Mangrove Restoration

This Protocol provides the requirements and procedures for calculating the net carbon dioxide equivalent (CO₂e) removal from the atmosphere via the restoration of mangrove habitat. Mangrove restoration refers to activities that lead to the re-establishment and recovery of mangrove ecosystems in areas where they have been degraded or lost, thereby restoring the ecological integrity and carbon storage capacity of native mangrove habitats. Such activities include, but are not limited to, active replanting of mangrove propagules, modification of the environment to restore hydrological conditions, and/or active management that results in CO₂ removal from the atmosphere.

Mangrove ecosystems are among the most carbon-dense forests in the world, globally storing up to 11.7 Pg C, with as much as 85% of the total stored within their soils^1,2. Conversely, degradation or loss of mangrove habitat results in the release of stored carbon back into the atmosphere through decomposition and oxidation of biomass and soils, making them both a critical sink and a potential source of emissions. Beyond their carbon sequestration potential, mangroves provide co-benefits to local communities, including coastal protection, nursery habitat for fisheries, improved water quality, and enhanced biodiversity in coastal landscapes.

This Protocol accounts for the quantification of the net amount of CO₂e removed via the gross removal of CO₂ through the growth and regeneration of mangrove vegetation and natural accretion of soil organic carbon, in addition to all cradle-to-grave life-cycle Greenhouse Gas (GHG) emissions associated with the process. This Protocol is developed to adhere to the requirements of ISO 14064-2: 2019 — Greenhouse Gasses — Part 2: Specification with guidance at the Project level for quantification, monitoring, and reporting of greenhouse gas emission reductions or removal enhancements.

The Protocol ensures:

• Consistent, accurate procedures are used to measure and monitor all aspects of the restoration process required to enable accurate accounting of net CO₂e removals;
• Consistent system boundaries and calculations are utilized to quantify net CO₂e removal for mangrove restoration projects;
• All net CO₂e removal claims are verified by a third party;
• Removals are additional through the use of dynamic baselines and other guardrails set forth in the Isometric Standard;
• Comprehensive guidance on project design and monitoring mechanisms to confirm Durability and protect against Reversals, ensuring transparent Credit delivery; and
• Market leakage impacts are quantified.

This Protocol and all standardized approaches therein — including but not limited to the dynamic baseline (see Section 9.4) — are informed by the best available scientific knowledge and undergo external review by subject matter experts and relevant stakeholders. All comments received during consultation are publicly addressed, with revisions incorporated as appropriate, to ensure the certified version of the Protocol will yield high quality Carbon Credits via rigorous, conservative, and appropriate methodologies.

Throughout this Protocol, the use of "must" indicates a requirement, whereas "should" indicates a recommendation.

This Protocol relies on and is intended to be compliant with the following standards and protocols:

• The Isometric Standard
• ISO 14064-2: 2019 Greenhouse Gases Part 2: Specification with guidance at the project level for quantification, monitoring, and reporting of greenhouse gas emission reductions or removal enhancements

Additional reference standards that inform the requirements and overall practices incorporated in this Protocol include:

• ISO 14064-3: 2019 Greenhouse Gases Part 3: Specification with Guidance for the verification and validation of greenhouse gas statements
• ISO 14040: 2006 Environmental Management Lifecycle Assessment Principles & Framework
• ISO 14044: 2006 Environmental Management Lifecycle Assessment Requirements & Guidelines

Protocols and Methodologies that were assessed as part of a literature review during the development of this Protocol include:

• Coastal Blue Carbon: methods for assessing carbon stocks and emissions factors in mangroves, tidal salt marshes, and seagrass meadows
• H. Kennedy et al., "IPCC 2014, 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands. Chapter 4: Coastal Wetlands." Intergovernmental Panel on Climate Change, 2013
• VM0033 Methodology for Tidal Wetland and Seagrass Restoration, v2.1, Verra, 2023
• Sustainable Management of Mangroves, v1.0, Gold Standard
• Plan Vivo Climate Methodology Concept Note: Coastal Blue Carbon Methodology, v1.0

This Protocol was developed based on the current, publicly available science regarding wetland restoration and long-term monitoring of mangrove systems. This Protocol aims to be scientifically stringent and robust. We recognize that some requirements may exceed the current market standards and that there are numerous opportunities to enhance the rigor of this Protocol. Key future improvements to the Protocol are outlined in Appendix D.

Additionally, this Protocol will be reviewed when there is an update to published scientific literature, government policies, or legal requirements which would affect net CO₂e removal quantification or the monitoring guidelines outlined in this Protocol, or at a minimum of every 2 years.

This Protocol applies to Projects that restore degraded mangrove habitat to a state of ecological integrity and are resilient to future climate scenarios (see Section 10.3). While the primary purpose of Projects is to sequester CO₂, Projects should also emphasize the protection and restoration of ecosystem function, biodiversity, and social livelihoods.

To restore ecological integrity and ecosystem function, demonstrate additionality, and ensure trust and transparency, it is incumbent upon Projects to adhere to the following requirements, which must be demonstrated in the Project Design Document.

In the context of this Protocol, degraded lands are defined as areas that currently contain less than the expected biomass for mature mangrove habitat and where growth has been stagnant or declined over the past 10 years.

Historical mangrove habitat may be degraded due to a range of possible biophysical issues. In many scenarios, Project Proponents will need to undertake interventions that modify the environment to ensure the successful recovery of mangroves. However, these interventions must be carefully considered to avoid any unintended harmful consequences.

While mangroves are known for their high productivity and ability to trap carbon-rich sediments, increasing the sequestration of atmospheric carbon, concerns remain about the positive radiative forcing effects of methane (CH₄) and nitrous oxide (N₂O) emissions from their soils. However, because of the saline environment in which they exist, mangrove forest restoration projects have fewer concerns regarding these non-CO₂ GHG emissions than freshwater wetland restoration^5,6.

Most mangrove restoration activities focus on reconnecting tidal regimes to areas where tidal connections have been impounded or restricted^7,8, which is expected to increase salinity and sulfate concentrations in most conditions, thus reducing CH₄ emissions. However, hydrological alterations of restoration project areas that decrease salinity have the potential to increase methane emissions.

Increased N₂O emissions in mangroves are usually the result or byproduct of denitrification of increased input of nitrates. The increased nitrate supply is often from adjacent agricultural areas, upstream residential sewage or pollution, or as a legacy of former agricultural practices at the restoration site. However, CH₄ emissions in these restored sites may decrease⁹, offsetting the global warming potential. Conversely, mangroves not receiving such N inputs are often N₂O sinks¹⁰, and thus offsetting positive radiative forcing by CH₄ emissions. As with methane, reduction in N₂O emissions are not eligible for removal Credits.

Isometric will review all activities listed within the PDD that may alter conditions that would increase CH₄ or N₂O emissions as described above. Projects that potentially decrease salinity or increase nitrogen inputs either within or outside of the project area are ineligible under this Protocol. For this reason, the use of nitrogen-based fertilizers is not an allowable activity under this Protocol.

Mangrove habitat encompasses a variety of physiognomic types depending on local coastal geomorphologies, topography, hydroperiods, salinities, and other variables. Typically, mangroves may be classified into zones that represent homogenous environmental conditions and vegetative communities^11,12. Successful mangrove restoration projects will recognize the different conditions and plan their project activities and planting strategies accordingly.

Additionally, this Protocol applies to Projects and associated operations that meet all of the following project conditions:

• The Project must provide a net-negative CO₂e impact (net CO₂e removal) as calculated in the GHG Statement, in compliance with Section 9.
• The Project must be considered additional, in accordance with the requirements of Section 7.4.
• The Project must provide 40+ years of CO₂ storage in the project area, as defined by the length of the Monitoring Period (see Section 5.4).
• The Project Proponent must provide evidence that the area to be restored can be conserved throughout the Project Commitment Period. Failure to maintain land tenure of the Project location may result in the cancellation of Credits.
• The Project must meet the transparency requirements of this Protocol, outlined in Section 7.6.
• The Project must not negatively impact ecological conditions outside of the project area.

• Definition. The Project Commitment Period encompasses two distinct periods, the Crediting Period (see Section 5.2) plus a minimum 40-year Ongoing Monitoring Period (see Section 5.4).

Project Termination. Abandonment or failure to perform project activities at any point in the Project Commitment Period will result in project failure. All Credits issued under The Project will be canceled.

• Definition. The Crediting Period is the interval between project initiation (first activity on site associated with The Project) and the end of the last Reporting Period (see Section 5.3). The Crediting Period is made up of successive Reporting Periods.
• Duration. The duration of a Crediting Period is variable and is initially determined by the Project Proponent based on the expected age to forest maturity as calculated in the ex-ante model of biomass growth (see Section 11). The Crediting Period may be adjusted in response to slower or faster biomass accumulation than initially expected.
• Credit Issuance. Credit issuances occur throughout the Crediting Period. Credits are issued upon Verification of a Reporting Period.

• Definition. The Reporting Period is the interval of time over which removals are calculated. The first Reporting Period starts at project Validation at the beginning of the Crediting Period. Subsequent Reporting Periods begin at the end of the previous Reporting Period.
• Duration. The minimum duration of a Reporting Period is one year. The maximum duration of a Reporting Period is five years. Project Proponents may request an extension for a longer Reporting Period provided they submit suitable justification for the delay (e.g., slower forest growth than expected).
• Verification. Verification of project activities by a third-party VVB is conducted for each Reporting Period (see Section 7.2).
• First Reporting Period. Due to higher levels of error in biomass in stands of younger trees^13,14, the first Reporting Period may be longer than 5 years to allow for tree growth. Project Proponents should perform project surveys at 6-month intervals before the first Reporting Period to document and mitigate early tree mortality.
• Last Reporting Period. Project Proponents must indicate the last Reporting Period to be submitted for Verification. Failure to initiate a Verification within 5 years of the previous Reporting Period or request an extension will conclude the Crediting Period and shift the Project into the Ongoing Monitoring Period.

• Definition. The Ongoing Monitoring Period is the interval between the end of the Crediting Period through the end of the Project Commitment Period.
• Duration. The minimum duration of the Ongoing Monitoring Period is 40 years. The maximum duration of the Ongoing Monitoring Period is 100 years.
• Durability. The durability of Credits are determined by the duration of the Ongoing Monitoring Period (see Section 10.1).
• Monitoring. Monitoring for Reversals is conducted by Isometric throughout the Ongoing Monitoring Period, as described in Section 10.5. Reversals are compensated by a Buffer Pool (see Section 10.4).

• Definition. The indefinite period of time after the Project Commitment Period has ended.
• Long-term durability plan. Projects must have a plan for long-term maintenance of forest carbon stocks after the Project Commitment Period to prevent Reversals after The Project ends.

Figure 1 Summary of project periods. Colors represent actions owned by different stakeholders. Blue Project Proponent. Green VVB. Pink Isometric.

A project starting in 2025 has a Project Commitment Period of 100 years composed of a 40 year Crediting Period followed by 60-year Ongoing Monitoring Period. Credits issued have a 60+ year durability. Monitoring for quantification is conducted by the Project Proponent through the Crediting Period, and the reported activities are verified by a Validation and Verification Body (VVB) for each Reporting Period. At the end of the Crediting Period, maintenance of carbon stocks and monitoring for Reversals occurs for the remaining 60 years of the Project Commitment Period.

The Project must consider environmental and social impacts at all project locations. Appropriate measures must be implemented to identify and eliminate potential risks to terrestrial and aquatic ecosystems and biodiversity. Where risks cannot be eliminated, the Project Proponent must identify measures to monitor ecosystem health and mitigate adverse effects through a site-specific mitigation plan. Mitigation plans must be prepared by subject matter experts, in consultation with Isometric, the VVB, and relevant local authorities, if applicable. Refer to the Isometric Standard for further guidelines on environmental and social impacts.

Following the Isometric Standard, Credits issued under this Protocol are contingent on the implementation, transparent reporting, and independent Verification of comprehensive safeguards. These safeguards encompass a wide range of considerations, including environmental protection, social equity, community engagement, and respect for cultural values. The process mandates that safeguard plans be incorporated into all major project phases, with detailed reports made accessible to stakeholders. Adherence to and verification of environmental and social safeguards is a condition for all Crediting Projects.

An environmental and social risk assessment in compliance with the Isometric Standard must be completed to identify potential risks, followed by the development of tailored mitigation plans. These plans must encompass specific actions to avoid, minimize or rectify identified impacts. Effective implementation of these measures must also be accompanied by a robust monitoring plan to detect adverse effects and pause project activities if necessary, using the principles of adaptive management described below.

Environmental and social risk identification, assessment, avoidance, and mitigation planning will be unique to the technical, environmental, and social contexts of The Project. To accommodate this variation, the requirements outlined in this section serve as a minimum to which the Project Proponent and Isometric can add risks on a case-by-case basis, to be included in the PDD, if applicable.

Adaptive management incorporates learnings and takeaways from project monitoring into project development¹⁵. Regular data collection and sharing is necessary to implement adaptive management.

The High Conservation Values (HCV) Approach, developed by the HCV Network, identifies regionally specific facets of local communities and ecologies that must be considered during project developments resulting in land use change. The HCV Network has identified six values that may be at risk as a result of land use change projects. The values, along with corresponding requirements for Project Proponents to uphold them, are listed below:

Species Diversity: Rare, threatened, endangered, or endemic species, at populations significant to regional, national, or global levels.

Requirements: Population density of these species in the project area must not decrease as a result of project activities (see Section 6.4.1). It is recommended that Project Proponents strive to increase the populations of these species during project activities to improve the climate adaptation potential of the local ecosystem, which in turn increases the durability of carbon stored in aboveground biomass.

Landscape-level ecosystems, ecosystem mosaics and intact forest landscapes: Broad-scale regions of interacting ecosystems which contain species in their natural patterns or distributions at populations significant on regional, national, or global scales.

Ecosystems and habitats: Rare, threatened, or endangered ecosystems or habitats.

Ecosystem services: Fundamental ecosystem functions critical to ecological integrity and life, e.g., oxygen production, water filtration and protection of catchments, soil formation and erosion prevention, temperature regulation, nutrient cycling, habitat formation, provisioning of food and forage for fauna, etc.

Community needs: Commodities, resources, and community functions that are necessary for the livelihoods of local communities and Indigenous Peoples. This may include food, water, and infrastructure sources.

Cultural values: Sites, landscapes, and habitats of significant cultural, historical, religious, economic, or archaeological value to local communities, Indigenous Peoples, or other groups identified to engage in those locations.

For each value above, the Project Proponent must identify in the PDD if the value is present or absent in the project area. This list must be constructed in consultation with relevant stakeholder groups, as identified in Section 6.6.1 and carried out in accordance with the Isometric Standard. The Stakeholder Engagement Plan for HCV identification must also be included in the PDD.

If a value is absent from the project area, the Project Proponent must provide an explanation or justification such as survey results or recent publications. If a value is present in the project area, the Project Proponent must include a plan to monitor and protect it throughout the Project Commitment Period in the PDD. We encourage Project Proponents to review the Common Guidance for the Management and Monitoring of HCV in developing this plan. If protection is not feasible during the project activities and an HCV is damaged as a result of project activities, the Project Proponent must provide a restoration plan to return the area to its prior condition and quality.

If an HCV is threatened or damaged by forces or parties outside of the Project Proponent's jurisdiction and not as a result of or response to project activities, the Project Proponent must report such instances to Isometric, but may not be responsible for enacting a restoration plan. Failure to properly identify, monitor, and protect an HCV may result in the cessation of Credits.

The Project Proponent must provide due diligence to ensure that the population density of rare, threatened, and endangered species in the project area does not decrease, nor are new species added to this list of endangered species, as a result of project activities. If either of these adverse impacts do occur, the Project Proponent must work with Isometric and the VVB to identify sources and explanations for these impacts in order to rule out project activities as the primary cause.

It is recommended that Project Proponents strive to increase the population of rare, threatened, and endangered species. Endangered species are defined as species under threat of extinction from all or a significant amount of their natural habitat. Threatened species are defined as those that are at risk of becoming endangered. Rare species are defined as those uncommon and found in isolated geographical locations. Project Proponents must consult local authorities for further regulations on these or similar groups. If local regulations exist, the Project Proponent must state them in the PDD.

As stated in Section 4.1, restoration projects must occur on degraded lands or lands that were historically classified as mangroves to be eligible for crediting under this Protocol. Because of this applicability requirement and the nature of restoration projects to plant and maintain species in the project area, mangrove restoration projects are well placed to restore historic biodiversity in the region.

The species used for restoration must follow the principles outlined below.

Mangrove species are taxonomically diverse, encompassing multiple families and several dozen genera. Species selected for restoration must be scientifically recognized as a mangrove species.

The definition of 'invasive species' in this Protocol is consistent with the Convention on Biological Diversity's definition of Invasive Alien Species, being a "species whose introduction and/or spread threatens biological diversity"²¹. Projects that plant invasive species will not be eligible for crediting under this Protocol.

Project Proponents are highly encouraged to consult with Isometric, the VVB, and/or external subject matter experts to ensure that species included in the restoration plan meet these requirements.

Local stakeholders may contribute an in-depth understanding of the project area and operations, and provide invaluable insights and recommendations on potential risks, necessary safeguards and specific monitoring needs. Engaging local stakeholders in restoration projects creates community buy-in, providing long-term commitment and investment in the success of restoration projects^22,23. Furthermore, lack of community support, stakeholder engagement, and perceived community benefits has been identified as a primary source of project failure in previous forestry projects²⁴.

The Project Proponent must develop a Stakeholder Engagement Plan in accordance with the requirements outlined in the Isometric Standard, ensuring that all risk mitigation strategies contribute to sustainable project outcomes. The plan and supporting documentation, including evidence of meetings or other forms of engagement, must be submitted in the PDD.

• Free: Stakeholders are not subject to intimidation, coercion or manipulation during the decision making process.
• Prior: Engagement is sought in the early stages of project development before commencement of project activities. Consent must be sought as part of project development, regardless of local requirements. The timeline for the decision making and deliberation periods is set in consultation with all stakeholder groups and is informed by customary, local, and/or traditional practices.
• Informed: Information is presented in a manner that is accessible to all stakeholder groups. Accessible content may differ across stakeholder groups. The Project Proponent must consider in the information sharing process the language and medium of communication. For example, if information is presented electronically, stakeholders must have access to and familiarity with the necessary technology to review the information. If information is presented during in-person meetings, the meetings must be held at a time and in a location that is conducive to stakeholder attendance. Information presented to stakeholders must be objective and present trade-offs fairly and accurately. Finally, information must be provided on an ongoing basis. The following due diligence is strongly recommended to ensure stakeholder groups are well informed of project development and outcomes:
  • Stakeholders should be made aware of the value of the Credits, and anticipated revenue of The Project at-large. The Project's anticipated growth and issuance should be modeled, and simulations describing the value of Credits at current market prices should be made clear to proponents.
  • Stakeholders should have full access to the Project's finances, budget, and forecasted returns.
  • Stakeholders should be aware of alternative land-use scenarios.
  • Stakeholders should be aware of the value of the timber on The Project once the Crediting Period nears an end, so that they can better commit to conservation and upholding the contract.
  • Stakeholders should have a clear understanding of the breakdowns in project income expenditure, and a clear understanding of the precise percentage of revenue that they are entitled to.
• Consent: Must be freely given and may be withdrawn. Consent may be conditional upon milestones in project development or the emergence of new information. Stakeholder consent is not guaranteed as a result of the Stakeholder Input Process.

The Project Proponent is encouraged to prepare alternatives for the withdrawal or denial of consent to project activities by stakeholder groups.

The VVB may conduct random surveys or interviews with stakeholder groups, and/or witness some or all of the processes described above.

As previously mentioned, community buy-in is critical to the success of a restoration project^27,28,29. Community buy-in may be established when stakeholders are properly informed about the benefits they can expect from the restoration project. Equally important in maintaining buy-in is for the positive impacts resulting from the Project to match the (perception of) potential benefits presented to community stakeholders at the Project onset. A mismatch in benefits expected and benefits realized may similarly hinder project success.

While this Protocol will not prescribe requirements for community impacts, the Project Proponent is strongly encouraged to consider establishing the following programs and activities:

• Employment opportunity programs favoring local community members and underrepresented stakeholders, especially in the creation of long-term jobs;
  • Such programs should be equal opportunity and promote gender equity;
• Establishment of community benefit-sharing arrangements;
• Construction of infrastructure, such as roads, that are accessible to the community; and/or
• Development of site-specific mitigation plans for potential negative community impacts.

Positive impacts should be felt by all stakeholder groups identified in Section 6.5.1. Project Proponents should consider which groups may face the brunt of negative community impacts, and how positive community benefits may be shared equitably with these and other marginalized groups.

It is recommended that the Project Proponent provide support to the local communities and ecosystems to establish region-specific mitigation strategies to adapt to changing climates. This may include providing guidance on land use planning, establishing reef breaks, or developing climate-friendly infrastructure.

The following topics are covered briefly in this Protocol due to their inclusion in the Isometric Standard, which governs all Isometric Protocols. See in-text references to the Isometric Standard for further guidance.

For each specific Project to be evaluated under this Protocol, the Project Proponent must document project characteristics in a Project Design Document (PDD) as outlined in the Isometric Standard. The PDD will form the basis for project Validation and evaluation in accordance with this Protocol.

Projects must be validated and net CO₂e removals verified by an independent third party, consistent with the requirements described in this Protocol, as well as in the Isometric Standard.

The Validation and Verification Body (VVB) must consider the following requisite components:

• Verify that The Project meets the Applicability conditions described in Section 4
• Verify that the Environmental & Social Safeguards outlined in Section 6 are met
• Verify that the System Boundary & Leakage assessment adheres to the requirements of Section 8
• Verify that the quantification approach and monitoring plan adheres to requirements of Section 9
• Verify that the conditions for ensuring durability and monitoring for Reversals in Section 10 are met
• Verify that The Project is compliant with requirements outlined in the Isometric Standard

As part of this evaluation, the VVB must also review the characterization and quantification of all individual uncertainty sources within the listed components that contribute to the calculation of net CO₂e removal.

The threshold for Materiality, considering the totality of all omissions, errors and misstatements, is 5%, in accordance with the Isometric Standard.

Verifiers should also verify the documentation of uncertainty of the GHG Statement as required by the Isometric Standard. Qualitative Materiality issues may also be identified and documented, such as:

• Control issues that erode the verifier's confidence in the reported data;
• Poor management documented information;
• Difficulty in locating requested information; and
• Noncompliance with regulations indirectly related to GHG emissions, removals or storage

Project Validation and Verification must incorporate site visits to project facilities, namely in situ field plots, in accordance with the requirements of ISO 14064-3, 6.1.4.2. This is to include, at a minimum, site visits during the first Validation or Verification of a Project, to the project site(s). Validators should, whenever possible, observe project operation to ensure full documentation of process inputs and outputs through visual observation and validation of instrumentation, measurements, and required data quality measures.

A site visit must occur at least once during each Project Validation. Additional site visits may be required if there are substantial changes to field operations over the course of a Project's Validation period, or if deemed necessary by Isometric or the VVB. Site visit plans are to be determined according to the VVB's internal assessment, in consultation with Isometric.

Verifiers and Validators must comply with the requirements defined in the Isometric Standard. In addition, verification teams must maintain and demonstrate expertise associated with the specific technologies of wetland restoration including both field measurements and Earth System remote sensing data processing and analysis.

CDR via mangrove restoration is a result of a multi-step process (e.g., propagule planting, managing hydrological conditions, monitoring), with activities in each step potentially managed by a different operator, company, or owner. A single Project Proponent must be specified contractually as the sole owner of the Credits when there are multiple parties involved in the process, and to avoid Double Counting of net CO₂e removals. Contracts must comply with all requirements defined in the Isometric Standard.

The Project Proponent must be able to demonstrate additionality through compliance with the Isometric Standard, including a Common Practice analysis. The Baseline scenario and Counterfactual utilized to assess additionality must be project-specific and comply with Section 9.4 of this Protocol and is assessed each Reporting Period.

Government subsidies or civil contractual obligations for restoration, such as organization bylaws, may inhibit additionality and fall under the Regulatory criteria in the Isometric Standard.

Additionality determinations should be reviewed and completed at every Verification at a minimum, or whenever project operating conditions change significantly, such as the following:

• Regulatory requirements or other legal obligations for project implementation change or new requirements are implemented;
• Project financials indicate Carbon Finance is no longer required to operate the Project.

If a review indicates the Project has become non-additional, the Project will be ineligible for future Credits. Current or past Crediting Periods will not be affected.

The following steps must be taken to demonstrate that without Carbon Finance the project activity is not Common Practice, in accordance with the requirements defined in the Isometric Standard.

1. Define the project activity (e.g., propagule planting).
2. Identify the applicable geographic area, as described in the Isometric Standard.
3. Identify a similar class of adopters or landowners (e.g., aquaculture, community-held land, private concessions).
4. Identify and explain any essential distinctions between the proposed Project and similar activities, as described in the Isometric Standard.
5. Assess the market penetration rate using either a) a survey-based approach, or b) using relevant data from existing literature, as follows:

• a) Survey-based approach:
  • Survey a representative sample of similar landowners from within the relevant geographic domain within five years of the Project start date.
  • Calculate the cumulative market penetration rate (as a percentage) of the project activity by landowners who have not received Carbon Finance revenue (e.g., are neither part of a registered Isometric Project, nor registered under other GHG programs) in the sample of adopters.
• b) Data from existing literature: Statistics on restoration activities derived from data collected within five years of the Project start date may be used for this demonstration, provided they are relevant to the project area, do not distinguish between activities incentivized by and not incentivized by Carbon Finance (thus are conservative), and are publicly available as:
  • i) agricultural or aquacultural census, survey or other government data;
  • ii) peer-reviewed scientific literature; or
  • iii) independent research or reports, with full and transparent methods and documentation of results.

In accordance with the Isometric Standard, the proposed project activity is considered to demonstrate Common Practice additionality where the market penetration rate is below or equal to 20%.

The uncertainty in the overall estimate of the net CO₂e removal as a result of The Project must be accounted for. The total net CO₂e removed for a specific Reporting Period, $RP$, ${CO}_{2}^{}e_{Removal, RP}^{}$, must be conservatively determined in accordance with the requirements outlined in the Isometric Standard.

In addition, a sensitivity analysis that demonstrates the impact of each input parameter uncertainty on the final net CO₂e uncertainty must be provided. Details of the sensitivity analysis method must be provided such that a third party can reproduce the results. Input variables may be omitted from an uncertainty analysis if they contribute to a 1% change in the net CO₂e removal. For all other parameters, information about uncertainty must be specified.

In accordance with the Isometric Standard, all evidence and data related to the underlying quantification of CO₂e removal and environmental and social safeguards monitoring will be available to the public through the Isometric platform. That includes:

• Project Design Document
  • See Section 11 for a list of pre-deployment requirements that must be included in the PDD
• GHG Statement
• Measurements taken, with supporting documentation (e.g., calibration certificates)
• Emission factors used
• Scientific literature used
• Proof of approval for necessary permits
• Remote sensing and field plot data collected by The Project
• All maps generated for calculating carbon stocks in the project area
• All maps generated for calculating carbon stocks in control areas (geospatial reference data can be removed for privacy reasons)
• All data and methodological details used for the baseline calculation
• Model specifications and output

The Project Proponent can request certain information to be restricted (only available to authorized Buyers, the Registry, and VVB) where it is subject to confidentiality. This includes emission factors, specific data, and/or proprietary models from licensed databases. However, all other numerical data produced or used as part of the quantification of net CO₂e removal will be made available.

The scope of this Protocol includes the GHG sources, sinks, and reservoirs (SSR) associated with a mangrove restoration project.

A cradle-to-grave GHG Statement must be prepared encompassing the GHG emissions relating to the activities outlined within the system boundary.

GHG emissions and removals associated with The Project may be direct emissions from a process, or indirect emissions from combustion of fuels, electricity generation, or other sources. Emissions must include all GHG SSRs within the system boundary, from the construction or manufacturing of each physical site and associated equipment, closure and disposal of each site and associated equipment, and operation of each process, including embodied emissions of equipment and consumables used in the Project. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities.

Any emissions from sub-processes or process changes that would not have taken place without the CDR Project must be fully considered in the system boundary. Any activity that ultimately leads to the issuance of Credits should be included in the system boundary.

The system boundary must include all relevant GHG SSRs controlled, related and affected by The Project, including but not limited to the SSRs set out in Table 1. If any GHG SSRs within Table 1 are deemed not appropriate to include in the system boundary, they may be excluded provided that robust justification and appropriate evidence is provided in the PDD.

Table 1 Scope of activities and GHG SSRs to be included in the system boundary.

Miscellaneous GHG emissions are those that cannot be categorized by the GHG SSR categories provided in Table 1. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities and must report any outside of the SSR categories identified as miscellaneous emissions.

Emissions associated with The Project's impact on activities that fall outside of the system boundary of The Project must also be considered. This is covered under Leakage in Section 8.3.

In line with the GHG Accounting Module v1.1, the Project must:

• Consider all GHGs associated with SSRs, in alignment with the United States Environmental Protection Agency’s definition of GHGs. This includes: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and fluorinated gasses such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆) and nitrogen trifluoride (NF₃). For CO₂ stored, only CO₂ will be included as part of the quantification. For all other activities, all GHGs must be considered. For example, the release of CO₂, CH₄, and N₂O is expected during diesel combustion;
• Quantify emissions in tonnes CO₂ equivalent (t CO₂e) using the 100-year Global Warming Potential (GWP) for the GHG of interest, based on the most recent volume of the IPCC Assessment Report (currently the Sixth Assessment Report); and
• Consider Materiality of SSRs in line with Isometric requirements.

The Baseline scenario for restoration assumes that the activities associated with The Project do not take place and that any infrastructure associated with The Project is not built.

The Counterfactual is the CO₂ stored that would have occurred due to natural regeneration of biomass over the Crediting Period in the absence of The Project. This Protocol uses a dynamic baseline approach to quantify the Counterfactual. This is detailed in Section 9.4.4.

Leakage emissions, $CO_2e_{Leakage}$, occur when project activities lead to emissions that occur outside the system boundary of restoration projects. They include increases in GHG emissions as a result of restoration projects displacing emissions or causing a secondary effect that increases emissions elsewhere. Three key types of leakage can occur for restoration projects:

• Activity-shifting leakage. Mangrove restoration projects may displace activities in their project areas, leading to an increase in those activities outside of the project area, which may result in potential land conversion. Examples are where the local community can no longer use the project site for subsistence, or where farming is displaced as a result of project activities. This type of leakage is known as "Direct" leakage as the relevant stakeholders can be identified and the activity-shifting is traceable.
• Market leakage. Mangrove restoration projects may displace activities, which results in a reduction in supply of a commodity. Changes to the supply and demand equilibrium causes other market actors to shift their activities, leading to potential land conversion. This type of leakage is known as "Indirect" leakage because its effects cannot be isolated and measured directly. Quantifying the likelihood and potential magnitude of market leakage is complex and relies heavily on modeling and available literature.
• Ecological leakage. Project activities may lead to an increase in emissions in areas outside of the project site as a result of ecological interactions, for example changing hydrological conditions that lead to increased methane (CH₄) or nitrous oxide (N₂O) emissions. Project activities that adversely alter the water table, harming ecological integrity within the project area and surrounding landscape and watershed, are not permitted under this Protocol. Isometric will review all proposed hydrological modifications laid out in the PDD (see Section 4.1.1). If any activities are deemed to be a significant risk to increasing GHG emissions (i.e., CH₄ and N₂O), the Project will be ineligible. Therefore, projects that are eligible under this Protocol will have a low risk of ecological leakage.

The overall process for addressing activity-shifting and market leakage is set out in the flowchart in Figure 2.

Figure 2 Flowchart of process for addressing activity-shifting and market leakage.

The flowchart is based on the following principles:

• If the commodity was used for subsistence this presents a risk of activity-shifting leakage.
• Activity-shifting leakage risk can be directly identified and mitigated.
• If the commodity was commercial, there is always a risk of market leakage.
• If the commodity was commercial, there might also be a risk of activity-shifting leakage.
• Where Direct Actors have been identified as impacted, activity-shifting leakage mitigation activities will address both activity-shifting leakage and market leakage. However, if only market leakage mitigation is implemented, this will not satisfy the activity-shifting leakage risk. For this reason, if only market leakage mitigation is undertaken, additional activity-shifting leakage monitoring must take place. If only partial or no leakage mitigation is in place, then the market leakage deduction must be applied, as well as a requirement for activity-shifting leakage monitoring.
• Where the commodity was used for subsistence and is not mitigated in full, The Project is not eligible. This is on the grounds of a very high risk of activity-shifting leakage due to dependencies on the land, but also because the project area was an area fundamental for the livelihoods of communities.
• Leakage mitigation has different requirements depending on whether it is addressing activity-shifting leakage or market leakage.

Implementation of the flowchart for addressing activity-shifting and market leakage (Figure 2) requires an understanding of Pre-Project Productivity, $PPP$, including pre-project information about Direct Actors and how the commodity was used. Direct Actors are defined as site owners, tenants or other users that engaged with the project site in a way that produced commodities before the project activities commenced.

$PPP$ is defined as the annual productivity of a commodity type at the project site in relevant units (e.g., tonnes/ yr).

The following considerations and assumptions should be made when determining the type of commodity, $c$:

The following considerations and assumptions should be made when determining productivity:

The Project Proponent must determine the previous use of the commodity and whether it was:

• A commercial commodity: a commodity that is destined for regional, national, or global commercial markets; or
• A subsistence commodity: a commodity that is not destined for regional, national, or global commercial markets and is consumed by the local community.

In addition, Isometric will undertake remote sensing analysis on project sites which claim that $PPP$ is zero. Remote sensing mapping will be transparently displayed on the registry. Only where remote sensing analysis indicates there are no signs of agricultural or aquacultural production will the Project be eligible for claiming zero $PPP$.

$CO_2e_{Leakage}$ is part of the calculation of $CO_2e_{Emissions}$, as set out in Section 9.5.

$CO_2e_{Leakage}$ is quantified with the following equation:

$$CO_2e_{Leakage}\; =\; CO_2e_{Market\; Leakage}\;   +\;   CO_2e_{Activity-shifting\;Leakage\:Adjustment}\; +\; CO_2e_{Leakage\; Mitigation\; Emissions}$$

(Equation 1)

Where:

• $CO_2e_{Leakage}$ is the total emissions associated with leakage during the first Reporting Period, $RP$, in tonnes CO₂e.
• $CO_2e_{Market\ Leakage}$ is the total emissions associated with market leakage for a Reporting Period, $RP$, in tonnes of CO₂e, see Section 8.3.5.
• $CO_2e_{Activity-shifting\ Leakage\ Adjustment}$ is the adjustment to leakage emissions as a result of activity-shifting leakage being identified via monitoring for a Reporting Period, $RP$, in tonnes of CO₂, see Section 8.3.6.2.
• $CO_2e_{Leakage\ Mitigation\ Emissions}$ is total emissions associated with leakage mitigation activities for a Reporting Period, $RP$, in tonnes of CO₂e, see Section 8.3.4.

$CO_2e_{Leakage}$ is quantified for every Reporting Period, $RP$, however the following should be noted:

• $CO_2e_{Market\ Leakage}$ is only estimated once during the first Reporting Period. The emissions associated with market leakage must be allocated to the first Reporting Period.
• $CO_2e_{Activity-shifting\ Leakage\ Adjustment}$ is based on ongoing monitoring and therefore must be reported at every Verification. It is not reported during the first Reporting Period. For the first Reporting Period, and any preceding Reporting Periods where no activity-shifting leakage is identified, $CO_2e_{Activity-shifting\ Leakage\ Adjustment}$ is zero. Activity-shifting leakage adjustments identified (up to a maximum of total possible leakage) should be allocated to the Reporting Period in which they are identified.
• $CO_2e_{Leakage\ Mitigation\ Emissions}$ must be allocated to the Reporting Period in which they occur. For example, emissions that occur as a result of establishment should be allocated to the first Reporting Period. Ongoing emissions, such as fuel use must be allocated to the Reporting Period in which they occur.

The aim of leakage mitigation activities is to reduce the amount of leakage by increasing production of the displaced commodity elsewhere. Leakage mitigation must take place in areas called Leakage Mitigation Sites.

The following equation is used to calculate the effectiveness of leakage mitigation:

$$uPPP_c = PPP_c - MAP_c$$

(Equation 2)

Where:

• $uPPP$ is unmitigated Pre-Project Productivity of commodity, $c$, in appropriate units (e.g., tonnes per year).
• $PPP$ is Pre-Project Productivity average annual production of commodity that would have been produced in the absence of The Project, in appropriate units (e.g., tonnes per year).
• $MAP$ is Mitigation area productivity, in appropriate units (e.g., tonnes per year).

When $PPP$ is 0, the Project had zero productivity.

When $PPP$ is 0 and $uPPP$ is 0, the Project has achieved full leakage mitigation and does not take a market leakage emissions deduction.

When $PPP$ is 0 and $uPPP$ is 0, the Project takes a market leakage emissions deduction.

Leakage mitigation requirements are different depending on whether mitigation is to address activity-shifting leakage (see Section 8.3.3.1) or market leakage (see Section 8.3.3.2). Activity-shifting leakage will also by nature address market leakage, however market leakage alone will not address activity-shifting leakage.

In addition to the leakage type specific requirements, all leakage mitigation activities must meet the following requirements:

For mitigation of activity-shifting leakage, the Project Proponent must have a full understanding of the information set out in Section 8.3.2.1. The Project Proponent should engage with Direct Actors associated with the site's prior productivity to understand how the project activity impacted the previous users of the project site.

If information from Direct Actors is unavailable, the Project Proponent will be unable to undertake activity-shifting leakage mitigation.

For mitigation of market leakage, the following must be true in addition to the requirements set out in Section 8.3.3:

At minimum, the following emissions sources must be considered:

$CO_2e_{Market\ Leakage}$ considers emissions associated with land conversion as a result of market leakage. It is noted that other emissions may result from market leakage, such as fertilizer use as part of intensification to produce an increase in commodity supply. These emissions sources have been excluded at this time given a lack of globally appropriate data availability. These emissions are also expected to be negligible compared to land conversion emissions.

Market leakage emissions are quantified using the following equations:

$$CO_2e_{Market\ Leakage} = \sum\limits_{c=1}^n  CO_2e_{Market\ Leakage, c}$$

(Equation 3)

Where:

• $CO_2e_{Market\ Leakage}$ is total leakage emissions, in tonnes CO₂e.
• $c$ is the commodity type.

and:

$$CO_2e_{Market\;Leakage, c} = ha_{LC, c} \times EF_{Carbon\;Stock}$$

(Equation 4)

Where:

• $ha_{LC}$ is induced land conversion to bring new land into production, in hectares.
• $EF_{Carbon\;Stock}$ is the carbon stock factor for mangrove habitat, including biomass and soil organic carbon, in tonnes CO₂ per hectare.
• $c$ is the commodity type.

The new land brought into production must be calculated separately for each commodity type being displaced as a result of the Project.

Land conversion for production is quantified using the following equation:

$$ha_{LC, c} = \frac{aPPP_{c} \ \times \:IS_{c}\  \times \:NL_{c}}{Y_{NL, c}}$$

(Equation 5)

Where:

• $ha_{LC}$ is induced land conversion to bring new land into production, in hectares.
• $aPPP$ is adjusted unmitigated Pre-Project Productivity, in appropriate units (e.g., tonnes per year.)
• $IS$ is increased Supply proportion of foregone $PPP$ that will be replaced by increased supply elsewhere, as a percentage.
• $NL$ is increased supply that will result in new land brought into production, as a percentage.
• $Y_{NL}$ is yield on new land brought into production, in appropriate production units (e.g., tonnes per hectare).
• $c$ is the commodity type.

Adjusted unmitigated Pre-Project Productivity, $aPPP$, must be calculated using the following equation:

$$aPPP_c = uPPP_c \times (1+GR_c)$$

(Equation 6)

Where:

• $aPPP$ is the adjusted unmitigated Pre-Project Productivity, in appropriate units (e.g., tonnes per year).
• $uPPP$ is the unmitigated Pre-Project Productivity, average annual production of commodity that would have been produced in the absence of the Project, in appropriate units (e.g., tonnes per year).
• $GR$ is the annual growth rate in productivity of the commodity type.
• $c$ is the commodity type.

The annual growth rate in productivity of the commodity type and region must be assigned as part of Equation 6 This is a requirement to ensure that any likely future increases in productivity are accounted for as part of the assessment.

Growth rate must be calculated using the following equation:

$$GR_c =(\frac{yield_{c,t}}{yield_{c,t-x}})-1$$

(Equation 7)

Where:

• $GR$ is the growth rate, as a percentage.
• $yield$ is the yield as sourced from regional or national datasets, in production unit per hectare per year.
• $c$ is the commodity type.
• $t$ is the most recent year of recorded yield data.
• $t-x$ is the historic year yield data.

Average growth rate is determined by taking the difference between yield in the most recent year of recorded data ($t$) and a historic year ($t-x$). Where possible $t-x$ should represent 25 years prior to t. Where this is not possible, a minimum of 10 years prior to t is allowable.

If a recent negative shock leads to a negative growth estimate of yield growth, a value of zero should be used.

Increased Supply is the proportion of foregone productivity that will be replaced by increased supply elsewhere. This is underpinned by the premise that foregone production will not necessarily be replaced in totality by increased supply elsewhere as a result of elasticities of supply and demand. Global markets for commodities have been assumed for the purposes of the leakage assessment.

Estimates for $IS$ are determined using the following equation:

$$IS = \frac{ε_{s,c}}{ε_{s,c} + |ε_{d,c}|}$$

(Equation 8)

Where:

• $IS$ is increased supply, as a percentage.
• $ε_{s}$ is elasticity in supply, as a ratio.
• $ε_{d}$ is elasticity in demand, as a ratio.
• $c$ is the commodity type.

$NL$ considers the percentage of increased supply that will result in new land brought into production for the commodity type. This is underpinned by the premise that not all increased supply will result in new lands being brought into production. Some increased supply may be made up of intensification of activities and increased yields on existing production lands.

$Y_{NL}$, considers the yield on new land brought into production for commodity $c$. To determine yield on new land, follow the regional and national approach set out in the assessment of Productivity (Section 8.3.2.1.2).

Carbon stocks should be determined using the same ratio of mass of CO₂ to mass of $C$, and carbon fraction, $CF$, as set out in Section 9.3.1.1.

Where activity-shifting mitigation is in place, activity-shifting leakage monitoring is not required. Where only market leakage mitigation is in place, activity-shifting leakage monitoring must be undertaken for the Project. This is because market leakage mitigation does not necessarily mitigate activity-shifting leakage and Direct Actors may still be implicated. Where only partial or no leakage mitigation is in place, activity-shifting leakage monitoring must be undertaken in addition to a full or partial market leakage emissions deduction.

Activity-shifting leakage monitoring requires satellite imagery of a buffer or boundary zone along the Project perimeter, called the Leakage Monitoring Zone. The Leakage Monitoring Zone will form a consistent buffer zone along the perimeter of the project site. The distance between the exterior perimeters of the project site and Leakage Monitoring Zone (i.e., the buffer width) will be determined by the smaller of the following:

• A five-kilometer buffer width extending outward from the project site exterior perimeter; or
• A uniform buffer width extending outward from the project site boundary such that the total area of the Leakage Monitoring Zone equals five times the project area.

The Leakage Monitoring Zone sizing is based on the likelihood that most of the displacements from the project area will not go beyond a five-kilometer radius, as well as to reflect the relative impact of variations in project size.

Isometric will undertake monitoring of the Leakage Monitoring Zone. The satellite imagery will be monitored at every Verification and will account for seasonal differences in vegetation cover. The satellite imagery will compare the deforestation rate of the Leakage Monitoring Zone with the average deforestation rate in the region. Whenever the deforestation rate in the Leakage Monitoring Zone is higher than the average for the region, the Project Proponent must provide additional information. The additional information must include:

• Identification of the actors responsible for deforestation and whether they are the same, or affiliated in any way to the Direct Actors; and
• Analysis of the motivations and contributing factors that resulted in the above-average rates of deforestation, to include the commodity type if the deforestation was motivated by commodity production.

If the Project Proponent is able to provide justification that the above-average rates of deforestation observed are unrelated to the Project and not as a result of actions relating to the Direct Actors, then no further action is required. Acceptable evidence includes documentation from government authorities or other local records that show the observed deforestation was unrelated to the Project and the Direct Actors. This can be further supplemented with remote sensing observations and notarized statements. Both Isometric and the VVB must independently review the evidence and determine whether the Direct Actors were responsible. If either Isometric or the VVB determine the evidence is insufficient, then the above-average area of deforestation must be considered as part of the leakage calculation.

Consider two mangrove conservation projects with different areas:

Example 1: Small Project

The small restoration project has a project area of 1 km². Using the first approach, a 5 km buffer width would create a Leakage Monitoring Zone of 120 km² (calculated as an 11 km x 11 km total area minus the 1 km² project area). Using the second approach, the Leakage Monitoring Zone would only need to be 5 km² (five times the project area). In this case, the second approach would be used as it results in the smaller Leakage Monitoring Zone.

Example 2: Large Project

The large restoration project has a project area of 100 km². Using the first approach, a 5 km buffer width would create a Leakage Monitoring Zone of 300 km² (calculated as a 20 km x 20 km total area minus the 100 km² project area). Using the second approach, the Leakage Monitoring Zone would need to be 500 km² (five times the project area). In this case, the first approach would be used as it results in the smaller Leakage Monitoring Zone.

The amount of above-average mangrove deforestation that should be attributed to the Project as activity-shifting leakage is determined by the total amount of possible activity-shifting leakage. The difference between market leakage and identified activity-shifting leakage is included in the calculation of $CO_2e_{Leakage}$ in Equation 9. $CO_2e_{Activity-shifting\ Leakage\ Adjustment}$ is calculated with the following equation:

$$CO_2e_{Activity-shifting\ Leakage\ Adjustment} = max(ha_{ASL} \times EF_{Carbon\ Stock}-CO_2e_{Market\ Leakage}, 0)$$

(Equation 9)

Where:

• $CO_2e_{Activity-shifting\ Leakage\ Adjustment}$ is the adjustment to market leakage emissions as a result of activity-shifting leakage as identified with monitoring for a Reporting Period, RP, in tonnes of CO₂e.
• $CO_2e_{Market\ Leakage}$ is the total market leakage emissions for the Project, in tonnes CO₂e (see Equation 3).
• $ha_{ASL}$ is the activity-shifting leakage attributed to the Project, in hectares.
• $EF_{Carbon\ Stock}$ is the carbon stock factor for mangroves, as per Section 8.3.5.2.

The amount of above-average mangrove deforestation that should be attributed to the Project as activity-shifting leakage, $ha_{ASL}$, is determined by the total amount of possible activity-shifting leakage. This is represented in the following equation:

$$ha_{ASL} = min(\frac{ha_{Monitored\ LC}}{ha_{Max\ LC}},1) \times ha_{Max\ LC}$$

(Equation 10)

Where:

• $ha_{ASL}$ is the activity-shifting leakage attributed to the Project, in hectares.
• $ha_{Monitored\ LC}$ is the monitored land conversion area of above-average deforestation as identified from activity-shifting leakage monitoring, in hectares.
• $ha_{Max\ LC}$ is the maximum land conversion that can be attributed to leakage for the Project for all commodities combined, in hectares.

$ha_{Max\ LC}$ is calculated using the following calculation:

$ha_{Max\:LC} = \frac{aPPP}{Y_{NL}}$

(Equation 11)

Where:

• $aPPP$ is the adjusted unmitigated Pre-Project Productivity, in appropriate units, e.g., tonnes per year (see Section 8.3.5.1.1).
• $Y_{NL}$ is the yield on new land brought into production, in appropriate production units, e.g., tonnes per year (see Section 8.3.5.1.5).

The Reporting Period for mangrove restoration projects represents an interval of time over which removals are calculated and reported for Verification. The minimum duration of a Reporting Period is one year and the maximum duration of a Reporting Period is five years (see Section 5.3).

Total net CO₂e removal is calculated for each Reporting Period and is written hereafter as $CO_2e_{Removal, RP}$. The net CO₂e removal quantification must be conservatively determined, giving high confidence that at a minimum, the credited amount of CO₂e was removed and stored.

GHG emission calculations must include all emissions related to the project activities that occur within the Reporting Period (see Table 1). This includes:

• any emissions associated with project establishment allocated to the Reporting Period (see Section 9.5.1);
• any operations emissions that occur within the Reporting Period (see Section 9.5.2);
• any end-of-life emissions that would occur after the Reporting Period that have been allocated to the Reporting Period (see Section 9.5.3); and
• market and activity-shifting leakage emissions that occur outside of the system boundary that are associated with the Reporting Period (see Section 9.5.4).

In line with the Isometric Standard, this Protocol requires that Removal Credits are issued ex-post. Credits may be issued once CO₂ has been removed from the atmosphere and is stored in living biomass or organic soil.

Net CO₂e removal for a restoration project for each Reporting Period (RP), is calculated with the following equation:

$$CO_2e_{Removal,\ RP} = CO_2e_{Stored,\ RP} - CO_2e_{Counterfactual,\ RP} - CO_2e_{Emissions,\ RP}$$

(Equation 12)

Where:

• $CO_2e_{Removal, RP}$ is the total net CO₂e removal for the $RP$, in tonnes of CO₂e.
• $CO_2e_{Stored, RP}$ is the total net CO₂e removal in living biomass or soil for the $RP$, in tonnes of CO₂e.
• $CO_2e_{Counterfactual, RP}$ is the total counterfactual CO₂ removed from the atmosphere and stored as organic carbon in biomass in the absence of project activities for the $RP$, in tonnes of CO₂e. This must be calculated for every $RP$.
• $CO_2e_{Emissions, RP}$ is the total GHG emissions for the RP, in tonnes of CO₂e.

As part of the cradle-to-grave GHG Statement, Project Proponents must calculate the gross amount of CO₂e removed and durably stored as a result of the Project operations. Mangrove habitats may sequester carbon into multiple different carbon pools, but not all pools are eligible for quantification and Credits (Table 2).

Table 2 Carbon pools considered for quantification.

The total amount of CO₂ stored from a restoration project is calculated as:

$$CO_2e_{Stored,\ RP} = \sum\limits_{z=1}^n (CO_2e_{StoredBiomass,\ RP,\ z} + CO_2e_{StoredSoil,\ RP,\ z})$$

(Equation 13)

Where:

• $CO_2e_{StoredBiomass,\ RP}$ is the total CO₂ removed from the atmosphere and stored as organic carbon in living biomass for the $RP$, in tonnes of CO₂e. This must be calculated for every $RP$.
• $CO_2e_{StoredSoil,\ RP}$ is the total CO₂ removed from the atmosphere and stored as organic carbon in biomass for the $RP$, in tonnes of CO₂e. The Project Proponent may choose whether this will be calculated in a given $RP$. In years when it is not calculated, this term shall be set to 0.
• $z$ is the Restoration Zone being measured.
• $n$ is the total number of Restoration Zones across the Project Area.

Due to the variable environmental conditions and vegetative communities across mangrove habitats, both soil and biomass accumulation rates may vary across the Project. Therefore $CO_2e_{Stored, RP}$ must be calculated separately for each Restoration Zone identified in Section 4.2. Project Proponents should have a monitoring plan for each Restoration Zone that contains enough field plots to minimize uncertainty in their estimates of carbon stocks.

The total amount of CO₂ stored from a restoration project within biomass is calculated as:

$$CO_2e_{StoredBiomass,RP}=CO_2e_{AGB,\ RP}\ +\ CO_2e_{BGB,\ RP}$$

(Equation 14)

Where:

• $CO_2e_{AGB,\ RP}$ is the total carbon stored in living aboveground woody biomass (AGB) over the $RP$, in tonnes CO₂e.
• $CO_2e_{BGB,\ RP}$ is the total carbon stored in living belowground woody biomass (BGB) over the $RP$, in tonnes CO₂e.

The carbon pools within the scope of this Protocol are aboveground and belowground woody biomass (see Table 1), since they can be quantified with the highest level of accuracy and are able to be effectively monitored over time. Deadwood and litter carbon pools are excluded from the calculation of $CO_2e_{StoredBiomass,\ RP}$ due to large uncertainties in quantification approaches, short durability, relatively small contributions to the total carbon pool, and potential Double Counting concerns as it becomes soil organic carbon. For the remainder of the Protocol, the use of AGB and BGB refers to only the living aboveground and belowground woody biomass, respectively, unless otherwise noted. Details of how to calculate $CO_2e_{AGB,\ RP}$ and $CO_2e_{BGB,\ RP}$ are described below.

The total carbon stored in aboveground biomass over a Reporting Period is calculated by taking the difference between the start and end of the Reporting Period:

$$CO_2e_{AGB, RP} = CO_2e_{AGB}(t_2) - CO_2e_{AGB}(t_1)$$

(Equation 15)

Where:

• $CO_2e_{AGB}(t_1)$ and $CO_2e_{AGB}(t_2)$ are the total aboveground biomass carbon stock in the project area at times $t_1$ and $t_2$.
• $t_1$ and $t_2$ denote the start and end of the $RP$, respectively.

Reporting Periods are consecutive, so that $t_2$ then becomes the start of the next $RP$.

The aboveground biomass carbon stock at a point in time, $t$, is further calculated as:

$$CO_2e_{AGB}(t) = \frac{44}{12} \times CF \times M_{AGB}(t)$$

(Equation 16)

Where:

• $\frac{44}{12}$ is the ratio of mass of CO₂ to mass of $C$, used to convert to tonnes CO₂.
• $CF$ is the average fraction of carbon content for the tree species in the project area, in $\frac{tonne\ C}{tonne\ dry\ biomass}$.
• $M_{AGB}(t)$ is the total aboveground woody biomass over the project area at time $t$, in tonnes of dry biomass.

This Protocol currently supports the following three Modules for quantifying the total AGB over the project area at a point in time, $M_{AGB}(t)$:

Requirements for each approach are described in the corresponding Modules.

Project Proponents have two options to calculate the total carbon stored in belowground biomass over a Reporting Period: using a single root-to-shoot ratio or a species-specific allometric equation for belowground biomass.

Option 1: Allometric Equations

Project Proponents may quantify belowground biomass using allometric equations to directly estimate $M_{BGB}(t)$.

Calculation of $CO_2e_{BGB,\ RP}$ follows the same structure as the calculation for $CO_2e_{AGB,\ RP}$ as described in Equations 15 and 16 in Section 9.3.1.1.

Option 2: Root-to-Shoot Ratio

Project Proponents may alternatively quantify belowground biomass using a generalized root-to-shoot ratio³⁰. When using a root-to-shoot ratio, the total belowground biomass stored in a Reporting is calculated as follows:

$$CO_2e_{BGB,\ RP} = RS \times CO_2e_{AGB,\ RP}$$

(Equation 17)

Where:

• $CO_2e_{AGB,\ RP}$ is the total carbon stored in aboveground biomass over a Reporting Period, $RP$, as calculated in Section 9.3.1.1, in tonnes of CO₂e.
• $RS$ is the root-to-shoot ratio, which is a dimensionless belowground biomass to aboveground biomass ratio.

Mangrove forests are well known to be conducive to the production and long-duration storage of carbon in the underlying soil. As such, soil organic carbon is a carbon reservoir eligible for crediting under this Protocol.

This Protocol does not distinguish between allochthonous and autochthonous soils. Instead, Project Proponents must differentiate organogenic soils from minerogenic soils (see Section 9.3.2.2.2) as this is a more direct indicator of additionality. While minerogenic carbon is considered recalcitrant and would unlikely revert to CO₂ in the absence of the Project, the same is not true of organogenic carbon. Thus, regardless of source, the Project may prevent remineralization of organic carbon by trapping the soils in the mangrove root systems, where it may be buried and protected.

Soil accretion often occurs over different time scales than biomass accumulation and may only accumulate a few cm each year.

Gross CO₂e removal within soil organic carbon for the $RP$ within a Restoration Zone is calculated with the following equation:

$$CO_2e_{StoredSoil,\ RP,\ Zone} = CO_2e_{StoredSoil,\ Zone}(t_2) - CO_2e_{StoredSoil,\ Zone}(t_1)$$