Talking Forests: Cristina Banks-Leite on Restoring the Amazon

Professor Cristina Banks-Leite (Imperial College London) discusses the realities of tropical forest restoration: from large-scale reforestation projects and the practical challenges of seedlings, land tenure and finance, to why measured “success” can look counter-intuitive. She explains why current biodiversity metrics often miss the point, and how novel tools (like acoustic monitoring and AI) could transform how we listen to and protect ecosystems. A thoughtful conversation about balancing people, money and ecological intactness in nature recovery.

You can also see Cristina Banks-Leite's talk on our YouTube channel
What drives species sensitivity to deforestation? Clue: it’s not what you think 

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Transcript

Nature Recovery Podcast — Interview with Professor Cristina Banks-Leite (Imperial College London)
Host: Stephen Thomas

Transcript

Stephen Thomas:
Welcome to the Nature Recovery Podcast. We’re going to take a closer look at some of the solutions to counter biodiversity decline, and we’ll find out more about the people behind these ideas. I’m delighted to say that today I’m joined by Professor Cristina Banks-Leite from Imperial College London, whose research explores how we can restore and conserve tropical forests in ways that genuinely support biodiversity and the people who depend on it.

Cristina’s work spans from measuring ecological recovery in fragmented landscapes to developing new approaches for monitoring and policy. Her research offers crucial insights into what nature recovery really means beyond single-tree planting — looking at how ecosystems function, how partnerships can succeed or struggle, and how data and measurement can help us track progress more meaningfully. I’m delighted to have you here today. Thank you for coming.

Cristina Banks-Leite:
Thank you very much, Stephen.

Stephen Thomas:
We normally end our podcast with “what does nature recovery mean to you?” — but so much of your work is involved with that. First, can you tell me a bit about some of the projects you’ve been involved with, and what recovery of nature means in the context of tropical forests?

Cristina Banks-Leite:
Absolutely. I’ll start with a bit of background. I’ve always studied how forests are lost — my interest has been understanding how species are affected by forest and habitat loss. But, partly through circumstance and new opportunities, I started working a lot more with reforestation. It’s a far more uplifting subject and something I truly believe in, because I think it’s one of the main ways we can mitigate impacts on species and biodiversity.

A few years ago I saw on social media that a colleague, Renato Crozales — one of the top restoration ecologists in Brazil — had a new job at a company called Mombak. I reached out and offered to help, and he said they were just getting started and really needed to monitor biodiversity in their restoration areas. Their main interest was carbon — they wanted to sell carbon credits — but they wanted to show what they were doing was genuinely good for biodiversity. They had bought, I think, about 22,000 hectares for restoration and were planting a very large mix of species, around 60+ species, with strong ecological input.

Since then I’ve been in touch with many companies doing restoration, as well as banks and insurers funding restoration. It’s been eye opening: the range of actors involved, the practical challenges, and the hard questions about what we mean by “biodiversity” and what different stakeholders actually care about. Do people want a tiger, or a tiger in a nice forest? If we want a “nice forest,” how do we measure that? We’ve been working with Mombak for the last three years and learning a lot.

Stephen Thomas:
I used to buy trees — I did some forestry and once ran a tree-planting project in East Africa. It felt evangelical at the time, but it was complicated and, to be honest, a bit of a disaster. The social side was good — money went to communities — but an ecologist there asked why I was planting trees in a savannah. It’s not as simple as planting and forgetting.

When you talk about restoration in the Amazon, what are some of the surprising positives and the main challenges you’ve found in partnerships between ecologists, funders, companies, and communities?

Cristina Banks-Leite:
Mostly I work in South America. One semantic challenge is that people use words like afforestation, reforestation and restoration interchangeably, but they’re not the same. Afforestation is planting trees where they shouldn’t be (e.g., savannas or deserts). Reforestation often means planting, sometimes single species. Restoration is about returning a degraded habitat toward its original conditions.

The literature shows that ideally you let nature recover by itself — remove the pressures (cattle, agriculture) and let succession happen. But when you’re doing 22,000 hectares, natural recovery is too slow. If you want quicker results, you have to plant, and that’s when many issues arise. In the Amazon, seedling nurseries are not common and don’t supply the diversity you need. Procuring thousands of seedlings of many species is challenging.

I was also surprised by the difficulty of buying farmland legally in Brazil — there’s a robust system of paperwork. Working with farmers to improve productivity, so restoration doesn’t spill into primary forests, is complex. There are many hands-on management issues — what species mix suits particular soils, how to handle pests and invasive species. These may seem small to a global perspective, but they’re the practical problems projects face.

Stephen Thomas:
How have you and your team adapted to the social dynamics — working with people who live and farm there? And when choosing species do you plan for the short term or think 50 years ahead, especially considering climate change?

Cristina Banks-Leite:
Right now, many projects choose species for the short term — fast-growing species that establish quickly and adapt to a range of environments. On passive vs active restoration: given enough time, landscapes will recover, but we don’t have centuries to wait. I have small land I left to regenerate for 20 years and it’s still mostly grass. If we want restoration to be a tool for climate mitigation or biodiversity recovery, we need quicker outcomes and economic incentives — people must be able to make money from restoring land. Private landowners won’t do it unless it’s economically viable.

There are trade-offs between carbon and biodiversity. Fast-growing trees sequester carbon quickly but aren’t always best for biodiversity. Some companies cut corners and plant monocultures or non-native fast growers like eucalyptus, which capture carbon but cause other problems. In the projects I work with, they aim for high-quality, biodiverse restoration. That said, we might need to be pragmatic — a small proportion of fast-growing trees to generate income might be acceptable if the overall trajectory is toward more biodiversity. In southern Brazil, for instance, forest fragments surrounded by eucalyptus performed better for birds than fragments surrounded by pasture — so there are middle grounds, even if eucalyptus isn’t ideal.

Stephen Thomas:
I saw that in East Africa — locals prefer fruit or fuelwood trees for direct benefits, not slow-growing native species. Local values matter. Your group also uses monitoring methods like remote sensing and acoustic monitoring. There’s a worry I’ve heard: we’re getting better at measuring biodiversity, but that doesn’t ensure outcomes — compliance is hard and markets could reward the wrong things. Where do advanced measurement techniques fit into nature recovery?

Cristina Banks-Leite:
First, we should be humble: we may be getting better, but we’re still far from measuring biodiversity properly. Biodiversity is extraordinarily complicated — we don’t always agree on what a species is, we can’t count many species individually, and we lack names for most organisms. Everything is interconnected and changing through space and time. That complexity is hard to communicate.

I focus on measurement because that’s where I can influence things. Right now, many accreditation systems and metrics are inadequate — some weren’t designed by ecologists and rely too much on counting species richness. Species richness is important, but in a successional restoration trajectory you’ll start with pioneer species and later have climax species. Richness isn’t linear — it can go down at times as pioneer species decline and are replaced by later-successional species. For example, early results from Mombak show that many commonly seen species in pastures are declining in restored plots — that’s a good sign, because we want pasture-associated species to decline as forest rebuilds. Metrics that don’t account for species replacement give the wrong impression.

There are many problems — compliance, monetisation, social factors — and they’re all important. I don’t work on the social systems directly, so I focus on measuring biodiversity properly, and I think much of that is currently done wrong.

Stephen Thomas:
If you had unlimited funding, what would you most like to understand or achieve? Measurement? Something more specific?

Cristina Banks-Leite:
I have a pet project connected to acoustics. At the moment we put recorders out, capture sounds, and classify a handful of vocal species, like some birds and frogs. But I’ve been reading that individuals have unique acoustic signatures and many species use “names” — individual-specific calls. A large proportion of studied species use individually distinct vocalizations.

There are fascinating projects at Imperial working on syntax in bird song and applying methods from linguistics to animal communication. I think in 50 years we might be able to decode meaningful information in animal acoustic signals — for instance, understand alarm calls or more complex messages and maybe even see dialogues. People who live in forests often “read” animal behaviour and sounds; we’ve lost that skill. With AI and big acoustic datasets, we might uncover much more structure and information than we currently appreciate. That would transform how we understand ecosystems.

Stephen Thomas:
That reminds me of work with dolphins and attempts to interpret their calls. It raises ethical questions too: if we can interpret-and act on—animal communication, it could be misused (for fishing, for example). But it’s an incredible frontier.

Cristina Banks-Leite:
Yes, there are ethical issues. People are already trying to “talk” to whales experimentally, and results are interesting. It’s not just whales — many animals and even plants communicate in ways we don’t yet grasp. Understanding that will hopefully make it harder to justify destructive behaviours.

Stephen Thomas:
To bring us back, what does “nature recovery” mean to you?

Cristina Banks-Leite:
To me it’s intactness. It’s hard to define and to quantify — getting that into numbers is challenging — but in an old-growth forest you see the interactions, connections and complexity. That intactness is what nature recovery should aim toward.

Stephen Thomas:
Final quick one: if I gave you a carbon-free trip to any ecosystem, where would you go for solace?

Cristina Banks-Leite:
I was lucky to grow up near São Paulo in a place I think is one of the most beautiful in the world: beaches with mountains behind them, fully forested — you have beach, sea and forest. That combination is perfect for me. I love being in those forests and then being at the beach with a caipirinha. If I could retire there, I would.

Stephen Thomas:
Great. I wish you well with your research and talking to animals. Thank you so much for your time, Professor Cristina Banks-Leite.

Cristina Banks-Leite:
Thank you.

Stephen Thomas (outro):
You’ve been listening to the Nature Recovery Podcast with me, Stephen Thomas. Please don’t forget to subscribe wherever you get your podcasts, and if you can, please consider leaving us a review — it helps other people find us. Also, consider sharing this episode with someone you know; you never know, you might get them interested in the wonderful field of nature recovery.