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Scientists say deforestation may threaten a staggering half of Amazon tree species with extinction

Forest on a plateau in a bauxite concession (Nassau Mountains) in North Suriname. (Image credit: Hans ter SteegeS)

Tropical tree species could be in much bigger trouble than scientists had thought: A new study, which involved collaboration from dozens of researchers, suggests that at least 36 percent and up to 57 percent of all Amazon tree species are likely at risk of extinction, depending on future deforestation rates. If true, this information would raise the number of threatened plant species on Earth by about 22 percent.

The research, which was published Friday in the journal Science Advances, combined spatial distribution models of the Amazon with both historical and projected data on deforestation to determine the conservation status of more than 15,000 Amazonian tree species, about two-thirds of which the authors considered rare species. The researchers used listing criteria from the International Union for Conservation of Nature (IUCN), which maintains a “red list” of threatened species on Earth, to decide which species should be considered in danger of extinction.

Using the IUCN framework is one of the paper’s major strengths, said Nigel Pitman, a senior conservation ecologist at the Field Museum in Chicago and one of the paper’s co-authors, during a teleconference about the paper on Friday morning.

“The problem is there are lots of definitions of the word ‘threatened,’” Pitman said at the teleconference. “Each country — oftentimes agencies with a country, NGOs, researchers — have different definitions. One thing that’s special about this paper is that we’ve made a real point of reporting our results using the most common currency of conservation status, the IUCN red list framework.”

However, Pitman added, about 90 percent of plant species on Earth have yet to be assessed by the IUCN, as it requires an enormous amount of resources to go through every species one by one.

“What we’ve tried to do with this paper is a kind of shortcut, a kind of triage, that can give us a preliminary look at the conservation status of all these species,” he said. And what he and his colleagues found is that “several thousand Amazonian trees that aren’t currently on the red list probably deserve to be.”

The tree inventory data the authors used came from the Amazon Tree Diversity Network, which includes more than 1,700 tree inventory plots throughout the Amazon. And their deforestation data came from published work on deforestation up through 2013 and projections for future deforestation in the year 2050. The IUCN red list framework takes future threats into account when determining a species’ conservation status, which is why the authors included future projections for deforestation in their study.

They considered two different future scenarios: a “business-as-usual” scenario, in which deforestation continues at its current rate, and an “increased governance” scenario, in which deforestation is slowed in the future. Under the business-as-usual scenario, 57 percent of the Amazonian species can be considered threatened, and under the increased governance scenario, 36 percent.

In 2009, a similar study was conducted on the extinction risks of Amazonian plants. Kenneth Feeley, the lead author of that study and an associate professor of biology at Florida International University, told The Post that this new paper helps confirm the results he and his colleagues produced at the time. Feeley was not involved with the new paper.

“We came up with very similar numbers,” Feeley said. “That’s a great thing in science. The fact that we have different assumptions, different sources of potential errors, and we still came to this similar number really helps to say that this is something we can believe in.”

Although Feeley’s paper did not use the IUCN framework to draw its conclusions, he noted that the strategy “is very useful because it’s a language a lot of policymakers are used to and comfortable with and know how to act on. This new paper will be very useful in pushing conservation and leading us into hopefully what needs to be done next to reduce these possible extinction rates.”

And what needs to be done, according to the authors, is an improvement in the management of protected areas in the Amazon. The authors noted that about 52 percent of the Amazon basin is currently composed of protected areas, although the degree of protection they offer varies. And even in these protected zones, trees can still be threatened, if logging is still permitted to take place under certain exceptions or if not enough resources are allocated to combating illegal deforestation.

However, there’s hope, according to the authors: In their analysis, they found that if deforestation were not permitted to occur within protected areas, the percentage of threatened species would fall to 32 percent under the increased governance scenario and 44 percent under the business-as-usual scenario.

“If we can protect these areas… the Amazon could be a showcase of large-scale conservation worldwide,” said Hans ter Steege, the paper’s lead author and a research fellow at the Naturalis Biodiversity Center in the Netherlands, during the teleconference.

Cracking down on deforestation will be one challenge moving forward — but not the only one, according to Feeley. This paper only takes deforestation into account when considering the trees’ conservation status. But there are other significant future threats to the trees as well, most notably climate change. “My guess would be, yes, the number of extinctions is potentially even higher than what the authors estimate,” Feeley said.

And to add to the alarm bells, the new study could imply that other tropical tree species, in places other than the Amazon, are also in worse shape than we thought.

“The vast number of threatened plant species uncovered by this new approach begs the question: how many others have been overlooked at a global scale?” said Thomas Crowther, a postdoctoral fellow at Yale University’s School of Forestry and Environmental Studies, in an e-mail to The Post. Crowther was not involved with this study, but was the lead author on a recent, high-profile paper mapping tree density across the world.

And, indeed, Pitman — the new study’s co-author — noted at the teleconference that “most tropical forests have lost a lot more forest coverage than the Amazon. It may be the case that most tree species in the tropics, if we were to do this same sort of analysis, would qualify as globally threatened.”

So there’s work cut out for conservationists hoping to prevent a large-scale extinction of tropical tree species in the future. Cutting down on global deforestation, particularly in the tropics, will likely be a topic at the UN’s climate conference in Paris, which begins on Nov. 30. Protecting trees is a safeguard against the loss of biodiversity, but forests are also valuable carbon sinks, meaning they absorb carbon emissions that would otherwise end up the atmosphere and contribute to global warming. So there are climate-related reasons to be concerned about the loss of tropical trees, as well.

With any luck, the study will be taken by policymakers as a clear warning that action is needed, Feeley said.

“What this study shows is that we already have a significant number of species that are likely to be threatened,” he said. “If we keep going in the direction we’re going, we’re going to put a lot more species at risk of extinction very quickly.”