新澳门六合彩内幕信息

Grasslands More Reliable Carbon Sink Than Trees

In Wildfire-Prone California, Grasslands a Less Vulnerable Carbon Offset Than Forests

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California grassland
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Quick Summary

  • 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

Forests have long served as a critical carbon sink, consuming about a quarter of the carbon dioxide pollution produced by humans worldwide. But decades of fire suppression, warming temperatures and drought have increased wildfire risks 鈥 turning California鈥檚 forests from carbon sinks to carbon sources.

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鈥檚 cap-and-and trade market, which is designed to reduce California鈥檚 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. 

鈥淟ooking ahead, our model simulations show that grasslands store more carbon than forests because they are impacted less by droughts and wildfires,鈥 said lead author Pawlok Dass, a postdoctoral scholar in Professor Benjamin Houlton鈥檚 lab at 新澳门六合彩内幕信息 Davis. 鈥淭his doesn鈥檛 even include the potential benefits of good land management to help boost soil health and increase carbon stocks in rangelands.鈥

sheep ranchers in California
Sheep from Skyelark Ranch graze a field planted with a cover crop in Brooks, California. (Joe Proudman/新澳门六合彩内幕信息 Davis)

Carbon up in smoke

Unlike forests, grasslands sequester most of their carbon underground, while forests store it mostly in woody biomass and leaves. When wildfires cause trees to go up in flames, the burned carbon they formerly stored is released back to the atmosphere. When fire burns grasslands, however, the carbon fixed underground tends to stay in the roots and soil, making them more adaptive to climate change.

鈥淚n a stable climate, trees store more carbon than grasslands,鈥 said co-author Houlton, director of the John Muir Institute of the Environment at 新澳门六合彩内幕信息 Davis. 鈥淏ut 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.鈥

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 Ni帽a/El Ni帽o weather patterns
  • Megadrought, which can last for a century or longer.
California climate map
Study Figure 1: Grassland (A) and forest (B) retreat or expansion in response to 21st century climate changes. Blue indicates expansion; red indicates contraction. Forests retreat in all future climates except those associated with aggressive emissions reductions (RCP 2.6) 

The only scenario where California鈥檚 trees were more reliable carbon sinks than grasslands was the first one, which requires even more aggressive global greenhouse gas reductions than the Paris Climate Agreement. The current path of global carbon emissions reveals grasslands as the only viable net carbon dioxide sink through 2101. And grasslands continue to store some carbon even during extreme drought simulations.

Grassland carbon solutions

The model results can help guide 鈥渃limate-smart鈥 options for maintaining carbon sinks in natural and working lands in California. Ranchers are beginning to use nnovative management approaches to improve carbon storage, which can further boost the ability of grasslands to store carbon in the future.

Trees are still critical

The study does not suggest that grasslands should replace forests on the landscape or diminish the many other benefits of trees. Rather, it indicates that, from a cap-and-trade, carbon-offset perspective, conserving grasslands and promoting rangeland practices that promote reliable rates of carbon sequestration could help more readily meet the state鈥檚 emission-reduction goals.

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鈥檚 20 most destructive fires have occurred in the past four years, with the five largest fire seasons all occurring since 2006.

鈥淭rees and forests in California are a national treasure and an ecological necessity,鈥 Houlton said. 鈥淏ut when you put them in assuming they鈥檙e carbon sinks and trading them for pollution credits while they鈥檙e not behaving as carbon sinks, emissions may not decrease as much as we hope.鈥

The study was funded by the National Science Foundation.

 

Media Resources

Pawlok Dass, 新澳门六合彩内幕信息 Davis Land, Air and Water Resources, 413-801-6133, dass@ucdavis.edu

Benjamin Houlton, 新澳门六合彩内幕信息 Davis Land, Air and Water Resources, 530-752-2210, bzhoulton@ucdavis.edu

Kat Kerlin, 新澳门六合彩内幕信息 Davis News and Media Relations, 530-750-9195, kekerlin@ucdavis.edu

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