Over-hunting contributes to forest carbon loss, claims a study published this week in the AAAS journal Science Advances.

After looking at data from 31 sites from the Atlantic Forest researchers conclude that the over-hunting of large animals in those forests will eventually result in the widespread loss of the larger tree species responsible for storing the most carbon.

The study lends further support for the need for conservation efforts that focus on protecting ecosystem services as a whole, as opposed to focusing on isolated measures such as hectares of forest, or numbers of trees left standing.

Over-hunting contributes to forest carbon loss, claims a study published this week in the AAAS journal Science Advances. After looking at data from 31 sites from the Atlantic Forest — found along the southeast coast of Brazil — the researchers conclude that the over-hunting of large animals in those forests will eventually result in the widespread loss of the larger tree species responsible for storing the most carbon.

The team of Brazilian and European researchers, led by Carolina Bello from Universidade Estadual Paulista, looked at seed dispersal by frugivores as well as the relationship between seed size and a tree’s carbon storage potential, and discovered a disturbing trend.

Hunters in the region tend to harvest larger species of birds and mammals at unsustainable rates. These animals are often the species that eat, carry, and disperse large fruits and seeds. The tree species that produce largest animal-dispersed seeds tend to be taller and have higher wood density. Therefore, as these animals disappear, the trees with the greatest carbon storage capacity are less likely reproduce. Gradually, these tree species are replaced by smaller and less dense trees, and the total carbon storage capacity of the forest is reduced.

“We found a positive correlation between seed diameter and wood density … as well as maximum tree height,” the authors write, and those correlations were especially pronounced in species with animal-dispersed seeds.

After analyzing 5000 fruit-frugivore interactions, the authors found that 12 mm is the maximum seed diameter that is regularly dispersed by non-threatened animals (such as small birds and rodents). In the Atlantic Forest, 21 percent of the trees produce seeds larger than 12 mm, and of those, 70 percent are classified as having high wood density (more than 0.7 grams per cubic centimeter.) The study authors then modeled what will happen if the frugivores disappeared, and found that the larger-seeded, denser trees would see a 10 to 100 percent decrease.

Although the study focused on the Atlantic Forest of Brazil, the authors warn that this decline can happen anywhere the dominant tree species are dispersed by large fruit-eating animals commonly targeted by unregulated hunting.

“Our findings may also translate into the Amazonian forests where most of the tree species that retain 50 percent of the carbon are also dispersed by large frugivores,” the authors write. However, in other forests where the seeds of the dominant carbon-storing trees are dispersed by other means — such as the small wind-dispersed seeds of the dipterocarp trees in Southeast Asia — carbon loss would be less pronounced.

The study lends further support for the need for conservation efforts that focus on protecting ecosystem services as a whole, as opposed to focusing on isolated measures such as hectares of forest, or numbers of trees left standing.

“Restoration and REDD+ programs should achieve a complete vision of biotic interactions and processes,” the authors write, “to guarantee carbon storage capacity and its co-benefits.”

CITATION: Carolina Bello et al. Defaunation affects carbon storage in tropical forests. Science Advances 18 Dec 2015: Vol. 1, no. 11, e1501105. DOI: 10.1126/sciadv.1501105