Brazil’s cerrado biome may store more carbon than the Amazon
The Amazon and other tropical forests are known for being the planet’s natural carbon reservoirs. As such, they are key allies in the fight against climate change.
A study published in the scientific journal New Phytologist in early March shows that wetlands in Brazil’s cerrado biome can store approximately 1,200 metric tons of carbon per hectare – up to six times more than the average density in the Amazon.
The study was led by researcher Larissa Verona, in partnership with scientists from the State University of Campinas (Unicamp), the Federal University of Minas Gerais (UFMG), the Cary Institute of Ecosystem Studies, in the US, the Max Planck Institute, in Germany, and the Rio de Janeiro Botanical Garden.
This is the first in-depth assessment of carbon stocks in the soils of these cerrado wetlands.
Researchers collected soil samples from depths of up to four meters. Previous studies were only able to examine surface layers – 20 cm to one meter deep – which led to results that underestimated total carbon by up to 95 percent.
Buildup
The analysis also showed that some of this carbon is extremely old. Radiocarbon dating tests indicate that the organic material present in these soils has an average age of about 11 thousand years, with records dating back more than 20 thousand years.
“This carbon took a long time to accumulate. If it is lost, we cannot quickly rebuild it, as is the case with a forest that can be replanted,” Larissa Verona said.
The cerrado is the second-largest biome in South America, covering about 26 percent of Brazil’s territory. In addition to being considered the most biodiverse savanna in the world, it is home to the headwaters of approximately two-thirds of Brazil’s major river basins, including systems that feed the Amazon river.
“Humid conditions of the wetlands cause a lack of oxygen, which slows down the decomposition of plants and other debris. As a result, organic matter accumulates over time and allows these environments to store large amounts of carbon,” expert Amy Zanne, co-author of the study, stated.
Climate risks
According to the researchers, the cerrado’s importance to the global climate is still underestimated.
“The cerrado’s enormous carbon stock is not usually included in climate calculations because, until recently, we didn’t know it was there,” Zanne pointed out.
The expansion of agriculture, the drainage of wetlands, and the withdrawal of water for irrigation are among the main threats. When the soil dries out, organic matter decomposes rapidly and turns into carbon dioxide and methane, gases known to cause global warming.
“If we start draining these peatlands and releasing this accumulated carbon, we’ll be unleashing carbon bombs into the atmosphere. It’s an amount of organic carbon previously unknown, covering a vast area and found in an unlikely biome,” Unicamp Professor Rafael Oliveira warned.
In addition, measurements taken by the team indicate that about 70 percent of the annual greenhouse gas emissions from these ecosystems occur during the dry season, a period when the soil loses moisture and decomposition accelerates.
With higher temperatures and longer dry periods, a larger portion of the carbon stored in the soil is likely to be released in the coming years.
Cerrado under pressure
The biome is already facing growing pressures from changes in land use. Large areas of the cerrado are being converted for agricultural production, often involving the drainage of wetlands.
The authors advocate for expanded protection of wetlands and greater recognition of their role in the climate. Even though Brazilian legislation already calls for protection of these environments, researchers estimate that up to half of these areas have already suffered some form of degradation.
“We call the cerrado a ‘sacrificial biome’ because Brazil wants to protect the Amazon, but it also wants to maintain agriculture. So, agribusiness ends up converting the cerrado for commodity production,” Larissa Verona argues.
“The cerrado is also crucial for its large long-term carbon stocks – and we need to fight to protect it.”
