Amazon rainforest adapts to long-term drought, but loses important carbon storage

Scientists have found surprising evidence that Amazon rainforests can survive long-term drought conditions, but pay a huge price for their carbon storage capacity and structure.

In a 22-year experiment, the researchers found that after losing more than one-third of biomass in the initial 15-year “transitional phase”, forests achieved “ecological flow-water stability” and that surviving trees no longer suffered from drought stress. This discovery, published in natural ecology and evolution, provides important insights into how the planet’s largest rainforest might respond to climate change, which has brought people to a resilience of a total collapse, but warns of substantial carbon losses that could accelerate global warming.

The study, led by researchers from the University of Edinburgh and researchers from the Federative University of Brazil, represents the world’s longest rainforest drought experiment. Since 2002, by transferring about 50% of rainfall to a hectare of forest land, scientists have created conditions that simulate long-term droughts, and many climate models have predicted many climate models in the Amazon.

Forest transformation rather than collapse under long-term drought

For decades, scientists have feared that the Amazon drought increase could trigger a catastrophic “cutting point” that transforms lush rainforests into Savannah. This experiment provides evidence of more subtle results for the results.

“While some rainforests may be able to survive long-term droughts caused by climate change, their capacity as important carbon stores and carbon sinks may be greatly reduced.”

During the first 15 years of experimental drought, the forest lost about 85 meg of carbon per hectare, a 34% reduction from the initial biomass. This loss disproportionately affects the largest trees, which is crucial for carbon storage and ecosystem functions.

But something unexpected happened next. Forests did not continue to decline in the next seven years, but instead were about 164 megacities of carbon per hectare. This biomass level is still higher than that of the savanna (49 MGRAM) and is closer to the tropical dry forest (125 MGRAM).

After the forest is sparse, the trees reach “hydraulic steady state”

The team found that surviving trees showed significant adaptability to dry conditions. By 2023 (two decades of experimentation), trees in arid plots exhibit similar levels of hydraulic stress as trees in controlled plots, despite half the rainfall.

How did this happen? As the forest loses trees during the transitional phase, the rest of the trees gain more water per unit of biomass water, which researchers call “the availability of biomass relative to water.” This ecological adjustment allows surviving trees to maintain healthy transpiration rates and tissue water content even in dry seasons.

This surprising discovery contradicts the concern that drought can lead to ecosystem collapse. Instead, the forest undergoes structural reorganization, transitioning to a more open canopy, with fewer large trees but still maintaining its forest characteristics.

Major carbon losses before stability

This adaptable ecological price is very high. This experiment reveals several key changes in forest carbon dynamics:

• Loss of 34% of initial forest biomass (85 megawatts per hectare)
• Disproportionate mortality among the largest trees
• Forests transition from carbon source to carbon sink during transition phase
• Carbon accumulation in stable forests remains lower than undisturbed rainforests
• Structural changes lead to more open canopies, while fewer emerging trees

“Although it prevents drought-induced collapse, ecological flow theory stabilizes forests reduce biomass and carbon accumulation in wood,” the researchers noted in the paper. If this pattern occurs in much of the Amazon, it will release a large amount of stored carbon into the atmosphere and possibly accelerate climate change.

Impact on Amazon’s future under climate change

What do these findings mean for the larger Amazon Basin, which stores about 123 billion tons of carbon in trees and plays a crucial role in regulating the Earth’s climate?

The researchers warned that their experiments simulated soil drought in only a small area. Real-world climate change may bring more stressors, including higher temperatures, increased atmospheric dryness, stronger winds and more frequent fires. Before stabilization, the combined effect may result in more severe or longer biomass loss.

“Ecological responses to climate can have a big impact on our local and global environments; without such long-term collaborative research, we would not be able to understand and predict them.”

However, the study is cautious about the basic resilience of Amazon. Instead of experiencing “ecosystem collapse,” forests appear to be able to transition to alternative stable states, albeit with significantly less biomass.

As climate change intensifies and parts of the Amazon become more frequent and severe droughts, the study provides vital insights into how this key ecosystem can change in the decades to come. While Amazon may avoid the worst of converting to Savanna completely, the huge carbon loss during its adaptation phase could have far-reaching impacts on global climate goals and the fight against climate change.