Defaunation, the severe decline of animal populations from natural ecosystems, is a process faced by tropical forests that can go unnoticed. Several large birds and mammals are threatened by hunting and human persecution. However, the loss of animals can generate large unforeseen impacts. The extinction of large mammals implies the loss of functions that maintain diversity and ecosystem services of which humans depend.
A recent study published in the journal Science Advances and conducted by Brazilian researchers from the Universidade Estadual Paulista (São Paulo State University) in Rio Claro, in collaboration with researchers from Spain, England, and Finland, demonstrated that the loss of large frugivores negatively affects the capacity of tropical forests to stock carbon and, therefore, their potential to counter climate change.
“The big frugivores, such as large primates, the tapir, the toucans, among other large animals, are the only ones able to effectively disperse plants that have large seeds. Usually, the trees that have large seeds are big trees with dense wood that store more carbon” explains Professor Mauro Galetti from the Department of Ecology at São Paulo State University.
Figure 1. Large frugivores and large-seeded trees of the Atlantic Forest. a) Anta (Tapirus terrestris), b) Muriqui (Brachyteles arachnoides), c) Jacutinga (Aburria jacutinga), d) Jatoba (Hymenaea courbaril), e), f) Atlantic Forest.
Mauro Galetti author of the photos a, d, e and f. Pedro Jordano author Photo b, c.
Then, “When we lose large frugivores we are losing dispersal and recruitment functions of large seeded trees and therefore, the composition of tropical forests changes. The result is a new forest dominated by smaller trees with milder woods which stock less carbon”, complements Carolina Bello, a PhD student from the São Paulo State University.
Figure 2. Replacement process of tropical forests when they lose large dispersers. Forests with large trees and hardwood (initial community) are replaced by forests with smaller trees with mild wood (final community).
The recent study showed that when large-seeded trees are removed from the forest and are replaced by trees with smaller seeds, the carbon stock potential of the forest decreases.
Pedro Jordano, Research Professor at the Biological Station of Doñana (CSIC, Spain), explains that this is the result of the loss of crucial interactions that support the Web of Life in tropical forests. “Not only we are facing the loss of charismatic animals, but we are facing the loss of interactions that maintain the proper functioning and key ecosystem services such as carbon storage.”
Carlos Peres, a Professor of Tropical Conservation Ecology at the University of East Anglia (UK), says “to date, tropical forest degradation has been entirely defined by REDD programs in terms of structural forms of human disturbance such as timber extraction and wildfires. Yet, even an apparently intact but otherwise defaunated forest should be considered as degraded because the insidious carbon erosion processes we highlight in this paper are already well underway”.
Therefore, the present study alerts current REDD+ programs that seek to counteract climate change by storing carbon in tropical forests, about the importance of considering the animals and their functionality as a fundamental part of the maintenance of carbon stocks. “The effectiveness of these programs will be improved if the preservation of ecological processes that sustain the ecosystem service of carbon storage over time is guaranteed” concludes Carolina Bello.
The study also included Marco A. Pizo (UNESP), Otso Ovaskainen (University of Helsinki), Renato Lima (USP), Luiz Fernando S. Magnago (Federal University of Lavras) and Mariana Rocha Ferreira (Federal University of Viçosa).