CDM AR-Tool14: Estimating Carbon Stocks in Trees and Shrubs

Updated 2026-11-02 · 3 min read · By the akar.earth specialist team

AR-Tool14 explained: the CDM tool for estimating carbon in trees and shrubs, its measurement and modelling options, uncertainty rules and use in Indonesian ARR.

AR-Tool14 is the Clean Development Mechanism (CDM) tool for estimating carbon stocks and changes in carbon stocks of trees and shrubs in afforestation and reforestation projects. It turns field measurements of trees into tonnes of carbon and CO2 with a defined level of statistical precision.

Most CDM A/R methodologies, including AR-ACM0003 and AR-AMS0007, call AR-Tool14. Many ARR projects in Southeast Asia still report under it, and its logic remains the basis of tree carbon estimation under newer methodologies.

What AR-Tool14 estimates

The tool covers two vegetation types:

• Trees, measured individually in plots or estimated from growth models.
• Shrubs, estimated from crown cover rather than individual stems.

It estimates above-ground biomass, then adds below-ground biomass with a root-to-shoot ratio, and converts dry biomass to carbon with a carbon fraction. It then converts carbon to CO2 by the molecular weight ratio of 44/12.

Options for trees

Measurement of sample plots. The most common option. Teams measure diameter at breast height and, where needed, height in fixed-area plots. Biomass comes from:

• allometric equations, which convert diameter (and often height and wood density) into biomass. Read allometric equations for choosing between species-specific and pantropical models.
• biomass expansion factors, which convert stem volume to total biomass using wood density and expansion factors.

Modelling. Where measurement is impractical, the tool allows estimation from tree growth models or yield tables, with conservative conditions.

Proportionate crown cover methods are used for shrubs and for sparse tree cover in some cases.

How AR-Tool14 works step by step

1. Stratify the project area by species, age and site conditions.
2. Design sampling. Use the CDM sample plot tool to calculate how many plots are needed for the target precision. See plot sampling design.
3. Measure plots. Record diameter, height and species for every tree above the minimum diameter.
4. Calculate tree biomass with the chosen equations or factors.
5. Add below-ground biomass using a root-to-shoot ratio.
6. Convert to carbon and CO2 with the carbon fraction and 44/12.
7. Estimate the mean and its uncertainty for each stratum and for the project.
8. Apply the uncertainty rule. If the precision target is not met, apply the tool’s discount or measure more plots. Read uncertainty deductions.
9. Calculate the change in stock between monitoring events.

Using AR-Tool14 in Indonesia

Indonesian ARR uses a mix of fast-growing and native species: sengon (Falcataria), jabon, gmelina, mahogany, teak, meranti and many fruit and agroforestry trees. Practical points:

• Pick equations that fit the trees. Species-specific equations from Indonesian research exist for several plantation species. Where they do not, a pantropical model with wood density, such as Chave et al. (2014), is the usual fallback. Check that diameters fall within the equation’s calibration range.
• Wood density varies. Use published species values and say which source you used. Our tree CO2 calculator shows how sensitive results are to this input.
• Mixed agroforestry needs care. Coffee, cocoa and banana are not trees in the AR-Tool14 sense for every methodology. Check how the methodology treats them.
• Plot location quality matters. RTK GNSS positioning lets verifiers relocate plots precisely. Read RTK GNSS plot mapping.

Pitfalls verifiers flag

• Allometric equations applied outside their diameter range.
• Height measured inconsistently, or estimated by eye.
• Plots placed by convenience near roads or nurseries.
• Missing trees below the minimum diameter in young plantings.
• Wrong or undocumented wood density values.
• Precision targets missed without the discount applied.

Field protocol checklist

A field protocol that holds up at verification usually specifies:

• plot shape, size and nested subplots for small trees;
• minimum diameter and the height at which diameter is measured, including rules for buttresses and leaning stems;
• how height is measured and with which instrument;
• species identification method and how unknown species are handled;
• plot centre marking and coordinates;
• photos and data entry checks in the field.

Write it down before the first plot is measured, and train every crew on it.

Train crews on the same protocol every season and audit a sample of plots internally before the VVB arrives.

AR-Tool14 under VM0047

VM0047 replaced CDM A/R methodologies under Verra. It has its own quantification rules, but plot-based biomass estimation still uses the same building blocks: plots, allometry, root-to-shoot ratios and carbon fractions. Well-documented AR-Tool14 data is usually a good foundation for a VM0047 project.

Our field data campaigns collect plot data to these standards. See also the standards hub.