Is Toucan Sam responsible for pulling carbon out of the atmosphere? A paper published today in Forest Ecosystems says yes—in a way. Large fruit-eating animals, like toucans, tapirs, curassows, and spider monkeys, help keep our woods in tip-top carbon-capturing shape by eating fruits, spreading seeds, and filling the forest with hardy new trees.
Forests have long been known to be giant traps for carbon and an effective defense against global warming. Collectively, they absorb as much as 30 percent of the world’s CO2 emissions, and store more than 1,600 gigatonnes of carbon in their soil. In the tropics, tall, hardwood species with dense, thick trunks are the best trappers. But in order to regenerate, these trees need to disperse their seeds—and most times, wind just doesn’t cut it.
That’s where the fruit eaters, also known as frugivores, come in: They eat and deliver seeds to new locales, which stops trees from growing right on top of each other. Scientists estimate that more than 80 percent of tropical trees depend on other creatures for dispersal. Animals that can open their mouths really wide are the most effective, since they can swallow entire fruits and pass out (okay, poop) the seeds, still intact. Chestnut-mandibled Toucans, for example, can easily throw back a few guava-sized virola fruits with their seven-inch beaks. And Horned Guans—turkey-like birds that have a red, party-hat-like crest—are known for gobbling up avocados . . . pits and all.
“You have a lot of large birds that play a fundamental role for large trees,” study author Mauro Galetti says. They increase the likelihood that seeds will turn into actual photosynthesizing plants.
But big tropical birds are constantly under threat of hunting, poaching, and habitat loss—the IUCN Red List notes that 14 of the world’s 16 toucan species are decreasing in population size. And that could really hurt forests: In the study, researchers from Sao Paulo State University in Brazil used models to look at what would happen in 31 South American forests if all of the large frugivores were eliminated.
They found that even if small fruit eaters replaced bigger ones (think bats and songbirds instead of toucans and monkeys), there was still a major carbon loss within the system. Without the help of high-capacity frugivores, there’d be no way for seeds larger than half an inch to grow into towering trees that stash carbon, the model found. Instead, smaller seeds would sprout into light-wooded trees, which are not so great for storage. Eventually, the entire forest would be transformed.
The research suggests defaunation (the removal of animals from an ecosystem) is just as problematic as deforestation. “We need to keep the trees safe, but we also need to have the animals in the forest that keep the cycle of life going,” Galetti says.
He and his fellow Sao Paulo scientists now want to study individual species to calculate how much each animal’s services are worth in terms of battling climate change. Putting a dollar amount on a species, Galetti says, could be the only way to persuade governments to protect it.