Defaunation of Large-Bodied Frugivores Reduces Carbon Storage in a Tropical Forest of Southeast Asia

Background

Tropical forests are vital for carbon storage, but recent studies suggest that defaunation—the loss of large-bodied seed dispersers due to hunting and habitat fragmentation—can significantly impact this function. While previous research has shown reductions in above-ground carbon storage due to defaunation in South America and Africa, its effects on Southeast Asian forests remain debated. Some scientists argue that the dominance of wind-dispersed Dipterocarpaceae trees in the region buffers against carbon losses from defaunation. This study examines the extent to which defaunation influences carbon storage in a tropical forest in Thailand, where large frugivores such as primates, hornbills, and terrestrial mammals still persist.

Goals and Methods

The study aimed to determine the impact of defaunation on tree species composition and carbon storage. Researchers used data from a 30-hectare forest dynamics plot in Thailand, where an intact community of large-bodied frugivores still exists. They simulated two defaunation scenarios: (1) the extirpation of primates alone, and (2) the extirpation of all large-bodied frugivores, including gibbons, macaques, hornbills, and terrestrial mammals. The researchers then analyzed how these scenarios would affect forest biomass and carbon storage, varying the intensity of defaunation from 20% to 100%.

Conclusion

The findings show that tree species dependent on large-bodied frugivores for seed dispersal account for nearly one-third of the total carbon biomass in the study plot. The simulations indicated that complete defaunation would lead to a 2.4% to 3.0% reduction in carbon storage, depending on the scenario and modeling assumptions. When defaunation reached at least 40%, the reduction in carbon storage consistently exceeded 1%. These results suggest that the impact of defaunation on carbon deficits in Southeast Asian forests is comparable to that seen in the Neotropics, challenging the idea that wind-dispersed Dipterocarpaceae species compensate for the loss of animal-dispersed trees.