A central goal in conservation biology is to understand how the extinction of species will affect key ecosystem services. Carbon storage is widely acknowledged as one of the most valuable forest ecosystem services. Deforestation, logging, fire, and climate change have significant effects on tropical carbon stocks; however, an elusive and yet undetected decrease in carbon storage may be due to defaunation of large vertebrates. Many large tropical trees with sizeable contributions to carbon stock rely on large vertebrates for seed dispersal and regeneration, however many of these frugivores are threatened by hunting, fragmentation, illegal trade, and habitat loss.
We used a large data set on tree species composition and abundance, seed, fruit, and carbon-related traits, and >8,000 plant-animal interactions to estimate the loss of carbon storage capacity of tropical forests in defaunated scenarios. By simulating the local extinction of trees that depend on large frugivores, we found that defaunation has the potential to significantly erode carbon storage even when only a small proportion of large-seeded trees are extirpated. Because we known that several plant species rely on several frugivores and that seed predators can also modulate plant recruitment, we studied the net contribution of each disperser and predator on the recruitment of a hardwood tree species. We found that both the loss of large seed predators and dispersers reduce plant recruitment affecting directly the potential carbon storage. The loss of large seed predators triggers the abundance of small rodents, leading to an increase in seed predation, reducing tree recruitment and carbon storage. Our studies are demonstrating that frugivores play a central role in shaping carbon storage in tropical forests.