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 functions 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 to maintain ecological integrity.

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 CO₂ 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 mangrove habitat to a state of ecological integrity in areas where they have historically existed and are resilient to future climate scenarios (see Section 10.3). Projects should emphasize the protection and restoration of ecosystem function, biodiversity, and social livelihoods.

The geographic Project Boundary must encompass all geographic areas where the Project Proponent is conducting restoration activities for crediting purposes. This Protocol applies across the spatial and temporal (see Section 5) scope of the Project. The Project Boundary must be set at the time of project initiation and cannot be modified beyond the addition of new areas to the Project once the crediting period begins. Any adjacent planting activities or land management by the Project Proponent must be disclosed with justification and evidence that they do not pose any risks to the restoration activities within the Project Boundary.

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.

Project activities must include reforestation and/or assisted natural regeneration on degraded lands that historically held mangroves. 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. For demonstrating eligibility of degraded areas, Project Proponents must provide evidence demonstrating the deficit between current and expected biomass in the Project Boundary that will be addressed via project activities.

• Acceptable forms of evidence include, but are not limited to, field surveys, peer-reviewed scientific studies, remote sensing data products, and peer-reviewed scientific models.

Project activities must restore lands that have historically supported mangrove habitats. This historical presence must be evidenced by data of the following types:

• Publicly available databases of ecological suitability based on scientific consensus (e.g., Global Mangrove Watch);
• Historical documentation or imagery showing mangrove presence;
• Traditional ecological knowledge documenting historical mangrove presence.

Project activities must not restore lands where deforestation occurred within the 10 years prior to project initiation.

• Exceptions are permitted when land clearing at < 10-year intervals is the result of a documented natural disaster or is the result of non-industrial common practice in the region that is unrelated to carbon market activities and incentives. For the latter, evidence must be provided to demonstrate past land ownership and land use, and can include management logs, traditional ecological knowledge, remote sensing data, or photography.
  • The Project Proponent must also provide a timeline of their contact and communication with any current or previous landowners.
  • To further evaluate common practices in the region, Isometric will examine historical deforestation patterns in the region to assess whether there is a consistent pattern of deforestation, which would be indicative of deforestation as non-industrial common regional practice.

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.

Project Proponents must document all proposed activities in the Project Design Document (PDD). The following activities with conditions are considered eligible under this Protocol:

• Replanting or reseeding of native plant species (see Section 6.4.1).
• Management practices that enhance the regeneration of native species (e.g, removal of invasive species, prescribed burning, etc.).
  • The removal of biomass must be inventoried in accordance with Section 9.5.1 or Section 9.5.2.
• Restoring hydrological conditions (e.g., improving connectivity, restoring tidal flow).
  • Isometric will review all proposed hydrological modifications. If any activities are deemed to be a significant risk to increasing GHG emissions (i.e., CH₄ and N₂O), the Project will be ineligible (see Section 4.1.2).
• Improving water quality (e.g., reducing nutrient load).
• Dredging and re-allocation of sediment.
  • Sediment that is exposed to an aerobic environment as a result of Project activities must be documented in accordance with Section 9.5.1.1.

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 many other types of wetland restoration^{3, 4}.

Most mangrove restoration activities focus on reconnecting tidal regimes to areas where tidal connections have been impounded or restricted^{5, 6}, which is expected to increase salinity and sulfate concentrations in most conditions, thus reducing CH₄ emissions. Reduced emissions are not eligible for removal Credits under the Isometric Standard. 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 or as a legacy of former agricultural practices at the restoration site. However, CH₄ emissions in these restored sites may decrease⁷, offsetting the global warming potential. Conversely, mangroves not receiving such N inputs are often N₂O sinks⁸, 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. Exception may be made the Project Proponent can provide evidence, either through field measurements or relevant scientific models, that the net change in CH₄ and N₂O emissions would lead to a negative radiative forcing.

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 communities⁹. Successful mangrove restoration projects will recognize the different conditions and plan their project activities and planting strategies accordingly.

Project Proponents must delineate Restoration Zone(s) within the geographic Project Boundary that guides a uniform restoration plan, including species selected for planting (see Section 6.4.1). These zones should represent ecologically homogenous areas. Stratification should be based on:

• intertidal zone;
• hydroperiod;
• elevation and topography;
• salinity; and/or
• soil characteristics.

Each delineated Restoration Zone must minimize the area that is considered open water and should be constrained to areas where planting activities are actively occurring.

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 Project Commitment Period (see Section 5.1).
• 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 plus a minimum 40-year Ongoing Monitoring Period after the end of the Crediting Period.
• Requirements. Projects must provide the following to evidence the length of the Project Commitment Period (see Section 11).
  • Land tenure and contractual obligation. The Project Proponent must have legal, documented land tenure for the duration of the Crediting Period and contractual access to the project area throughout the Ongoing Monitoring Period for the purposes of meeting the Reversal reporting requirements under Section 10.5.2. Additionally, Project Proponents are obligated to maintain carbon stocks throughout the Project Commitment Period in accordance with the requirements of this Protocol and applicable Modules. If the Project Proponent is contracting on smallholder land, smallholders should be contractually obligated to maintain carbon stocks in accordance with the requirements of this Protocol and applicable Modules.
    • In the event of land ownership transfer, including inheritance, sale, or other forms of succession, the Project Proponent should --- subject to local, national, and regional laws --- ensure that the new owner(s) or heir(s) are uphold the commitments outlined in the Project Design Document (PDD). This includes maintaining carbon stocks in accordance with the requirements of this Protocol and applicable Modules, and upholding any other project requirements for the duration of the Project Commitment Period. Such obligations should be legally binding and must be detailed in the PDD to mitigate risks of tenure disputes or non-compliance.
  • Financial plan. Credit issuances will decrease over time, and continued financial payments are needed to incentivize maintenance of carbon stocks. To evidence the continued financial viability of The Project over the full Project Commitment Period, Project Proponents must provide a financial model and cash flow statement which demonstrates a clear payment structure for the duration of the Ongoing Monitoring Period. Methods to maintain continued financial incentives may include, but are not limited to:
    • Investing a portion of revenue into a trust which shifts payments over the full Project Commitment Period; and/or
    • Transitioning to alternative income streams which promote the maintenance of forest carbon stocks.
  • Ex-ante duration estimate. The duration of the Crediting Period is determined by an ex-ante estimate of forest growth rates to reach forest maturity. Due to the variability of forest growth factors and tree biology, the Crediting Period may vary by project.
• 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. The Crediting Period is made up of successive Reporting Periods.
• 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^{10, 11}, 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 Section 3.7 of 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 Section 3.7 of 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.

Project Proponents must comply with all national and local laws, regulations and policies, and receive any necessary permits for project activities, if applicable. Where relevant, projects must comply with international conventions and standards governing human rights and uses of the environment.

Project Proponents must document activities that trigger environmental permitting requirements.

Adaptive management incorporates learnings and takeaways from project monitoring into project development¹². Regular data collection and sharing is necessary to implement adaptive management. Results from data collection at the end of each Reporting Period must be shared with local stakeholders, as described in Section 6.5.1 of this Protocol, and be used to inform future iterations of project management and development.

Project Proponents are required to predict and plan for potential unintended outcomes of project activities and construct mitigation plans for such instances. Foreseeable risks identified during the preparation of the environmental and social risk assessment must be included in the PDD and the following must be detailed for each potential risk:

• A region specific mitigation plan
• The measured or observed outcome that will trigger the mitigation plan
• Plan for information sharing
• Emergency response plan, if applicable

The Project should not hinder the ability of the community or local ecosystem to adapt to climate change as a result of the CDR activity.

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 6.3.1). 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.
    • In cases where restoration will lead to a decrease in the population of rare, threatened, or endangered species which occupy non-forested or degraded lands, The Project may proceed if permitted by law and after a mitigation plan is developed in consultation with Isometric and included in the PDD. Mitigation plans must ensure no decrease in population density and should include activities such as:
      • Translocation of populations to areas within the same region as the Project area, which can support and maintain the species' population;
      • Maintenance of population in the Project area through the development of ecologically appropriate reserves and wildlife corridors;
      • Active monitoring plans.
    • In some instances, endemic species may be overpopulated prior to project initiation and decrease as a result of project activities. These or similar situations may be allowable under this Protocol, in consultation with Isometric. Project Proponents must demonstrate that a population decrease in the Project area will not adversely impact the species' metapopulation and that an endemic species was overpopulated in the Project area through one of the following:
      • Peer-reviewed scientific literature;
      • Authoritative national- or regional-body publications; or
      • A population census conducted by an independent third party in consultation with Isometric.
• 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.
  • Requirements. Ecological integrity in the Project area must be maintained throughout project activities.
• Ecosystems and habitats: Rare, threatened, or endangered ecosystems or habitats.
  • Requirements. Rare, threatened, and endangered ecosystems and habitats in the Project area must be maintained and protected throughout project activities.
    • These ecosystems and habitats within the Project area must be excluded from restoration activities. The total area degraded by project activities should not exceed 10% and must not exceed 30% in these ecosystems and habitats^{13, 14}.
• 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.
  • Requirements. Ecosystem services should be restored to those rendered by forests within the Project area region and maintained throughout project activities.
• 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.
  • Requirements. Community needs must be identified in consultation with local stakeholder groups. Community needs must not be damaged as a result of project activities. Access to community resources must not be limited as a result of project activities.
• 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.
  • Requirements. Cultural values must be identified in consultation with local stakeholder groups. Cultural values must not be damaged as a result of project activities.

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 6.5.1 and carried out in accordance with Section 3.5 of 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, 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.

The Project Proponent must consult reputable and current sources on rare, threatened, and endangered species to develop a list of these species, in the following order of priority:

1. Local and/or regional registries;
2. National registries;
3. Peer-reviewed publications; and
4. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species¹⁵.
   • For the purposes of this Protocol, the IUCN Red List designation of Vulnerable (VU) shall be considered Threatened, and Near Threatened (NT) shall be considered Rare.

The results of the rare, threatened, and endangered species list review must be included and referenced in the PDD.

For each rare, threatened, or endangered species identified, the Project Proponent must list the following in the PDD:

• Ecosystem services vital to the ecology and population stability of the rare, threatened, or endangered species found in the Project area.
• How The Project will maintain or enhance these ecosystem services so as to promote the survival of the rare, threatened, or endangered species.
• A population monitoring plan if there is an identified risk to the species as a result of Project activities. We encourage Project Proponents to consult Isometric, external subject matter experts, and/or authoritative resources in developing their plan.

The Project Proponent must handle data and information related to rare, threatened, and endangered species with discretion for the protection of these species, especially regarding species and/or regions that have histories of poaching, over-harvesting, or other elevated threats to population density and livelihoods.

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. Acceptable scientific sources include but are not limited to Duke et al. (1998)¹⁶ and Hogarth (2015)¹⁷. The species must be appropriate for both the geographic region and the Restoration Zone (see Section 4.2).

The Project Proponent must list the species planted and/or maintained in the Project area via project activities in the PDD.

In addition to mangrove species, Project Proponents may also plant other native species that naturally co-exist with mangroves but are not considered mangroves themselves, and would enhance the ecological integrity of the area. These species should not be the predominant species planted within the Project area. For the purposes of this Protocol, native species are defined as:

• Species indigenous to the Project area that would be found naturally (not planted or introduced anthropogenically via assisted migration) in the Project area prior to deforestation or degradation, and/or species that are indigenous to and found naturally in land adjacent to the Project area; or
• Species indigenous to the region that have not grown in the Project region for the past 100+ years due to displacement via anthropogenic factors or competition from invasive species, but are still well suited to the climate of the Project area, as demonstrated by scientific literature, presence of these species in similar climates, and/or evidence of displacement via one of these two forces.
  • Indigenous species that have not existed in the Project region for the past 100+ years due to failure to adapt to changing climatic conditions may not be suitable for reintroduction for the purposes of GHG removal, but may be suitable for other ecosystem benefits. Reintroduction of such species should be done in consultation with Isometric.

Project Proponents must not introduce species invasive to the region or similar climates, geographies, or ecosystems of the Project area^{18, 19}. 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 threaten[s] biological diversity"²⁰. Projects that plant invasive species will not be eligible for crediting under this Protocol. Additionally, Project Proponents must not introduce any species that harm rare, threatened, or endangered species or adversely impact the integrity of rare, threatened, or endangered ecosystems and habitats (see Section 6.3). 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 and the criteria described below.

In accordance with Section 3.5 of the Isometric Standard, Project Proponents must demonstrate active stakeholder engagement throughout project planning and operation, ensuring that all risk mitigation strategies contribute to sustainable project outcomes. 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^{21, 22}. Furthermore, lack of community support, stakeholder engagement, and perceived community benefits has been identified as a primary source of project failure in previous forestry projects²³.

The Project Proponent must develop a Stakeholder Engagement Plan in accordance with the requirements outlined in Section 3.5 of the Isometric Standard. The plan and supporting documentation, including evidence of meetings or other forms of engagement, must be submitted in the PDD.

Prior to the commencement of project activities, Project Proponents are required to assess if Indigenous Peoples will be impacted by project activities. Impacts may include, but are not limited to:

• Project activities that occur on land or territories that are owned, occupied, or utilized by Indigenous Peoples, regardless of whether or not this claim is recognized by the local governing body or held by rights to self-determination, as recognized by the United Nations;
• Project activities that will affect natural resources necessary for the livelihoods or cultural rights of Indigenous Peoples.

Project Proponents must consult a reputable third party or subject matter expert to assess if Indigenous Peoples will be impacted by project activities. The results of this report must be included in the PDD. If the report identifies potential impacts to Indigenous Peoples, the Project Proponent must enact a Stakeholder Engagement Plan consistent with the principles of Free, Prior, and Informed Consent (FPIC) as outlined by the United Nations (UN) Declaration on the Rights of Indigenous Peoples²⁴ in 2007 and expanded upon by the Food and Agriculture Organization of the United Nations in 2016²⁵.

• 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.

If required, the stakeholder engagement process must be enacted early in the Project development process, prior to the initiation of project activities. The stakeholder engagement schedule must be circulated prior to project initiation, and with enough notice to engage stakeholders in the planning processes. In some instances, Project Proponents that initiated project activities prior to engaging with Isometric and did not engage Indigenous Peoples stakeholders under the principles of FPIC may still be eligible for crediting under this Protocol, in consultation with Isometric, by demonstrating how stakeholder engagement will be incorporated into future project planning.

The following may serve as burdens of proof that the Stakeholder Input Process conforms with the principles of FPIC. The Project Proponent must indicate how these steps in the stakeholder engagement process were or will be carried out during the Project lifetime. Multiple rounds of stakeholder engagement may take place during a project lifetime, as needed. The Project Proponent may identify other burdens of proof demonstrating that the principles of FPIC have been observed and submit them in the PDD in addition to, or instead of, those below, in consultation with Isometric.

• Measures taken to effectively reach (i.e., identify and locate) all stakeholder groups. If the Project Proponent is not able to reach all adult community members, the percentage of adults in the community reached must be included in the PDD, as well as proof of the attempt to reach the remaining community members. The majority of adult community members must be successfully reached to be eligible for crediting under this Protocol.
• The manner in which information was presented to stakeholders, including the medium and language.
• How stakeholder input was obtained, including the medium and language.
• How stakeholder input was incorporated into the Project design.

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

Project Proponents that do not identify Indigenous Peoples that will be affected by project activities are encouraged to consider if other relevant stakeholders rely on land or resources located within the Project area, and engage them following the principles of FPIC described above. All stakeholder groups and local communities have valuable and unique perspectives on developments in the Project area, which can contribute to project success.

The following information from the stakeholder engagement process must be made publicly available, with personal information anonymized or redacted to protect stakeholders, project personnel, and project outcomes. This may include:

• Due diligence that the FPIC processes were carried out (e.g., meeting recordings or copies of information shared with stakeholders)
• Budget reports, including revenue sharing agreements

The Project Proponent must identify and develop processes for the protection and promotion of community well-being in the PDD, as follows:

• Protection of human rights:
  • Policies and practices upholding anti-discrimination on the basis of gender, sexual orientation, etc.
• Grievances, feedback, and complaints:
  • The process by which the Project Proponent accepts grievances, feedback, and complaints. Project Proponents must consult a third party to address grievances. The grievance redress process must be outlined in the PDD.
  • Mediation and resolution process for grievances and complaints.
• Employment Opportunities:
  • Hiring practices and policies, including the number of short-, medium-, and long-term employment opportunities that were recruited for in the local community relative to total new jobs created.

As previously mentioned, community buy-in is critical to the success of a restoration project^{26, 27, 28}. 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, especially in the creation of long-term jobs;
• Establishment of community benefit-sharing arrangements;
• Construction of infrastructure, such as roads, that are accessible to the community;
• 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.

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 Section 3.2 of 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 Section 4 of 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 Section 4.3 of the Isometric Standard.

Verifiers should also verify the documentation of uncertainty of the GHG Statement as required by Section 2.5.7 of 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 to the Project site during Validation and initial Verification. Validators should, whenever possible, observe project operations to ensure full documentation of process inputs and outputs through visual observation (see Section 4 of the Isometric Standard).

Additional site visits may be required if there are substantial changes to field operations over the course of Validation, 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 Section 4 of 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 Section 3.1 of the Isometric Standard.

The Project Proponent must be able to demonstrate additionality through compliance with Section 2.5.3 of the Isometric Standard. The Baseline scenario and Counterfactual utilized to assess additionality must be project-specific and comply with Section 9.4 of this Protocol.

Government subsidies or civil contractual obligations for restoration, such as organization bylaws, inhibit additionality and fall under the Regulatory criteria in Section 2.5.3 of the Isometric Standard. Additionality is assessed each Reporting Period using dynamic baselining as outlined in Section 9.4.

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 Section 2.5.3.1 Common Practice Analysis of the Isometric Standard.

1. Define the Project activity (e.g., propagule planting).
2. Identify the applicable geographic area, as described in Section 2.5.3.1 Common Practice Analysis of 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 Section 2.5.3.1 Common Practice Analysis of 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 Section 2.5.3.1 Common Practice Analysis of 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 Section 2.5.7 of the Isometric Standard.

Projects must report a list of all key variables used in the net CO₂e removal calculation and their individual uncertainties, as well as a description of the uncertainty analysis approach, including:

• field measurements used for the net CO₂e removal calculation
• parameters that impact the estimation of the total aboveground woody biomass, such as allometric equation parameters, canopy height, wood density, etc.
• parameters used for calculating carbon stocks, including root-to-shoot ratios and carbon fractions
• parameters used for soil organic carbon estimation, including estimates of organogenic vs minerogenic components
• emission factors utilized, as published in public and other databases used

The uncertainty information should at least include the minimum and maximum values of each individual variable. More detailed uncertainty information should be provided if available, as outlined in Section 2.5.7 of 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 v1.0, 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. Project Proponents may exclude SSRs where the total emissions for that SSR, and all excluded SSRs collectively, are expected to be < 1% of net CO₂e removals.

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.

The information required is set out below:

• $PPP$ including the type of commodity and yield; and
• Whether the commodity was used for subsistence or commercial production.
  • For the purposes of this assessment, commodities that are commercial, but primarily sold to the local community, are considered subsistence.

$PPP$ is defined as the annual productivity of a commodity type at the Project site in relevant units (e.g., tonnes/ yr). This should be an average of the three years of production prior to the Project activities starting.

The data hierarchy for obtaining information for $PPP$ is set out below:

1. Farm or aquaculture records or permits, including physical production records and financial logs including income and expense records and receipts;
2. Land registry data which details previous land holdings at the Project site and production information related to land holdings; or
3. Remote sensing data which can be used to inform commodity production, with support from municipal data and scientific literature values, as available.

The hierarchy must be followed and data choices evidenced. For example, if land registry data is used, sufficient evidence of no available farm records will be required. Sufficient evidence may include, but is not limited to, official government statements, reports, or affidavits and/or written sworn statements or affidavits by Direct Actors regarding the lack of records.

As part of determination of $PPP$, the Project Proponent must confirm the following:

• The type of commodity, $c$, that existed at the Project site pre-project (see Section 8.3.3.1.1)
• The productivity of commodity production, $Y_c$ (see Section 8.3.3.1.1)

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

• Where land registry data is used to determine commodity type and commodities produced by one land holding are not quantified separately, or spatially separated, the most conservative assumption on commodity type for the site as a whole must be made. The most conservative assumption should be determined by running the calculations for $ha_{LC}$ (see Equation 5) assuming 100% of the production for each commodity and zero mitigation. The commodity that contributes to the highest value for $ha_{LC}$ should be assumed as full commodity production at the site.
• Where remote sensing data is used:
  • Conservative assumptions on commodity type must be made in any areas of uncertainty. Any assumptions made must be transparently documented and justified.
  • If the land use changed within the five years prior to the Project start date, for example from charcoal production to aquaculture, the most recent commodity type should be used if it was in use for at least one year.
  • If more than one commodity type is identified, they must both be assessed as part of the leakage assessment provided that the spatial extent of each commodity type is clear.

Productivity must be reflective of an average of the three years prior to the Project activities starting.

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

• Farm records must reflect the most recent relevant commodity or ownership class where estimates have been disaggregated by those attributes, and must be substantiated with a signed attestation from the farmer or landowner.
• Any assumptions made to interpret productivity data from farm records or land registry data must be of a conservative nature and be transparently reported.
• Methodologies that determine productivity data from remote sensing may be reviewed on a case by case basis. Models must be regionally- and commodity-appropriate and should have a minimum observation frequency of twice per year over a three-year period. Any inferences of productivity made using remote sensing data must be clearly referenced and justified. These must be of a conservative nature and be transparently reported. Future revisions of this Protocol will consider appropriate requirements for using remote sensing data to determine productivity as standard methodology.
• Where productivity related information is not available, average yield for the region may be used as a proxy for productivity. An average over the last five years must be taken to account for anomalies.
• Where region-specific data is not available, average yield data at a national level may be used as a proxy for yield. For example, annual yield data for the commodity type from the Food and Agriculture Organization of the United Nations. An average over the last five years must be taken to account for anomalies.
• Where regional or national averages are not available for fuelwood production, average above-ground biomass growth rates published by the IPCC that are applicable to the region should be used.

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.

The Project Proponent must determine this using the following information:

• An affidavit from the identified Direct Actors confirming the end-users of the commodity, or the majority buyer(s) the commodity was sold to. Direct Actors must include the previous site owners, tenants, or other users that engaged with the Project site in a way that produced commodities.
• An affidavit from the local authority claiming that the Project area was publicly owned and used for subsistence.
• An affidavit from members of the local community confirming that the Project area was used for subsistence.
• An affidavit or records from local intermediaries such as wholesalers, distributors, food processors, grain elevators, or livestock auctions, confirming that they purchased commodities from the Project site in the past.

If it is not possible to determine whether the commodity was for subsistence or commercial use, then the Project Proponent must assume it was subsistence.

If the Project determines that $PPP$ is zero, this must be evidenced appropriately. This includes:

• Evidence of no farm records on open source sites;
• Land registry data which details no previous agricultural land holdings at the Project site;
• Self-assessment from Direct Actors regarding prior use of the site, including photo evidence;
• Written confirmation from project site neighbors or community members regarding the prior use of the site, including photo evidence. This may be land owners or managers from adjacent areas. Where possible this must include a diverse range of stakeholders.

Evidence must be provided for three years preceding the Project Proponent's purchase of the site for restoration, or the Project start date, whichever is earlier.

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. These must be separate to the Project site, but may be directly adjacent. Leakage mitigation activities should be equal to or greater than the expected displacement of production. The efficacy of mitigation will be assessed and appropriate deductions applied in the event that mitigation activities do not match the level of displacement (see Equation 2).

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:

• A written agreement must be in place stating that the landowner of the Leakage Mitigation Site allows the Project Proponent to uniquely claim the increases in productivity as leakage mitigation associated with the Project. This must be covered via legal agreements for a five year term.
• Leakage mitigation activities must provide support to landowners of the Leakage Mitigation Site for a minimum of five years. This is on the basis that the initial leakage mitigation activity leads to sustainable recurring revenue for landowners of the Leakage Mitigation Site.
• Leakage mitigation may lead to increased productivity via creating new production on lands that were not previously used for production, or via intensifying production on existing production lands.
• Land selected for leakage mitigation must not have any other productivity that is negatively impacted by mitigation.
• The mitigation activity must lead to an increase in productivity as a direct result of intentional action from the Project Proponent.
• The spatial extent of the Leakage Mitigation Site and full details of activity must be provided as part of the PDD.

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 mitigation must be informed by the Direct Actors and be undertaken in agreement with Direct Actors. Mitigation activities must lead to new productivity or productivity increases that directly benefit the Direct Actors. This likely means that the increase in production should be limited to the same commodity type, but this decision should be informed by the Direct Actors. This also likely means that the Leakage Mitigation Site should be in the same locality, but again this should be informed by the Direct Actors.

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. Direct Actors include the previous site owners, tenants or other users that engaged with the Project site in a way that produced commodities.

The Project Proponent must receive an affidavit from the identified Direct Actors confirming the following:

• Their occupation;
• How they previously used or engaged with the Project site;
• How the Project activities impacted their use of the Project site; and
• How they designed mitigation activities with the Project Proponent.

Full records of correspondence, including meeting notes, and signed agreements must be made available as part of the PDD.

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:

• The mitigation may increase productivity of a similar substitute commodity, as this will result in a land sparing effect.
• The Leakage Mitigation Site should be in the same region. If this is not possible, the Leakage Mitigation Site must be in the same national boundary.

The emissions impact of leakage mitigation activities, $CO_2e_{Leakage\ Mitigation\ Emissions}$ must be considered. The same system boundaries set out in Table 1 must be considered, noting that it is likely only certain GHG SSRs will be included. At minimum, the following emissions sources must be considered:

• Embodied Emissions associated with any new construction or materials (e.g., fencing);
• Emissions associated with fertilizer use (e.g., if fertilizers are used to increase productivity);
• Emissions associated with farm or aquaculture operations (e.g., fuel use and waste management); and
• Emissions associated with land clearance, including dredging activities, for mitigation activities.

Only activities that are additional as a result of the leakage mitigation activity should be considered as part of $CO_2e_{Leakage\ Mitigation\ Emissions}$. Activities that were already occurring and would continue to occur without the leakage mitigation activity may be omitted from the emissions accounting, if evidence that the activity was already occurring and would have continued to occur in the absence of the leakage mitigation activity is provided.

$CO_2e_{Market\ Leakage}$ 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.

If $PPP$ includes multiple commodity types, $CO_2e_{Market\ Leakage}$ must be quantified for each commodity type.

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.

Project Proponents are required to estimate the amount of new land brought into production, $ha_{LC}$. This estimate must be informed by:

• Pre-Project Productivity of a commodity type at the Project site;
• the estimated proportion of this productivity that would be replaced with new production via an increase in supply of the commodity type;
• the increase in supply that would result in new land being brought into production; and
• the yield of new land being brought into production.

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:

$aPPP_c = uPPP_c \times GR_c$

(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 based on the following hierarchy:

1. Regional commodity specific data should be used to source yield values to determine growth rates, where available. For example from the United States Department for Agriculture for the commodity type and state;
2. National commodity specific data for agriculture from FAOSTAT may be used to source yield values to determine growth rates.

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.

Guidance for estimating IS for a commodity can be found in Appendix A. Future version of this Protocol will provide default values for common commodities.

$NL$ 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.

Guidance for estimating $NL$ for a commodity can be found in Appendix A. Future version of this Protocol will provide default values for common commodities.

$Y_{NL}$, 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 8.3.2.1.1).

$EF_{Carbon\ Stock}$ must be derived from the IPCC average national aboveground biomass, belowground biomass and soil carbon content of mangroves. Mean carbon stocks should be derived from the following tables in the 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories - Wetlands³⁰:

• Aboveground biomass in mangroves estimates in Table 4.3;
• Ratio of belowground to aboveground biomass in mangroves in Table 4.5;
• Soil carbon stocks for mangroves in Table 4.11.

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 roject 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;
• any operations emissions that occur within the Reporting Period;
• any end-of-life emissions that would occur after the Reporting Period that have been allocated to the Reporting Period; and
• market and activity-shifting leakage emissions that occur outside of the system boundary that are associated with the Reporting Period.

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.

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.

The carbon fraction, $CF$, must be chosen from the following hierarchy:

1. A regional and species-specific factor that is justified based on scientific literature (e.g., Doraisami et al., 2022³¹). This is the preferred approach to have the most accurate estimate and avoid overestimation;
2. If the above is not available, then a genus-specific or national average factor that is justified based on scientific literature can be used;
3. As a last resort, if it is proven that the above two factors are not available, then a default factor of 45%, which is a mean across mangrove species, can be used³²

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 must describe in the PDD which option is used, and adhere to the requirements of that approach. Note that Projects using LiDAR and Global Maps for quantification still require field plots as the source of truth for benchmarking. This list of acceptable approaches may be expanded upon in future versions of the Protocol.

The total carbon stored in belowground biomass over a Reporting Period is calculated as:

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

(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.

Appropriate root-to-shoot ratios should be selected by regional and species-specific factors that are justified based on scientific literature. This is the preferred approach to have the most accurate estimate and avoid overestimation. If sufficient evidence is provided to demonstrate that no suitable project-specific factor can be obtained, matching to the ecological zone and continent of the Project area, based on the 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories - Wetlands Table 4.5, must be used. In this case, sufficient evidence documenting the unsuccessful search for project specific factors must also be supplied. Acceptable evidence must show (1) a list of search terms used within a research database (e.g., Web of Science, Google Scholar) that encapsulate the region and species relevant to the Project, and (2) the relevant species are not included in the list of species for which root-to-shoot ratio data are available on the TRY Plant Trait Database³³.

The uncertainty in selected $RS$ factors must be reported from the same source dataset. For example, the 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories - Wetlands provides an uncertainty in the root-to-shoot 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. Project Proponents seeking to include soil organic carbon stocks must quantify the carbon stocks present in each Restoration Zone of the Project area during project establishment and at the end of each Reporting Period for which soil organic carbon is measured.

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 instead and may only accumulate a few cm each year. Therefore, Project Proponents may choose the frequency they measure soil organic carbon for Credit issuance.

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

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

(Equation 18)

Where:

• $CO_2e_{StoredSoil,Zone}(t_1)$ and $CO_2e_{StoredSoil,Zone}(t_2)$ are the total soil organic carbon stock within the Restoration Zone, $Zone$, at times $t_1$ and $t_2$.
• $t_1$ and $t_2$ denote the previous and current $RP$ for which $CO_2e_{StoredSoil,\ RP,\ Zone}$ was calculated, respectively.

The stored soil organic carbon at a point in time, $t$, is further calculated as:

$CO_2e_{StoredSoil,\ Zone}\ =\ C_{Stock}\ \times A_{Zone}\ \times \frac{44}{12}$

(Equation 19)

Where:

• $C_{Stock}$ is the total organic carbon stock per unit area (e.g., Mg C ha^-1).
• $A_{Zone}$ is the area in ha for the Restoration Zone, $Zone$, over which the soil measurements apply.
• $\frac{44}{12}$ is the ratio of mass of CO₂ to mass of $C$, used to convert to tonnes CO₂.

The mean organic carbon stock density is calculated with the following equation:

$C_{Stock}\ =\ \sum\limits_{i=1}^n(D_i \times BD_i \times C_{Org,\ i})\times 100$

(Equation 20)

Where:

• $D_i$ is the total soil accumulation expressed as the thickness of the $i$-th soil layer (cm).
• $BD_i$ is the bulk density of the $i$-th soil layer (e.g., g cm^-3).
• $C_{Org,\ i}$ is the organic carbon content of the $i$-th soil layer (in %).
• $n$ is the total number of layers sampled within the depth profile.
• 100 is the conversion factor from g C cm^-2 to Mg C ha^-1

$C_{Stock}$ must be calculated by taking sufficient field plot measurements to obtain a mean soil carbon stock density. Field sampling must be conducted within a number of representative plots spanning the Restoration Zone. These field plots may be co-located with the field plots used to quantify $M_{AGB}$ (see Section 9.3.1.1.1). Project Proponents should consider the following when establishing field plots and inventories:

• Fixed-radius permanent sample plots are recommended. Field plots must be determined a priori, and any changes in field plots during the Crediting Period must be justified.
• There should be a sufficient number of plots so as to ensure a +/-10% uncertainty at 90% confidence.
  • The number of field plots needed will vary based on the size of the Project area, but at minimum should be greater than 30 (as the Central Limit Theorem suggests that the mean values from a population ≥ 30 will yield a normal distribution).

Within each plot, Project Proponents must take soil cores to measure bulk density, $BD$, and organic carbon content, $C_{Org}$, to accurately determine the $C_{Stock}$. It is recommended that the methods of Howard et al., (2014)³⁴ are followed to ensure good practice and accurate sampling, while minimising compaction. If other methods are used, Project Proponents must provide full justification in the PDD.

To measure soil accumulation, $D$, Project Proponents must use marker horizons such as feldspar. As described in Whelan and Prats (2016)³⁵, a known volume of white feldspar powder can be spread evenly on the soil surface within the plots. Over time, new sediment layers will accumulate on top of this marker horizon. During subsequent sampling events, Project Proponents can measure the depth of the new layer inserting a soil corer and identifying the location of the marker horizon.

As only additional organic carbon is quantified as a removal under this Protocol, only soil deposited above the marker horizon will be quantified. After coring, any soil below the marker maker should be removed. Subsequently, the remaining core should be separated into subsamples for subsequent analysis. It is recommended that each of these subsamples represents depth ranges of 0-15 cm, 15-30 cm, 30-50 cm, 50-100 cm, and > 100 cm until the marker horizon is reached. At depths > 100 cm, soil samples are recommended to be collected at a maximum of 2 m intervals^{36, 37}. These subsamples should then be divided in two to determine the bulk density, $BD$, and organic carbon content, $C_{Org}$.

It is generally accepted that organic matter consists of particulate- and mineral associated- organic matter (POM and MAOM, respectively). Although there are several methods to chemically and physically factionate POM and MAOM³⁸, we recommend wet sieving to 53 um with MOAM passing through the 53 um sieve and POM remaining above due to its low cost and ease³⁹. Other methods may be used, as long as they are fully described and justified in the PDD.

For separation of organogenic carbon for analysis, soil should be fractionated to separate the POM (minerogenic) carbon. This portion of the samples should then be dried at 60°C until it reaches a constant weight, and ground to homogenise for analysis.

To determine dry bulk density, $BD$, the original volume of the sampling device must be known, the soil must then be dried at 60°C until it reaches a constant weight. The dry bulk density is calculated as:

$BD_{Dry}\ =\ \frac{2\times m_{Dry}}{V_{Sample}}$