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Why a Simple Law Governs Tropical Rainforest Trees

Why a Simple Law Governs Tropical Rainforest Trees
Tropical rainforests play a vital role in the well-being of our planet, soaking up carbon dioxide and helping stabilize the global climate. Around the world, tropical rainforests vary widely in climate and species composition, but when scientists plot out the numbers of trees by size, a puzzling consistency emerges: each rainforest follows the same pattern in the distribution of trees of different heights.

Today in the journal Science, researchers explain the biological mechanisms behind the pattern, a finding that could impact forecasts of how much carbon might be stored in forests in the future.

The lead author of the study is Caroline Farrior, who will join the faculty of the University of Texas at Austin as an assistant professor of integrative biology this fall. Farrior did the research as a postdoctoral fellow at the National Institute for Mathematical and Biological Synthesis. 

Using data on tree sizes within the tropical forest on Barro Colorado Island in the middle of the Panama Canal, the research team found that the consistent pattern appears to be driven by the competition among trees for light. 

"When a large tree dies, it creates a gap allowing sunlight to hit the forest floor," says Farrior. "Then many small trees exposed to the full sun grow quickly until they begin to overtop each other. The unlucky individuals then begin to grow very slowly, effectively stuck at their size when overtopped. It is the process of competition among trees for light following a gap disturbance that leaves behind a characteristic pattern of tree sizes, explaining the consistency in tree size distributions across otherwise very different tropical forests."

Photo credit: Smithsonian Tropical Research Institute

The study's findings have significant implications for how tropical rainforests are modeled. This is especially important now as modelers are trying to predict the sustainability of the tropical forest carbon sink – a service provided by tropical forests that currently slows the rate of atmospheric increase in carbon dioxide by about one-sixth.

"Without reproducing this size distribution for the right reasons, models are likely to get the wrong answer when used to predict carbon storage into the future," Farrior said.

Farrior said it's too early to tell whether current forecasts overestimate or underestimate the amount of carbon that forests will store in the future.

The research team also includes researchers from Princeton University, University of Florida, Gainesville, University of California, Los Angeles and the Smithsonian Tropical Research Institute.

This post was adapted from a press release by NIMBioS.

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Sunday, 23 January 2022

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