Burned Amazon rainforest areas remain hot and stressed for decades

The damage caused by fires in the Brazilian Amazon isn't just immediately visible. According to the results of a study published in Environmental Research Letters , areas of the Amazon forest damaged by fires remain about 2.6°C warmer than surrounding areas that are intact or subject to controlled logging. And this effect can last for decades, with temperatures dropping by only 1.2°C in the 30 years following the event. This makes damaged forests much more vulnerable, for example, to the consequences of climate change . "We're finding that fires have significant ecological impacts over very long timescales, and that regeneration is much more at risk: it's slower or doesn't happen at all," explains Savannah Cooley , who holds a PhD in Ecology, Evolution, and Environmental Biology from Columbia University (USA), and is the study's lead author and a researcher at NASA Ames Research Center. The study's authors specifically analyzed an area of the Brazilian Amazon rainforest known as the "Arc of Deforestation," which has been the site of deforestation and fires in recent decades. The researchers explain that it now represents an ideal case study because it is essentially a mosaic of intact, burned, deforested, and regenerating areas.

The research was conducted by combining data on Earth's surface temperature obtained through NASA's Ecostress instrument with data collected by the GEDI (Global Ecosystem Dynamics Investigation) lidar mission. The latter is essentially designed to produce high-resolution images of the Earth's three-dimensional structure and to scan from above the state of forests, especially the canopies , whose integrity is crucial for controlling temperatures in these areas. In addition to being warmer on average, burned forest areas within the Deforestation Arc were also found to be more thermally unstable. Compared to intact areas or those subject to controlled logging, those that have experienced fires in the past show greater temperature fluctuations throughout the day and are also more likely to exceed physiological thresholds that compromise the trees' functionality. For example, during the peak heat of the dry season, nearly 87% of sunlight-exposed leaves in burned forests would reach temperatures where cellular respiration prevails over photosynthesis (where plants burn more energy reserves than they store), compared to 72-74% in logged or intact forest areas.

Furthermore, in areas that have been affected by past fires, the probability of leaf temperatures exceeding the threshold for permanent damage was found to be ten times higher . This is because fires completely change the structure of the forest , thinning the canopy, clearing the undergrowth, and reducing the leaf surface area, which is the basis of the two main cooling mechanisms of plants (shade and transpiration). In contrast, the researchers explain, in areas subjected to controlled logging and where the integrity of the canopy was maintained, temperatures were similar to those recorded in intact forests. "Degraded tropical ecosystems, particularly burned forests, are experiencing thermal stress," Cooley concludes. "But we can do a lot to minimize the damage to biodiversity and the species that are experiencing this stress, both in terms of forest management, helping to reduce fires in the Amazon, and in terms of carbon mitigation, continuing to aggressively and rapidly reduce emissions and transitioning to a sustainable and clean energy economy."