Animal Loss and Climate Change

A healthy ecosystem depends on all its inhabitants. You remove one species from the community, and even though hundreds may remain, the loss of a single species can affect the habitat—and Earth—in unseen ways.

Brazilian researchers recently discovered an interesting correlation between the loss of large animals in a rainforest ecosystem and climate change. Writing in Science, they determined that if you remove too many large vertebrates from a forest—through over-hunting and/or habitat destruction—you also drastically reduce that forest’s capacity to store carbon.

In general, tropical forests store about 40 percent of the world’s terrestrial carbon, which means they play a critical role in stabilizing our planet’s climate. While all the trees in a forest contribute to carbon capture, much of the work is done by species of large hardwood trees.

Some plants’ seeds are dispersed by wind or gravity (simply falling to the ground), but others need a bit more help. Large hardwood trees—the ones that do the heavy lifting of carbon capture—have large fruits. And these seeds are often distributed by animals, large and small, when they eat the fruit of the plant and defecate. Pretty efficient system, right? But what happens when the animals aren’t around to eat the fruit and poop out the seeds?

The scientists decided to create simulations to find out because, in the last few decades, bushmeat hunting in tropical forests has been on the rise. “Hunting threatens approximately 19 percent of all tropical forest vertebrates,” the team writes. They entered data for over 2,000 tree species and 800 animals species within Brazil’s Atlantic Forest to determine how these losses could affect the forest ecosystem and beyond.

“We show that the decline and extinction of large animals will over time induce a decline in large hardwood trees. This in turn negatively affects the capacity of tropical forests to store carbon and therefore their potential to counter climate change,” says co-author Carlos Peres.

Another author, Mauro Galetti explains why. “The big frugivores, such as large primates, the tapir, the toucans, among other large animals, are the only ones able to effectively disperse plants that have large seeds. Usually, the trees that have large seeds are also big trees with dense wood that store more carbon.” And lead author Carolina Bello elaborates further: “The composition of tropical forests changes. The result is a forest dominated by smaller trees with milder woods which stock less carbon.”

“Not only are we facing the loss of charismatic animals,” says senior author Pedro Jordano, “but we are facing the loss of interactions that maintain the proper functioning and key ecosystem services such as carbon storage.”

The team believes these losses will affect forests beyond the Atlantic, too. The team recommends that intergovernmental policies should consider this defaunation, along with deforestation, when trying to protect tropical forest carbon storage. “For instance,” they write, “restoration and REDD+ programs should achieve a complete vision of biotic interactions and processes to guarantee carbon storage capacity and its co-benefits.”

In other words, it takes more than trees to make a forest. To protect forests, we must recognize them as systems—each species playing a crucial role in a larger whole.

Image: Male golden capuchin,​ Miguelrangeljr/Wikipedia