Project Esecaflor Tests Amazon Rainforest Drought Resistance in Caxiuanã National Forest
The Amazon rainforest can adjust to long-term experimental drought conditions through structural changes and eco-hydrological stability, according to a study published in Nature Ecology & Evolution. The research, which forms part of the ongoing Project Esecaflor in Brazil’s Pará state, demonstrates that the world’s largest tropical rainforest manages to redistribute scarce soil water even when subjected to prolonged artificial water stress. Project Esecaflor (Projeto de Estudo da Seca Florestal) is the longest-running and most extensive scientific investigation of its kind ever conducted in a tropical forest.
Establishing the Caxiuanã Drought Experiment in 2001
The long-term investigation began in 2001 within a one-hectare plot inside the Caxiuanã National Forest, which comprises about 318 thousand hectares. To simulate severe drought conditions, researchers installed 6,000 rectangular and transparent plastic panels beneath the forest canopy, positioned between one and four meters above the ground. These panels diverted roughly 50 percent of incoming rainfall away from the experimental plot using gutters and channels. A neighboring plot of identical size was left untouched to serve as a direct scientific control. Teams continuously track soil moisture, air temperature, tree growth, sap flow, and root development across both parcels.
Origins of the Longest-Running Forest Stress Study
Meir stated, I knew there was a huge gap in understanding the functioning of this sensitivity, and we wondered if there was a risk of widespread tree mortality increasing with future climate change. Meir noted that computer models at the time predicted widespread tree mortality from climate change, but empirical data regarding forest-scale drought response remained sparse. Meir added, We needed a new type of experiment that explored drought response at the forest scale, as well as in leaves, branches, or individual trees. This was the new science we developed over the past quarter of a century, to help understand the difficult question of the Amazon tipping point. Funding initially covered just a three-year window, but the initiative expanded into a 25-year endeavor. The project has generated more than 100 international scientific papers and supported the completion of over 100 graduate degrees, including doctorates, postdoctoral research, and master’s degrees.
Structural Shifts and Biomass Reduction Over Two Decades
Decades of intense competition for limited soil moisture have fundamentally altered the plant communities within the Esecaflor plot. The experimental area evolved into a shorter, less dense forest characterized by a net loss of biomass—including leaves, branches, trunks, and roots—alongside a diminished capacity to store carbon dioxide. Antonio Lôla da Costa explained that instruments measure individual tree growth every 15 minutes, noting that monitoring tree pulses functions similarly to an electrocardiogram. When trees experience severe stress, the recorded pulse slows down significantly, whereas a flatline indicates mortality. Lôla da Costa further observed, It is a living being that breathes, that feels. Only it doesn’t know how to run, it doesn’t leave its place. If they disappear, all of us on planet Earth will go together.
Despite these structural declines, the surviving vegetation achieved a new baseline of eco-hydrological stability by optimizing water usage under stress.
Forest Resilience Contrasts with Human Deforestation
Lôla da Costa noted during field observations, Every day, when we travel there to our forest, we pass barge after barge loaded with timber logs.
He contrasted the research with external pressures, stating, Esecaflor is a controlled experiment of soil drought, very different from the major fires and generalized deforestation that humans inflict on nature.
The forest will not collapse if we know how to manage it.
But if you go there with a machine and destroy 100, 200, 300 hectares in a day, then it will never react.
While the controlled drought experiment reveals a high degree of local resilience, project coordinators emphasize that these adaptive capacities have clear limits when compared to widespread human-driven deforestation and mechanized clear-cutting. Whether the Amazon can indefinitely sustain continuous climate pressures without crossing a critical tipping point remains unquantified as field observations enter their second quarter-century.
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