to try and achieve that potential with monocultures of a single species, you would lose more than half of that potential. We can only be getting anywhere near that potential if we do so with healthy, diverse ecosystems.

Robin Pomeroy: Why is that? Because you would think, all other things being equal and we've got the biodiversity we need, if there is a vast piece of land that we can just put in a monoculture, it will suck up carbon.

Thomas Crowther: So simply put, in ecology, the most fundamental principle is every species depends on other species to survive. When you bang a monoculture of trees there, first, it just won't survive very long. Any drought or insect pest is going to decimate the whole thing. So the systems aren't very resilient.

But also when you have mixtures of species, they all take up different resources in different ways and that means they can collectively fill out more of the space. Some are capturing more light or more of also capturing water at depth or some are capturing different nutrients. And collectively that means that the whole system can add a huge amount more biomass than just the monocultures on their own.

So there's a plethora of reasons why no systems in nature grow like a monoculture and they don't store carbon for very long.

Robin Pomeroy: So finally, then, let's talk a little bit about 1t.org. You don't want anyone to make the mistake that we've got to plant a monoculture of a trillion trees. If anyone had understood that, that's not what's happening. Could you say what can an organisation like 1t.org do?

Thomas Crowther: Organisations like 1t.org can learn from the science to set ambitious targets for organisations to commit to.

Now it's important that those targets, as I said, are socially and ecologically responsible. So those targets need to be around the health of nature and the well-being of people who depend on it.

1t.org does a great job in engaging organisations all across the planet and what they need to do is use that position to keep pushing those organisations towards socially and ecologically responsible commitments.

Nature is not an excuse to avoid cutting greenhouse gas emissions. We can't offset those emissions with nature. What we need is to move continuously towards our climate and biodiversity targets together. And only then will nature help our climate action and climate action will help our nature goals too.

Robin Pomeroy: Tom, where can people find your research?

Thomas Crowther: Our research is obviously available at ETH Zurich, but if you want to actually delve in and see how the global data looks, go to restore.eco where you can find all of those maps and you can see the implications for your garden.

Robin Pomeroy: Brilliant. Tom Crowther, thanks very much for joining us on Radio Davos.

Thomas Crowther: Thanks so much. Great to meet you.

Robin Pomeroy: Tom Crowther is a professor in the Department of Environmental Systems Science at ETH Zurich.

Find out more about a trillion trees at 1t.org.

We have many more episodes about climate and nature, search through our back catalogue at wef.ch/podcasts, where you’ll also find our sister podcasts Meet the Leader, Agenda Dialogues and the Book Club.

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This episode of Radio Davos was presented by me, Robin Pomeroy. Editing was by Jere Johansson. Studio production by Gareth Nolan.

We will be back next week, but for now thanks to you for listening and goodbye.