Overhunting Rainforest Animals Makes Climate Change Worse

Researchers find that tropical forest mammals play an important role in keeping carbon-absorbing Amazon forests healthy.

(Photo: Wolfgang Kaehler/LightRocket via Getty Images)

Jan 29, 2016· 1 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

The large animals in some Amazon forests have been so thoroughly hunted that it has affected the composition of the forests themselves, dramatically reducing their ability to store carbon and slow the effects of climate change, according to new research.

The study, published this week in Proceedings of the National Academy of Sciences, found that overhunting could result in Amazon forests losing 5.8 percent of their ability to store carbon within large, dense, living trees.

That might seem like a fairly small amount, but it adds up to a projected 690 billion pounds of carbon that the forests would no longer be absorbing, according to the study. That would have an economic effect of between $5.9 trillion and $13.7 trillion on the world’s carbon markets.

Researchers from the U.K.’s University of East Anglia and other institutions surveyed 166 forest areas, many of which experienced significant hunting pressure. Those hunted areas, the researchers found, were often either completely or almost completely devoid of the largest mammals—spider monkeys, woolly monkeys, and tapirs—that inhabit such woodlands.

All three of those species are fruit eaters, so they play an important role in healthy forests by distributing seeds in their droppings. Tall woody trees that produce large fruit depend on this dispersal service, because seeds that fall too close to the parent trees have very low chances of survival owing to lack of space and sun in which to grow.

Virtually all of these woody tree species have very dense wood, so they store greater amounts of plant biomass and carbon than other species, said the study’s lead author, Carlos Peres, a professor of conservation ecology at the University of East Anglia.

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Without large mammals to distribute these seeds, the researchers found, smaller mammals and birds take over. These animals, however, don’t eat the fruit from the large woody trees. The seeds that they distribute result in forests dominated by smaller trees with lighter, less dense wood that stores less carbon.

The researchers calculated that 77 to 88 percent of the hunted forests had lost some of their biomass, a situation that would only continue with unabated hunting.

“The issue of unsustainable hunting within tropical forest protected areas has been flagged in all major tropical land masses, and the Amazon is no exception,” said Peres.

The authors have called for better efforts to preserve forests not just from deforestation but also from defaunation—the elimination of animals within them. “Protecting forest cover alone but failing to protect the forest wildlife is not enough to ensure that these forests continue to exercise ecosystem services such as carbon retention,” Peres said.

Beyond their vital role in maintaining the climate, many of these large woody trees face another threat: They could go extinct before they have even been officially named.

“There are an estimated 16,000 tree species in the whole Amazon but only about 5,000 of which have actually been described to science,” Peres said. A paper he contributed to last year estimated that between 36 and 57 percent of the Amazon’s tree species now face the threat of extinction. That, in turn, would only accelerate the forests’ loss of ability to store carbon, accelerating climate change.