In 2013, researchers dug up a 3,775-year-old cedar log in Québec. Nearly a millennium older than the Roman Empire, this ancient Canadian tree had been so well-preserved by the local clay soil that it still held over 95% of its original carbon. As trees usually release their stored carbon back into the atmosphere when they die, this amazing scientific discovery – by a team from the University of Maryland, USA – became central to the establishment of a new climate solution: Terrestrial Storage of Biomass (TSB).

Also called wood vaulting or biomass burial, Terrestrial Storage of Biomass is an emerging pathway for durable carbon dioxide removal (CDR) that involves storing waste wood inside a purpose-built vault that denies fungi, insects, and bacteria the oxygen, moisture, or warmth they need to break it down. As a result, the carbon the tree absorbed and stored during its lifetime stays in place instead of drifting back into the air as greenhouse gases like methane or carbon dioxide.

With a process that doesn’t require pyrolysis, combustion, or conversion to slurry or bio-oil, Terrestrial Storage of Biomass is quickly gaining ground. CDR.fyi's most recent review found that the category has gone from a niche concept to a practice, with registries publishing dedicated methodologies and several suppliers now issuing credits. Indicative pricing today runs $100 to $350 per tonne of CO₂, depending on the exact burial method used - with room to fall to $50 to $150 per tonne as the approach scales and construction gets more standardized.

Here's what I check to evaluate the quality of a Terrestrial Storage of Biomass project.

Is the baseline real?

The first question I ask: What would have happened to this wood anyway? A high-quality Terrestrial Storage of Biomass project uses residuals that were going to decompose or get burned regardless: urban waste wood, storm- and fire-damaged trees, invasive species clearing, forest-thinning residue. Take forest-thinning debris in wildfire-prone regions: after crews clear excess trees and brush to reduce fuel loads, the leftover wood is typically piled up and burned on-site within the same year, a practice called slash pile burning, releasing that carbon straight back into the atmosphere. Burying the wood instead is a genuine climate solution because it stops that from happening. If the wood had a legitimate higher-value use and got diverted instead, the so-called counterfactual falls apart, and both Puro.earth and Isometric treat this as a hard eligibility line, not a gray area.

Was the biomass sorted?

Not all wood belongs in a vault. Dry wood runs about 47-51% carbon by mass regardless of species, but only coarse woody biomass, trunks and branches roughly 10 cm across or larger, should go into the vault. Fine woody biomass, such as twigs, chips, and leaves are nutrient-rich and decay fast, which is exactly what feeds a decomposer population and produces methane.

Does it preserve nutrient cycling?

There's a tradeoff to removing decomposing wood from a landscape. Coarse woody debris left in place provides habitat for insects, fungi, and small animals, and its slow decay is part of how forest soils build organic matter over time. I look for projects that account for this by sourcing wood that was already coming out of the ecosystem: storm damage, fire-damaged trees, thinning residue, rather than pulling material out of forests where it was still doing that ecological work.

Does the engineering match the site, not the other way around?

Site selection has to come first: soil permeability, water table behavior through the seasons, seismic and flood exposure, land ownership. Low-permeability clay is what you want, because it keeps oxygen and water out. The common benchmark is at least a meter of compacted clay on every side. I want to see that spec matched to the specific site's geology and climate, whether the approach is anaerobic, dry, or cold, not a generic design dropped onto whatever land was available.

Is permanence actually legally binding?

Puro.earth certifies Terrestrial Storage of Biomass CORCs for a minimum of 100+ years. Isometric, whose equivalent protocol is Subsurface Biomass Carbon Removal and Storage, takes a different approach: it declines to commit to a single durability number at all, on the grounds that variation in biomass composition, storage conditions, and site geochemistry makes a blanket claim inappropriate, and instead assesses durability project by project. Either way, a well-built vault means nothing if someone digs it up in twenty years. I look for a conservation easement or equivalent instrument that blocks future excavation and survives a change in land ownership, not just an operator's current intentions.

How is reversal risk managed?

Every durable CDR method has to reckon with stored carbon not staying stored, and Terrestrial Storage of Biomass is no exception: a degraded seal, erosion, wildfire or flood damage, or human interference can all let oxygen or water back into the vault and restart decomposition, releasing carbon dioxide or methane. A quality project treats this as a quantified risk rather than an afterthought: registries hold back a buffer pool of unissued credits sized to that uncertainty, whether it's Puro.earth's default 10% or Isometric's risk-scored range of 1-20% based on methane potential, disaster exposure, and monitoring history. That buffer should shrink only as real monitoring data comes in, never ahead of it, and if a reversal is actually detected, credits already issued need to be invalidated or replaced, not just logged.

Is monitoring built in?

A good project layers several kinds of monitoring together. Sensors track carbon dioxide, oxygen, methane, temperature, and moisture inside the vault, while surface instruments watch for any gas escaping upward. On top of that, buried samples get dug up periodically and tested in a lab, and surveyors keep an eye on land settling, since unexpected sinking can be an early sign that something is decomposing that shouldn't be. This continuous monitoring, above and within the chamber, is key to ensuring there is no decomposition of the wood.

Does the project know its own limits?

The projects I trust are upfront about where Terrestrial Storage of Biomass stops making sense: wood with a competing higher-value use, sites with high exposure to extreme weather, or scale pushed past what local transport economics support. Wood is heavy and expensive to move, which is also why projects tend to work best close to where the biomass is sourced rather than at one central facility.

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Terrestrial Storage of Biomass earns its place in the durable CDR mix precisely because it doesn't ask much of physics or engineering. But the quality of any given project lives almost entirely in the decisions made before the wood goes in the ground: what biomass, from where, on which site, under what legal protection, and monitored how. The projects that get those decisions right can offer durable carbon removal and storage.

Learn more about how Terrestrial Storage of Biomass works as a durable carbon removal solution.