The full Tree-Nation carbon calculation methodology: the ex-ante carbon estimation basis used across the Tree-Nation system, applied to all Tree-Nation projects regardless of the certification pathway they follow.
Introduction
Tree-Nation's mission is to help reforest the world. We team up with reforestation, afforestation, agroforestry, and conservation projects around the world to fund their activities, converting their reforestation effort into a volume of trees that can be sponsored on our platform.
Traditional certification standards, such as VCS, Gold Standard, and Plan Vivo, calculate CO₂ per hectare of grown forest, using methodology-based sampling and on-site measurement. This works well for large, mature projects, but creates a high barrier to entry for smaller or newer ones.
Tree-Nation takes a different approach: sponsors fund individual trees, particularly newly planted ones. This lets sponsoring companies make their environmental commitment tangible, "gifting" a tree to a customer or employee, linked to a real, trackable planting rather than an abstract CO₂ value.
To support this, Tree-Nation developed its own methodology to estimate the CO₂ sequestration of each individual tree planted through the platform, calculated on a per-tree basis using the physical characteristics of each species, rather than per hectare. This allows Tree-Nation to fund a broad and diverse range of projects, from large-scale to modest, that would otherwise have no access to funding under traditional certification pathways.
The methodology defined here provides the ex-ante carbon estimation basis used across the Tree-Nation system. It applies to all Tree-Nation projects regardless of the Tree-Nation certification pathway they follow.
The model is intentionally conservative: precision is deliberately traded for prudence, so that any sponsor can confidently claim the resulting value as an offset. A "low" estimate is a good estimate for the purposes of the platform.
How this differs from traditional carbon certifications
Tree-Nation's methodology departs from traditional certification in two defining ways. Where traditional certifications build a custom paper model per project, anchored in a counterfactual baseline of what would have happened without the project, Tree-Nation determines the CO₂ capture potential of a tree over its lifetime directly from the established biological characteristics of its species. And where traditional methodologies calculate carbon at the hectare level, Tree-Nation calculates per tree, since each species' characteristics, and therefore its contribution value, vary considerably.
| Traditional certification | Tree-Nation methodology |
|---|---|
| Calculated per hectare | Calculated per tree |
| Crediting up to 100 years | Crediting capped at 10 years |
| Sample-based verification at least every 5 years | Continuous verification via remote sensing & geolocated field data |
| Expensive | Low cost |
| Limited selection of species | Unlimited |
| Limited plantation methods | Unlimited |
| Large projects only | All project sizes |
The trade-off is precision, which Tree-Nation offsets by applying a prudence ratio that lowers the final CO₂ value. The goal is not to produce the single most accurate number, but a number any sponsor can confidently claim as their offset — a conservative estimate is, for this purpose, the right estimate.
Carbon estimation logic: overview
Tree-Nation estimates carbon uptake at the tree level using species-specific biological models. Each tree's expected CO₂ uptake over its first 10 years is calculated using:
Soil moisture has been identified as a relevant variable, but is not yet integrated into the calculation.
The model is intentionally conservative in several ways: input measures are capped to median rather than ideal specimens, since scientific literature tends to report best-case data; survival and culling rates are built directly into the calculation; prudence coefficients reduce the risk of overestimation; results are cross-checked, where available, against existing certification calculations and scientific literature on comparable species and systems; and per-tree results are capped at 500 kg of CO₂.
This produces a risk-adjusted estimate of CO₂ uptake per tree over 10 years, reflecting expected real-world performance rather than ideal growth conditions.
The CO₂ sequestration formula
Tree-Nation calculates expected carbon sequestration using a species-level formula based on tree structure and biological growth parameters. The calculation follows six stages.
Step 1: Tree volume estimation
Tree volume is estimated from species morphology by modelling the trunk as a cylinder, using the trunk diameter range, height range, and wood density of the species. Two additional carbon pools are then added on top of trunk volume: branches and leaves (+15%), and roots (+20%). Prudence coefficients are applied throughout to keep estimates conservative.
Fixed model parameters
| Parameter | Description | Value |
|---|---|---|
| h_trunk_coef (trunk_tree_ratio) | Ratio of trunk size to full tree size (including crown). Applied as: h_avg × h_trunk_coef = h_trunk | 45% |
| d_coef (average_specimen_reductor) | Literature typically studies ideal specimens; this coefficient reduces estimates to a more average specimen | 60% (baseline; reduced further for all species under the Version 5.0 radius-estimation improvement — current per-species figures held in the species database) |
| radius_cap | Cap on trunk radius, to avoid excessive values | 0.5 m (50 cm) |
| branches_coef (branches_stored_co2) | Additional CO2 stored in branches and leaves, on top of the trunk | 15% |
| roots_coef (roots_stored_co2) | Additional CO2 stored in roots, on top of the trunk | 20% |
| c_to_co2 (carbon_co2_ratio) | Ratio of carbon mass to CO2 mass |
Default values (used only when species data is missing)
| Parameter | Description | Value |
|---|---|---|
| h_avg_default | Average tree height, if no data available | 5 m (currently unused) |
| d_avg_default | Average trunk diameter, if no data available | Not yet set (currently unused) |
| tree_density_default | Wood density, if no data available | 0.50 g/cm³ |
Species data requirements
| Field | Description |
|---|---|
| h_min / h_max (m) | Minimum / maximum tree height |
| d_min / d_max (cm) | Minimum / maximum trunk diameter |
| tree_density (g/cm³) | Wood density of the species |
Derived (measurable) values
h_trunk (m) = (h_min + h_max) / 2 × h_trunk_coef
Both outputs are in meters, ready to plug into the cylinder volume formula that follows, which yields volume in m³.
Step 2: Carbon content calculation
Tree biomass is converted to carbon using wood density and dry-mass ratios:
- Convert tree density from g/cm³ to kg/m³ = (g/cm³) × 1000
- Wood mass (kg fresh biomass) = Volume of the tree (m³) × tree density (kg/m³)
- Dry mass = Wood mass × 65% (dry mass ratio)
- Carbon sequestered per tree (kg) = Dry mass × 50% (carbon content of dry wood)
Wood density varies with species genotype and environmental conditions — luminosity, water availability, temperature, soil fertility, spacing, and management. Dry wood has an elemental composition of approximately 50% carbon, 6% hydrogen, and 44% oxygen, with trace inorganics, which is what justifies the 50% carbon ratio above.
Intermediate mass/carbon breakdown (internal detail)
| Quantity | Formula |
|---|---|
| tree_density (kg/m³) | tree_density (g/cm³) × 1000 |
| mass_trunk (kg) | Volume of trunk (m³) × tree density (kg/m³) = π × radius² × h_trunk × tree_density (kg/m³) |
| dry_mass_trunk (kg) | mass_trunk (kg) × 0.65 |
| carbon_stored_in_trunk (kg) | dry_mass_trunk (kg) × 0.5 |
| carbon_stored_in_branches (kg) | carbon_stored_in_trunk × branches_coef |
| carbon_stored_in_roots (kg) | carbon_stored_in_trunk × roots_coef |
| carbon_stored_in_tree (kg) | carbon_stored_in_trunk × (1 + branches_coef + roots_coef) |
Step 3: Conversion to CO₂
Carbon mass is converted to CO2 equivalent using the standard molecular conversion ratio:
This reflects the relative molecular weights of CO2 and carbon: atomic weight of C = 12, atomic weight of O = 16, atomic weight of CO2 (C + 2×O) = 44, giving 44 ÷ 12 = 3.667.
The pre-adjustment CO2 volume, before growth, management, and prudence factors are applied.
Step 4: Growth & climate adjustments
Growth-rate and climate parameters scale the raw CO2 estimate to reflect how quickly and how well a species grows in its planting region.
| Climate region | Growth factor (100% = optimum growing conditions) |
|---|---|
| Tropical | 90% |
| Subtropical | 70% |
| Warm temperate / dry | 43% |
| Dry | 37% |
| Cool temperate | 35% |
| Boreal | 28% |
| Default (unknown region) | 50% |
| Growth rate class | Growth-period ratio (share of lifespan to near-full growth potential) |
|---|---|
| Fastest-growing | 50% |
| Fast-growing | 60% |
| Moderate | 70% |
| Slow | 80% |
| Default (unknown) | 80% |
Additional defaults: climate_region_default = 50%; growth_rate_default = 80%; life_span_default = 70 years.
co2_per_year_pre (kg) = CO2_per_tree_pre × climate_region / growth_period
Step 5: Management adjustments
Two field-observed, project-level factors reduce the estimate to reflect real planting-site outcomes:
| Parameter | Description | Default |
|---|---|---|
| survival_rate | Share of trees surviving after 2 years. | 50% (fallback, if no project data) |
| cull_back | Share of trees surviving to adult age after natural competition for space (cull-back) | 70% (fallback, if no project data) |
Step 6: Prudence parameters & final caps
The final stage applies Tree-Nation's prudence coefficient and the structural caps that keep the methodology conservative.
| Parameter | Description | Current value |
|---|---|---|
| model_prudence | Final prudence cut applied to the calculated value, to keep results conservative | 70% |
| co2_anteperiod_cap | Years of tree growth accounted for in the ex-ante calculation | 10 years |
| co2_postperiod_cap | Years of tree growth accounted for in ex-post verification measurement | 20 years (legacy internal parameter; ex-post tracking is superseded in practice by the 10-year ex-ante cap and the 500 kg per-tree cap — see below) |
| Per-tree cap | Maximum CO2 creditable to a single tree, regardless of calculated value | 500 kg CO2 |
If a tree's project-specific expected lifespan, tree_co2_period, is shorter than the ante-period cap, that shorter value is used instead.
This is the headline CO2 figure displayed against each tree, prudently capped at 500 kg. Where available, results are further refined by contrasting Tree-Nation's values against existing certification calculations and scientific publications on comparable species and systems, and adjusted accordingly.
Current parameter reference
| Parameter | Current value |
|---|---|
| Trunk-to-tree ratio (h_trunk_coef) | 45% |
| Average-specimen reductor (d_coef) | 60% baseline, reduced per-species under v5.0 |
| Radius cap | 0.5 m |
| Branches carbon add-on | +15% of trunk |
| Roots carbon add-on | +20% of trunk |
| Dry mass ratio | 65% |
| Carbon content of dry wood | 50% |
| Carbon-to-CO2 ratio | |
| Ex-ante growth period cap | 10 years |
| Per-tree CO2 cap | 500 kg |
| Model prudence ratio | 70% |
| Default survival rate (fallback) | 50% (fallback) |
| Default cull-back rate (fallback) | 70% (fallback) |
| Default wood density (fallback) | 0.50 g/cm3 (fallback) |
| Default life span (fallback) | 70 years (fallback) |
| Default climate region factor (fallback) | 50% (fallback) |
| Default growth rate factor (fallback) | 80% (fallback) |
Governance & recalculation notes
The methodology is designed to evolve: hypothesis parameters and defaults are treated as adjustable model inputs, and refined as better data becomes available.
Lifetime CO2 per tree is stored at the point of tree creation. A separate "lifetime_co2" field exists for manual, admin-panel-only edits and is kept outside the automated calculation. A project-level "recalculate" capability is planned to allow species-table values to be refreshed and re-versioned as the model improves.
Soil moisture remains an identified but not-yet-integrated variable, flagged here as a candidate for a future version.
Glossary of symbols
| Symbol | Meaning |
|---|---|
| h_min, h_max | Minimum / maximum species height (m) |
| d_min, d_max | Minimum / maximum trunk diameter (cm) |
| tree_density | Wood density of the species (g/cm³) |
| radius | Estimated trunk radius (m), capped at radius_cap |
| h_trunk | Estimated trunk height (m) |
| mass_trunk | Estimated trunk mass (kg) |
| carbon_stored_in_tree | Total carbon stored in trunk + branches + roots (kg) |
| CO2_per_tree_pre | CO2 volume before growth/management/prudence adjustments (kg) |
| climate_region | Growth factor for the project's climate region |
| growth_rate | Growth-period ratio for the species' growth-rate class |
| growth_period | Years to near-full growth potential (life_span × growth_rate) |
| co2_per_year_pre / co2_per_year_post | Annual CO2 rate, before / after management adjustments (kg) |
| survival_rate, cull_back | Field-observed survival and thinning rates |
| model_prudence | Final conservative cut applied to the model (70%) |
| co2_anteperiod_cap | Ex-ante accounting period cap (10 years) |
| co2_offset_exante | Final headline ex-ante CO2 figure per tree, capped at 500 kg |
