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, is a major driver of ecological change in tropical forests. Many tropical tree species rely on animals for seed dispersal, and the decline of large frugivores can significantly alter forest composition and function. Prior studies have shown that defaunation leads to a shift from large-seeded, animal-dispersed species to small-seeded or abiotically dispersed species. Since large-seeded trees tend to have higher biomass, their decline could reduce 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 aimed to quantify 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 analyzed data from over 25,000 trees representing 2,500 species and conducted simulations in which different levels of large-seeded species were removed (from 25% to 100%). They then examined how these losses influenced aboveground carbon stocks, accounting for changes in tree size, wood density, and species composition. Control scenarios were used to distinguish defaunation effects from random species loss and sampling artifacts.

Conclusion

The results revealed regional differences in the effects of defaunation on carbon storage. Forests in Africa, South America, and South Asia, which have a high proportion of animal-dispersed species, showed consistent carbon losses of 2–12% when large-seeded trees were removed. In contrast, Southeast Asian and Australian forests, where abiotically dispersed species are more common, showed little to no carbon losses or even slight increases in carbon stocks. The study found that these changes were primarily driven by reductions in stand volume rather than wood density, as large-seeded species tend to grow into bigger trees. This suggests that forests where defaunation leads to smaller tree species may experience long-term declines in carbon sequestration potential.