An ex-ante carbon estimate rests on two inputs that projects rarely scrutinise as closely as they scrutinise allometry: how fast the trees grow, and how heavy the wood is. Both are usually taken from published sources, and both transfer badly between contexts.
Growth Trajectories
A growth model describes how diameter and height develop over time for a species under given conditions. The conditions qualifier carries most of the risk.
| Source of growth data | Transferability |
|---|---|
| Local trial plots, same species and site type | High |
| Regional plantation records | Moderate |
| Published curves from another region | Low — climate and soil differ |
| Generic fast/medium/slow classifications | Very low; useful only for screening |
The systematic bias worth knowing: growth data disproportionately comes from managed plantations on good sites, because that is where measurement happens. Applying plantation-derived curves to degraded restoration sites overstates growth, sometimes substantially.
Wood Density Deserves More Attention Than It Gets
Density converts volume to mass, so it scales the entire biomass estimate linearly. A 20% error in density is a 20% error in carbon, and density varies more between species than most people assume.
Two practical issues recur.
Matching level. Species-level values are best; genus-level substitution is common and introduces error that should be stated rather than buried.
Intra-species variation. Density varies with site, age and position in the stem. Published values are means, and a project on an atypical site may sit consistently to one side of that mean.
Species With Thin Evidence
Every mixed planting includes species with almost no published data. The honest options are the same as for allometry: use a well-validated generic relationship, substitute a comparable species and say so, or treat the species conservatively and document why.
The failure mode is assigning a plausible-looking value from an unrelated context and carrying it forward as though it were measured. At verification, an unsourced density value is treated as an assumption and assumptions attract the conservative default.
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.
