Mangroves have been converted and degraded for decades. Rates of loss have declined over the past decades, but achieving resilient coastlines requires both conservation and restoration. Here, we outline the challenges for the global restoration of mangroves and what actions could enhance restoration. Ambitious global targets for mangrove restoration, if successful, could deliver global benefits of carbon sequestration, fisheries production, biodiversity, and coastal protection. However, large-scale mangrove planting efforts have often failed, and smaller projects may not deliver landscape-scale benefits, even though they are more suited to community management. Solutions to achieving global targets include reducing risks of large projects and increasing the uptake and effectiveness of smaller projects. Sustainable mangrove restoration requires investment in capacity building in communities and institutions, and mechanisms to match restoration opportunities with prospective supporters and investors. Global reporting standards will support adaptive management and help fully understand and monitor the benefits of mangrove restoration.

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Tackling the mangrove restoration challenge

The protection, management and restoration of vegetated ecosystems on land and in the ocean (‘natural climate solutions’) can be a useful strategy for reducing net greenhouse gas emissions to help limit global warming. Their potential contribution to reducing net emissions has led to the development of policies and financial incentives for their protection and restoration. These have in turn created a set of expectations among some stakeholders, and interest in expanding these to encompass other ecosystems. However, there are specific rules about how abatement is calculated in international policy and climate finance, and the frameworks and terminology associated with them are often complex. This can be a barrier to stakeholders who want to leverage the potential of natural climate solutions, sometimes leading to incongruence between realised and anticipated benefits. In this article, we attempt to outline some of the key international policy and carbon market frameworks for coastal ‘blue carbon’ ecosystems, and the extent to which different ecosystems are accommodated. Currently, among the coastal ecosystems, only mangrove forests, seagrass meadows, and tidal marshes are typically considered in international policy and carbon market frameworks. The defining feature of these ecosystems is that the foundation species are plants that grow in sediment (soil). They are the only coastal ecosystems currently included in IPCC guidelines for national greenhouse gas inventories, and in compliance and voluntary carbon markets. There is interest in potentially including other marine ecosystems, such as kelp forests and unvegetated tidal flats, into carbon accounting frameworks, but there are unresolved questions about whether sequestration and storage of carbon by these ecosystems meets the rigorous standards required. Voluntary carbon markets have greater flexibility than mechanisms linked to national greenhouse gas inventories, and so might be early implementers of expanding methods to include other ecosystems. Incorporating coastal ecosystems into national greenhouse gas inventory is a useful action countries can take that will likely help generate incentives for protection and restoration of these important ecosystems.

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A Guide to International Climate Mitigation Policy and Finance Frameworks Relevant to the Protection and Restoration of Blue Carbon Ecosystems

Blue carbon: A new paradigm of mangrove conservation and management in Indonesia

Mangroves are a globally important ecosystem experiencing significant anthropogenic and climate impacts. Two subtypes of mangrove are particularly vulnerable to climate-induced impacts (1): tidally submerged forests and (2) those that occur in arid and semi-arid regions. These mangroves are either susceptible to sea level rise or occur in conditions close to their physiological limits of temperature and freshwater availability. The spatial extent and impacts on these mangroves are poorly documented, because they have structural and environmental characteristics that affect their ability to be detected with remote sensing models. For example, tidally submerged mangroves occur in areas with large tidal ranges, which limits their visibility at high tide, and arid mangroves have sparse canopy cover and a shorter stature that occur in fringing and narrow stands parallel to the coastline. This study introduced the multi-dimensional space–time randomForest method (MSTRF) that increases the detectability of these mangroves and applies this on the North-west Australian coastline where both mangrove types are prevalent. MSTRF identified an optimal four-year period that produced the most accurate model (Accuracy of 80%, Kappa value 0.61). This model was able to detect an additional 32% (76,048 hectares) of mangroves that were previously undocumented in other datasets. We detected more mangrove cover using this timeseries combination of annual median composite Landsat images derived from scenes across the whole tidal cycle but also over climatic cycles such as EÑSO. The median composite images displayed less spectral differences in mangroves in the intertidal and arid zones compared to individual scenes where water was present during the tidal cycle or where the chlorophyll reflectance was low during hot and dry periods. We found that the MNDWI (Modified Normalised Water Index) and GCVI (Green Chlorophyll Vegetation Index) were the best predictors for deriving the mangrove layer using randomForest.

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Turning the Tide on Mapping Marginal Mangroves with Multi-Dimensional Space-Time Remote Sensing

Marine ecosystem restoration is fast becoming the primary tool for repairing the socio-ecological functions and economic benefits of coastal ecosystems. Healthy seascapes are characterized by many interacting species and intermingled habitats (e.g., seagrass, kelp, shellfish, sedimentary) that co-create ecological functions of substantial socio-economic value. These co-created functions not only build stability and resilience at seascape scales, but synergistically combine to enhance ecological productivity that is greater than the sum of the individual habitats. Yet, restoration practice is dominated by single-habitat approaches underpinned by single-species monocultures, potentially limiting the range of benefits that restoration can provide. We propose that for ecosystem restoration to meet its full potential in delivering socio-ecological benefits that are resilient to environmental change, restoration practices should plan beyond single-species and single-habitats to a multi-habitat seascape. Where multiple habitats are co-restored, their positive interactions mutually benefit each other to stabilize and even accelerate ecosystem recovery; such as co-restored shellfish and kelp forests on constructed reefs, which combine to stabilize sediment for seagrass recovery. As fisheries scientists and managers, food and social scientists, and ecologists and oceanographers, we describe multi-habitat marine restoration activities that are readily achievable and provide a vision for the diverse socio-ecological, economic, and culture benefits that may emerge from future seascape-level repair.

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Multi-habitat seascape restoration: optimising marine restoration for coastal repair and social benefit

Restoration of coastal wetlands has the potential to deliver both climate change mitigation, called blue carbon, and adaptation benefits to coastal communities, as well as supporting biodiversity and providing additional ecosystem services. Valuing carbon sequestration may incentivize restoration projects; however, it requires development of rigorous methods for quantifying blue carbon sequestered during coastal wetland restoration. We describe the development of a blue carbon accounting model (BlueCAM) used within the Tidal Restoration of Blue Carbon Ecosystems Methodology Determination 2022 of the Emissions Reduction Fund (ERF), which is Australia's voluntary carbon market scheme. The new BlueCAM uses Australian data to estimate abatement from carbon and greenhouse gas sources and sinks arising from coastal wetland restoration (via tidal restoration) and aligns with the Intergovernmental Panel for Climate Change guidelines for national greenhouse gas inventories. BlueCAM includes carbon sequestered in soils and biomass and avoided emissions from alternative land uses. A conservative modeled approach was used to provide estimates of abatement (as opposed to on-ground measurements); and in doing so, this will reduce the costs associated with monitoring and verification for ERF projects and may increase participation in blue carbon projects by Australian landholders. BlueCAM encompasses multiple climate regions and plant communities and therefore may be useful to others outside Australia seeking to value blue carbon benefits from coastal wetland restoration. 

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Sarah Perry

Papers

An Australian blue carbon method to estimate climate change mitigation benefits of coastal wetland restoration