Over-hunting Threatens Amazonian Forest Carbon Stocks

Tropical forests are important because they represent about 7 per cent of the world’s land mass but capture 50-70 per cent of all biodiversity globally. They store more than 460 billion tonnes of carbon and account for 60 per cent of worldwide terrestrial productivity. The Amazon is the largest and most species-rich tropical forest on Earth.

We have been looking at the impact of over-hunting on this diverse habitat and the implications for the future. In particular, over-hunting of large seed-dispersing mammals in tropical forests is thought to have a great impact on the plant diversity with a reduction of the forest biomass which could lead to 313 billion kg of carbon gradually being lost over one tree generation.

Forest plants are sedentary organisms and need animals to disperse their seeds in order for species to reproduce. Those plants with large seeds, which are most frequently associated with large trees that store the most amount of carbon in their wood, need large animals to disperse their seeds, yet it is those animals that are most at risk of over-hunting.

Amazonian forest wildlife has been declining through a combination of habitat destruction, habitat degradation and overhunting since the 1970s, but until now there was a poor understanding of the status of wildlife populations in hunted forests that otherwise remain intact and free from other human disturbances.

Forests are being emptied of their wildlife through over-hunting with large-seeded species being more vulnerable to the effects of the loss of large mammals from the ecosystem. This is particularly so in the Amazon forest where large-bodied frugivorous (fruit eating) wildlife are needed to disperse the heavy wooded species of plants. Without these animals, carbon dense species over time are gradually replaced with those with low carbon density.

As more of the Amazon forest becomes fragmented and moves within 500 metres of the edge of the forest, species that prefer the dense forest are being lost or squeezed into ever smaller habitats and the microclimates they need to survive are being lost.

We show that dense-wooded, large-seeded Amazonian tree species are replaced by light-wooded small-seeded trees that stock lower amounts of forest carbon, because those species continue to be dispersed in overhunted forests by more resilient small-bodied mammal and bird species. 

Professor Carlos Peres, Lead Researcher

Professor Carlos Peres has been researching the Amazon ecosystems for almost 30 years. His latest study uses data from 2,345 one-hectare forest plots that were surveyed throughout the Amazon forest in Brazil. Simulations from the research show that between 77 and 88 per cent of all plots lose above-ground biomass in overhunted forests.

Peres and collaborators estimate 5.8% or more of the above ground carbon stock of Amazonian forests could be lost if these mammals continue to be hunted out. 

Amazonian protected areas, sustainable-use reserves and indigenous territories now cover nearly half of the Amazon basin, but these forest reserves should effectively protect the forest megafauna, rather than just the forest cover. If properly managed, these protected areas could still protect most large animals, which are critical seed dispersers that maintain the full spectrum of tropical forest dynamics.

There has been little evidence to date that the environmental services provided by tropical forests are really conditional on fully functional forest ecosystems that can retain a full complement of wildlife species, but this research shows that biodiversity and natural ecosystem services are inextricably linked. 

"Even protected areas decreed on paper do not necessarily ensure the protection of large vertebrates in most remaining tropical forests. Either we stand up and effectively protect all components of forest ecosystems, or overhunting will erode critical wildlife populations until we see major losses in both forest biodiversity and the services provided by these ecosystems." 

Prof Carlos Peres, Lead Researcher.

The research has helped the Brazilian government identify additional areas for protection and it has also led to working with local communities who are managing their local resources and increasingly are empowered to do that. The research also brings together investigators from different disciplines, for example, working with local management systems and social scientists to create the largest freshwater fisheries zoning system in western Amazonia today, minimising conflicts over resource access in different parts of the Amazon river basin.

SOURCES

‘Dispersal limitation induces long-term biomass collapse in overhunted Amazonian forests’ published in the Proceedings of the National Academy of Sciences (PNAS) on January 25, 2016.  

Press release: Over-hunting threatens Amazonian Forest Carbon Stocks. <link to https://www.uea.ac.uk/about/-/over-hunting-threatens-amazonian-forest-carbon-stocks>

Campos-Silva, J. V. and Peres, C. A. Community-based management induces rapid recovery of a high-value tropical freshwater fishery. Sci. Rep. 6, 34745; doi: 10.1038/srep34745(2016).  

M. Pfeifer, V. Lefebvre, C.A. Peres, ......, R. Ewers (2017) Creation of forest edges has a global impact on forest vertebrates. Nature 551, 187-191   doi:10.1038/nature24457   

Press release: Caught on camera: Amazonian crop raiders