Impact Methodology

How We Calculate Impact

Every ForestNation Impact Certificate shows four numbers: CO₂ absorbed, oxygen produced, work hours created, and hectares reforested. This page explains exactly where those numbers come from, what they are based on, and why we are confident they are accurate — and deliberately conservative.

At a Glance

The Numbers — Simply Explained

Every tree planted generates four verified impact estimates. Here is what each one means, how it is calculated, and how to use it.

CO₂ Absorbed0.025 tonnesper tree, per yearEach tree absorbs an estimated 25 kg of CO₂ per year. Calculated from GPS-measured field data using peer-reviewed Tanzanian allometric equations, with a 30% uncertainty discount applied. Independently consistent with Trees for the Future's estimate of 22.7 kg/tree/year.
O₂ Produced0.1 tonnesper tree, per yearEach mature tropical tree produces an estimated 100 kg of oxygen per year — gross production across the full photosynthesis cycle, not just the oxygen derived from CO₂ sequestration alone.
Work Hours Created0.04 hoursper tree planted — total, not annualEach tree creates 0.04 hours of paid community employment covering planting, watering, and transplanting. Based on Tanzania field labour rates ($2.15/day, 7-hour day). A conservative floor — additional employment from harvests and maintenance is not included.
Land Reforested0.001 haper tree planted — total, not annualEach tree restores 10 square metres of land. Based on the IPCC LULUCF standard plantation density of 1,000 trees per hectare.
Food & Income Generated$77–$210per fruit tree, per year at maturityFruit trees in our programme (avocado, orange, papaya, mango and others) generate food and direct income for planting families from Year 3. Avocado: ~$77/tree/yr. Papaya: ~$210/tree/yr. Reported as a total programme figure per campaign. These figures represent estimated production capacity based on 2021 local market prices — actual income realised will vary depending on market access, distribution, and harvest conditions. We report this as economic potential created, not guaranteed income delivered.

Using the figures

To estimate the CO₂ contribution from a number of trees, multiply tree count by 0.025. For example: 10,000 trees contributes an estimated 250 tonnes of CO₂ absorbed per year.

Trees needed for a given CO₂ figure: Trees = annual tCO₂ ÷ 0.025
Example: 100 tCO₂/yr ÷ 0.025 = 4,000 trees

Planting trees is a contribution to verified reforestation — not a mechanism to offset or neutralise emissions. ForestNation does not make or support net zero or carbon neutral claims. See the Disclaimer section below for full detail.

The Data

Real Trees. Real Measurements.

Our calculations start with physical field data, not theoretical models. In 2023, our planting partner Friends of Usambara Society conducted a GPS-tagged measurement study across all five of our Tanzania planting sites — Kitopeni, Yamba, Mkusu, Kivuga, and Mmanyai.

Every individual tree in the study was measured for diameter at breast height (DBH) and height. Each measurement was recorded with GPS coordinates, species, planting date, and site. The dataset spans three age cohorts (5, 10, and 14 years) and 14 species, giving us thousands of real-world data points to work from.

This field data was reviewed and validated by Working Trees, a Stanford-founded carbon measurement company. The raw dataset and allometric calculation model are available to enterprise clients and regulatory reviewers on request.

Metric 1

CO₂ Absorbed Yearly

Carbon sequestration is calculated using species-specific allometric equations validated for Tanzanian forest ecosystems. These translate a tree's measured diameter into an estimate of total biomass, from which carbon content and CO₂ equivalence are derived.

Calculation steps

1

Above-ground and below-ground biomass (kg) calculated from measured DBH using Tanzania-specific allometric equations sourced from peer-reviewed research.
AGB (kg) = 0.9635 × DBH^1.944  |  BGB (kg) = 7.5811 × DBH^1.168

2

Carbon is typically 45–50% of total dry biomass, depending on species. Carbon fraction per species sourced from Nature Scientific Data (doi:10.1038/s41597-022-01396-1).

3

Carbon weight is converted to CO₂ using the molecular weight ratio of CO₂ (44 g/mol) to carbon (12 g/mol).
CO₂ (kg) = Carbon (kg) × 3.667

4

A 30% discount is applied to all calculated figures to account for natural variability in tropical species modelling. We also use only below-median field measurements as the baseline.

Independent cross-check: Trees for the Future — one of the world's most experienced tropical agroforestry organisations — independently estimates 50 lbs (22.7 kg) of CO₂ per tree per year for tropical agroforestry trees. Our field-measured, uncertainty-discounted figure of 25 kg/tree/year is consistent with this independent estimate.

CO₂ absorbed0.025tonnes per tree, per yearApplied to all Forest Profiles and Impact Certificates

Metric 2

Oxygen Created Yearly

The oxygen figure on our certificates represents the estimated annual gross oxygen production of a mature tropical tree — the total O₂ made available to the atmosphere through the tree's full photosynthesis cycle.

This is different from the oxygen that can be derived by cross-multiplying our CO₂ figure (which would give ~18 kg/year via photosynthesis stoichiometry). We report gross production because it better reflects the full ecological contribution of a living tree. A mature tropical tree continuously cycles oxygen throughout the day well beyond what is captured by sequestration alone.

Our figure of 100 kg/year (0.1 tonnes) is based on an estimate of 200 lbs per mature tropical tree per year, consistent with established estimates for trees of this type and size.

Transparency note: The CO₂ and O₂ figures use different methodological bases and should not be directly cross-multiplied. CO₂ is derived from field-measured biomass; O₂ is based on gross mature-tree production. Both are legitimate and widely used metrics — this page clearly distinguishes them.

Oxygen produced0.1tonnes per tree, per year (gross production)Applied to all Forest Profiles and Impact Certificates

Metric 3

Work Hours Created

Work hours data comes from a livelihoods impact study commissioned by ForestNation and conducted by Katrina Sill, an impact economist. The model quantifies paid employment generated across the planting and establishment lifecycle of each tree.

Activities measured

Planting10 trees per person per hour — the most labour-intensive activity
Watering100 trees per person per hour — repeated across the establishment phase
Transplanting5 trees per person per hour — nursery to field transfer

Calculations are based on a 7-hour working day and a local daily wage of $2.15 USD (Tanzania, 2021 data). The 0.04 hours per tree figure represents a conservative, averaged estimate of establishment-phase labour — normalised across all trees including those that do not survive.

Note: 0.04 hours per tree is a floor, not a ceiling. Additional employment from fruit harvest, ongoing forest maintenance, and nursery operations is not included in this figure. Real community benefit is meaningfully higher than what is reported on certificates.

Work hours created0.04hours per tree (establishment phase, conservative)Applied to all Forest Profiles and Impact Certificates

Metric 4

Hectares Reforested

Land reforestation is calculated using the standard managed plantation tree density of 1,000 trees per hectare, as specified in the IPCC LULUCF (Land Use, Land-Use Change and Forestry) guidelines, Table 3A.1.5. This is the appropriate standard for our partner-managed planting sites in Tanzania.

At 1,000 trees per hectare, each tree represents 0.001 hectares (10 square metres) of reforested land.

Land reforested0.001hectares per treeBased on IPCC LULUCF plantation density standard: 1,000 trees/ha

Our Approach

Deliberately Conservative

We apply five layers of conservatism to ensure our figures never overstate impact.

Below-median filteringOnly tree measurements below the median diameter for each species and age cohort are used. Larger, faster-growing outliers are excluded.
30% uncertainty discountA 30% discount is applied to all biomass-derived CO₂ figures after allometric calculation, to account for variability in tropical species modelling.
75% survival rateForecasts assume only 75% of planted trees survive to maturity. Actual survival at established sites is typically higher.
15% buffer poolAn additional 15% buffer is held in reserve within sequestration forecasting, consistent with Verra and leading carbon registry standards.
CO₂ & O₂: annual figuresCertificates report annual ongoing impact, not cumulative lifetime totals. Lifetime impact would be substantially higher.
Work hours & hectares:These reflect the full establishment-phase contribution per tree planted, not an annual rate.

The combined effect of these layers means our reported figures are very likely to understate — not overstate — actual environmental and community impact. This is by design.

Scientific Partners

Who Worked on This

Dr. Aakash Ahamed — Working TreesCarbon biomass methodology & tree measurement technologyPhD in Geophysics, Stanford University (Exceptional Thesis Award). Former research scientist, NASA Goddard Space Flight Center. Assistant Professor of Geospatial Sciences, Cal Poly SLO. Co-founder and Chief Scientist, Working Trees. Author of 9 peer-reviewed publications on remote sensing, water resources, and forest carbon.
John Foye — Working TreesProgramme design & carbon market alignmentMBA/MS, Stanford University GSB. Recipient of the Stanford Climate Solutions Prize. Co-founder, Working Trees. Founded at Stanford with the mission of making tree carbon measurement accurate, affordable, and scalable.
Katrina SillCommunity livelihoods & economic impact modellingImpact economist. Designed ForestNation's livelihoods model covering work hours, daily wage calculations, fruit tree economic projections, and community income estimates across 9 fruit tree species.
Trees for the Future (founder: Dave Deppner)Foundational carbon sequestration methodologyOne of the world's most experienced tropical agroforestry organisations. Their independently derived carbon estimate (50 lbs CO₂/tree/year for tropical agroforestry) serves as an independent cross-check on our field-measured figures. ForestNation founder Andrew Pothecary worked personally with founder Dave Deppner in ForestNation's early years.
Friends of Usambara SocietyField implementation, GPS measurement & tree monitoringOur Tanzania planting partner of 8+ years. Conducted the 2023 GPS-tagged individual tree measurement study across all five planting sites, providing the field data that anchors all calculations.

Sources

References

[1]Mugasha, W.A. et al. (2016). Allometric volume and biomass models for tree species in Tanzania. ResearchGate. https://www.researchgate.net/publication/303840753
[2]Forestry Carbon Storage Dataset (2022). Nature Scientific Data. https://doi.org/10.1038/s41597-022-01396-1
[3]Chave, J. et al. Wood Densities of Tropical Tree Species. ResearchGate. https://www.researchgate.net/publication/237339477
[4]Trees for the Future. How to calculate the amount of CO₂ sequestered in a tree per year. Agroforestry methodology document. treesftf.org
[5]Sill, K. (2020–2021). ForestNation Tanzania Impact Model. Commissioned livelihoods study covering labour rates, fruit production, and community income.
[6]IPCC (2006). Guidelines for National Greenhouse Gas Inventories. Volume 4: AFOLU. Table 3A.1.5 — Average Annual Increment in Aboveground Biomass.
[7]Ahamed, A., Foye, J. et al. (2023). Measuring Tree Diameter with Photogrammetry Using Mobile Phone Cameras. Forests, 14(10), p.2027. https://doi.org/10.3390/f14102027
[8]Ryan, C.M. et al. (2017). Ecosystem services from Southern African woodlands. Biological Conservation. Sciencedirect. https://doi.org/10.1016/j.scitotenv.2021.150635

Questions about our methodology? Contact us at [email protected]. The full methodology white paper, including worked examples and the complete calculation model, is available to download below.

Download Full White Paper (PDF)

Important

Disclaimer

All impact figures shown on ForestNation Forest Profiles and Impact Certificates are estimates. They are based on physical field measurement data, peer-reviewed allometric models, and deliberately conservative assumptions. They represent projected averages across species, sites, and tree lifetimes. Actual impact per individual tree will vary.

These figures have not been independently verified by a third-party carbon registry and do not constitute verified carbon credits or carbon offsets under any voluntary or compliance carbon market standard.

ForestNation does not claim that tree planting neutralises, offsets, compensates for, or eliminates any quantity of greenhouse gas emissions. Trees planted through ForestNation fund verified reforestation — a positive contribution to forest restoration. They are not a mechanism for reaching net zero or carbon neutrality claims.

This methodology was prepared in good faith and reviewed against the EU ECGT Directive 2024/825, the UK CMA Green Claims Code, the UK ASA CAP Code, and the US FTC Green Guides. It will be updated as our measurement methodology evolves and as regulatory guidance develops.

Last updated: April 2026  ·  Version 1.0  ·  Questions: [email protected]