Carbon Sequestration Methods

To estimate carbon emission reductions, TerraBio estimates carbon sequestration through biomass accumulation rates based on tree growth, by associating forest age with published growth curves. TerraBio used satellite imagery to monitor vegetation gains and losses of tree cover (biomass change) overtime. This metric quantifies increases, maintenance, or decreases in carbon stored as above-ground and below ground tree biomass over time for the ABF deals. Changes in carbon stored in trees are expected in TerraBio due to reforestation activities and growth of trees (agroforestry and/or natural forests).

Note, the changes that we capture in carbon storage over time is from changes in tree canopy cover. A different set of methods will be needed to monitor changes in carbon over time with changes to other land covers, such as grasses and shrubs.

TerraBio utilizes remote sensing approaches to calculate the total metric tons of carbon stored through biomass on an annual and cumulative basis. Forest stand age is determined by compiling both observations from Hansen forest loss maps and LandTrendr maps. Stand age is estimated by 1) calculating the time since a forest loss event was detected with recovery; 2) calculating the length of time since planting was established in non-forest areas (vegetation gain events from LandTrendr); 3) Assigning an age to forest cover that was established prior to 1985 (earliest images from Landsat).

From there, biomass is determined on an annual basis using equations built on stand age growth rates (the Chapman-Richards growth function using coefficients for South American humid forest). Biomass is used to estimate carbon stored as plant mass. Changes in carbon are estimated based on differences of annual estimates spanning 2017 and 2021.

Reporting details

We calculate this metric for the full farm boundary, but also provide details by land use.

Table 1. Summary of reporting details |ABF KPI |TerraBio metric|Reporting Unit |Measurement Unit| |—————|—————|—————|—————–| | CO2 e Reduction | Carbon Sequestration - Emission Reductions | total and by land use |tons CO2 equivalent removed, normalized by area|

Methods Overview Summary

  • Methodology:

Overview

Methodology: Changes in carbon stored in above and below-ground biomass are estimated using four steps:

  1. Map forest cover and stand age at annual increments.
    • LandTrendr: The Kennedy et al. (2010) paper describes LandTrendr, an algorithm that detects changes (decrease or increase) in forest canopy and can be used to date forests that have regrown
  2. Generate a probabilistic sample (e.g., simple random or stratified random). At each sample, we will interpret stand age by looking at time series plots and associated remote sensing imagery (e.g., Landsat).
    • Oloffson et al. (2014): map and sample based approaches to estimate area of stand ages. We conduct image interpretation in CEO Saah et al. 2019 to correct for systematic map errors of stand age.
  3. Apply growth curve functions to forest stands using growth curve functions developed for our region of interest
    • Bernal et al. (2018): The Bernal et al. (2018) paper provides biomass accumulation curves for different areas of the world. In particular, “…we developed biomass accumulation rates for a set of FLR activities (natural regeneration, planted forests and woodlots, agroforestry, and mangrove restoration) across the globe and global CO2 removal rates with corresponding confidence intervals, grouped by FLR activity and region/climate”.
  4. Assess the uncertainty of the estimates using a sample based approach and propagation of confidence intervals.
  • Input Data:
    • Landsat time series (NBR),
    • Potential forest layer (from supervised classification of NICFI and Map Biomass)
  • Computing Environment:
    • GEE: to map stand age,
    • CEO: image interpretation
    • R or GEE: generate statistics
  • Output: Carbon sequestration per year per land use

Resources

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