Deforestation adds up. New research finds that the Amazon region could lose more than half of its tree species by the year 2050 due to a combination of logging, agriculture, dams, fires, mining, climate change and human development.

All told, at least 36 percent and as many as 57 percent of the Amazon’s more than 15,000 tree species should now be considered threatened with extinction, according to a paper published today in Science Advances.

The paper, the work of 158 researchers from 21 nations, examined the forests of the Amazon basin and the Guiana Shield under two deforestation scenarios. Under the first “business-as-usual” scenario, which is based on deforestation rates matching what we’ve seen in recent years, the Amazon would lose about 40 percent of its forests by 2050. That would fall to 21 percent under the second scenario, which would see improved forest governance and a reduction in habitat loss.

Either way, the collective impact would be huge. The paper estimates under these scenarios that the number of Earth’s threatened plant species is now at least 22 percent higher than realized. Many of the Amazon’s tree species, the researchers found, would probably quality as either endangered or critically endangered. At least 1,600 tree species will have fewer than 1,000 individuals by 2050. Some would undoubtedly face extinction.

Even common species won’t be spared. The researchers found that commercially valuable species such as Brazil nut (Bertholletia excelsa), cacao (Theobroma cacao) and açai palm (Euterpe oleracea) will decline by at least 50 percent.

Still, the problem is actually not quite as bad as the researchers expected, according to the paper’s lead author, Hans ter Steege, senior research fellow with the Naturalis Biodiversity Center in the Netherlands. “I had thought the situation was much worse,” he says. “If you are in the ‘arc of deforestation,’ it seems as if all is lost. But you can also realize that, just as in Europe, this deforestation offers opportunities for people to live. The good news is that over 80 percent of the Amazon forest is not deforested and that is an immense amount of forest.” About half of that land, he says, is in some form of conservation area. Some of it set aside as conservation reserves, while other areas are regulated for sustainable use or indigenous territories.

All the same, some regions would be harder hit than others. “Many of the species that are predicted to go extinct have their full range in Eastern or Southern Amazon,” ter Steege says. “Species with small ranges or small populations are likely to go extinct more than species with large ranges.”

One of the most striking things about this paper is that many of the species that are most at risk are already so rare that they have never been fully, or even at all, described by science. Instead, just a few common trees dominate our understanding of the Amazon forests. A previous paper by the same team found that the 227 most common Amazon tree species represent more than half of the individual trees in the region. The new paper, meanwhile, documents population counts for fewer than 5,000 species. Many of the rest of the Amazon tree species—about 10,000 additional species—remain unknown or understudied, what the researchers dubbed dark biodiversity. “The majority of extinctions will indeed be in the ‘dark biodiversity,’” ter Steege says.

The loss of so many trees would obviously have a cascading effect on the Amazon’s biodiversity and put many other species at risk. “Extinction is not just one species,” ter Steege says. “Many species will be affected. For large carnivores and primates, deforestation coupled with immense habitat fragmentation will have a much more immediate effect. Hunting in fragments may also decrease other mammals and affect the dispersal of many other species.”

The paper warns that tropical trees may now be one of the world’s most threatened groups of species—on par with cycads, amphibians and corals—but it also makes clear that the existing system of protected networks in the Amazon is working and that many species may be saved if we continue to improve these protections. “The message that we can make a difference should be embraced,” ter Steege says.

Photo © Hans ter Steege. Used with permission

Previously in Extinction Countdown: