In recent years, scientists have identified numerous other threats to the region — which spans across eight countries — including damming and mining. And now, a new study is calling attention to yet another way human activity can harm the forest and its inhabitants. Published Wednesday in the journal Nature, the new paper explores the effect of other human disturbances, besides deforestation, on the Amazon’s biodiversity — including selective logging (which typically targets specific types of trees while leaving the rest of the forest intact), wildfires, hunting, altering or fragmenting the landscape, and other forms of habitat degradation.
Many people might assume that a forest’s biodiversity, or the amount of different organisms present in an area, more or less depends simply on how much forest has been cleared by humans — that more forest equals more life, in other words.
“But that’s ignoring this impact of degradation, which we know is pervasive in forests,” said Alexander Lees, a postdoctoral research fellow and Amazon expert at the Cornell Lab of Ornithology and one of the study’s co-authors.
Under Brazilian law, property owners in the Amazon are not supposed to allow more than 20 percent of primary forest to be cleared on their land, the study’s authors point out. But even in places that follow the rules — which is not the case everywhere — other types of human activities may still be causing problems in the forest.
To understand these effects, many previous studies have investigated the isolated impacts of one type of disturbance or another — the specific influence of logging, for instance, or the effects of wildfires on a particular area. The new paper, however, is among the first to examine the issue through a broad-scale lens.
“By focusing on only one form of disturbance, such studies may have overlooked much greater conservation losses from the combined effects of forest disturbances,” wrote David Edwards, a research fellow and tropical biodiversity fellow at England’s University of Sheffield, in a comment on the new paper, also published Wednesday in Nature. (Edwards was not involved with the research, itself.)
The researchers behind the new paper — who include more than two dozen experts from multiple institutions in Brazil, the United States and elsewhere — sampled bird, plant and dung beetle species in dozens of different sections of forest in the heavily deforested Brazilian state of Pará, which had been subjected to varying degrees of both deforestation and other disturbances, such as fire. Altogether, the study included about 2,000 species.
The researchers divided the concept of disturbances into two categories.
“Landscape disturbances” include the direct, downstream effects of deforestation — namely fragmentation and other changes to the landscape itself. Removing trees in one area inevitably ends up dividing the remaining forest into patches, which are broken up by cleared spaces. Research has suggested that this type of fragmentation can have serious consequences for forest-dwelling animals, who are suddenly forced to live much closer to cleared spaces — and, typically, human activities — than before, and who must also cross these spaces to get from one part of the forest to another.
The second category includes “within-forest disturbances,” which includes things like selective logging (the deliberate removal of certain types of trees, rather than whole-scale deforestation), wildfires or hunting.
The researchers developed a mathematical system for figuring out how severely an area has been affected by disturbances. They assumed that, in the absence of any other disturbances, the number of species in an area should correspond with the amount of forest cover present — with less forest cover (which is presumably caused by deforestation) equating to fewer species.
For each area included in the study, they calculated how much biodiversity they might expect based just on forest cover, and then they compared this estimate to the actual species richness observed in each place. They assumed that any differences in the predicted and real-life values were caused by additional disturbances in that area. They called this their “conservation value deficit.”
Their findings were alarming. “What we find is with this forest degradation — with fire or logging or both — we can quickly lose a high portion of biodiversity value,” Lees said.
The researchers observed that even areas containing 80 percent of their primary forests, according to Brazilian code, lost between 39 and 54 percent of their conservation value in terms of biodiversity losses. In some cases, up to half of these losses were attributed to disturbance, rather than just forest losses. The researchers estimated that conservation losses as a result of disturbances across the whole state of Pará were equal to the losses one might expect as a result of 123,000 square kilometers (or nearly 50,000 square miles) of deforestation.
Additional analysis of the types of species being affected revealed that organisms currently presenting the greatest concern to conservationists are the most vulnerable. These include species with small ranges or species only living in one place, who can’t be found anywhere else in the world, Lees noted.
So the research presents a clear hurdle for continued conservation efforts in the Amazon. The question of how it should be addressed is more complex. While efforts to continue curbing deforestation should certainly continue, the researchers recommend that additional steps be taken to cut down on the effect of other disturbances as well.
Illegal logging, for instance, is a widespread problem in many parts of the Amazon — and even in places where logging is permitted, more trees are sometimes removed than should be allowed. Finding better ways to make sure the correct amount of trees are being removed from any given site — and no more — can help crack down on the issue, said Toby Gardner, a research fellow at the Stockholm Environment Institute and co-author of the paper.
Governments could also consider putting better incentives in place to encourage local farmers to adopt more sustainable farming techniques and avoid risky land-use practices that might result in large fires, Gardner said. And he pointed out that many of these issues are connected anyway, so addressing one type of disturbance can help cut down on others. Logging, for example, can make forests more vulnerable to fire.
“Brazil does have legislation that cuts across all of those issues,” Gardner added. “There is legislation in the Brazilian forest service about trying to improve management of forests. There’s lots of rules on fire regulation. Brazil is not short on regulation — what it’s short on is the ability to implement these regulations.”