PCS TA 009 Trees & Shrubs Carbon Stock Tool_v1.0

Document Control

Document identification

• Document code: PCS-TA-009

• Title: Trees & Shrubs Carbon Stock Tool

• Scope: Quantification tool for estimating above-ground and below-ground biomass and carbon stocks for trees and shrubs using field measurements, allometric equations, wood density and carbon fraction values, plot expansion, stratification, scaling, uncertainty and QA/QC procedures.

• Application: Used whenever an applicable PCS methodology includes woody biomass pools (trees and/or shrubs) in baseline and/or monitoring carbon accounting.

Version history and change log

Table DC-1. Revision history

Version	Date	Status	Summary of changes	Prepared by	Approved by
v1.0	TBD	Draft	Release for public consultation	PCS	TBD

Superseded versions

No superseded versions for v1.0.

Governance note on versioning and archiving

Only the latest approved version of this tool shall be used for new project registrations and for quantification/verification of monitoring periods unless PCS specifies otherwise. Superseded versions shall be archived and retained for traceability and audit purposes, including for projects assessed under earlier versions where applicable, consistent with PCS governance rules.

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Chapter 1 - Introduction and Purpose

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Overview

1. The Tree & Shrub Carbon Stock Estimation Tool defines the standardized procedures required to quantify above-ground and below-ground biomass carbon in woody vegetation within PCS Nature-Based Solutions project boundaries. The tool provides the technical framework for estimating carbon stocks and stock changes in forests, woodlands, agroforestry systems, mangrove stands, shrublands, and mixed vegetation complexes.

2

Purpose

1. The purpose of this tool is to ensure that carbon stock estimates are produced consistently, transparently, and conservatively across all PCS projects. It supports the quantification of baseline carbon stocks, monitoring-period stocks, and changes attributable to project activities. The tool aligns with internationally recognized scientific approaches, including allometric biomass equations, wood density integration, carbon fraction conversion, and statistical procedures governing sample plot design and uncertainty assessment.

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Mandatory application

1. This tool must be applied whenever trees or shrubs contribute to the carbon pools included in the applicable PCS methodology. It provides the calculation structure for biomass and carbon estimation at the tree, plot, stratum, and project levels. The tool accommodates species-specific, region-specific, and generalized allometric equations, allowing project developers to select the most appropriate equation set for local ecological conditions while ensuring methodological consistency.

4

Integration of inputs

1. The tool further establishes the procedures for integrating tree measurements, wood density values, root-to-shoot ratios, and carbon fractions into final carbon stock estimates. It describes how sampling plots must be designed, measured, and analyzed to ensure sufficient statistical confidence in project results. The tool also specifies how biomass estimates must be scaled from plot-level measurements to strata and to the full project area.

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Objective

1. By providing a standardized, auditable pathway for estimating tree and shrub carbon stocks, this tool supports the generation of robust and verifiable carbon credit outcomes under the Planetary Carbon Standard.

Chapter 2 - Scope and Applicability

1

1. This tool applies to all PCS projects in which woody biomass contributes to carbon stocks or emission reductions. It provides the procedures for estimating above-ground and below-ground biomass in trees and shrubs using field measurements, allometric equations, and conversion factors. The tool is applicable in forests, mangroves, woodlands, agroforestry systems, revegetated landscapes, and mixed vegetation mosaics where tree and shrub components form a measurable carbon pool.

2

1. The tool must be used to estimate carbon stocks in all strata containing woody vegetation, regardless of species composition, stand structure, or management regime. It applies both to natural and planted stands and accommodates monoculture plantations, multi-species systems, degraded forests, regenerating vegetation, shrublands, and anthropogenically altered landscapes. The tool also applies to mangrove ecosystems when allometric equations are used to estimate tree biomass; however, soil carbon in mangroves is addressed through other PCS tools.

3

1. The tool is required for baseline establishment and for all monitoring periods where changes in woody biomass carbon stocks must be quantified. It provides the basis for estimating carbon removals through growth, carbon losses from harvesting or disturbance, and net carbon stock changes from reforestation, afforestation, restoration, enrichment planting, and natural regeneration.

4

1. The tool does not apply to non-woody vegetation, herbaceous biomass, grasses, or agricultural crops that lack woody structure. These vegetation types may be included under separate PCS guidelines if required by specific methodologies. Similarly, dead wood, litter, and soil carbon pools are addressed under separate PCS tools and are excluded from the scope of this document unless the applicable methodology specifies their inclusion.

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1. The procedures described in this tool must be applied consistently across the project boundary and throughout all reporting periods. When project developers use species-specific or region-specific allometric equations, the selection and application of such equations must conform to the criteria established in this tool. Any deviation from these procedures must be justified and documented in the Monitoring Report.

Chapter 3 - Key Concepts and Definitions

3.1 Above-Ground Biomass (AGB)

1. Above-ground biomass refers to the total dry mass of living woody vegetation located above the soil surface, including stems, branches, and leaves where applicable. AGB is typically estimated using allometric equations derived from measurable tree attributes such as diameter at breast height, tree height, and wood density.

3.2 Below-Ground Biomass (BGB)

1. Below-ground biomass represents the dry mass of living root systems associated with trees and shrubs. It is not measured directly but is estimated using root-to-shoot ratios or allometric equations. BGB contributes significantly to total biomass in many ecosystems, particularly in mangroves, drylands, and deep-rooted species.

3.3 Diameter at Breast Height (DBH)

1. DBH is the diameter of a tree stem measured at 1.3 meters above the ground. It is the primary variable used in most allometric models. DBH must be measured consistently, following standardized protocols to ensure accurate biomass estimation.

3.4 Wood Density (ρ)

1. Wood density is the ratio of oven-dry mass to green volume of wood. It is a critical parameter influencing biomass estimation because trees with higher wood density store more carbon per unit of stem volume. Wood density values may be species-specific, genus-level, or regional averages, depending on availability.

3.5 Allometric Equations

1. Allometric equations are mathematical relationships that estimate biomass based on observable tree characteristics. Equations must be scientifically validated and appropriate for the species, ecological zone, and structural characteristics of the vegetation being measured. The selection and justification of allometric equations must follow the criteria in this tool.

3.6 Expansion and Conversion Factors

1. Expansion factors convert plot-level biomass estimates to per-hectare estimates. Conversion factors convert biomass to carbon mass based on the carbon fraction of wood. These factors must be applied consistently across strata.

3.7 Stratum

1. A stratum is a subdivision of the project area defined by vegetation type, species composition, stand age, canopy structure, management history, or ecological condition. Stratification ensures that sampling and biomass estimation reflect the heterogeneity of the project landscape.

3.8 Sample Plot

1. A sample plot is a defined area where field measurements of trees and shrubs are conducted. Sample plots may be circular, square, or rectangular, but the plot size and shape must remain consistent within a stratum. Plots form the basis for estimating biomass at the stratum level.

3.9 Root-to-Shoot Ratio (R:S)

1. The root-to-shoot ratio estimates below-ground biomass based on above-ground biomass. It varies by species, ecology, and tree maturity. When below-ground biomass must be included, R:S ratios must be selected from credible literature or default tables provided in this tool.

3.10 Carbon Fraction of Biomass (CF_biomass)

1. Carbon fraction represents the proportion of dry biomass that is carbon. A typical default value is 0.47, although species- or region-specific values may be used when available. The carbon fraction is applied to both AGB and BGB to estimate carbon stocks.

3.11 Plot Expansion Factor (PEF)

1. The plot expansion factor converts biomass measured within a sample plot to biomass per hectare. It is calculated based on the plot area and is essential for scaling measurements from the plot to the stratum.

3.12 Biomass Increment

1. Biomass increment represents the change in biomass over a monitoring interval. It is estimated by comparing biomass measurements from successive monitoring periods. Biomass increment forms the basis for estimating carbon removals attributable to project activities.

3.13 Uncertainty in Biomass Estimates

1. Uncertainty arises from measurement errors, sampling variability, model selection, and parameter values such as wood density. Projects must quantify uncertainty where required by the methodology and apply conservative adjustments consistent with PCS standards.

Chapter 4 - Parameters and Symbols

1. This chapter defines the parameters and symbols used throughout the biomass and carbon estimation procedures. These values must be applied consistently and documented clearly in all calculations. Deviations from standard parameter values must be justified in the Monitoring Report.

Table 1. Parameters and Symbols Used in Biomass Estimation

Symbol	Description	Units	Notes
DBH	Diameter at breast height	cm	Standardized measurement at 1.3 m
H	Tree height	m	Used when allometric equations require height
ρ (rho)	Wood density	g/cm³	Species-, genus-, or region-specific
AGB	Above-ground biomass	kg or t	Estimated using allometric models
BGB	Below-ground biomass	kg or t	Estimated using root-to-shoot ratios or allometry
CF_biomass	Carbon fraction of dry biomass	—	Default = 0.47 unless species-specific values available
R:S	Root-to-shoot ratio	—	Used to estimate below-ground biomass
P	Plot area	m²	Required for expansion to per-hectare values
PEF	Plot expansion factor	—	Converts plot biomass to t/ha
Biomass_plot	Biomass per plot	t	Sum of AGB and BGB for all individuals in the plot
Biomass_ha	Biomass per hectare	t/ha	Biomass_plot × PEF
Carbon_stock	Carbon mass per hectare	tC/ha	Biomass_ha × CF_biomass
n	Number of plots in a stratum	—	Must meet sampling adequacy requirements
SE	Standard error	—	Derived from plot-level biomass variation
CI	Confidence interval	—	Used in uncertainty estimation and deductions
ΔC	Change in carbon stock	tC/ha	Difference between baseline and monitoring values
ΔC_total	Total change in carbon stock	tC	Sum of stratum-level ΔC × area

Parameter Notes:

1. Diameter at breast height (DBH) is the primary variable in most allometric equations and must be measured consistently according to the field protocols required under this tool. Tree height (H) is included only when the chosen allometric model requires it; height measurement must follow standardized procedures to avoid bias.

2. Wood density (ρ) must be selected from reputable databases or literature sources, using species-specific values where possible. When species-level information is unavailable, genus or regional averages may be applied.

3. Plot expansion factors (PEF) convert biomass measured in the plot area to biomass per hectare. These must be calculated based on the plot size and applied uniformly within each stratum.

4. The carbon fraction of biomass (CF_biomass) converts biomass to carbon stock. The standard value of 0.47 reflects widely used defaults; species-specific values may be used when supported by scientific evidence.

5. Uncertainty-related parameters (SE and CI) must be calculated when required by the methodology and reported transparently.

Chapter 5 - Allometric Equations and Biomass Estimation Procedures

1. Allometric equations form the core of tree and shrub biomass estimation. They allow project developers to convert measurable tree attributes—such as diameter, height, and wood density—into statistically robust biomass estimates. This chapter outlines the principles for selecting appropriate allometric equations, describes how these equations must be applied, and provides the procedures for deriving plot-level and stratum-level biomass estimates for PCS projects.

5.1 Principles for Selecting Allometric Equations

1. Allometric equations must be scientifically validated, published in peer-reviewed literature, and applicable to the species, ecological zone, and vegetation structure of the project area. Equations selected must reflect the biological characteristics of the vegetation being assessed, including crown architecture, wood density, and growth form.

2. When species-specific equations exist for the dominant species in a stratum, these equations should be applied. In mixed-species or heterogeneous vegetation, equations developed for the broader ecological region or functional group may be used. For mangroves and coastal vegetation, specialized equations must be used due to distinctive morphology and root systems.

3. If no appropriate equation exists for the vegetation type, a generalized tropical, temperate, or dryland equation from recognized authorities may be applied, provided it is justified in the Monitoring Report.

5.2 Structure of Allometric Equations

1. Allometric equations typically express above-ground biomass (AGB) as a function of tree diameter (DBH), height (H), wood density (ρ), or combinations of these variables. Common equation forms include:

• DBH-only models

• DBH–height models

• DBH–wood density models

• DBH–height–wood density combined models

1. The general structure may be expressed as: the form and coefficients must be used exactly as specified in the source publication.

5.3 Incorporating Wood Density

1. Wood density (ρ) is a fundamental component of many allometric models and must be sourced from peer-reviewed or scientifically recognized databases. Species-specific values should be used whenever possible. If these are unavailable, genus-level or ecological-zone averages may be applied. Wood density values must be documented in the Monitoring Report with references.

5.4 Application of Allometric Equations

1. For each measured tree or shrub within a sample plot, the selected equation must be applied using the collected field measurements. Each tree yields an individual AGB estimate. When equations output values in kilograms, they must be converted to tonnes where necessary.

Shrub biomass must be estimated using equations specific to shrub species or growth forms. Shrub biomass may be estimated directly or using simplified forms that relate canopy dimensions to biomass, provided the methodology allows such approaches.

Below-ground biomass (BGB) must be estimated using root-to-shoot ratios or allometric models appropriate to the vegetation type. The selected ratios or equations must be scientifically defensible.

5.5 Plot-Level Biomass Estimation

1. The biomass of all individual trees and shrubs measured within a plot must be summed to derive total plot biomass. This sum represents the combined above-ground and below-ground biomass for the plot area. If height is used in the allometric equation, height measurements must be consistently applied across all plots.

2. Plot biomass must then be converted to biomass per hectare using the plot expansion factor (PEF), which depends on the area of the sample plot. The Monitoring Report must document the method used to derive PEF and the area of each sample plot.

5.6 Scaling Biomass From Plot to Stratum

1. Biomass per hectare estimates from sample plots must be averaged within each stratum to generate a stratum-level mean biomass estimate. The number of sample plots must meet precision requirements described in the sampling design tool. Where stratification is used, each stratum must be treated as a separate unit for the purposes of biomass computation and uncertainty assessment.

2. Stratum biomass is calculated as the mean biomass per hectare multiplied by the total area of that stratum.

5.7 Combining Above-Ground and Below-Ground Biomass

1. Total biomass is the sum of above-ground and below-ground biomass. Both components must be estimated using consistent allometric or ratio-based methods. If the methodology excludes below-ground biomass, only AGB values must be used.

5.8 Conversion of Biomass to Carbon Stock

1. Biomass must be converted to carbon using the carbon fraction (CF_biomass). The default value of 0.47 must be applied when species-specific data are unavailable.

Carbon stock must be reported per hectare and then aggregated to the stratum and project scale.

Chapter 6 - Sampling Design and Plot Establishment

1. Sampling design ensures that biomass and carbon stock estimates are representative of vegetation conditions within each project stratum. This chapter describes the principles and procedures for selecting sample plots, defining their layout, and applying statistically valid sampling frameworks consistent with PCS requirements.

6.1 Sampling Objectives

1. The sampling design must provide unbiased estimates of biomass and carbon stocks within each stratum and must meet the precision requirements defined in the applicable methodology. The design must ensure that spatial variation in vegetation structure is captured through an adequate number of sample plots and through a sampling pattern that reflects the heterogeneity of the project area.

6.2 Stratified Sampling Framework

1. Sampling must be conducted separately within each stratum. Strata may be defined by vegetation type, stand age, management regime, degradation level, or other characteristics relevant to biomass variability. Stratification helps reduce variance within sampling units and improves estimate precision. Each stratum must have its own sampling intensity, number of plots, and plot layout.

6.3 Determination of Sample Size

1. The number of sample plots required in each stratum must be determined through a statistical assessment that meets the minimum precision or confidence level established by the methodology. The sample size must account for expected variability in biomass, plot size, and measurement error. When remeasurement occurs, the same sample plot locations must be used to ensure temporal consistency unless a plot is lost or inaccessible.

6.4 Plot Size and Shape

1. Sample plots may be circular, square, or rectangular. Circular plots are commonly used due to ease of layout and reduced boundary error, while rectangular plots may be preferred in dense vegetation or where transect methods are applied. Plot size must be consistent within a stratum and selected based on the density and size distribution of trees and shrubs. Larger plots are typically required in heterogeneous or high-biomass forests.

2. The area of each plot must be calculated precisely, as it directly influences the plot expansion factor used to convert plot biomass to per-hectare estimates.

6.5 Plot Distribution and Spatial Arrangement

1. Plots must be distributed in a manner that provides representative coverage of each stratum. Systematic sampling, stratified random sampling, or grid-based designs may be used. The selected arrangement must avoid bias and must not favor convenient or easily accessible areas.

2. Plot locations must be identified using GPS coordinates and recorded accurately to ensure repeatability in future monitoring periods. If plot relocation is required, the new location must be documented with justification.

6.6 Tree and Shrub Inclusion Criteria

1. Clear rules must be defined for including or excluding trees and shrubs within a plot. These criteria must include the minimum diameter threshold for measurement (e.g., DBH ≥ 5 cm), height thresholds for shrubs, and procedures for measuring trees located exactly on plot boundaries. The criteria must be applied consistently to avoid bias in biomass estimates.

6.7 Plot Marking and Long-Term Identification

1. Permanent sample plots must be marked with durable and visible identifiers to ensure accurate relocation during monitoring periods. Markings may include tags, stakes, or paint applied to trees. The Monitoring Report must describe the marking system used and must document the condition of plot markers during field visits.

6.8 Measurement Protocols

1. Field measurement protocols must follow established forestry standards. Measurements must include DBH, height when required by allometric equations, species identification, and wood density information. Height measurements must follow a consistent technique, using hypsometers or other calibrated instruments. Measurements of multi-stemmed trees, buttressed stems, leaning trees, and irregular forms must follow standardized rules provided in this tool.

6.9 Quality Assurance in Sampling

1. Quality assurance procedures must be applied throughout sampling to minimize measurement error. This includes calibration of measurement instruments, verification of species identification, cross-checking of DBH measurements, and periodic field audits of measurement teams. Any deviations from standard procedures must be documented.

Chapter 7 - Wood Density, Carbon Fraction, and Root-to-Shoot Ratios

1. Reliable biomass estimation depends on accurate parameter values associated with tree species, wood structure, and their allocation of biomass between above-ground and below-ground components. This chapter establishes the procedures for selecting and applying wood density values, carbon fractions, and root-to-shoot ratios in PCS projects.

7.1 Wood Density (ρ)

1. Wood density is a critical variable in many allometric models because it reflects the mass of woody material per unit volume. Species-level wood density values should be used whenever possible. These values may be obtained from peer-reviewed datasets, national forest inventory databases, or published scientific literature. When species-specific values are unavailable, genus-level or ecological-zone averages may be applied. All wood density values used in calculations must be documented with proper citations.

2. If the project area includes species with significant intra-species variability or natural hybrids, representative wood density values must be selected. Where mixed-species stands occur, each species must be assigned its appropriate wood density. When species cannot be identified, conservative values must be used based on the average wood density of the dominant functional group.

7.2 Carbon Fraction of Biomass (CF_biomass)

1. The carbon fraction represents the proportion of oven-dry biomass that is carbon. A default value of 0.47 must be applied for biomass unless species-specific values are available. When project developers use species-specific carbon fractions, the values must be supported by laboratory analyses or reputable scientific publications.

2. Carbon fraction must be applied consistently across above-ground and below-ground biomass unless distinct values are justified scientifically. Any deviation from the default or recommended values must be explained and documented in the Monitoring Report.

7.3 Root-to-Shoot Ratios (R:S)

1. Below-ground biomass is typically estimated using root-to-shoot ratios unless an allometric model provides direct estimates. R:S ratios may vary by ecosystem type, species, climate zone, and forest age. Default values must be selected from authoritative sources, such as IPCC guidelines or published biome-specific studies.

2. Ratios must be applied consistently within each stratum, based on the dominant vegetation type or functional group. When mixed vegetation occurs, weighted averages may be applied. The Monitoring Report must describe the selected ratios and the justification for their application.

7.4 Integration of Parameter Values in Biomass Estimation

1. Once the appropriate wood density, carbon fraction, and root-to-shoot ratio values are selected for each species or stratum, they must be integrated systematically into the allometric biomass calculations. Above-ground biomass is first estimated using allometric equations. Below-ground biomass is then derived using the selected R:S ratio. Total biomass is computed as the sum of the two components.

2. After total biomass has been calculated, carbon stock is derived by applying the carbon fraction. Parameter values must remain consistent throughout the reporting period unless new scientific evidence or improved data sources justify an update. Any changes between baseline and monitoring periods must be transparently documented.

7.5 Documentation and Verification of Parameters

1. The Monitoring Report must present a consolidated table of all parameter values used, including species names, wood density sources, carbon fraction sources, and root-to-shoot ratios. References to data sources must be included. When field sampling is used to determine wood density or carbon fraction, the procedures, laboratory methods, and sample locations must be documented for verification.

Chapter 8 - Plot-Level Biomass Calculation

1. Plot-level biomass estimation converts field measurements of trees and shrubs into quantitative biomass values using the selected allometric equations and parameter inputs defined in earlier chapters. This chapter outlines the procedures for calculating the above-ground and below-ground biomass of individual trees and shrubs and for aggregating these estimates to the plot level.

8.1 Tree- and Shrub-Level Biomass Estimation

1. Each tree or shrub measured within a sample plot must be assigned an above-ground biomass value based on the allometric equation selected for that species or vegetation type. The equation must be applied exactly as published. Required inputs may include DBH, height, and wood density. All measurements must be checked for accuracy before use.

2. Below-ground biomass is then estimated using either a root-to-shoot ratio or an allometric equation, depending on the methodology and data availability. If a root-to-shoot ratio is used, the below-ground biomass is computed as a proportion of above-ground biomass. When allometric models provide direct estimates of below-ground biomass, these must be applied according to their specific structure and assumptions.

3. The total biomass of an individual tree or shrub is the sum of its above-ground and below-ground biomass.

8.2 Summation of Biomass Within a Plot

1. After calculating biomass for each measured individual, biomass values must be summed to derive total plot biomass. This includes all trees and shrubs meeting the inclusion criteria for the plot. If the plot contains multiple vegetation layers or mixed species, all components must be included according to the procedures defined for each layer or vegetation type.

2. The sum of the biomass values represents the total dry mass of woody vegetation present in the plot at the time of measurement.

8.3 Conversion to Per-Hectare Biomass

1. To convert plot-level biomass to a per-hectare basis, the plot expansion factor (PEF) must be applied. The PEF is derived from the ratio of one hectare to the plot area.

Accurate calculation of the plot area is essential. Any errors in plot area will propagate through to per-hectare estimates and must therefore be avoided.

8.4 Treatment of Special Cases

1. Certain forest or vegetation conditions require special consideration during plot-level calculations. For multi-stemmed trees, stems must be measured and combined using standardized rules before applying allometric equations. Leaning or deformed stems must be measured following consistent protocols. Trees located on plot boundaries must be included or excluded according to predefined boundary rules.

2. When mortality, harvesting, or disturbance has occurred, reductions in biomass must be recorded and incorporated into plot-level values. Dead wood resulting from disturbance is excluded from this chapter and must be addressed using the designated PCS tool for dead wood and litter.

8.5 Plot-Level Carbon Calculation

1. Once total biomass per hectare has been determined, carbon stock is calculated by applying the carbon fraction.

Carbon stock must be reported for above-ground and below-ground components when required by the applicable methodology.

8.6 Documentation Requirements at Plot Level

1. The Monitoring Report must include the biomass calculation steps used for each plot. This includes the equations applied, parameter values, field measurements, and intermediate calculation results. Plot-level tables must show DBH, height, wood density, individual biomass estimates, and summed biomass values. Any adjustments made due to field conditions must be documented clearly.

Chapter 9 - Scaling Carbon Stocks to Stratum and Project Levels

1. Scaling procedures convert plot-level biomass and carbon estimates into stratum- and project-wide values. These procedures ensure that estimates accurately represent the spatial distribution of vegetation and the variability within each stratum. This chapter outlines how to aggregate biomass values from individual plots and how to apply these results consistently across the project.

9.1 Stratum-Level Biomass and Carbon Estimates

1. Each stratum must be analyzed independently. Plot-level biomass per hectare values derived in earlier steps are used to calculate the mean biomass for the stratum. This mean must be computed using all valid sample plots within the stratum. If sampling intensity varies between monitoring periods, each dataset must meet the methodological precision requirements.

2. After biomass per hectare is determined, the carbon fraction is applied to derive carbon stock. If the methodology requires separate reporting of above-ground and below-ground pools, these values must be computed and documented individually before summation.

9.2 Scaling to Stratum Area

1. Once stratum-level biomass or carbon per hectare is known, total stratum carbon stock is calculated by multiplying the per-hectare value by the area of the stratum. Stratum area must be derived from accurate spatial data and must remain consistent across reporting periods unless stratification is updated for justified reasons.

When multiple vegetation types or age classes exist within a stratum, sub-stratification may be applied to improve accuracy, provided it is implemented consistently.

9.3 Aggregation to Project-Level Carbon Stock

1. Project-level carbon stock is the sum of carbon stocks across all strata. This aggregation must reflect the complete project boundary and all vegetation types included in the carbon accounting framework.

If certain strata are excluded under the applicable methodology, this exclusion must be documented clearly.

9.4 Scaling Carbon Stock Changes Over Time

1. Carbon stock changes must be estimated by comparing baseline values with monitoring-period values. Differences must be calculated separately for each stratum. For restoration or afforestation activities, positive carbon stock changes reflect carbon removals. For areas experiencing degradation or disturbance, negative changes represent carbon losses.

Project-level carbon stock change is the sum of the stratum-level changes.

9.5 Treatment of Disturbance and Harvesting

1. When harvesting, natural disturbances, or anthropogenic losses occur, these events must be reflected in the stratum-level carbon calculations. The reduction in biomass must be incorporated into the project’s carbon stock for that monitoring period. If dead wood and litter are tracked separately, losses must be reallocated to the appropriate carbon pools according to methodology requirements.

9.6 Spatial Consistency Across Monitoring Periods

1. Stratum boundaries must remain consistent unless ecological changes or management practices justify reclassification. If stratification changes, the project must demonstrate that the new classification enhances accuracy and does not compromise comparability across reporting periods. All spatial data must be archived and submitted in geospatial format.

9.7 Documentation Requirements for Scaling

1. The Monitoring Report must present all calculations used to derive stratum- and project-level carbon stocks. This includes tables showing:

• Mean biomass and carbon per hectare for each stratum

• Stratum areas

• Total carbon stock by stratum

• Project-wide totals

• Changes in carbon stock since baseline

All scaling assumptions and data sources must be documented clearly to allow replication and verification.

Chapter 10 - Uncertainty Analysis and Conservativeness

1. Uncertainty analysis is required to demonstrate that carbon stock estimates are statistically robust and that project results do not overstate carbon benefits. This chapter establishes the procedures for quantifying sampling uncertainty, addressing model and parameter uncertainty, and applying conservativeness where necessary. All uncertainty assessments must be transparent, replicable, and aligned with the precision requirements of the applicable PCS methodology.

10.1 Sources of Uncertainty

1. Uncertainty in biomass estimation arises from several components:

2. Sampling variability, which reflects the natural heterogeneity of vegetation within a stratum;

3. Measurement errors associated with DBH, height, and species identification;

4. Model uncertainty arising from the allometric equations used;

5. Parameter uncertainty associated with wood density, carbon fraction, and root-to-shoot ratios.

Each source must be addressed to ensure that final carbon estimates reflect realistic and conservative values.

10.2 Sampling Uncertainty Within a Stratum

1. Sampling uncertainty must be quantified for each stratum using the variability of biomass estimates across sample plots. The standard error of the mean and the confidence interval must be calculated following accepted statistical procedures. The calculated precision must meet the minimum requirement established by the applicable methodology. When precision is insufficient, additional sampling must be conducted or conservative deductions must be applied.

2. Stratified sampling must treat each stratum independently. Uncertainty in one stratum cannot be offset by higher precision in another.

10.3 Model Uncertainty in Allometric Equations

1. Allometric equations carry inherent uncertainty due to their empirical nature and the conditions under which they were developed. When multiple validated allometric models are available for a species or vegetation type, the model must be selected based on scientific suitability rather than the magnitude of the biomass estimate. If the methodology requires, additional conservativeness may be applied through selection of an equation that yields moderate or lower estimates to avoid overstatement of carbon stocks.

2. If a project uses a generalized equation instead of a species-specific model, the project must justify that the model is appropriate for the vegetation conditions. In such cases, a conservative approach may be required to address wider variability.

10.4 Parameter Uncertainty: Wood Density and Carbon Fraction

1. Wood density values may vary within species due to growth conditions, age, and ecological gradients. To address this uncertainty, species-level values from recognized databases must be prioritized. When only genus-level or regional averages are available, these values must be applied conservatively. Carbon fraction values must be applied consistently, and deviations from the default must be justified based on scientifically defensible evidence.

Any adjustments to parameter values between reporting periods must be fully documented.

10.5 Combined Uncertainty Across Biomass Pools

1. Total uncertainty for a stratum reflects the combined influence of sampling, model, and parameter uncertainty. If required by the methodology, these uncertainties must be integrated to derive a comprehensive uncertainty estimate. When the combined uncertainty exceeds allowable thresholds, conservativeness must be applied through deductions to ensure environmental integrity.

2. Projects must ensure that uncertainty treatment remains consistent throughout the crediting period unless methodological updates require otherwise.

10.6 Application of Conservativeness

1. Conservativeness must be applied whenever uncertainty leads to potential overestimation of carbon stocks or emission reductions. This may involve selecting higher wood density values for destructive species, using generalized rather than species-specific allometries, or applying deductions to stratum-level carbon estimates.

2. When sampling uncertainty exceeds thresholds and additional sampling is not feasible, conservativeness may be applied by reducing the estimated carbon stock by a defined proportion consistent with methodology-specific rules.

10.7 Reporting Requirements for Uncertainty

1. The Monitoring Report must include a clear description of how uncertainty was quantified and how conservativeness was applied. This includes:

• Presentation of standard error and confidence interval calculations;

• Explanation of model selection and justification for chosen parameters;

• Description of any deductions made due to uncertainty;

• Changes in sampling effort or methodology between reporting periods;

• Tables summarizing uncertainty values by stratum.

All supporting data and analytical procedures must be available for verification.

Chapter 11 - Reporting Requirements

1. Accurate and transparent reporting is essential for the verification of carbon stocks and stock changes derived from tree and shrub biomass. The Monitoring Report must present all relevant data, methods, assumptions, and results in a manner that allows independent replication by a Validation and Verification Body (VVB). This chapter outlines the minimum reporting requirements.

11.1 Description of Project Strata

1. The report must describe all strata used in the biomass assessment. This includes the ecological characteristics of each stratum, the area represented, and the rationale for stratification. Any changes in stratum boundaries since previous reporting periods must be explained. The report must include maps and geospatial files that define each stratum clearly.

11.2 Sampling Design and Plot Information

1. The report must document the sampling design applied during the monitoring period. This includes the number of sample plots per stratum, the plot size and shape, and the sampling framework used to determine plot placement. Plot coordinates must be provided in geospatial format. Any adjustments to sampling design due to access limitations or environmental changes must be described.

2. A table summarizing all measured plots must be included, showing plot ID, coordinates, plot area, number of trees measured, and field conditions observed.

11.3 Tree and Shrub Measurement Data

1. The Monitoring Report must present all field measurements used to estimate biomass. This includes DBH, height where applicable, species identification, and any special notes relating to measurement conditions. When trees exhibit irregular forms, multi-stem structures, buttresses, or deformation, the measurement rules applied must be documented.

2. Field measurement data may be presented as annexes or supplemental files, provided the Monitoring Report clearly references them.

11.4 Allometric Equations and Parameter Values

1. The report must state the allometric equations used for each species or vegetation type. Each equation must be accompanied by the source reference and the justification for its applicability. The report must also present the wood density values, carbon fraction values, and root-to-shoot ratios used in the calculations, along with citations.

2. If region-specific or species-specific parameter values are unavailable, the report must document how default or generalized values were selected.

11.5 Plot-Level Biomass and Carbon Estimates

1. Plot-level results must be presented in a structured format. Each plot must include:

• Above-ground biomass,

• Below-ground biomass where applicable,

• Total biomass per plot,

• Biomass per hectare (after applying the plot expansion factor),

• Carbon stock per hectare.

These values must be clearly linked to the field measurements and parameter values applied.

11.6 Stratum-Level Biomass and Carbon Results

1. The report must provide the mean biomass per hectare for each stratum, derived from the set of sample plots. It must also present the number of plots used, the standard deviation, the standard error, and the confidence interval for each stratum. Total carbon stock per stratum must be calculated using stratum area and presented in tabular form.

2. If biomass pools were excluded or reported separately (e.g., mangroves, shrub-only strata), the methodology and rationale must be described.

11.7 Project-Level Carbon Stock and Stock Change

1. The Monitoring Report must present the aggregated carbon stock across all strata. Stock changes must be calculated by comparing baseline and monitoring-period carbon stocks. The report must clearly distinguish carbon removals, carbon losses, and any disturbances or harvesting events that occurred during the period.

2. The report must explicitly state the total carbon stock change attributed to project activities, in tonnes of carbon and tonnes of CO₂ equivalent.

11.8 Uncertainty Results and Conservativeness

1. The report must summarize sampling uncertainty, model uncertainty, and parameter uncertainty. It must show how each uncertainty source was quantified and how final uncertainty values were integrated at the stratum level. If deductions or conservative adjustments were applied to satisfy methodological requirements, the report must document them clearly.

2. Uncertainty tables must be provided to show confidence intervals, sampling error values, and any adjustments applied.

11.9 Documentation and Archiving

1. All supporting materials must be archived and made available for verification. This includes:

• Field measurement sheets,

• GPS coordinates for all plots,

• Wood density and carbon fraction references,

• Allometric equation sources,

• Calculation spreadsheets,

• Geospatial files defining strata and plot locations.

1. The Monitoring Report must reference the location of these materials and confirm that they are stored in accordance with PCS record-keeping requirements.

Annex A - Recommended Allometric Equations

1. This annex provides a curated list of scientifically validated allometric equations suitable for common vegetation types encountered in PCS projects. Project developers may use species-specific, regional, or generalized models depending on data availability. The equations listed here represent widely accepted standards in forest carbon measurement.

A.1 General Tropical Forest Equations

• Chave et al. (2014) Moist Tropical Forest Equation

• Chave et al. (2014) Dry Tropical Forest Equation

• Chave et al. (2005) DBH-Only Pantropical Equation (applicable when height is not available)

A.2 Mangrove-Specific Equations

• Komiyama et al. (2005) Mangrove Equation

These equations are suitable for Rhizophora, Avicennia, Sonneratia, and mixed mangrove stands.

A.3 Temperate Forest Equations

• Jenkins et al. (2003) U.S. Temperate Forests (general hardwoods and conifers)

A.4 Shrub Biomass Equations

• Brown (1976) Shrublands

• Crown-based shrub models (coefficients must be sourced from regional studies)

A.5 Criteria for Selecting Equations

1. Equations should be selected based on:

• Vegetation type

• Ecological zone

• Species presence

• Diameter and height range validity

When multiple models exist, project developers must select the equation that best matches site conditions and provide justification.

Annex B - Wood Density Reference Tables

1. Wood density values must be sourced from credible datasets. The tables below provide representative values when species-level data are unavailable. Values are illustrative; final tables will be expanded with region-specific data during PCS finalization.

B.1 Tropical Wood Density Averages

Species / Genus	Wood Density (g/cm³)
Acacia spp.	0.60
Shorea spp.	0.52
Eucalyptus spp.	0.58
Rhizophora spp. (mangroves)	0.83
Avicennia spp. (mangroves)	0.65

B.2 Temperate Wood Density Averages

Species / Genus	Wood Density (g/cm³)
Oak (Quercus spp.)	0.67
Pine (Pinus spp.)	0.42
Birch (Betula spp.)	0.55
Spruce (Picea spp.)	0.43

B.3 Dryland and Woodland Species

Species / Genus	Wood Density (g/cm³)
Prosopis spp.	0.75
Boswellia spp.	0.53
Commiphora spp.	0.47
Acacia tortilis	0.63

B.4 Documentation Requirements

1. For each species used in biomass estimation, the Monitoring Report must include:

• Wood density value

• Source reference

• Justification for selection

When species cannot be identified, conservative density values must be applied based on dominant functional group.

Annex C - Root-to-Shoot Ratios and Carbon Fraction Values

1. This annex provides default values for estimating below-ground biomass and converting biomass to carbon.

C.1 Default Root-to-Shoot Ratios (R:S)

Vegetation Type	R:S Ratio
Tropical forests	0.24
Temperate forests	0.20
Boreal forests	0.27
Mangroves	0.39
Shrublands	0.30
Dryland woodlands	0.28

These ratios may be replaced with species- or region-specific values when available.

C.2 Carbon Fraction Values

Biomass Component	Carbon Fraction
Above-ground biomass	0.47
Below-ground biomass	0.47
Mangrove biomass	0.48
If species-specific values available	Use published values

Default values must be applied unless high-quality laboratory data are available.

Annex D - Field Measurement Templates and Plot Forms

1. These templates ensure standardization of field data collection and ease of verification.

D.1 Plot Summary Template

Plot ID	Stratum	Coordinates	Plot Area (m²)	Date Measured	Observations

D.2 Tree Measurement Template

Tree ID	Species	DBH (cm)	Height (m)	Wood Density (g/cm³)	Notes

D.3 Shrub Measurement Template

Shrub ID	Species	Stem Count	DBH or Crown Dimensions	Height (m)	Notes

D.4 Biomass Calculation Template

Plot ID	AGB (t/plot)	BGB (t/plot)	Total Biomass (t/plot)	Biomass per ha (t/ha)	Carbon Stock per ha (tC/ha)