How Tropical Trees Became Chemists in a Battle for Survival

New research shows that the secrets to biodiversity may lie in the microscopic chemistry of tree leaves

I still remember the first time I climbed through lowland rainforest, soaked and mosquito-bitten, staring up at a dizzying tangle of life. It was overwhelming; so many species competing for light, space, and nutrients! And yet, somehow, they coexisted.

As a young researcher, I found that coexistence puzzling. Years later, I’ve spent enough time with fossils and forests and even worked for an Amazon-based conservation non-profit to know that biodiversity isn’t just about where species live. It’s also about how they interact, and sometimes, those interactions happen on a scale too small to see.

A new study out of the Bolivian Andes adds a fascinating piece to that puzzle. It turns out that tropical trees aren’t just passively growing — they’re quietly waging a chemical war. And their weapons? Thousands of unique compounds in their leaves, tailored to ward off enemies like insects and fungi.

According to Dr. Jonathan Myers, one of the lead researchers, “Tropical plants produce a huge diversity of chemicals that have practical implications for human health.” But more than that, the study suggests this chemical arms race may help explain why tropical forests are so incredibly diverse in the first place.

The research, published in Ecology, included scientists from Washington University, the Missouri Botanical Garden, and several Latin American institutions. Together, they analyzed tree leaves from 16 forest plots stretching across a steep elevation gradient in Bolivia, from steamy lowland forests to cooler mountain slopes.

Using mass spectrometry, they identified over 20,000 unique chemical compounds from 473 tree species. Many of these compounds fell into two categories: terpenoids and alkaloids, both well-known for their roles in plant defense — and, incidentally, in medicine. Terpenoids have been explored for everything from cancer drugs to antiviral treatments; alkaloids form the basis of morphine, quinine, and chemotherapy drugs.

But this wasn’t a pharmaceutical treasure hunt. The scientists wanted to know: do forests with more species also host more chemical diversity? And if so, why?

Their approach combined fieldwork with a relatively new field known as ecological metabolomics; aka, the study of all chemical compounds (metabolites) produced by organisms, especially in response to their environments and interactions. The team tested four key predictions, including whether warmer, wetter climates would lead to greater chemical differences between species, and whether those differences could help explain why species diversity is higher at lower elevations.

The results were compelling. In plots rich in species, especially at lower elevations, tree species were chemically distinct from one another. Each tree seemed to be brewing its own unique cocktail of defenses. But as the team moved upslope into colder, more stressful environments, two things changed. First, the number of species dropped. Second, their chemical profiles began to converge: trees started using the same general defense strategies.

This makes intuitive sense when you think about it. In lowland forests, where herbivores and pathogens are abundant and specialized, using the same chemical defense as your neighbor is risky. If an insect can digest your neighbor’s toxins, it can probably eat you, too. So, trees evolve distinct chemical signatures to keep their enemies guessing. “If a tree has the same chemistry as a neighbor, it could be vulnerable to the same herbivores and pathogens,” Dr. Myers explains. “Those enemies will do less damage overall if they have to search for different weaknesses for each tree.”

Higher up in the mountains, though, life is harder for different reasons. Cold, UV radiation, poor soils. Instead of chemical one-upmanship, trees shift to shared survival strategies, often producing similar compounds to cope with the environment rather than outwit their neighbors.

One of the study’s more intriguing findings was that chemical diversity and species diversity are tightly linked, but only when looking at secondary metabolites (those used in defense and signaling). Primary metabolites, which are essential for growth and survival (like sugars and fats), didn’t vary much across plots and had no relationship to species richness. That suggests it’s the defensive chemistry, not just metabolism, that helps shape who can coexist.

And there’s an evolutionary angle, too. In the most diverse forests, even closely related tree species showed little overlap in their chemistry. That means chemical traits are evolving quickly, under strong selective pressure from enemies. In contrast, forests with fewer species showed more chemical similarity among relatives, a sign that evolution was proceeding more slowly there, or at least under different pressures.

What’s striking is how this research ties together climate, evolution, and biodiversity using molecular fingerprints. It reframes forests not just as collections of trees but as chemical neighborhoods: each species developing its own way of living with and defending itself from others.

Beyond the science, the implications are huge. The compounds cataloged in this study have enormous potential for medicine, agriculture, and biotechnology. But we’re only scratching the surface. As Dr. Myers put it, “With such a database, researchers could look for unique chemicals that could have real value for society.”

Tropical forests are often described as biodiversity hotspots. This study suggests they’re also biochemical powerhouses. Complex, finely tuned systems of evolutionary innovation. Protecting them isn’t just about saving species; it’s about preserving the molecular blueprints of resilience, cooperation, and survival.

And maybe, just maybe, some of those compounds might help us, too.

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I’m thrilled you’re here. Stay curious, and thank you for sharing this journey with me!

Best,

Sílvia P-M, PhD Climate Ages