'A Spiraling Loop of Feedbacks': Worst-Case Scenario for Amazon Rainforest

Despite efforts to prevent the destruction of critical rainforests like the Amazon, they are continuing to decline due to human action, and may fall into a Catch-22 of further degradation.

A paper to be published in the journal Science on January 27 has found that humans have degraded more than one-third of the remaining trees in the Amazon rainforest.

This degradation could eventually lead to "a spiraling loop of feedbacks," Jos Barlow, a professor of conservation science at Lancaster University in the U.K. and co-author of the paper, told Newsweek.

Up to 38 percent of the remaining Amazon has been affected by human actions, researchers from Brazil's University of Campinas (Unicamp), the Amazon Environmental Research Institute (IPAM), National Institute for Space Research (INPE), and Lancaster University found.

burned trees amazon rainforest
A photo taken in Belterra, in the Brazilian Amazon in 2018, three years after a fire affected this logged forest that was also affected by edge effects. Degradation like this affects over a third of the remaining Amazon, a new paper has found. Erika Berenguer

The degradation of this area—equivalent to 5.5 times the size of the state of California—releases carbon emissions equivalent to or greater than those from deforestation.

Degradation of the Amazon is different from deforestation, which is what most of us think of when we picture human impacts in the rainforest.

The Amazon rainforest is a 2,100,000 square-mile rainforest encompassing a large proportion of South America. It is one of the most dense areas of biodiversity in the world, and provides a number of essential environmental functions that we might not even think about.

The Amazon contributes 16 percent of all the land-based photosynthesis in the world, and strongly regulates global carbon and water cycles, sucking in carbon dioxide and producing oxygen. Additionally, despite only covering around 0.5 percent of the Earth's surface, the Amazon is home to over 10 percent of all named plant and vertebrate species on Earth.

It is also thought that this number is massively underestimated: scientists think that the species they have found in the Amazon so far comprise only 10 percent of the total number of species present, with thousands yet to be officially discovered.

"Healthy rainforests provide amazing habitat for biodiversity—this is what the Amazon is most famous for," Sally Thompson, an ecohydrologist at The University of Western Australia, told Newsweek. "They usually support clean water in rivers, make it rain, and cool the surrounding area. You can hunt, harvest timber or foods sustainably from healthy and well-managed forests. And a healthy forest can often recover from disturbance. Degraded forests aren't as good at doing any of those things, and often they struggle to recover from disturbance."

Deforestation involves a loss of the forest canopy and a change in land use (e.g., from forest to agriculture or urban land use), while degradation is a process affecting the remaining forests. Degradation essentially means that there is still forest in place but it is not as healthy or as good at providing benefits for the environment or for people.

"Until recently, the role of forest degradation (in Amazon and elsewhere) was difficult to quantify in terms of carbon emissions," Robin Chazdon, professor emerita of ecology and evolutionary biology at the University of Connecticut, told Newsweek. "But more recent work and technology using airborne or satellite-based lasers (LiDAR) can detect fine-scale changes in the forest canopy and three-dimensional structure, and can reveal cases where the forest has been affected by logging, clearing or burning of understory, tree dieback and disease, and road building."

rainforest degradation
A summary figure from the paper showing the effects of degradation on the rainforest. Alex Argozino/Studio Argozino/Science magazine

The authors of the new paper evaluated four key activities driving forest degradation: forest fires, edge effects (changes in forests next to deforested areas), selective logging (including illegal logging) and extreme drought. More than one of these effects can act in tandem in a single area of rainforest.

The authors of the newest research paper predict these four degradation factors will continue to be major sources of carbon emissions into the atmosphere by 2050, regardless of the changes in the deforestation of the forest.

"Droughts and agricultural expansion drive more forest fires; these burned forests are more open, and drier in the understorey, and are much more susceptible to future fires; the carbon emitted and the loss of dry-season evapotranspiration drives further climate change and local heating; the outcome is a flammable landscape that suffers frequently repeated fires, rapidly degrading the Amazon's ecological and social integrity," Barlow said.

"This has already occurred in some regions—the challenge now is to prevent it occurring across much larger areas, which will be increasingly difficult as climate change progresses."

amazon rainforest
Photo taken in 2015 of a burning forest in Belterra, in the Brazilian Amazon (left), and a landscape drone photo from 2019, four years after a fire affected this forest inside a protected area in Belterra, in the Brazilian Amazon. The white crowns are those of trees that were killed by the 2015 fires, but remain standing. Adam Ronan / Marizilda Cruppe /Rede Amazônia Sustentável

Climate change is also increasing drought in the rainforest, which can lead to rivers drying up and other plant and animal species dying out.

A large fraction of the water that falls as rain in the Amazon basin came from a tree in a different part of the basin. Droughts in one part of the Amazon will spread when there isn't enough water for the trees to make rain anymore.

"So the scary scenario is that global warming causes droughts which spread, cause big trees to die, and collapses the Amazon's ability to make its own rain. Then you don't really have a rainforest anymore," Thompson said.

"Since the Amazon is also responsible for using a lot of carbon dioxide, this would also increase the CO2 in the atmosphere and make global warming worse. The 'Amazon collapse' scenario due to global warming has been considered a lot. It is a very scary 'planetary threshold' that we do not want to cross."

amazon fragmentation
Photo taken in Belterra, in the Brazilian Amazon in 2019, four years after a fire affected this forest fragment, which has been previously also affected by multiple anthropogenic disturbances, including selective logging, edge effects and fires. Marizilda Cruppe/Rede Amazônia Sustentável

So, what can we do to stop this occurring?

"It is important to avoid degradation from forest areas that have not yet been disturbed (or at least within the past 200-300 years) and are critical areas for carbon storage, biodiversity conservation, and protecting watersheds," Chazdon said. "Some people call these "intact forest landscapes."

In most cases of low to moderate levels of degradation, forests can recover well on their own as long as they are protected from incursions and fires. In highly degraded areas, however, some restoration practices will be needed to assist recovery (such as control of grasses or other weedy plants that prevent trees from re-establishing) and in other cases replanting may be needed.

Thompson suggested one of the most immediate things that could be done on the ground is to stop road-building and limit access into the rainforest.

"Where roads go, forest loss and degradation follow," she said.

"An important first step is to prevent further deforestation, which of course has many other benefits for climate, biodiversity and society as a whole," Barlow said. "But this also needs to be accompanied by multi-scale actions that tackle the disturbances that cause degradation."

Locally, Barlow suggested actions to improve fire management, reducing the risks of forest fires in dry years.

"Improvements to legislation and governance would help prevent the pervasive illegal logging that occurs along the frontier. And globally, action to limit climate change is key to preventing worsening droughts and the accompanying forest fires," Barlow said.

"Climate change is so important to address as it is a driver on its own, with extreme droughts killing some of the largest forest trees that take many hundreds of years to grow. These droughts are also a key driver of forest fires, causing rapid and severe degradation across millions of hectares of forests."

Hopefully, if these sources of degradation are slowed and mitigated, the remaining two-thirds of the Amazon rainforest will persist for years to come.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about the degradation of the Amazon? Let us know via science@newsweek.com.