Selecting one allometric equation is a judgement. Selecting twenty, for twenty species, across a mixed planting, is a documentation problem, and the way most projects fail it is by making twenty good decisions and recording none of them.
The Matrix
One row per species, and these columns:
| Column | What it records |
|---|---|
| Species | Botanical name as identified in the field |
| Equation selected | Full citation, including version |
| Evidence tier | Local species-specific, regional, multi-species, pantropical, default |
| Calibration range | Diameter range and region the equation was fitted on |
| Fit to project | Whether project trees fall inside that range |
| Alternatives considered | What else was available and why it was not chosen |
| Wood density source | Database and whether matched at species or genus level |
The sixth column is the one projects omit and assessors want. It converts "we used this equation" into "we considered the options and this was the best available" — which is the difference between a defensible choice and an arbitrary one.
Handling Species With Weak Evidence
In mixed tropical plantings, several species will have no published species-specific equation anywhere. There are three honest responses.
Use a well-validated multi-species equation with wood density as a variable, which is precisely what pantropical models are designed for.
Or group the species with a congener that has a published equation and comparable wood density, clearly stating the substitution.
Or, where the species is a minor component, apply the most conservative available option and note that it is conservative.
What is not acceptable is silently applying a convenient equation and leaving the reader to discover the mismatch.
Why Record the Range
Calibration range is the most common source of undeclared extrapolation. In a mixed planting, some species will exceed the range of their chosen equation as the project matures, which often involves the fastest growing species that also contribute the most biomass.
Recording the range at selection time means the project knows when it has crossed it, rather than finding out when a verifier asks.
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.
