akar.earthThe Five Carbon Pools in Forest Accounting
The five forest carbon pools explained: above- and below-ground biomass, dead wood, litter and soil organic carbon, and which ones projects must measure.
Forest carbon accounting uses five pools: above-ground biomass, below-ground biomass, dead wood, litter and soil organic carbon. These definitions come from IPCC guidelines and are used by Verra, Gold Standard, ART and national inventories. Each methodology says which pools a project must measure and which it can leave out.
Choosing pools well is one of the biggest decisions in a project design. Including a pool can add credits; it also adds measurement cost and uncertainty. In Indonesia, the answer differs sharply between mineral-soil forests, where trees dominate, and peat and mangroves, where soil dominates.
The five pools
| Pool | What it includes | How it is measured | Notes |
|---|---|---|---|
| Above-ground biomass | Stems, branches, leaves of living trees and other vegetation | Plot inventory (DBH, height, species), allometric equations, remote sensing | Usually the core of ARR and REDD+ accounting |
| Below-ground biomass | Living roots | Root-to-shoot ratios or root equations | Rarely measured directly |
| Dead wood | Standing dead trees, fallen logs, stumps | Line-intersect transects or plot surveys with decay classes | Can be significant after logging or fire |
| Litter | Fallen leaves, twigs and fine debris above the mineral soil | Small sample frames, weighed and dried | Usually small; often excluded |
| Soil organic carbon | Organic carbon in mineral or organic soils | Soil cores, bulk density, lab analysis | Dominant in peat and mangroves |
Harvested wood products are sometimes accounted for as an additional pool when timber leaves the site, especially in improved forest management.
Which pools to include
Methodologies usually set rules like these:
- Required: above-ground tree biomass for almost all forest methodologies.
- Conditional: a pool must be included if the project or baseline causes it to decrease significantly.
- Optional: a pool can be excluded if leaving it out is conservative, meaning it would not reduce credits.
For ARR on degraded land, projects typically include above- and below-ground tree biomass and often exclude litter, dead wood and soil. For REDD+, dead wood and soil may matter because clearing releases them. For peat, soil carbon and emissions from drainage and fire are central. For mangroves, soil carbon often holds most of the stock; see mangrove soil carbon.
Step-by-step: deciding your pools
- Read the methodology’s pool table. Each methodology lists required, conditional and optional pools.
- Identify the ecosystem. Mineral soil forest, peat swamp, mangrove or agroforestry.
- Estimate the size of each pool from literature or a pilot inventory.
- Estimate the change each pool is likely to show under baseline and project scenarios.
- Weigh cost against credit gain. Soil sampling, for example, can be expensive and highly variable.
- Document conservative exclusions with evidence for the validator.
- Design plots to measure included pools consistently. See plot sampling design.
Indonesia specifics
- Lowland dipterocarp forests in Kalimantan and Sumatra hold large above-ground biomass in big trees, so plot design must capture large-diameter stems.
- Peat swamp forests store most carbon in deep peat; drainage and fire release it. See peatland REDD+.
- Mangroves store large amounts in sediments, often more than in trees.
- Agroforestry in coffee, cocoa and rubber stores most creditable carbon in shade tree biomass.
Typical pool choices by project type
| Project type | Usually included | Often excluded or optional |
|---|---|---|
| ARR on degraded mineral land | Above- and below-ground tree biomass | Dead wood, litter, soil (if not decreasing) |
| Smallholder agroforestry | Shade tree biomass, sometimes crop trees | Litter, dead wood, often soil |
| REDD+ on mineral soil | Above- and below-ground biomass, often dead wood | Litter; soil depends on methodology |
| Peatland REDD+ or rewetting | Biomass plus peat emissions from drainage and fire | Litter |
| Mangrove restoration | Biomass and sediment carbon | Litter, depending on methodology |
This table is a guide only. The methodology you use sets the binding rules, and the validator checks your justification for each choice.
How pools affect monitoring cost
Every included pool needs its own measurement protocol, staff training and quality checks. Tree biomass can be monitored efficiently with plots and calibrated satellite products. Soil and dead wood require more field time per sample and show more variability, which raises uncertainty deductions. When budgets are tight, it is often better to measure fewer pools well than many pools poorly.
Common mistakes
- Excluding a pool that the project’s own activities will reduce, such as soil carbon during site preparation.
- Using default root-to-shoot ratios without checking they suit the forest type.
- Measuring dead wood once and then assuming it stays constant.
- Applying mineral-soil methods to peat.
For the calculation from biomass to CO2, read from tree biomass to tonnes of CO2. For IPCC background see IPCC AFOLU guidelines. Explore the forest carbon hub or try the tree CO2 calculator.
Frequently asked questions
What are the five carbon pools in a forest?
Above-ground biomass, below-ground biomass, dead wood, litter and soil organic carbon. Dead wood and litter together are sometimes called dead organic matter. Harvested wood products are sometimes treated as an additional pool.
Which carbon pool is largest?
In most dryland tropical forests, above-ground biomass is the largest pool that projects measure. In peat swamp forests and mangroves, soil carbon is usually far larger than biomass.
Do carbon projects have to measure all five pools?
No. Methodologies specify which pools are required and which are optional. Projects can usually exclude a pool conservatively if the project will not reduce it, which saves measurement cost.
How is each pool measured?
Living biomass through tree measurements and allometric equations, roots through root-to-shoot ratios, dead wood through line-intersect or plot surveys, litter through small sample frames, and soil through cores and lab analysis.