What is Biomass Burial?

Biomass burial—also referred to as terrestrial storage of biomass (TSB) or wood vaulting—is a negative emissions technology (NET) that sequesters atmospheric carbon captured by plants through photosynthesis. In this approach, lignocellulosic biomass (e.g., wood chips, invasive shrubs) is buried in engineered pits where oxygen and liquid water are excluded, thereby greatly slowing microbial decomposition and oxidative decay (Zeng, 2008). Under these anoxic and stable conditions, carbon can be retained for 500 to 1,000 years or more, with recent archaeological and geochemical studies providing empirical validation of this durability (Yao, 2024).

Because nature provides the carbon capture step and the storage infrastructure relies primarily on earth-moving rather than energy-intensive processes, biomass burial offers a highly scalable and low-cost climate solution. Estimates place its scalability of up to 5–10 Gt CO₂ per year globally, using less than 5% of annual net primary production (Zeng & Hausmann, 2022; Amelse, 2025). This positions biomass burial as one of the most viable options to close the gap between current emissions and net-zero targets, while avoiding the energy penalties of direct air capture or bioenergy with CCS.

How is Biomass Burial Performed?

Feedstock preparation begins with chipping, shredding, or bundling of woody biomass. To ensure net-negative emissions, biomass must be dried to ≤20% moisture content, either via natural air-drying (windrowing) or low-temperature kilns (Amelse, 2025). Particle size is optimized for the burial method—typically 2–5 cm chips or coarse slash.

Vault design must ensure long-term anoxia and hydrological stability. Burial pits are excavated to depths of 2–6 meters, with low-permeability native clay, bentonite layers, or HDPE liners installed to reduce water and air infiltration. The ideal subsoil hydraulic conductivity is ≤1 × 10⁻⁹ m·s⁻¹. A surface cap of compacted clay or composite geomembrane protects against rainfall and erosion. Modular design—e.g., 1-hectare Wood Vault Units (WVUs)—allows for phased build-out. Each WVU can store approximately 0.1 million tonnes of CO₂, and fewer than 1,000 such units could support a global 1 Gt CO₂/year program (Zeng & Hausmann, 2022).

Filling and sealing involve placing biomass in compacted layers interspersed with clay or other inert materials. Operations aim to complete capping within three months to limit aerobic degradation. Gas wells are used to verify anoxic conditions (O₂ < 1% v/v) post-closure.

Monitoring, Reporting, and Verification (MRV) is critical. Mass input is tracked using weighbridges and digital inventory systems; post-burial gas measurements and remote sensing (for subsidence or vegetation cover) confirm vault integrity over time. Standardized protocols such as ISO 14064-2 or Isometric's MRV framework for biomass burial are already in use.

Why Biomass Burial Solves the Global Ulex Problem ?

Ulex europaeus (common gorse) is among the world's most aggressive woody invaders. It produces dense, thorny thickets of woody biomass, displaces native vegetation, and fuels catastrophic wildfires. Chemical analysis of gorse shows it contains ~48% cellulose and ~22% lignin—a composition that is inherently resistant to decomposition and well-suited to long-term anoxic storage (Celis et al., 2014; Jobson & Thomas, 1964).

From a biomass burial perspective, gorse is an ideal candidate: it produces abundant, non-merchantable biomass (up to 100 tonnes dry matter per hectare) and is already targeted for clearance by landowners and governments due to its biodiversity and wildfire threats (Dent et al., 2019). Unfortunately, conventional management fails to solve the problem. Cutting or burning triggers seed bank germination, and herbicide use is costly, environmentally risky, and usually temporary (Hill et al., 2001).

By integrating gorse removal with biomass burial, both problems—carbon emissions and invasive spread—are addressed simultaneously. 

The technical process involves:

• Mechanical harvesting using flail mulchers or drum chippers to process stems (≤5 cm diameter) into 2–5 cm chips, minimizing worker injury and improving handling density.

• Field drying, typically via windrowing for 4–6 weeks during Chile's dry season, reduces moisture content to below 18%.

• Loading and logistics: Chips are packaged in 1 m³ FIBC "big bags" (~250 kg dry mass) or transported loose in walking-floor trailers. There is no need for energy-intensive pelletizing or briquetting.

• Burial: Chips or bags are placed in engineered vaults in compacted layers, covered with native clay or geomembrane, and sealed to ensure long-term carbon retention.

Lifecycle analysis indicates a net carbon removal of ~1.0 tonne CO₂ per tonne of dry gorse, after accounting for emissions from harvesting (~10 kg CO₂/tonne), transport (~5 kg), and burial (~1 kg). At current rural Chilean operational rates (~USD 13 per filled FIBC), this  is comparable to forestry slash burial, with the added ecological co-benefit of eliminating a major pest (Amelse, 2025).

Moreover, the dispersed nature of gorse stands makes hub-and-spoke logistics ideal. Local cooperatives handle chipping and drying, while centralized vaults at disused gravel pits or mine sites receive and bury the biomass. Once built, the same vault infrastructure can serve other regional invasive species, offering a scalable model for both ecological restoration and climate mitigation.