Earth Sciences

In Brazil’s Amazon, indigenous-managed woods absorb thousands of harmful contaminants from wildfires.

According to new research that was just published in Communications Earth and Environment, the Amazon rainforest and its indigenous territories can absorb up to 26,000 metric tons of harmful pollutants each year that are released by fires, preventing thousands of cases of deadly respiratory and cardiovascular diseases and drastically lowering health care costs in some of the most deforested cities in the area.

The new study’s authors analyzed ten years’ worth of data and discovered that each hectare of burned forest costs cities at least US$2 million in medical expenses for treating related illnesses. However, they also demonstrated that Indigenous forests, by absorbing pollutants from the fires, avoid an estimated 15 million cases of respiratory and cardiovascular disease annually, saving the healthcare system US$2 billion.

The study also reveals that densely forested Indigenous lands are defending urban and rural populations, frequently on the opposite bank of the Amazon, in the “arc of deforestation,” the area of the rainforest’s southeast where agroindustry and other legal and illegal activities have caused the most loss of forest cover.

“Forests are known around the world for absorbing pollutants from fires through pores on the surface of the leaves, but this is the first time we have estimated the capacity of tropical forests to do so,”

Dr. Paula Prist, senior research scientist at the EcoHealth Alliance and lead author on the study.

We have never calculated the capacity of tropical forests to do this, according to Dr. Paula Prist, senior research scientist at the EcoHealth Alliance and the study’s lead author. “Forests are known for absorbing pollutants from fires through pores on the surface of the leaves,” she said. Our findings show that the Amazon rainforest can take in up to 26,000 metric tons of particles annually, with Indigenous territories taking in 22% of this amount while occupying only 12% of the rainforest.”.

The findings, which were made public just days before President Lula completes his first 100 days in office, may give the Brazilian leader’s pledge to recognize and uphold Indigenous peoples’ land rights—which have already been shown to play a significant role in reducing deforestation and biodiversity loss in the Amazon—more urgency.

“Science has demonstrated that Indigenous-managed forests experience less of the deforestation that fuels climate change and pandemic risk, but this is the first effort to quantify how they benefit human and economic health, indicating that the benefits go far beyond the borders of these territories,” said Dr. Florencia Sangermano, a co-author of the new study and an expert in the use of geospatial analysis and satellite remote sensing to assess changes in the Earth system.

The research team, which included members from Clark University, EcoHealth Alliance, George Mason University, the National Autonomous University of Mexico, and the University of Sao Paulo, concentrated their analysis on the Brazilian Legal Amazon, an area that comprises 722 towns and cities and accounts for more than half of the country of Brazil. The area becomes “among the most polluted places on Earth” during the fire season, which lasts from the end of July to November, according to Prist and her co-authors.

90 percent of the particulate matter released by fires worldwide, including those in the Amazon basin, is caused by forest fires in tropical forest nations. Additionally, the Amazon’s evergreen broadleaf forests are more likely than forests in other biomes to release black and organic carbonaceous aerosols, which are the main elements of fine particulate matter and are thought to be a contributing factor to the region’s rising rates of respiratory and cardiovascular diseases.

The Amazon burned 519,000 hectares of forest between May 19 and October 31, 2021, with Brazil losing the most forest cover. According to Prist, the number of fires has been rising in recent years. And in the Brazilian Amazon in 2020, deforestation rates climbed to their highest levels in a decade.

Other studies have demonstrated how Indigenous land stewardship prevents large tracts of forest from burning, leading them to draw the conclusion that Amazon forests shield nearby communities and prevent smoke damage. The new study goes even further. The authors came to the conclusion that indigenous territories are providing health and economic benefits to populations that may be as far away as 500 kilometers from where the fires are burning, taking into account the ability of the pollutants to travel long distances and the capacity of the rainforest to absorb them.

In order to protect Indigenous peoples and their forests for the sake of public health, Prist said, “Our results suggest there is a need to act now—in advance of the fire season.”. Failure to acknowledge and uphold the land rights of Indigenous peoples in the Amazon could result in the deforestation of their lands, a rise in the number of infections reported, as well as a significant increase in health care costs, particularly in already deforested areas.

In the Brazilian Legal Amazon, which spans more than 1,160,000 square kilometers, there are currently 383 recognized indigenous territories. The new study discovered that only five territories, mostly in the heavily forested western region of the Brazilian Amazon, account for 8% of the rainforest’s capacity to absorb particles from forest fires.

The scientists linked two million cases of respiratory and cardiovascular disease to an estimated 1 point 7 metric tons of particles released every year by fires during the dry season, which typically starts in late July. This suggests that harming the rainforest could result in a far greater number of pollutants and higher rates of disease.

The scientists relied solely on satellite data to quantify emissions from fires, which are frequently started intentionally to illegally clear land for crops or pasture because they lack precise meteorological data.

The researchers made assumptions based on studies conducted in temperate regions rather than measuring the actual removal rates of the rainforest; instead, they estimated the Amazon’s ability to absorb the particles that fires emit during the dry season.

Sangermano, an assistant professor of geography at Clark University, said, “Despite the difficulties, we were able to assess the contribution of the Amazon forest and the Indigenous territories to the maintenance of human health and the economic benefits that its conservation can bring. Because there are no calculations for the pollutant absorption rates of tropical trees, our numbers most likely understate the ecosystem services offered by the Amazon rainforest and its Indigenous territories.”.

More information: Paula R. Prist, Protecting Brazilian Amazon Indigenous territories reduces atmospheric particulates and avoids associated health impacts and costs, Communications Earth & Environment (2023). DOI: 10.1038/

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