# Esecaflor experiment: 25 years of induced drought in an Amazon plot cut biomass by nearly 50%

- Published: 2026-11-12 09:46 UTC
- Section: Planet › Ecology & recycling
- Tags: Esecaflor project, Amazon drought experiment, Caxiuanã National Forest, tree mortality, forest biomass loss, carbon dioxide storage, Nature Ecology & Evolution, rainfall exclusion
- URL: https://realtech.media/news/rt-069ff842e721787ea98b5232_esecaflor_experiment_25/

**In Pará, Brazil, a forest plot has received about half its rainfall since 2001. After large trees died, smaller ones began growing again, the researchers report.**

![Esecaflor experiment: 25 years of induced drought in an Amazon plot cut biomass by nearly 50%](https://realtech.media/media/2026/11/d75ade51b3981ace.jpg)
*news.mongabay.com*

Researchers of the Esecaflor project (Forest Drought Study Project) have summarized a field experiment in Caxiuanã National Forest in Pará, northern Brazil, where a one-hectare forest plot has been kept under water stress since 2001, according to doi.org [1]. The British and Brazilian authors published their latest paper in May 2025 in Nature Ecology & Evolution. The project is described as the longest-running and most extensive investigation of its kind in a tropical forest [1].

## Experiment design

The plot lies within roughly 318,000 hectares of the national forest. Under the canopy, 1 to 4 meters above the ground, the team installed 6,000 transparent plastic panels that divert about 50% of rainwater away through gutters and channels [1]. An undisturbed plot of equal size serves as a comparison. In both plots, researchers monitor soil moisture, air temperature, tree growth, sap flow and root development. Two 40-meter towers with NASA radar transmit data to the Jet Propulsion Laboratory in California for processing [1].

The plan took shape at a 1998 meeting in Belém of Patrick Meir (University of Edinburgh), Antonio Lôla da Costa (Federal University of Pará) and Samuel de Almeida (Emílio Goeldi Paraense Museum). According to Meir, computer models already pointed to widespread tree die-offs, but forecasts of the Amazon's response to prolonged drought remained uncertain [1]. Funding was initially for three years. Since then, Lôla da Costa says, the group has published more than a hundred international papers.

## Timeline of changes

According to Lôla da Costa, nothing happened in the first three years because of the forest's moisture reserves. After five years, tree mortality began, especially among trees with trunks thicker than 50 centimeters. After eight years, 40% of total biomass was lost [1]. Biomass loss peaked in the 15th year. By 2024, with the large trees gone, nearly 50% of biomass had been lost, but the small amount of available water was enough for the smaller trees to redistribute it. Mortality reversed and they started growing again [1].

Over 25 years the plot became a shorter, less dense forest, with biomass loss in leaves, branches, trunks and roots and a reduced capacity to store carbon dioxide. By redistributing the limited soil water, it reached a new eco-hydrological stability [1].

Lucy Rowland of the University of Exeter notes that the reason large trees are more vulnerable remains an open question. The team first assumed their vessels were more prone to embolism. She now considers it more likely that taller crowns are more exposed to a hotter, drier atmosphere. Unlike the experiment, natural drought acts through both soil and atmosphere. Rowland says the plot is still a degraded tropical forest and objects to calling it "savanna" [1].

## Sources

1. [doi.org](https://doi.org/10.66709/news-335633)
2. [news.mongabay.com](https://news.mongabay.com/2026/11/how-would-the-amazon-react-if-it-dried-up-a-25-year-old-field-study-has-the-answer)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-069ff842e721787ea98b5232_esecaflor_experiment_25/