What role do trees really play in fighting climate change? An expert explains

“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 that carbon in the long term as a wonderful byproduct.”

So says Thomas Crowther – an ecologist at the department of Global Ecosystem Ecology at ETH Zurich and scientific advisor to the UN Decade on Ecosystem Restoration – as he describes the valuable contribution forest ecosystems make to nature and, in turn, to the fight against climate change.

In support of the UN Decade on Ecosystem Restoration (2021-2030), the World Economic Forum’s 1t.org initiative aims to accelerate nature-based solutions to conserve, restore and grow a trillion trees by 2030. The aim is to empower local communities around the world to cultivate the biodiversity that underpins their lives and livelihoods.

Crowther spoke to the World Economic Forum's Radio Davos podcast to discuss his latest research on forest ecosystems and explain some past misconceptions about what a Trillion Trees is all about. Edited excerpts follow:

"The whole world heard about Trillion Trees, but the whole world also had the misconception that this was about mass-planting a trillion trees.

"Instead, at least from the scientific perspective, a trillion trees 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 forest management 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.

"Over the last 10,000 years, almost a third of the world’s forests have been lost to land cultivated for agriculture, with half of the deforestation occurring in the 1900s. But with targeted action, some forest ecosystems can be rebuilt."

"Our research essentially aims to generate a holistic perspective of what nature is. In academia, there’s often a tendency to really focus 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. Taking a global perspective can help us understand how the planet’s ecosystems lock away carbon.

"And that makes it very relevant for the climate conversation because we can see where ecosystems are now and how they might 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. Then we can figure out the synergies, the ways that we can move towards our combined biodiversity and climate targets together.

"So now we've built this collaboration with hundreds of forest scientists across the planet, that provides a comprehensive range of people and approaches to studying the global forest system in every way possible. We had millions of ground source datasets, we had satellite observations, and by pulling all of that data together, we could see that outside of urban and agricultural areas, there's room for forest to capture about 226 gigatons of carbon.

"But what's really exciting is that we could also show how and where that carbon gets captured. We found that 61% of that capture potential can be achieved by conserving the ecosystems we still have. As most of our planet’s forests have only reached 30% of their full maturity, allowing them to grow and fully mature could make a huge contribution to the climate fight."

"The work builds on an earlier paper published in the journal Science, which showed that restoring Earth’s forests could capture around 200 gigatons – 200 billion tons – of carbon to help combat climate change.

"When that paper came out, it went viral and made headlines across the media. It gave rise to, or it inspired, the launch of the UN's Trillion Trees Campaign. The World Economic Forum launched its 1t.org and the UN Decade on Ecosystem Restoration was initiated.

"But it also came with downsides because it was a moment when 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.

"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 will carry on emitting carbon, plant a few trees in the ground and everything's done."

"In ecology, every species depends on other species to survive. When you plant a monoculture of trees, it won't survive very long as any drought or insect pest is going to decimate the whole thing because the systems aren't very resilient.

"But also, a mixture of species all take up different resources in different ways. Some capture more light, some are more evolved for capturing water at depth or some capture different nutrients, and collectively the whole system can add a huge amount more biomass than just the monocultures on their own.

"Most of the world's forests are nowhere near their full mature state. We need to conserve the ecosystems we have so they can reach that maturity, then they're absorbing as much carbon as they release. But it's that storage that is the biggest challenge in the climate movement.

"Storing billions of tons of carbon is an incredibly important role of forests. So we desperately need to conserve those ecosystems when they're at maturity.

"In the last 20 years, there's been this revolution of satellite data giving us an incredible. global perspective where you can see every tree everywhere, but this doesn't tell you what’s going on below the surface.

"But there's also been a revolution of big data with people on the ground sharing all of their measurements. With satellite and ground measurements, you can compare them and build models that can really accurately predict variation across the space."

"I hope that people recognize the value of forests for what they truly bring, as these ecosystems are fundamental to our survival on the planet.

"Yes, they contribute to tackling 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, we'll get wonderful carbon as a byproduct. But if instead we focus solely just on maximizing carbon capture in a place, this could incentivize solutions like mass plantations that have caused so much damage.

"So I think we need to recognize 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."

"Everybody wants nature to thrive because we all fundamentally know that we depend on it. We couldn't survive without the biodiversity on our planet.

"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 not worry about cutting emissions, they're going to do a lot more harm than good.

"Planting vast plantations of trees to capture carbon doesn't respect the rights of the indigenous populations that live on that land.

"But all of these things can be overcome if we refocus our goals away from just carbon and towards biodiversity and the well-being 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.

"There's one coffee farmer we work with in Ethiopia who has an amazing farm in the country’s cafe region, for example. Instead of removing the forest to grow coffee, this farm keeps the forest intact and plants local coffee varieties among the trees in sunny patches. Because the forest traps water and nutrients, the coffee plants grow without needing fertilizer or irrigation. Nature is making this agroforestry farm more productive."

"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 hundreds of millions of local communities being empowered by the nature they depend on.

"Scale is not 10 massive plantations or 100 massive plantations here or there. Global restoration means millions of communities being empowered by nature.

"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 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.

"I think there is ever-growing progress. While many of us are frustrated by the apparent emptiness of some climate pledges, they show sustainability is becoming important for every organization – and that is only going to grow as we continue to face the threats of climate change and biodiversity loss.

"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 on the number of trees, the amount of carbon and the amount of emissions you no longer need to cut.

"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."