Amazon Is Less Able to Recover From Droughts and Logging, Study Finds

Scientists reported Monday that the Amazon is losing its ability to recover from land-use changes and that the rainforest is approaching a critical threshold, which could have dire consequences for the environment.

The scientists did not know when this threshold might be reached.

Tim Lenton, one of the scientists, said that if it gets to that tipping point, then we need to commit to losing the Amazon rainforest.

Losing the rainforest could result in up to 90 billion tons of carbon dioxide being put back into the atmosphere, equivalent to several years of global emissions. It would be more difficult to limit global warming.

There is a lot of uncertainty as to when such a threshold might be reached. Some research shows that there could be a lot of forest dieback in the Amazon by the end of the century.

The new study is very compelling and Carlos Nobre, a senior scientist at the National Institute of Amazonian Research in Brazil, was one of the first to sound alarm over the potential loss of the Amazon more than three decades ago.

Dr. Nobre, who was not involved in the research, said that it raised his level of anxiety.

The Amazon is the largest rainforest in the world, and it helps mitigate climate change by taking in more carbon dioxide from the atmosphere than it releases. It is rich in both plant and animal species. It can affect weather outside of South America.

Climate change, along with burning for agriculture and ranching, has taken a toll on the Amazon, making it warmer and drier. Since 2000, the region has experienced three droughts.

Simulations were used in most previous studies of resilience in the Amazon. In the new research, the scientists used decades of satellite data to measure the amount of biomass in specific areas, which correspond to their health. The researchers found that since 2000 the areas have lost resilience. It took a long time for forested areas to regain their health after suffering through a dry spell.

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The lack of resilience in the study shows that there is only so much of a beating that the forest can take, said Paulo Brando, a tropical ecologist at the University of California, Irvine who was not involved in the study.

Dr. Brando pointed to the need to stop clear-cutting and forest degradation in the region, and said that this was not necessarily a sign that a tipping point was unavoidable.

The researchers found that more than three-quarters of the untouched rainforest lost its resilience over that time, and that the loss was greatest in areas that were closer to human activities. The journal Nature Climate Change published the study.

The lead author of the study, Chris Boulton, said that the Amazon was like a giant water recycling network because of the wind. The loss of some of the forest leads to more drying in other areas.

Dr. Boulton said that as the Amazon dries you can see that resilience is being lost even faster. Forests might decline and die off quickly and become more like savannas with fewer trees.

savannas would take up less carbon than the large, broad-leafed trees they replaced, and the loss of forest trees would add carbon to the atmosphere. It would support fewer species.

The research shows that the Amazon is on the edge of a cliff and that it would switch to a different environment.

Over the past 50 years, 17 percent of the Amazon has been deforested, and while the pace of deforesting slowed in Brazil, it has picked up again recently. Efforts to stop the destruction of the Amazon will have an effect on the Amazon as a whole, according to the researchers.

Dr. Nobre said that they are absolutely correct.