Is the Amazon forest approaching a tipping point?

In the 21^st century, parts of the Amazonian forests could reach a tipping point. A new study in Nature by an international team of authors including Utrecht University's Arie Staal and Hans ter Steege reviews the state of knowledge about the possible transitions that the Amazon may undergo. The authors conclude that by 2050, between 10-47% of the forest will have become vulnerable to potentially irreversible local ecological changes.

Critical transition

Every day, trees in the forest pump enormous amounts of water (up to 500 litres by a single tree) from the soil into the atmosphere, which makes the air more humid. Winds in the Amazon carry moisture over the Amazon where it comes down as rain. Forests create rainfall, and rainfall maintains the forests, and it has been this way for the last 65 million years. Now, due to climate change and land-use change, the forest is at risk of a so-called critical transition.

A small disturbance may cause an abrupt shift in the ecosystem.

Shift in the ecosystem

The new study analysed different causes of water stress on Amazonian forests and found that global warming, regional rainfall conditions and accumulated deforestation may interact to accelerate forest loss. The authors also found potential ‘thresholds’ of those stressors. “At these thresholds, a small disturbance may cause an abrupt shift in the ecosystem,” Arie Staal explains.

After the threshold

What happens after those thresholds are reached? “In some cases, the forest may recover, but remains trapped in a degraded state, dominated by opportunistic plants, such as lianas or bamboos. In other cases, the forest does not recover anymore, trapped in an open-canopy, flammable state,” said first author Bernardo Flores of the Federal University of Santa Catharina in Brazil. The expansion of open, flammable ecosystems throughout the core of the Amazon forest is particularly concerning because they can spread fires to adjacent forests.

We need to take a precautionary approach that will keep forests resilient in the coming decades.

Keep the forest resilient

“The Amazon is a complex system, which makes it extremely challenging to predict how different forest types will respond to global changes. If we want to avoid a systemic transition, we need to take a precautionary approach that will keep forests resilient in the coming decades,” says Staal.

Local and global approach

That approach depends on a combination of local and global efforts. Locally, Amazonian countries need to cooperate to end deforestation and degradation and to expand restoration, which will strengthen the forest-rainfall feedback, as well as use ancient ecological knowledge of Indigenous peoples and local communities. Globally, all countries need to cooperate to stop greenhouse-gas emissions, thus mitigating the impacts of climate change. Both fronts are crucial to preserve the Amazon forest system for future generations.

Publication

Flores, B.M. et al. (2024) “Critical transitions in the Amazon forest system”, Nature 626, 555-564, DOI:10.1038/S41586-023-06970-0.