akar.earthAllometric equation: Definition
What is an allometric equation? How tree diameter, height and wood density convert to biomass and carbon, with notes for Indonesian forest projects.
An allometric equation is a statistical model that estimates a tree’s biomass from easily measured dimensions, usually diameter at breast height, height and wood density. It lets projects calculate carbon stocks without cutting and weighing trees.
Why it matters
Every forest carbon estimate depends on allometry. Field teams measure DBH and height, the equation converts these to above-ground biomass, and further factors convert biomass to carbon and then to CO2. A biased equation can over- or under-state carbon stocks by a large margin, which flows straight into credit volumes.
How equations are built and used
Equations are fitted from destructive sampling: trees are felled, dried and weighed, and biomass is regressed against size. A widely used pantropical model is Chave et al. (2014), which takes the form AGB = 0.0673 × (ρD²H)^0.976, where ρ is wood density in g/cm³, D is DBH in cm and H is height in m. Species-specific equations exist for many plantation species.
Methodologies such as VM0047 and CDM tools require projects to justify the equation chosen and show it applies to the size range and conditions of the project’s trees. Our allometric equations guide covers selection and validation.
Indonesia angle
Indonesia has published equations for many native and plantation species, and for forest types from lowland dipterocarp forest to mangroves and peat swamp forest. Mangroves need dedicated equations because of stilt roots and dense wood. For smallholder agroforestry with coffee, cocoa or fruit trees, published equations are thinner, so a pantropical model with measured height is often the defensible choice.
Common mistakes
- Applying an equation outside its diameter range, especially to very small young trees in ARR plantings.
- Skipping height and using diameter-only models that were fitted in a different region.
- Using a single default wood density for mixed species.
- Not stating the source and applicability in the project documents.
Try our tree CO2 calculator to see how inputs change the result.
Related terms
Allometry links field measurement to carbon accounting, so it connects to DBH, wood density, root-to-shoot ratios and carbon fraction. The ARR hub shows where it fits in a full project.
Frequently asked questions
What inputs does an allometric equation need?
Usually diameter at breast height (DBH), often tree height, and for pantropical models the wood density of the species.
Should I use a species-specific or a generic equation?
Use a published species-specific or regional equation if it was built from trees of similar size and conditions. Otherwise a pantropical model such as Chave et al. (2014) is the usual fallback.