New research reveals that a decline in fruit-eating animals such as large primates, tapirs and toucans could have a knock-on effect for tree species and subsequently for forests’ carbon storage capabilities.
This is because large animals disperse large seeded plant species often associated with large trees and high wood density — which are more effective at capturing and storing carbon dioxide from the atmosphere than smaller trees. Seed dispersal by large-bodied vertebrates is via the ingestion of viable seeds that pass through the digestive tract intact. Removing large animals from the ecosystem upsets the natural balance and leads to a loss of heavy-wooded large trees, which means that less CO2 can be locked away.
The study was led by researchers from São Paulo State University in Brazil, in collaboration with University of East Anglia (UEA), the Spanish National Research Council (CSIC) and the University of Helsinki, Finland. The findings are published on 18 December in the journal Science Advances.
Prof Peres said: “Large birds and mammals provide almost all the seed dispersal services for large-seeded plants. Several large vertebrates are threatened by hunting, illegal trade and habitat loss. But the steep decline of the megafauna in overhunted tropical forest ecosystems can bring about large unforeseen impacts.”
The research team studied data from more than 2,000 tree species in Brazil’s Atlantic Forest, and more than 800 animal species. They found that frugivores which are not targeted by hunters — such as small birds, bats and marsupials — are only able to disperse small seeds, which are associated with small trees.
Meanwhile large heavy-wooded trees, which can capture and store greater amounts of carbon, are associated with larger seeds. And these are only dispersed by large animals.
Prof Mauro Galetti from São Paulo State University said: “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 also big trees with dense wood that store more carbon.”
Carolina Bello, a PhD student from the São Paulo State University, added: “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 forest dominated by smaller trees with milder woods which stock less carbon.”
Pedro Jordano, of the Spanish National Research Council (CSIC) said: “Not only are we 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.”
One of those charismatic animals is the Lowland or Brazilian tapir (Tapirus terrestris) which is classified as Vulnerable by the IUCN Red List of Threatened Species™. Its ongoing populations reduction is estimated to be slightly greater than a 30% in the past 3 generations (33 years) due to habitat loss, illegal hunting and competition with livestock, and estimated on current rates of decline this rate of decline is inferred to continue for the next 3 generations (33 years). The Lowland tapir has been extirpated over large portions of its range and severely reduced in other large portions.
Camera trap footage of a lowland tapir at night:
(Source: Yasuni Wilderness YouTube channel)
Prof Peres added: “Intergovernmental policies to reduce carbon emissions from tropical countries have primarily focused on deforestation, and to a lesser extent on forest degradation resulting from timber extraction and wildfires. But our research shows that a decline in large vertebrate populations and the loss of key ecological interactions also poses a serious risk for the maintenance of tropical forest carbon storage.
“We hope that our findings will encourage UN programmes on Reducing Emissions from Deforestation and Forest Degradation (REDD+) to consider faunally intact forests and their full functionality as a critical precondition of maintaining forest carbon stocks.”
Carolina Bello said: “The effectiveness of these programmes will be improved if the preservation of ecological processes that sustain the ecosystem service of carbon storage over time is guaranteed.”
(Source: University of East Anglia press release, 18.12.2015; IUCN Red List of Threatened Species™)