What Are the Consequences of a Drying Amazon Rainforest? Insights from Decades of Research

Caxiana National Forest, Brazil (AP) – A brief stroll beneath the thick Amazon canopy suddenly reveals a clearing in the forest. The logs lie decayed, trees become less frequent, the temperature climbs, and sunlight spills onto the ground. This is the visual representation of 24 years of severe drought in the world’s most extensive rainforest.

Yet, this degraded section of the forest, about the size of a soccer field, serves as a scientific experiment initiated in 2000 by Brazilian and British scientists. esecaflor – an abbreviation for “Forest Drought Research Project” in Portuguese – aims to portray a future where shifting climates could diminish the Amazon’s rainfall. It’s the longest-running project of its kind in the world, providing a wealth of academic insights ranging from meteorology to ecology and physiology.

Comprehending drought’s impact on the Amazon, which spans multiple South American countries and is twice the size of India, is crucial beyond this area. Rainforests capture vast amounts of carbon dioxide, a greenhouse gas significantly contributing to climate change. According to one study, the Amazon stores carbon equivalent to global emissions from the last two years, primarily generated by burning coal, oil, and gasoline. When trees perish due to drought or deforestation, the carbon stored within them is released into the atmosphere, further exacerbating global warming.

Simulating drought conditions and observing the outcomes

To replicate drought stress, the project Kakshiana National Forest assembled around 6,000 clear plastic panels over a hectare (2.5 acres) to bypass approximately 50% of the rainfall reaching the forest floor. These panels were positioned one meter (3.3 feet) above the ground, with water drained into ditches and channeled through trenches built around the plot.

Adjacent to this, a control plot remained untouched. In both settings, instruments were attached to trees, placed on the ground, and buried to assess soil moisture, air temperature, tree growth, sap flow, and root development. Each plot is monitored by two metal towers.

At each tower, NASA radar measures water content in the plants, aiding researchers in evaluating overall forest stress. The collected data is transmitted to the Jet Propulsion Laboratory in California for processing.

“Initially, the forests appeared drought-tolerant,” stated Lucy Roland, an ecology professor at the University of Exeter.

However, about eight years into the project, notable declines in biomass and significant mortality of larger trees were observed, according to Roland.

This led to a striking loss of around 40% of the vegetation’s total weight and the carbon it had sequestered. Detailed findings from the primary survey can be reviewed in the study published in Nature Ecology & Evolution in May, indicating that throughout vegetation years, the rainforest transitioned from being a carbon sink to emitting carbon before stabilizing.

However, there is some positive news: the rainforest has not transitioned into savannas or extensive grasslands due to prolonged drought.

Next steps involve measuring forest recovery

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