The voracious appetite of forest elephants can coax forests into storing more carbon

DAILY SCIENCE

The voracious appetite of forest elephants can coax forests into storing more carbon

New study documents how elephants plant the forest with high carbon-density trees and get rid of the weeds.
January 25, 2023

Elephants been called a lot of things: the world’s largest land creatures, imperiled, majestic, charismatic. Now scientists have a few more terms for describing them: foresters and climate champions.

In the jungles of equatorial Africa, scientists report that forest elephants play an important role in shaping the forest around them as they vacuum up as much as 200 kilograms worth of plants every day. Their appetites influence not just what trees survive but how much carbon the forest stores in leaves and trunks.

“Elephants are the gardeners of the forest,” said Stephen Blake, a Saint Louis University biologist who has spent years studying elephants. “They plant the forest with high carbon-density trees and they get rid of the ‘weeds,’ which are the low carbon-density trees.”

As the biggest animals around, elephants have earned a reputation as “ecosystem engineers.”  They spread seeds in their dung, turn forests into savannas, and create trails that extend for kilometers, among other things. Scientists have also pointed to their potential to alter how much carbon gets sucked up by African forests. But that evidence largely came from models, rather than on-the-ground observations. The details of how it works weren’t clear.

Blake and collaborators from French universities set out to better understand how elephants interact with the trees in the forest, and what that might mean for the climate. In the Republic of Congo’s Ndoki Forest, people walked fresh trails left by forest elephants. They tracked which plants showed signs of being eaten and how much of each plant they ate. They also spent three years sifting through some 855 piles of elephant dung to see what seeds were being deposited. The researchers combined this with similar data from other Congo forests to get a detailed accounting of the elephants’ diets.

The picture that emerged was that elephants had a particular taste for the leaves of faster-growing trees, but prefered the fruit of slower-growing trees. A comparison of the leaves and fruit on each tree species showed that the more dense, slower-growing trees tended to have leaves with defensive traits such as bitter-tasting chemicals. Those same trees, however, tended to have bigger, more sugary fruit.

 

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In both cases, this could raise the amount of carbon stored in jungle forests. The slower-growing trees create more dense wood. Since elephants demolish more of the fast-growing trees, that can create room for the more carbon-rich trees. “Elephants eat lots of leaves from lots of trees, and they do a lot of damage when they eat,” Blake said. “Our data shows most of this damage occurs to low carbon density trees. If there are a lot of high carbon density trees around, that’s one less competitor.”

At the same time the elephants’ preference for the fruit of these high-carbon trees means they will help spread the seeds through the forest as they poop. Based on the mechanisms that different trees use to distribute their seeds, if elephants vanished it could alter the forest so that carbon storage declined by between 6 and 9%, the researchers estimated in a new study in the Proceedings of the National Academy of Sciences.

The new elephant research is part of a growing body of studies seeking to tout the climate benefits of protecting biodiversity. The role of tropical jungles in storing carbon has been known for decades, and is often cited as a reason to fight continuing deforestation. But trees have now been joined by such unlikely climate warriors as whales. Scientists in late 2021 reported their feces could trigger an ecosystem reaction storing as much carbon as a continent worth of trees. Now elephants. Are conservationists trying to save dwindling species by hitching them to the push to tackle climate change?

Blake’s comments suggest as much. With elephant numbers in Africa down from 10 million to fewer than 500,000, he noted that appealing to people’s love of elephants hasn’t been enough to stop the carnage of illegal hunting. Nor has highlight the animals’ role in promoting biodiversity. Maybe adding climate change to the equation could help spur action. “Save the elephants and help save the planet,” said Blake. “It really is that simple.”

Berzaghi, et. al. “Megaherbivores modify forest structure and increase carbon stocks through multiple pathways.” Jan. 23, 2023. Proceedings of the National Academy of Sciences.

Image: Jukka Jantunen/Shutterstock.com

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