Home Science The carbon sink in the subtropical forests of South America is under...

The carbon sink in the subtropical forests of South America is under threat

During the El Niño climate phenomenon, extreme conditions occurred that negatively impacted the forest carbon sink in South America, causing it to decrease or stop altogether.

Recent research has found that the ability of tropical forests in South America to absorb carbon from the atmosphere decreases when conditions become extremely hot and dry. This raises concerns about the impact of climate change on these ecosystems, which are important for the global balance.

Tropical forests have long played a critical role as carbon sinks. This means they have been absorbing more carbon from the air than they are emitting, which has been instrumental in mitigating the effects of climate change.

El Niño and its impact on the carbon storage function of South American forests

South American forests were affected by a climate event called El Niño in 2015-2016, according to Amy Bennett, a researcher at the University of Leeds. As a result of this phenomenon, there were droughts and extremely high temperatures. These adverse conditions prevented forests from fulfilling their role as carbon sinks and efficiently capturing greenhouse gas emissions.

The El Niño phenomenon occurs when sea surface temperatures in the Pacific Ocean rise rapidly, leading to a significant change in the global climate system. South America experienced unusually warm weather in 2015–2016. We are currently facing a similar development event.

dr Bennett of the Leeds School of Geography has pointed out that the tropical forests of the Amazon have played a crucial role in slowing the rise of carbon dioxide in the atmosphere. This is further evidence of the critical importance of preserving and protecting these ecosystems in the fight against climate change.

Amazon trees, sensitive to climate change

Scientists know that trees in the Amazon are sensitive to changes in temperature and water availability. However, we do not know how individual forests might be altered by future climate changes.

Studying what was happening in the Amazon during this major El Niño event gave us a glimpse into the future and how record-breaking hot and dry weather is affecting forests.“.

Therefore, the researchers have published their results in the renowned journal nature climate change. This significant study was made possible through collaboration between the RAINFOR and PPBio research networks. Thanks to dozens of short-term grants, more than 100 scientists have been able to carefully map forests in 123 test plots over several decades.

study methodology

The plots cover a variety of forests in South America, both in the Amazon and in the Atlantic. This also includes drier forests in the tropical part of the continent.

Based on detailed records looking tree by tree, it was found that most forests functioned largely as carbon sinks over the past 30 years. This means that the growth of the trees exceeds the mortality rate. During the 2015–2016 El Niño phenomenon, the burrow closed due to increased tree mortality from heat and drought.

Professor Beatriz Marimon from the State University of Mato Grosso in Brazil contributed to the debate. Her experience and knowledge in this field are valuable and enrich the scientific discussion: “Here in the southeastern Amazon, on the edge of the rainforest, trees may have switched from storing carbon to emitting carbon. While tree growth rates withstood the higher temperatures, tree mortality increased in this extreme weather.“.

lower layer of the Amazon forest

Results of the carbon sink impact study

In a survey of 123 plots, it was found that 119 of them recorded an average monthly temperature increase of 0.5 degrees Celsius. In addition, it was observed that water deficits also occurred in 99 of these plots. These results suggest a link between the increase in temperature and the lack of precipitation, as the hottest areas also experienced greater aridity.

Before the climate phenomenon known as El Niño, scientists estimated that the plots were capable of storing and sequestering about a third of a ton of carbon per hectare per year. However, during the hottest and driest conditions associated with El Niño, this capacity was reduced to zero.

The reason for the change was the decrease in biomass due to the death of trees.

In the paper, the researchers emphasized that the El Niño event had a significant impact on forests that were already relatively dry over the long term.

surprise for researchers

Contrary to expectations, wetter forests were found to be less susceptible to extremely dry weather than previously thought. This surprised researchers as it was thought that these forests would be less adapted to such adverse conditions. However, forests in drier areas at the edge of the tropical forest biome are most vulnerable to drought. This is because they are used to dry climates and do not tolerate long periods without rain as well as wetter tropical forests.

This finding suggests that some trees are already functioning under tolerable boundary conditions.

Professor Oliver Phillips, a leading ecologist at the University of Leeds and leader of the global ForestPlots initiative, oversaw research that offered hope for the resilience of tropical nature in South America.

He added: “Our diverse team’s full 30-year perspective shows that this El Niño had no worse impact on intact forests than previous droughts. However, this was the hottest drought in history.”

Tree mortality increased in the drier areas bordering the Amazon, where forests were already fragmented. When conservationists and resource managers are aware of these risks, they can take steps to protect them.

Because of the complex dynamics that occur in forest environments, deforestation makes the environment drier and hotter, which puts additional stress on the remaining trees.”

So the big challenge is to preserve the forests in the first place. If we succeed, then our evidence on the ground shows that they can continue to help sequester carbon and slow climate change.


Two reports were published in Nature Climate Change related to this research. The scientific article “Sensitivity of South American tropical forests to an extreme climate anomaly‘, and an investigative report entitled ‘Effects of El Niño 2015-2016 on South American tropical forests“.

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