The extinction of large animals from tropical forests could lead to potentially stronger impacts of climate change, a new study warns. A decline in the number of fruit-eating animals could lead to lower number of large hardwood trees, reducing the capacity of tropical forests to store carbon and prevent climate change.

The decline in animals like large primates, tapirs and toucans has a significant impact on the environment. The study, published in the journal Science Advances, highlights that these animals tend to spread seeds of large trees.

Large trees play a key role in capturing and storing carbon dioxide from the atmosphere, far more effective than smaller trees. Researchers from the University of East Anglia (UEA) said large animals contribute to the number of the trees by ingesting seeds and spreading through their faeces.

Many large animals are already threatened by hunting, illegal trade and habitat loss. Removing these animals from the ecosystem could affect the natural balance and cause the reduction in heavy-wooded large trees, leading to more CO2 in the atmosphere, which contributes to climate change.

"Large birds and mammals provide almost all the seed dispersal services for large-seeded plants,” said Professor Carlos Peres, from UEA's School of Environmental Sciences. “The steep decline of the megafauna in overhunted tropical forest ecosystems can bring about large unforeseen impacts.”

The researchers studied the Atlantic rainforest of Brazil, where 95 percent of trees depend on animals to disperse seeds. They analysed the link between 2,000 tree species and 800 animal species.

Results show that small birds, bats and marsupials which are not targeted by hunters could only disperse small seeds, associated with small trees. Researchers found that larger animals, such as large primates, tapir and toucans, are the only animals that could effectively disperse large seeds.

“Usually, the trees that have large seeds are also big trees with dense wood that store more carbon,” said researcher Mauro Galetti, a professor at São Paulo State University.

Peres said that intergovernmental policies for the reduction of CO2 emissions from tropical countries have focused on deforestation, and suggests the decline in the population of large animals and the loss of key ecological interactions could also promote a serious risk in securing tropical forest carbon storage.

The researchers said the findings indicate “the fragility of carbon storage service in tropical forests under the current global change conditions.” Preventing the current fast-paced animal loss in tropical forests could significantly save large animals and plants and protect the world from climate change.

"We hope that our findings will encourage UN programmes on Reducing Emissions from Deforestation and Forest Degradation (REDD+) to consider faunally intact forests and their full functionality as a critical precondition of maintaining forest carbon stocks," Peres said.

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