Grasslands More Reliable Carbon Sink Than Trees
- Increased drought and wildfire risk make grasslands more reliable carbon sinks than trees
- Grasslands should be given opportunities in state’s cap-and-trade market as long-term investment
A study from the University of California, Davis, found that grasslands and rangelands are more resilient carbon sinks than forests in 21st century California. As such, the study indicates they should be given opportunities in the state’s cap-and-and trade market, which is designed to reduce California’s greenhouse gas emissions to 40 percent below 1990 levels by 2030.
The findings, published in the journal Environmental Research Letters, could inform similar carbon offset efforts around the globe, particularly those in semi-arid environments, which cover about 40 percent of the planet.
“Looking ahead, our model simulations show that grasslands store more carbon than forests because they are impacted less by droughts and wildfires,” said lead author Pawlok Dass, a postdoctoral scholar in Professor Benjamin Houlton’s lab at UC Davis. “This doesn’t even include the potential benefits of good land management to help boost soil health and increase carbon stocks in rangelands.”
“In a stable climate, trees store more carbon than grasslands,” said co-author Houlton, director of the John Muir Institute of the Environment at UC Davis. “But in a vulnerable, warming, drought-likely future, we could lose some of the most productive carbon sinks on the planet. California is on the frontlines of the extreme weather changes that are beginning to occur all over the world. We really need to start thinking about the vulnerability of ecosystem carbon, and use this information to de-risk our carbon investment and conservation strategies in the 21st century.”
The study ran model simulations of four scenarios:
- Global carbon emissions largely stop, resulting in up to 3.06 F (1.7 C) of warming by 2100
- Business as usual, in which carbon emissions continue at the current rate, leading to a temperature increase of up to 8.64 F (4.8 C) by 2100
- Periodic drought intervals, similar to La Niña/El Niño weather patterns
- Megadrought, which can last for a century or longer.
– Benjamin Houlton
As long as trees are part of the cap-and-trade portfolio, protecting that investment through strategies that would reduce severe wildfire and encourage drought-resistant trees, such as prescribed burns, strategic thinning and replanting, would likely reduce carbon losses, the authors note. But the study itself did not consider in its models forest management strategies that reduce wildfire threats.
Since 2010, about 130 million trees have died in California forests due to high tree densities combined with climate change, drought and bark beetle infestation, the U.S. Forest Service reports. Eight of the state’s 20 most destructive fires have occurred in the past four years, with the five largest fire seasons all occurring since 2006.
“Trees and forests in California are a national treasure and an ecological necessity,” Houlton said. “But when you put them in assuming they’re carbon sinks and trading them for pollution credits while they’re not behaving as carbon sinks, emissions may not decrease as much as we hope.”
The study was funded by the National Science Foundation.