A pandemic of lianas is sweeping through tropical forests, reducing their ability to store carbon and limiting their role in mitigating climate change. Two recent studies from Leiden University highlight the issue. "We now understand why lianas are visible in satellite imagery," say the researchers.

Tropical forests annually absorb roughly the amount of CO₂ emitted by the whole of Europe. They also house around half of the world's biodiversity. However, their contribution to climate regulation and biodiversity is under threat—not only from deforestation but also from an extraordinary surge in lianas. Ecologist Marco Visser from Leiden's Center for Environmental Sciences (CML) explains, "Lianas can smother and kill trees. When they dominate, the forest becomes choked, and mainly lianas continue growing over fallen trees."

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Lianas are rapidly expanding their territory in tropical forests, sometimes suppressing tree growth entirely in certain locations. In such areas, forest regeneration halts, and carbon storage can decline by as much as 95%. "That's almost equivalent to deforestation," Visser says.

He attributes this to rising atmospheric CO₂ levels. "All plants grow faster with more CO₂, but lianas benefit even more. They cheat—they don't invest in structural support, borrowing it from trees instead, and their leaves require less energy and nutrients to produce." A liana can quickly climb to the canopy, spread a leafy cover over tree crowns, and steal all the sunlight for itself.

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