Two projects measuring the same trees with the same care can report different biomass because they chose different equations. Standards handle this by expecting a documented preference order rather than a free choice.
The Hierarchy
| Preference | Equation type | When it applies |
|---|---|---|
| 1 | Species-specific, locally calibrated | Local destructive sampling exists for the species and region |
| 2 | Species-specific, regional | Published for the species in a comparable region |
| 3 | Multi-species regional | Covers the forest type, usually with wood density as a variable |
| 4 | Pantropical multi-species | No closer option; widely validated across tropical forests |
| 5 | Generic default | Last resort, corresponds to low-tier accounting |
Moving up the hierarchy narrows uncertainty. Moving down is acceptable where nothing better exists, provided the choice is stated rather than obscured.
Calibration Range Is the Test Projects Fail
Every published equation was fitted over a specific range of tree sizes, in specific conditions. Applying it outside that range produces extrapolation, and extrapolation error is not captured by the equation's own reported statistics.
The most common instance: a project with large emergent trees applying an equation fitted on stems up to 60 cm diameter. The biggest trees hold a disproportionate share of biomass, so this is precisely where the extrapolation hurts most.
Verifiers ask for the calibration range. Projects that can state it, and flag where their inventory exceeds it, are treated far better than those that cannot.
What to Document
Four things, all available at selection time and painful to reconstruct later: the full citation, the calibration range for species and diameter, the region and forest type it was developed in, and the reason it was preferred over the alternatives considered.
That last item is the one most often omitted and the one an assessor most wants to see, because it demonstrates the hierarchy was applied rather than an equation simply inherited.
Turn uncertainty into a plan
Sampling design and growth assumptions decide how much measured carbon survives conservative deduction. TREEO Carbon Simulator models sequestration scenarios and biomass growth before the field season.
