A new study by researchers at Washington University, St. Louis, and the Missouri Botanical Garden has uncovered a surprising layer of diversity in tropical forests. Not only are the forests populated by a large variety of tree species, but each species takes a different approach to chemistry, increasing the array of natural compounds that provide important functions for the plants and humans.
The research helped clarify the ecological and evolutionary forces that make tropical forests such hotbeds of biodiversity. And whilst the team wasn’t explicitly looking for compounds that could be useful for humans, their findings underscore the value of tropical forests as natural factories of plant chemicals that could have important uses in medicine and other fields, said Jonathan Myers, a professor of biology in Arts & Sciences at WashU.
“Tropical plants produce a huge diversity of chemicals that have practical implications for human health.”
The study, published in Ecology last week, was led by ecology and evolutionary biology graduate David Henderson. Missouri Botanical Garden researchers Sebastian Tello, Leslie Cayola, and Alfredo Fuentes, chemical ecologist Brian Sedio at the University of Texas at Austin, and ecologists Belen Alvestegui and Nathan Muchhala at the University of Missouri-St. Louis collaborated on the study.
The researchers examined tree leaves collected as part of the Madidi Project, a large-scale flora survey in Bolivia’s Madidi region of the Andes mountains. The team was especially interested in chemical compounds that plants use to help protect themselves from insect herbivores, pathogens and other enemies—a top priority for anything growing in the warm, wet and buggy tropics.
They set out to better understand how these compounds differ among species that grow together in tree communities at low and high elevations with contrasting climates. Using mass spectrometry, a technology that allows researchers to identify and count individual molecules in a sample, researchers uncovered a bounty of chemical compounds:
“We identified more than 20,000 unique metabolites in leaf samples from 470 tree species,” Myers said. “It’s an amazing level of chemical diversity.”
More than a third of those compounds were terpenoids, a class of natural chemicals that plants use to fend off insects and diseases. Terpenoids have also shown promise as pharmaceutical ingredients in fighting cancer, relieving inflammation, and killing harmful viruses and bacteria. About one-quarter of the compounds were alkaloids, a class of plant chemicals that form the basis of many medicines, including pain relievers, anti-malarial drugs, and cancer treatments.
“The remarkable chemical diversity of tropical forests highlights the need to study and protect these biological hot spots,” Myers said, adding that he and his collaborators have contributed data from this project to help create a global database of chemical compounds identified from plants. “With such a database, researchers could look for unique chemicals that could have real value for society,” he said.
In the latest study, Myers and his team analysed the diversity of tree species and leaf metabolites in wet and seasonally dry forest plots sampled at various altitudes ranging from approximately 2,000 to 11,000 feet above sea level. The higher they climbed, the fewer species they encountered. They identified nearly 140 different tree species in a single 1-hectare (2.5-acre) plot at an elevation of 4,000 feet, but fewer than 20 species in a plot at nearly 11,000 feet.
As species diversity dwindled, so did chemical differences among tree species. High in the mountains, even trees from different species use similar chemicals to protect themselves and cope with abiotic stress. Myers said natural chemical factories only reach their full potential at lower elevations.
In the super-diverse, hyper-competitive lowland tropical forests, it makes sense that a tree would employ chemical defences that are completely different from its neighbours: “If a tree has the same chemistry as a neighbour, it could be vulnerable to the same herbivores and pathogens,” Myers said. Those enemies will do less damage overall if they have to search for different weaknesses for each tree,” he said.
The link between species diversity and chemical diversity extends beyond the tropics. Myers is part of an ongoing NSF project that studies trees at multiple locations, including the Amazon’s lowlands, the northern forests of Canada, and local research plots at WashU’s environmental field station, Tyson Research Center.
Tyson’s expanses of oak, hickory and other types of trees can’t match the diversity of tropical forests, but its trees are much more diverse than the coniferous forests up north. Laboratory tests have found that the trees at Tyson are also chemically near the middle of the pack: They’re not as abundantly productive as the trees of the tropics, but they are veritable treasure troves of unique chemicals compared to northern forests.
Climate explains why chemical diversity is linked to species diversity. Warmer, wetter, and more stable climates can support higher species diversity if plants employ different chemical defences to limit the types of herbivores and pathogens that attack them, Myers said. “This could be one more way to explain the trends in plant diversity across the planet.”
More information: David Henderson et al, Testing the role of biotic interactions in shaping elevational diversity gradients: An ecological metabolomics approach, Ecology (2025). DOI: 10.1002/ecy.70069.
