We use two different approaches to calculate carbon stocks and CO2 sequestration of the regenerative agroforestry system used in our Community Reforestation Program. For a deep dive into the technology, formulas, and numbers, read this entire article. Here’s a snapshot of the numbers:
- Net carbon benefit per hectare: 191.6 tons CO2
- Net carbon benefit per acre: 77.5 tons CO2
- Cost per ton of CO2: $39.15
Contents of this Article
- Approach 1: FARM-TRACE
- Approach 2: Reference Studies
- Total Carbon Stocks
- Annual Carbon Sequestration Rates
- Calculating the baseline and risk buffer
- Carbon Tables
Approach 1: FARM-TRACE
We make ongoing measurements of the carbon stored in each reforestation parcel with a new digital technology platform called FARM-TRACE. Here’s how it works:
- Our field team visits the site and measures the height and diameter of every tree in specific sample plots within the parcel. They enter this information into a specialized app on a smartphone, which feeds the information into an algorithm that calculates biomass, based on existing allometric equations that have been created for precisely this type of calculation.
- Meanwhile, the app simultaneously references the GPS coordinates where these measurements are being taken. Finally, a machine-learning algorithm uses satellite imagery to “truth” this information from the sky.
- The program uses all of this information to calculate how much CO2 this parcel has absorbed from the atmosphere at this point in time.
- We take these measurements twice per year, and the increase in carbon is graphed over time.
That’s how we measure the carbon stocks of each specific parcel on an ongoing basis.
Approach 2: Reference Studies
Okay, be prepared for a deep dive into carbon calculation methodology.
To forecast the overall carbon storage that the agroforestry parcels in our program will achieve over the 30-year project lifespan, we have relied upon a collection of scientific and academic research studies that provide solid reference numbers on which to base our calculations.
The most important such scientific research report is titled “Carbon stocks and cocoa yields in agroforestry systems of Central America” by Somarriba et al., 2013. The study measured carbon stocks in a network of 229 permanent sample plots in cacao-based agroforestry systems and natural forests in five Central American countries. It is one of the most comprehensive and respected studies in this field.
The ecology of agroforestry farmland in coastal Ecuador is similar to that of the locations that were sampled by this study in Central America, for which it serves as a useful reference point.
Below are the carbon calculations and high-level conclusions from that study.
Total Carbon Stocks
- Average total carbon was 117 ± 47 tons per hectare in cacao agroforestry plots. This means that 117 tons was the average amount of carbon per hectare, with a standard deviation of 47 tons.
- To convert carbon (C) to carbon dioxide (CO2), the carbon weight is multiplied by 3.67. This means that an average of 429 tons of CO2 are stored in one hectare of land. (117 tC/hectare x 3.67 = 429 tCO2/hectare.)
- 1 hectare = 2.471 acres. So, to convert the CO2 per hectare number to CO2 per acre, we divide by 2.471. This means that an average 174 tons of CO2 are stored in a 1-acre cacao agroforestry plot. (429 tCO2/hectare / 2.471 = 174 tons tCO2/acre)
Annual Carbon Accumulation Rates
- Furthermore, the study found that the rate of carbon accumulation in aboveground biomass averaged 2.0 tons of carbon per hectare per year. This can be abbreviated as 2.0 tC/ha/yr.
- Once again, we convert this number to CO2 by multiplying the carbon weight with 3.67. This yields 7.34 tons of CO2 per hectare per year. Or, 7.34 tCO2/ha/yr.
- To convert to acres, once again we divide by 2.471. This means that, on average, each 1-acre cacao agroforestry parcel absorbs (or “sequesters”) 2.97 tons of CO2 per year.
- Note: carbon accumulation does not go on forever. At some point, a forest will reach its maximum carbon stock. This can take anywhere from 30 to 100 years. If we use the “average total carbon stock” number in the Somarriba study to also represent the “maximum total carbon stock” (which would be a conservative approach to calculating this number), we can conservatively assume that cacao agroforestry has the capacity to sequester a total of 429 tons of CO2 per hectare, or 174 tons per acre.
Note that these numbers are relatively conservative, compared to some other similar studies. A comparable study, called “Influence of tree cover on diversity, carbon sequestration and productivity of cocoa systems in the Ecuadorian Amazon” (Jadán et al., 2015) measured carbon stocks and carbon accumulation rates across three different land-use categories—primary growth forest, shade-grown cacao agroforestry, and cacao monocultures—in the Ecuadorian Amazon. The study included 28 sample plots for each land-use category.
This study found that the average total carbon stocks in the shade-grown cacao agroforestry plots were 141.4 tons of carbon per hectare, which equates to 519 tons of CO2 per hectare in total. Meanwhile, the average annual CO2 sequestration was 17.9 tons per hectare. When converted to acres, this equates to the total CO2 sequestration of 210 tons per acre and average annual CO2 sequestration of 7.2 tons per acre.
However, to be conservative, we decided to use the average carbon numbers from the Somarriba study—as opposed to the Jadán study—as the reference numbers for our forecast of the carbon accumulation and carbon stocks of our Community Reforestation Program. Both studies, however, have been tremendously useful in guiding our project design.
The Somarriba study even counted the exact number of shade trees, fruit trees, cacao trees, and banana plants per hectare in each of the sample plots. We used these numbers as the basis for the number of shade trees, fruit trees, cacao trees, and banana plants that farmers are asked to plant in our Community Reforestation Program. This, in turn, further justifies our use of Somarriba’s carbon estimates as a reliable reference for our own numbers.
Calculating the Baseline and Risk Buffer
The Community Reforestation Program has a 30-year project lifespan. An average annual carbon accumulation rate of 2.0 tons of carbon per hectare per year (in CO2: 7.34 tCO2/ha/yr) yields 220.2 tons of CO2 per hectare after 30 years of forest growth. This is the total carbon storage number.
To calculate the net carbon benefit of a given reforestation project, the next step is to deduct the estimated tonnage of carbon that would have likely existed in the parcel in the absence of this project. This is known as the baseline estimate. In other words, we need to estimate how much carbon is stored by a degraded parcel of land in the status quo scenario—namely, a cattle pasture or cornfield.
For these numbers, we used numbers from an excellent study titled “Tropical deforestation drivers and associated carbon emission factors derived from remote sensing data” (De Sy et al., 2019). In this study, the mean total carbon stocks for cattle pastures in tropical moist forest ecosystems in Latin America were estimated at 2 tons per hectare, which equates to 7.34 tons of CO2 per hectare. That’s not the annual number—that’s the total amount of CO2 stored in one hectare of cattle pasture, on average.
Therefore, we subtract this number (7.34 tCO2/ha) from total CO2 storage (220.2 tCO2/ha) which yields a net carbon benefit of 212.9 tCO2/ha.
But we’re not finished yet! It is customary for some carbon to be allocated to a risk mitigation buffer, in case the reforestation parcels ultimately fall short of their carbon targets, for whatever reason. We have applied the industry-standard rate of 10% to serve a risk buffer. This means that we must deduct 21.3 tons from our net carbon benefit. This yields 191.6 tons of CO2 per hectare. This is the net carbon benefit that we conservatively estimate that our program will achieve per hectare. It equates to 77.6 tons of CO2 per acre.
In the meantime, we’re also using FARM-TRACE to measure annual CO2 sequestration rates. Over time, we’ll be able to refine our forecast based on how these numbers continue to stack up each year.
|Carbon Estimates (Conservative Scenario)||tC/ha/yr||tCO2/ha/yr||Years||
Total CO2 (tons)
|Baseline (Cattle Pasture)||7.3|
|Net Carbon Benefit (without Risk Buffer)||212.9|
|RIsk Buffer (10%)||21.3|
|Net Carbon Benefit Per Hectare||6.4||191.6|
|Net Carbon Benefit Per Acre||2.6||77.5|
|Total CO2 Costs / Price of Carbon||USD $|
|Total cost per hectare||$7,500|
|Total cost per metric ton of CO2||$39.15|
- The notation “t/ha/yr” is used as shorthand for Mg C ha−1 y−1. They both mean the same thing: metric tons per hectare per year.
- Carbon (C) is multiplied by 3.67 to calculate Carbon Dioxide (CO2),
- For the baseline calculation, we followed Plan Vivo’s methodology for measuring the baseline in the context of a slash-and-burn cycle.
- Risk Buffer of 10% is the industry standard (eg. the Trees for Global Benefit Programme)
For more information on the carbon offsets, check out The Danger of Cheap Carbon Offsets: What is the true cost of 1 ton of CO2?
To learn more about how our Community Reforestation Program works, check out our 2-minute animated video below.