How the Amazon rainforest is likely to cope with the effect of future drought

Note to journaliststs. There are two linked press releases below: the first describes the scientific findings. The second describes the challenges of working in the Amazon forest.

How the Amazon rainforest is likely to cope with the effect of future drought

• New study identifies regions in the rainforest most at risk from drier conditions
• Drought will reduce the rainforest’s ability to remove carbon from the environment

A major collaboration involving 80 scientists from Europe and South America has identified the regions of the Amazon rainforest where trees are most likely to face the greatest risk from drier conditions brought about by climate change.

Based on the analysis, the scientists predict trees in the western and southern Amazon face the greatest risk of dying.

They also warn that previous scientific investigations may have underestimated the impact of drought on the rainforest because those studies focused on the central-eastern part of the forest, which is the least vulnerable to drought.

The latest study provides the first assessment across the entire Amazon Forest of how different areas are likely to respond to a climate that could get warmer and drier, and it comes as some studies predict the rainforest will experience increased periods of drought.

Professor David Galbraith, from the University of Leeds who supervised the study, said: “The Amazon is threatened by multiple stressors, including deforestation and climate. Understanding the stress limits that these forests can withstand is a major scientific challenge. Our study provides new insights into the limits of forest resistance to one major stressor - drought.”   

Some parts of the Amazon have already seen changes in rainfall patterns. In the southern Amazon, there is evidence that the dry season has become longer, and temperatures in this region have increased more than in other parts of the Amazon. The changes in the southern Amazon are partially due to extensive deforestation.

Dr Julia Tavares, who led the study while undertaking a PhD at Leeds and is now based at Uppsala University in Sweden, said: “A lot of people think of the Amazon as one large forest.  

“But it is not. It is made up of numerous forest regions that span different climate zones, from locations that are already very dry to those that are extremely wet, and we wanted to see how these different forest ecosystems are coping so we could begin to identify regions that are at particular risk of drought and drier conditions.”  

Writing in the scientific journal Nature, the research team said their findings were removing a “...major knowledge bottleneck of how climate change will impact this critical ecosystem”.  

The paper - “Basin-wide variation in tree hydraulic safety margins predicts the carbon balance of Amazon forests” - is published today (Wednesday, April 26. When the embargo lifts, the paper can be found at:  https://www.nature.com/articles/s41586-023-05971-3).

Tree doctors

The research team, known as the “tree doctors” to the communities living in the forest, took measurements and samples over a year from 11 separate sites across the western, central-eastern and southern Amazon – covering Brazil, Peru and Bolivia.

The study involved data from 540 individual trees across 129 species.  

The researchers wanted to determine how resistant different tree species and forests were to drought conditions. The scientists then used the data to test whether forest vulnerability to drought could predict its ability to accumulate and store carbon taken from the atmosphere.

From the data, the research team was able to quantify how safe the trees were from drought-related death.

Findings

In the southern part of the Amazon Forest, where historically there have been declining levels of rainfall, the trees showed the greatest degree of adaptation to cope with drought.

Despite that, though, the study revealed that the trees faced the biggest risk of dying due to drought. This is likely because the region has already seen rapid climate change and disruption to rainfall patterns caused by deforestation, which had pushed trees to the limits of their ability to cope.

In contrast, the tree species in the wettest parts of the Amazon Forest showed the lowest level of adaptation to drought yet they were the safest in terms of the risks from future climate change because, so far at least, they had not been impacted by changes in rainfall. 

Equipped with this more nuanced view of how different parts of the Amazon Forest could respond to drought, the researchers warn that scientific investigations, which have tended to concentrate on the central-eastern region, where trees have shown some of the greatest adaptations to cope with drier conditions, may have underestimated how vulnerable other forest regions are to climate change. 

They say the findings of the new study should be used to help update and refine existing models on how the Amazon may be impacted by drier conditions.

Carbon storage 

According to the researchers, the Amazon Forest holds between ten and 15 percent of the carbon stored by vegetation globally, and it plays a key role in taking up carbon which would otherwise be in the atmosphere.

Modelling revealed that as plant drought mortality risk increases, the ability of the trees to store carbon would be significantly reduced. The most water stressed part of the Amazon is in the south-eastern region. Analysis reveals that the trees in this location no longer act as a large-scale carbon store. 

Professor David Galbraith said: “This study reveals how forest risk to drought varies across the Amazon Basin and provides a mechanism for predicting carbon balance at the forest stand level. Forests that are ‘safer’ from drought-induced mortality are accumulating more carbon than those that face greater risk of drought-induced mortality.

Professor Emanuel Gloor, also from the University of Leeds who co-supervised the study, added: "The pattern of resilience and risks identified among the different tree populations across the in the study will be used to build more effective and accurate climate models of the way the Amazon may change as the region responds to climate change."

The study involved an international team of researchers from Europe, Brazil, Peru and Bolivia. The work was part of the TREMOR project funded by the UK’s Natural Environment Research Council to better understand mechanisms of tree mortality in Amazon forests and Julia’s PhD was supported by CAPES (Coordination for the Improvement of Higher Education Personnel), Brazil.

END

Second Press Release

Scientists take a portable laboratory into the Amazon  

As an ecologist, Dr Julia Tavares often has to consider how to collect data from remote locations.  

But nothing had quite prepared her for the challenges she faced when she started her PhD at the University of Leeds.  

As a doctoral researcher in the School of Geography, she took on the task of organising and eventually leading an expedition into the Amazon rainforest - and to record data from the dominant trees that existed at locations ranging from Brazil, Peru and Bolivia.  

The study involved overseeing the harvesting of hundreds of tissue samples, work which had to take place in the middle of the night, all in the quest of cutting-edge science.  

The research team worked in extreme humidity and temperatures that reached 30 degrees Celsius by eight in the morning and over 35 degrees by midday. And the hot and humid conditions brought out clouds of mosquitoes. 

Involving a collaboration of 80 scientists and support staff, the study was looking at how different tree species had adapted to drought, and how vulnerable different forest zones would be to further climate change.  

It was the first investigation into the water stress faced by trees across the entire Amazon basin and how they might cope if, as some climate models predict, the Amazon gets significantly warmer and rainfall patterns change.  

The findings of the research have been published today in the scientific journal Nature. (Wednesday, April 26. When the embargo lifts, the paper can be found at: https://www.nature.com/articles/s41586-023-05971-3). 

Sampling from the tree canopy 

Samples were taken from more than 540 trees. These were the dominant canopy species, with some reaching over 30 meters in height. The tissue samples were used to measure how hydrated the tress were, and this fluctuates over a 24-hour period. 

The scientists needed to measure hydration during periods of low and high-water stress. To do that, sampling was done at three in the morning - when the rainforest was in utter darkness and plants were recharging their water levels - and again at midday.  

As part of the expedition, the scientific team brought a mobile laboratory, packed in 16 flight cases, into the forest along with giant cylinders of nitrogen gas. 

Dr Tavares said: “We had a team of expert tree climbers whose job it was to use ropes and climbing gear to ascend the trees and get the samples.  

“We would survey the site the day before we intended to take the samples. Remember, we were working in a dense rainforest and some of the sampling was happening at night, so we needed to mark the trees and the branches that we wanted for the tissue samples.”  

The trees climbers used what are telescopic scissors, which can extend six or so metres, to reach out across the vegetation and harvest the branch they were after.  

Dr Carol Signori-Muller, an ecophysiologist formerly at University of Campinas, Brazil, and now with the University of Exeter, said the rainforest is a beautiful and fantastic place that took on a different character at night.  

She said: “At night it is very dark. The moonlight can be blocked out by the dense overhead vegetation. And it is very silent. 

“There is hardly any sound from the birds. All you can hear are the croaking of frogs or the movement of branches. You become attuned to the sounds around you because you need to be aware that something can suddenly appear from behind a bush.” 

During one off the daytime sampling sessions, a jaguar emerged from the undergrowth and started playing with the ropes attached to the climbing gear, in the way a cat would play with a ball of wool.  

Dr Tavares added: “The team had to stop what we were doing and keep away - and just watch the jaguar, who did end up destroying some of the climbing gear.” 

Reaching the different forest locations would involve a drive in four-by-four vehicles or by boat and would involve the scientists and support staff camping or staying in field station accommodation.  

The team wore long boots to protect themselves from the snakes that live in the rainforest.  

The results of the study will help identify those regions of the rainforest at greatest risk from climate change, enabling conservationists to target resources and policies to those areas.  

Dr Halina Soares Jancoski, who took part in the expedition while at the State University of Mato Grosso in Brazil and is now with the Environment Secretariat of the Municipality of Nova Xavantina, in the central west region of Brazil, said: “I consider this study very important because it helps us to understand how forests will behave with the effect of climate change. Especially in the Amazon - Cerrado transition areas, which are more susceptible to climate extremes than in the core areas.” 

Dr Tavares added: “At the start of my PhD, if you said to me that I would be involved in a major expedition into the Amazon and would have led a scientific collaboration into one of the most important ecological questions facing this hugely important ecosystem, I would have thought you were joking. 

“But, together with an amazing team, that is exactly what we have done.” 

END