According to a study published in Science Advances on 18 December and led by researchers from Brazil, large animals are crucial for dispersing hardwood tree seeds in tropical forests. These trees grow larger and remove more carbon dioxide from the atmosphere than smaller softwood trees.
The study analysed data from more than 2,000 tree species and 800 animal species in 31 forest areas in southeast Brazil. The researchers simulated the effects of the extinction of large, fruit-eating animals — such as primates, tapirs, large birds and large rodents — showing that it would cause a decline in hardwood species.
“Large animals are being overhunted and, with their disappearance, the large-seeded tree population will also decrease.”
Carlos Peres, University of East Anglia, United Kingdom
“The hard-wooded trees are the ones that lock [away] more carbon,” explains Carlos Peres, an ecologist at the University of East Anglia in the United Kingdom and one of the authors of the paper. He says that only big animals can eat, digest and disperse the large fruit these trees produce.
“However, these large animals are being overhunted and, with their disappearance, the large-seeded tree population will also decrease,” he tells SciDev.Net. “We are talking about a process that is very silent and very insidious.”
Because of large animal loss, forest composition could gradually change as trees with small seeds, which tend to be softwood species that lock away less carbon, become more prevalent. Their seeds are dispersed by bats, small birds and rodents, which are unaffected by hunting, the researchers say.
“This is happening all over the tropics,” says Peres. “Studies of forests in Thailand, Peru and West Africa show that, in hunting sites, the composition of young trees has already been altered, with a higher percentage of light-wooded trees.”
Sam Robinson, an environmental scientist at Lancaster University in the United Kingdom, says the study’s findings show that future projects to restore tropical forest should include efforts to revive the populations of large animals.
The results could also affect existing programmes, such as the UN’s REDD+ initiative, that aim to protect forests to retain their carbon storage capacity, says Pedro Brancalion, a forestry researcher at the University of Sao Paulo in Brazil. “This study provides a great example of the need to look beyond trees when conserving or restoring tropical forests for mitigating climate change,” says Brancalion. “We need a more holistic overview of degradation, which considers indirect consequences operating [over the] longer term.”