Degraded Amazonian peatlands are overlooked carbon source

Aguaje palms in degraded area, Loreto, Peru. Photo by Junior Raborg/CIFOR-ICRAF

Peru’s Amazonian palm swamp peatlands store large amounts of carbon, but the unsustainable harvesting of palm fruit causes degradation that increases carbon emissions. A new study by CIFOR-ICRAF scientists is the first to actually measure the carbon being lost from palm swamp peatlands, which will allow the country to calculate its greenhouse gas emissions more precisely.

“At an intact site, the soil is a sink,” said Kristell Hergoualc’h, a senior scientist with CIFOR’s Climate Change, Energy and Low-Carbon Development Team. “Under moderate degradation, the sink is suppressed by as much as 88 percent — the soil is not accumulating any more carbon because there are fewer palms and less leaf and root litter. Under heavy degradation, the soil of the palm swamp becomes a high source of carbon emissions to the atmosphere.”

Most of Peru’s Amazonian peatlands are palm swamps dominated by the Mauritia flexuosa palm, where leaf litter and decaying roots have built up over millennia deep layers of peat. To gather the fruit, however, harvesters usually cut down the palms, and over time, the palm swamp becomes degraded, eventually turning into a net source of emissions.

Combined emissions from vegetation and peat — as much as six tons of carbon per hectare annually in a moderately degraded swamp, and even more in a highly degraded site — were twice the amount that Hergoualc’h and her colleagues expected to find, and they make a big difference for the country’s carbon accounting. Unlike Southeast Asia, where peatlands are drained for agriculture, in the Peruvian Amazon degradation is more gradual. And while the country monitors deforestation, until now it had no way to calculate how much carbon was emitted from degraded peatlands.

“In the past, Peru has had to use emission factors based on studies of peatlands in Asia, but the ecosystems are different and the kinds of activity that are degrading the peatlands are different,” Hergoualc’h said. “Now Peru has these values and can use them for its national calculations, and we can compare emissions from the degradation of Amazonian peatlands with those in Southeast Asia.”

Palm swamps pass tipping point

In Peru’s flooded Amazonian lowlands, palm swamp peatlands naturally fluctuate between being carbon sinks and sources depending on rainfall and other climate conditions, but overall they are sinks, Hergoualc’h said. The study she headed, in a 500-hectare palm swamp at the edge of Iquitos, Peru’s largest Amazonian city, helped scientists understand both those natural fluxes and the impact of fruit harvesting.

The researchers compared intact swamp inside a protected area with two areas near villages. One of those areas had been heavily degraded by palm fruit harvesting and the other was moderately degraded. The scientists measured changes in the carbon stored in the peat and in the vegetation at the three sites over a five-year period.

Besides increasing emissions, they found that cutting palms to harvest the fruit has a cascade of impacts.

Cut trunks of M. flexuosa in a degraded palm swamp peatland. Photo by Kristell Hergoualch/CIFOR-ICRAF

The harvesters mainly cut down female palms to gather the fruit, though they also cut males to build roads to transport the fruit and to collect an edible grub that grows inside rotting trunks. That reduces the palms’ ability to reproduce and repopulate the swamp, as well as the food supply for animals that eat the fruit, she said.

Fewer palms mean less leaf and root litter, and therefore less peat buildup in the swamps — the intact site accumulated more than twice the amount of leaf litter as the highly degraded area. Cutting the palms allows more sunlight into the swamp, drying the soil, especially when water levels are low, and raising the temperature, which can also affect carbon emissions, Hergoualc’h said.

Sustainable harvesting needed

Removing the palms also changes the forest composition, as other tree species gradually move in.

The researchers saw this cascade firsthand, as the site that had been moderately disturbed became highly degraded within a few years after their study ended, and palm swamp virtually disappeared from the area that had been highly degraded at the start.

For a more detailed understanding of the combined impacts of climate and palm fruit harvesting on peatlands, Hergoualc’h hopes to expand the study beyond Peru’s Loreto region, where Iquitos is located, to the neighboring Ucayali region, which receives less rainfall during the dry season.

Besides quantifying carbon loss from degraded peatlands, she said, the study also points to the need for more sustainable harvesting techniques. In some communities, harvesters use harnesses to climb the palms and cut down the huge clusters of fruit, but that method is costlier than simply cutting the palm, and harvesters sometimes encounter poisonous snakes amid the fruit.

Newer climbing technology could help, along with more information for communities about the impacts of cutting down the palms and discussion with community members about how to manage the forests where they harvest palm fruit. Working with children, in schools and through social media, could also help change practices, Hergoualc’h said.

“It’s complex, because even in the same community, some people are very much aware and harvest sustainably, while others are less conscious of the impacts,” she added. “There’s a need for community members to understand the consequences and discuss the issue, but it’s a question of education as well.”

For more information on the topics discussed in this article, please contact Kristell Hergoualc’h at k.hergoualch@cgiar.org. 

This study was part of the Sustainable Wetlands Adaptation and Mitigation Program (SWAMP) and CIFOR’s Global Comparative Study on REDD+, and was conducted as part of the CGIAR Research Program on Forests, Trees and Agroforestry. It was supported by the government of the United States and the government of Norway.