Hunting Mammals Adds To Forest Fragility
The Amazon forests’ large mammals play a key role in maintaining the ecosystem that removes CO2 from the atmosphere and helps to slow climate change.
A healthy forest needs more than just healthy trees. It needs a healthy population of big, fruit-eating, seed-dispersing mammals to spread the species and keep the canopy green – and maintain the forest’s role as a store of atmospheric carbon.
The great tropical forests lock up 55% of the planet’s total woodland carbon. An estimated 460 billion tonnes of the stuff is drawn down from the atmosphere by photosynthesis and converted to leaf, root and branch.
But those forests are home to a vast web of species, and Carlos Peres, professor of environmental sciences at the University of East Anglia in the UK, and colleagues have been looking at the powerful roles played by primates, tapirs and other big frugivores that depend on the fruits of the Amazon forest.
Rates of hunting
They report in the Proceedings of the National Academy of Sciences that they looked at the outcome of 166 wildlife surveys and based their study on almost one million individually-mapped households to gain a measure of the rates of hunting and the impact on the forests, including those areas that are protected.
They also counted data from 2,345 one-hectare forest plots that were home to 129,720 large trees, to simulate the consequences of continued hunting.
At a conservative estimate, 5.8% of the above-ground carbon stock of the Amazon forests could be lost if large, vulnerable fruit-eating species are over-hunted. In some places, the rate was as high as 37%.
“Amazonian forests provide globally important ecosystem services, including carbon storage in the forest biomass,” Professor Peres says.
“Our research shows that if people continue to overhunt large mammals, tropical forests could lose much of their capacity for carbon storage. This is because several large mammal species play a vital role in dispersing large-seeded trees associated with high wood density.”
The world’s forests play a vital role in carbon accounting. An estimated 20% of the human greenhouse gas emissions that are warming the planet’s atmosphere and threatening worldwide climate change occur because of the loss or degradation of the forests.
So the ecology of the forests then becomes an important part of climate research, and this latest study is, so to speak, Professor Peres’s second bite at this particular cherry.
Loss of biomass
Last December, he was a partner in a study of the impact of 813 species on the Atlantic forests of Brazil that came to pretty much the same conclusion: even if you spare the trees, the forest suffers if you hunt the species that co-evolved with the trees.
The latest study shows that the total remaining forest area affected by hunting is far greater than the total area of forest destroyed or degraded so far. Between 77% and 88% of all the plots of forest had lost biomass − that is, carbon stored as trunk, branch and leaf.
Professor Peres says: “Amazonian forest wildlife has been declining through a combination of habitat destruction, habitat degradation and overhunting since the 1950s, 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.”.
“We show that dense-wooded, large-seeded Amazonian tree species are replaced by light-wooded trees that produce smaller seeds, which continue to be dispersed in overhunted forests by more resilient smaller mammal and bird species.”
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.