Mangroves of the Brazilian north coast. © T. Prost / IRD
On a global scale, mangrove forests occupy between 150,000 and 200,000 km2 (some 58,000 square miles and 78,000 square miles). These dynamic open ecotones, which are extremely rich in terms of biodiversity, are found in nearly three-quarters of tropical coastal areas. They perform unique ecological and environmental functions: they mitigate the impact of cataclysmic events (hurricanes, typhoons, cyclones, tsunamis); they protect against and mitigate coastal erosion (due to swells and currents); they are biotopes for abundant biodiversity (fish, crustaceans, birds, insects); they provide environments for reproduction, larval development and juvenile growth; they are biological "filters" of waters thanks to the very numerous micro-organisms they harbour; and carbon is stored in mangrove species and sequestered in the soils.
Mangroves are in fact a vital natural heritage, and their conservation is a key issue for human populations that are increasingly concentrated along coastlines, and that benefit from numerous ecosystem services.
Today, France's overseas territories are home to just under 100,000 hectares of mangrove, i.e. nearly 1,000 km2 (around 400 square miles) (source: Conservatoire du Littoral), distributed mainly between French Guiana (more than half of the French mangrove), the Pacific (New Caledonia), the West Indies (Guadeloupe, Martinique, Saint-Martin, Saint-Barthélémy), the Indian Ocean (Mayotte, the Scattered Islands) and in small proportions in Wallis and Futuna and French Polynesia. A recent study (Ong, J.E. & Gong, W.K., 2013) estimated that about 25% of the world’s mangrove forests will have been destroyed by 2025.
To succeed in curbing this dynamic, satellite observation instruments offer considerable advantages: they enable repeated revisit measurements over these hard-to-reach environments, with a wide range of available sensors and proven methods of processing the acquired data. France has a history of outstanding experience in the field, with expert communities organised into Skill Centres that are part of the national Data Terra research infrastructure.
The proposed project aims to mobilise these resources to further contribute to characterising the functioning of these environments, to support those who manage them and to help optimise their conservation and development.
The objective is to implement operational tools for the production and dissemination of validated environmental information, developed by scientists in the framework of studies and research in the field (understanding coastal dynamics and the dynamics of mangrove ecosystems, monitoring of global impacts/change) and used by national and local stakeholders for land use planning and conservation, as input for management dashboards and plans and ecological zoning.
Most of the satellite data from the high to very high resolution (decametric to sub metric) optical and radar satellites required to manufacture these products are disseminated or made available by current systems (e.g. Skill Centres, DINAMIS of the Data Terra research infrastructure). Reference methodology books (IFRECOR Methodological Guide, 2015) have been published to guide the construction of products dedicated to mangrove monitoring concerning their spatial distribution, state of maturity and growth, chlorophyll activity, vegetation height and canopy density.
In order to develop related indicators, the use or collection of additional information, or the application of other types of satellite data processing are necessary: the indicators concern species, biomass, the nature of sediments and substrates, the spatio-temporal dynamics of vegetation or hydro-sedimentary processes, detection systems or even alerts about forest clearing or forest degradation, extraction of specific resources, and monitoring of resources or uses with high social value (reforestation), etc.
In this context, the effort to set up a platform for operational monitoring of mangrove forests by remote sensing is of great interest. To achieve this, four types of activities must be considered:
- The mobilisation of the stakeholders, appropriation and co-construction of the project and joint specification and design of deliverables;
- The aggregation, compilation, takeover/adaptation of existing software tools and resources;
- Complementary methodological and thematic developments to be produced and qualified;
- The construction and online implementation of an operational tool for the production and dissemination of geo-information and services.
Such a platform would play a leading role in designing a federative and normative strategy for mangrove monitoring. It would guarantee the uniformity or interoperability of standardised products in all the territories to be considered, while allowing the implementation of harmonised protocols in French territories.
After a preliminary phase of analysis of the state of the art in the field, which will include determining specific expectations, prototyping and qualification, the tool should be integrated into the Data Terra shared infrastructure network.
The platform will perform 5 main functions:
- It will generalise or standardise methods and tools for mangrove monitoring;
- It will produce reliable and standardised (validated/qualified) geo-environmental background information characterising mangrove ecosystems on a regular basis and/or on demand;
- It will offer, in the form of products or services that can be mobilised ad-hoc, indicators or alerts of disturbances affecting ecosystems and their environment (deforestation, silting, other disturbances to be defined).
- It will disseminate this information to different audiences via a platform for the general public with specific access to institutional stakeholders, managers working for Ministries or local authorities, public institutions;
- It will aggregate and stimulate user communities (feedback and evolution of the offer).
TERRITORIES FOR EXPERIMENTATION
- French Guiana
- Mayotte, Scattered Islands
- French Polynesia
- New Caledonia
- By extension, any territory sheltering mangrove forests.
- Sentinel-1 and 2
- Spot 6-7
Reference data sets (official mangrove maps) will be drawn upon and adapted to train image classification models.
Other types of processing and additional data may be required to construct specific indicators to provide information on the dynamics and state of particular natural resources. The infrastructures will be those of the Data Terra Research Infrastructure and those of the laboratory leading the project.
Data collected in situ describing either the state of the environment or the practices used to extract natural resources of interest.
RESULTS - FINAL PRODUCTS
- End-user Web Portal containing information, data sets, resources and on-line methodological guides, on-line services to generate Mangrove data sets.
- Mangrove products: spatial distribution in different timelines, indexes; synthetic products (evolutions); anomalies and changes; human pressure indexes, natural resources monitoring indexes; product downloading; on-line processing possibilities.
- End-user tools and services for operational monitoring of Mangrove forests.
- News and events.
- Dodd, R. S. and J. E. Ong. 2008. Future of mangrove systems to 2025. Pp. 172–187, In: N. V. C. Polunin (ed.), Aquatic ecosystems: Trends and global prospects. Cambridge: Cambridge University Press
- Ong, J.E. & Gong, W.K. (2013). Structure, Function and Management of Mangrove Ecosystems. ISME Mangrove Educational Book Series No. 2. International Society for Mangrove Ecosystems (ISME), Okinawa, Japan, and International Tropical Timber Organization (ITTO), Yokohama, Japan
21/06/2022: How about Mangroves? Progress of the project at mid-term