The fire-damaged Brazilian Amazon forests are still about 2.6°C (4.7°F) higher than adjacent intact or selective logged stands, and the extra heat can last for at least 30 years. The results show that fires change tropical forests in ways that slow their recovery and may weaken their ability to tolerate climate stress and store carbon, a crucial role these forests play in global climate mitigation.
The study was published today in the journal Journal of Environmental Research.
“We found that combustion has a significant ecological impact on large time scales, and the risk of regeneration is greater or does not occur at all.” Research scientist at NASA Ames Research Center, Colombia’s Ecology, Evolution and Environmental Biology (E3B) program. (Cooley was co-advised by Duncan Menge and Ruth DeFries, professor and co-founded dean of the Columbia Climate School.)
Unlike ecosystems that adapt to fires such as fire forests or pine forests, Amazon rainforests evolved under rare wet conditions. As a result, many tropical tree species have not developed characteristics that can be tolerated or recovered from fire damage.
In addition to average hotter, forests in the study area were more unstable. They fluctuate more daily temperatures than selectively recorded or intact forests and are more likely to cross physiological thresholds that impair tree function. During the peak of the dry season, in leaves exposed to sunlight in burnt forests, breathing loses more energy than is obtained from photosynthesis, while selectively recorded or complete stands are 72-74%.
Burned forests are also 10 times more likely to cross the threshold for lasting damage.
Shows the warmest patch (top quartile).
These temperature differences reflect fundamental changes in forest structures that make burning areas more susceptible to heat. Thin the upper canopy, removing neutralization of the lower vegetation, reducing leaf area, reducing shadows, and usually cooling the transpiration of forests. Less leaves allow sunlight to heat exposed surfaces and air near the canopy. Burning also creates edges next to clean the land, allowing warmer air to move inward. The forest retains this extra heat until its vegetation layer is rebuilt, a process that can take decades.
The study shows that fires are the main driver of prolonged heat stress in degraded Amazon forests. In the area where the selective login, the canopy is mostly intact and the temperature is similar to that of the undisturbed forest. This contrast highlights the prevention of fire protection and low-impact logging as a key strategy for maintaining the health of tropical forests.
Insights from space
The study is based on satellite imagery from the city of Feliz Natal in Brazil’s deforestation arc, a region in the southeast of the Amazon, where fire and logging have accelerated since the 1980s. The researchers used integrated satellite observations to conduct the first systematic thermal comparison of the area’s combustion, selectively documented and complete forests. They combined three-year land surface temperature data from NASA’s Ecostress instrument with 3D canopy structure data from the GEDI LIDAR mission, an analysis that attracted more than 6,700 matching observations collected during the Amazon dry season.
Using the hierarchical model, the team integrated temperature and structural data to track the frequency of sunlight leaves exceeds the threshold for photosynthesis deceleration or tissue damage. Since the interference, they will take into account canopy height and time, and they reconstruct the long-term thermal recovery of the entire forest layer. The result is a unique, blade-level field of view on how long the thermal stress lasts after interference and how forest structures affect thermal vulnerability.
Hidden heat reveals new risks of recovery and elasticity
These findings provide nuances for understanding how climate policy addresses tropical forest degradation. Carbon mitigation and forest restoration strategies often view degraded forests as a single category. However, the study shows that fires have longer thermal effects that are not detectable by traditional optical satellite images. In optical satellite images, forests may cause fire damage, but many people still experience elevated heat stress.
The difference is important because tropical forests remove a lot of carbon dioxide from the atmosphere every year and are a key component of global recovery and offset plans. If forests have been damaged by fires for decades, the carbon benefits of passive regeneration may be exaggerated. Combining physiological thermal data allows for a more realistic assessment of forest function in climate strategies.
Although the discovery highlights the challenges, Curly says meaningful actions are possible.
“Degraded tropical ecosystems, especially burning forests, are experiencing thermal stress,” she said. “However, there are many things we can do to minimize the damage to biodiversity and the damage to species that are under this pressure – both in forest management, by helping reduce fires in the Amazon and fires in carbon mitigation, continuing to reduce emissions actively and rapidly and transition to a sustainable and clean energy economy.”
The study’s co-authors were Duncan NL Menge of Columbia University; Michael Keller, USDA Forest Service and NASA Jet Propulsion Laboratory; NASA Jet Propulsion Laboratory Kerry Cawse-Nicholson; Lawrence Berkeley National Laboratory Marcos Longo; André P. Vinicius Silgueiro and Raquel Carvalho, Instituto Centro de Vida; Wake Forest University Ovidiu Csillik; Doug Anderson, Micah Gilbreath and Paul Duffy, Neptune and Company, Inc.; and Marcos ADAMI
