Contrasting Effects of Defaunation on Aboveground Carbon Storage Across the Global Tropics

Background

Defaunation—the loss of large vertebrates due to hunting, habitat destruction, and other human activities—drives major ecological changes in tropical forests. Many tropical tree species rely on animals for seed dispersal, and the decline of large frugivores significantly alters forest composition and function. Prior studies show that defaunation shifts tree communities from large-seeded, animal-dispersed species to small-seeded or abiotically dispersed species. Because large-seeded trees typically have higher biomass, their decline reduces carbon storage. However, the magnitude and regional variation of these effects remain unclear. This study investigates how defaunation-driven changes in tree communities affect aboveground carbon stocks across the tropics, using a large dataset from forests in Africa, South America, Southeast Asia, and Australia.

Goals and Methods

The study quantifies the potential effects of defaunation on carbon storage by simulating the removal of large-seeded, animal-dispersed tree species from 10 relatively undisturbed tropical forests across four continents. Researchers analyze data from over 25,000 trees representing 2,500 species and conduct simulations removing different proportions of large-seeded species (from 25% to 100%). They then assess how these losses influence aboveground carbon stocks, accounting for changes in tree size, wood density, and species composition. Control scenarios help distinguish defaunation effects from random species loss and sampling artifacts.

Conclusion

The results reveal regional differences in defaunation’s impact on carbon storage. Forests in Africa, South America, and South Asia—which have a high proportion of animal-dispersed species—experience consistent carbon losses of 2–12% when large-seeded trees are removed. In contrast, Southeast Asian and Australian forests, where abiotically dispersed species dominate, show little to no carbon loss or even slight increases in carbon stocks. These changes primarily result from reductions in stand volume rather than wood density, since large-seeded species grow into larger trees. This suggests that forests experiencing defaunation-driven shifts toward smaller tree species may face long-term declines in carbon sequestration potential.