Diversity of Large Animals Plays an Important Role in Carbon Cycle

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Author: Taylor Kubota | Published: October 10, 2017

Trees in tropical forests are well known for removing carbon dioxide from the air and storing the potent greenhouse gas as carbon in their leafy branches and extensive roots. But a new analysis led by Stanford University researchers finds that large forest animals are also an important part of the carbon cycle.

The findings are based on more than a million records of animal sightings and activity collected by 340 indigenous technicians in the Amazon during more than three years of environmental surveys, coordinated by ecologist Jose Fragoso and supported by biologist Rodolfo Dirzo, who were working together at Stanford at the time. The team found that places where animals are most diverse correlate with places that have the most carbon sequestered in the soil.

“It’s not enough to worry about the trees in the world holding carbon. That’s really important but it’s not the whole story,” said Fragoso. “We also have to worry about maintaining the diversity and abundance of animals, especially mammals at this point, in order to ensure a well-functioning carbon cycle and the retention of carbon in soils.”

Although scientists have long understood that animals — through ingestion, digestion, breathing and decomposition — are part of the carbon cycle, the work, published Oct. 9 in Nature Ecology and Evolution is the first to suggest the importance of animal biodiversity rather than just animal numbers in the carbon cycle.

If we want to increase carbon sequestration, we have to preserve not only high numbers of animals but also many different species, the authors said.

Mining an unprecedented data source

The inspiration for this work came from a conversation during a Biology Department happy hour years ago. The scientists knew that an ecosystem with more species generally functions better, which they assumed should include the carbon cycle. Proving the relationship between animal diversity and carbon, however, was not so straightforward.

“It is a very difficult idea to test regarding vertebrates in a real-world system such as the Amazon,” said Mar Sobral, lead author of the paper, who was a postdoctoral researcher in the Dirzo Lab during this research. “The amount of data needed to test such an idea is massive and the type of data is a big challenge. The economic resources, time and logistics involved in our project are unprecedented.”

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