A prescribed fire in oak savanna at Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota. Data from Cedar Creek was used in the new carbon-storage study.
Savannas and grasslands in drier climates around the world store more heat-trapping carbon than scientists thought they did and are helping to slow the rate of climate warming, according to a new study.
The study, published online Oct. 2 in Nature Climate Change, is based on a reanalysis of datasets from 53 long-term fire-manipulation experiments worldwide, as well as a field-sampling campaign at six of those sites.
A prescribed fire in oak savanna at Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota. Data from Cedar Creek was used in the new carbon-storage study.
An oak savanna that resulted from decades of prescribed burning at the Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota. Data from Cedar Creek was used in the new carbon-storage study.As a result, the climate-buffering impacts of dryland savannas have likely been underestimated, Reich said. The new study estimates that soils in savanna-grassland regions worldwide have gained 640 million metric tons of carbon over the past two decades.
"Ongoing declines in fire frequencies have probably created an extensive carbon sink in the soils of global drylands that may have been underestimated by ecosystem models,” Reich said. "In other words, in the past couple of decades, global savannas and grasslands have slowed climate warming more than they have accelerated it-despite fires. But there is absolutely no guarantee that will continue in the future.”
An oak savanna that resulted from decades of prescribed burning at the Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota. Data from Cedar Creek was used in the new carbon-storage study.Across 888,000 square miles (2.3 million square kilometers) of dryland savanna-grasslands, where fire frequency and burned area declined over the past two decades, soil carbon rose by an estimated 23%.
But in more humid savanna-grassland regions covering 533,000 square miles (1.38 million square kilometers), more frequent wildfires and increased burned area resulted in an estimated 25% loss in soil carbon over the past two decades.
The net change, during that time, was a gain of 0.64 petagrams, or 640 million metric tons, of soil carbon. That works out to a 0.038 petagram (38 million metric ton) increase per year.
"In the grand scheme of things, no, this is not really a massive amount of carbon that will put a dent in heat-trapping anthropogenic emissions,” Pellegrini said. "But no one region-neither the Amazon rainforest nor the U.S. Great Plains grasslands nor Canada’s boreal forest nor dozens of other biomes around the world-can alone store sufficient carbon to make a large contribution to slowing climate change. However, in aggregate, they can.
"Plus, there are several savanna and grassland regions that have soil carbon-credit projects being developed, so understanding their capacity to sequester carbon is relevant to the region-even if it’s not a massive flux globally.”
