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In northwest Montana’s Swan Valley, about 100 small logs about 10 feet long are neatly stacked, surrounded by berry bushes, some white wildflowers and towering larch trees. Surrounding the logs are acres of U.S. Forest Service land that was thinned last year of dead, fallen and dense understory trees to reduce wildfire risk. The remaining piles of logs are too small to be processed into lumber, and the sawmill off the highway recently closed. Therefore, if the price is right, the wood may be sent to the pulp mill. Or it could have been in the forest for many years. Smaller limbs may be burned in a prescribed fire. But Ning Zeng, a climate scientist at the University of Maryland, is also assessing the issues. He saw another solution: bury the logs underground, along with all the planet-heating gases they release.
That’s the idea behind a carbon-sequestration technology called wood vaulting. Forests across much of the American West are overgrown with tangled trees and brush that threaten to burn. The Forest Service’s wildfire crisis strategy calls for clearing up to 50 million acres of excess vegetation on federal, state, tribal and private lands by 2032. The amount of flammable vegetation the agency will have to deal with in the coming years – estimated at 2.2 billion tons. This is roughly equivalent to the amount of carbon dioxide emitted by global cement production in 2016, and the amount of carbon dioxide emitted by the world’s forests that disappeared from the atmosphere last year.
“There’s more wood in the forest than there are markets for it,” said Nate Anderson, a research forester who studies product supply chains for the Forest Service’s Rocky Mountain Research Station in Missoula. Assessing the carbon stored in wood vaults could change that.
If done properly, burying debris may help limit the release of contaminants Greenhouse gases Warming the atmosphere and contributing to climate change. “I think it could actually be done at a pretty large scale, sequestering millions of tons of carbon dioxide per year, just in the U.S. alone,” said Sinéad Crotty, director of the nonprofit Carbon Containment Laboratory, a U.S.-based research institute at the University of California. Daniel Sanchez, a professor at Berkeley who studies carbon dioxide removal, agrees. “Wood arches are an emerging method that we believe are relatively low cost and relatively scalable,” he said.
Investors including Bill Gates have poured millions of dollars into startup coffers in recent years. Several smaller sites are under construction across the country, including in Maryland, Nevada, Texas and Colorado. The Department of Energy recently awarded $50,000 to two companies, including Zeng’s Carbon Lockdown Project, to build a wooden vault in Montana, one of many funded carbon dioxide removal (CDR) pilot projects. According to the 2023 Intergovernmental Panel on Climate Change synthesis report, CDR technologies (including direct air capture technology, land-based carbon sinks, etc.) are an “inevitable” component in limiting warming to 1.5 or even 2 degrees Celsius, and experts say that if This is necessary if we are to avoid the irreversible effects of climate change.
Wood vaulting is simple in concept: Use a backhoe to dig a hole and bury small trees, woody debris and other plant material that isn’t large enough or valuable enough to sell. The vaults are like a layer cake of trees, with the gaps filled with dirt, more trees piled on top, and finally covered with a layer of frosty topsoil.
Once a company acquires biomass, not just any hole will do. The intrusion of water, oxygen, and even termites may promote decomposition of the vault, thus compromising the durability of the vault. It is considered best practice to excavate vaults in clay or silty soils away from groundwater. (Some alternatives actually completely submerge the wood in water, but this is less common.) Conditions within the vault must remain stable – preferably permanently, without human intervention – for the project to live up to its promise. The same types of sensors already used in landfills can be installed to monitor oxygen, humidity and more Methane levels over time.
Digging a hole 15 to 25 feet deep could mean disturbing the soil, destroying habitat, or removing nutrients from the landscape—all potential drawbacks of wood arches—so companies are considering using already degraded sites, such as old Industrial sites or mines. (Some also plan to rehabilitate wood vault sites after the trees are buried, planting native seeds in the soil for pollinators to roost or graze.) Wood vaults are ideally located close to their biomass sources, which reduces transportation emissions and logistics . Other key factors are enough labor to transport the biomass and build the vaults, plus some kind of protection so they don’t get dug up for decades.
Another concern about timber vaults is that it may stimulate unnecessary logging. But so far, the industry has focused on burying leftovers from wildfire risk reduction treatments, as well as trees that have burned or been removed from urban environments as hazardous trees. Guidelines for Stripe Inc.’s Frontier Fund, one of the leading funds that buy CO2 emissions reduction credits from startups, recommend using leftovers from wildfire risk reduction projects as a sustainable source.
The science of understanding how long these vaults can keep carbon dioxide out of the atmosphere is still ongoing. “We want to be as clear-eyed as possible when making any promises about durability,” Crotty said. Sanchez believes that if done correctly, the vaults might be able to store carbon dioxide for hundreds to thousands of years. Figures shared by the company range from more than 100 years to more than 1,000 years.
While it’s difficult to say exactly how long wooden vaults can store carbon, previous findings provide clues. A bulldozer at the Carbon Lockup Project’s Canadian construction site discovered a red cedar log buried deep in the soil; it is still preserved in Mr. Zeng’s office. Further analysis, which has not yet been published in a peer-reviewed journal, confirmed it was 3,000 years old but had lost only 5 percent of its carbon, he said.
Another way to analyze the potential of wooden vaults is to compare the amount of carbon they can store with other, more established technologies. Wood vaults have a higher carbon yield than biochar, a charcoal-style soil amendment derived from partially burned organic material. Sanchez said biochar can retain about 30% of the original carbon in its biomass, while wooden vaults are thought to store more than 90%.
Read next: Biochar is a ‘ready to go’ climate technology, but can it be scaled up?
Wooden arches are also quite cheap compared to other methods. Calculations at one of Zeng’s test sites found the cost per ton of CO2 to be $105, mostly in transportation costs. For comparison, the average cost of biochar california At $400 per ton of CO2, direct carbon capture technology could cost Between $600 and $1,000 per ton of CO2. “This is the transformative aspect of this idea compared to many other biomass utilization strategies,” Zeng said. “It’s going to come down to economics.”
Several companies are currently experimenting with wooden vaults, mostly on private land. Zeng created the Carbon Lockup Project in 2013, which began at a research site outside Montreal. is covered.
Then there’s Mast Reforestation, a company that works to replant forests to earn carbon credits after they burn. Chief executive Grant Canary said he was particularly interested in burying trees that had been burned, posing a danger to workers and the saplings they planted. The company plans to sequester 5,000 to 20,000 metric tons of carbon dioxide equivalent from trees on hundreds of acres of recently burned private land in central Montana. Mast Reforestation is working with Zeng on the carbon lock-in project, and Canary said construction could begin as early as late 2024 or early 2025. .
Also out west, Kodama Systems is in the permitting stages of building a wood vault in western Nevada that could store about 1,000 tons of carbon dioxide equivalent. Materials could be put underground as soon as later this year. The area’s arid pastures were considered prime locations for timber vaults. Researchers at the Carbon Containment Laboratory also say the Four Corners region of Arizona, New Mexico, Colorado and Utah has significant potential for developing wood vaults. Carbon Curb Lab scientists work with companies including Kodama Systems to collect their own independent data.
So what will it take to move the timber vault program from the few pilots it currently exists to a large-scale CO2 removal technology? More science to verify longevity and storage claims, more funding to start other projects, and more buyers of CO2 removal credits. While companies and scientists aim to one day partner with the Forest Service, government land management agencies have been slow to try new things, meaning public-private partnerships on timber vaults remain far off.
For Zeng, standing in the middle of the woods and seeing everything from mill infrastructure to potential timber vault sites in Colorado, Montana and beyond was enlightening, blending theory with on-the-ground practice . “I was very inspired by this trip,” he said. “The dots are being connected.” While wood vaults are not a single solution to dense forests, wildfire risk and a rapidly warming climate, they could also be a simple solution to sequestering some carbon and reducing wildfire risk.
This article originally appeared in Grist at https://grist.org/solutions/wood-vaulting-carbon-storage-solution/. Grist is a nonprofit independent media organization dedicated to telling the stories of climate solutions and a just future. Please visit Grist.org to learn more
