A collaboration involving 80 scientists 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.”
The paper - “Basin-wide variation in tree hydraulic safety margins predicts the carbon balance of Amazon forests” - is published in the journal Nature.

Understand more about how the scientistst conducted the study – and the challenges of working deep in the rainforest.
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.