The beach of Anse Maurice, located in Guadeloupe in the Municipality of Petit-Canal, was chosen as a pilot experimental site for the Carib-Coast project due to the observation of a pronounced decline in the coastline and in the vegetation limit since 1950 (more than 30m), as well as the progressive loss of the natural character of this beach. In other words, it was considered to restore the site by relying on the natural services played by the coastal forest to mitigate the decline of the coastline (concept of ecosystem services).

FINDINGS :

The site faces a strong erosion having several origins:

• Marine erosion, partly natural but accentuated by the sea level rise generated by climate change (melting of the glaciers and thermal expansion of the warming oceans) and by the degradation of marine ecosystems (coral reefs, seagrass beds) natural swell attenuators, under the action of climate change and water pollution;
• Rainfall erosion: the rainwater coming from the slopes adjoining the site meets and is concentrated on the beach, carrying a large quantity of sediment in its path;
• Anthropogenic erosion, linked to :
  • The mechanical collection of Sargassum (a significant amount of sand is removed from the beach with Sargassum despite the use of screeners);
  • The passage of motorized vehicles on the seafront (cars, screeners, 2 wheelers) which result in strongly compacting the soil and destroying the spatial organization of sand grains, making the coastline more friable and fragile and preventing young seedlings to develop;
  • The direct human destruction of certain parts of the cay in order to create sandy areas for a better swimmers comfort.

The vegetation is in poor condition, the vegetation cover is sparse, and very few young seedlings and trees develop on the site. The sustainability of this fairly wild beach is therefore threatened.

WHAT SCIENCE TELL US :

It has been proven that the presence of a dense and species-diversified vegetal cordon makes it possible to constitute an ecosystem capable of playing a non-negligible role in mitigating the retreat of the coastline. So,

• The leaves attenuate the impact of rain on the ground, a phenomenon that causes soil surface destruction, which can set sediments and grains of sand in motion;
• The aerial parts of plants (trunks, branches, leaves) constitute obstacles to particles set in motion under the action of water or wind and allow them to be retained and aggregated;
• The roots of plants, and in particular those of the creeping vegetation (beach-bean – Canavalia rosea, bayhops – Ipomoea pes-caprae, sea purslane – Sporobulus virginicus), constitute a trellis which keeps the sand in up and prevents it from going off.

ACTIONS :

In view of these elements, ONF (French Forestry Institute) has chosen to develop this beach by relying on ecosystem services, also called Nature-based Solutions, In order to densify the plant cover and thus fight against erosion:

• Channeling of the vehicles and visitors flow;
• Cleaning of rain ditches;
• Establishment of regenerative enclosures supplemented with enrichment plantations of native species.

Eight regenerative enclosures were thus set up on the site by ONF Guadeloupe teams after a prior decompaction of certain areas. They occupy an area ​between 150 and 1000 m², for a total of 4130 m².

These enclosures constitute defended spaces materialized by wooden stakes linked together by 3 heights of wire. Protecting these areas by the creation of defended spaces prevents trampling responsible for the breakage of young seedlings and thus constitutes a pledge of regeneration and renewal of the site’s vegetation. Due to the presence of goats on Anse Maurice, which can graze on young plants, an additional protective fence has been installed around the enclosures.

Following the reduction of the pressure exerted by the frequentation, the vegetation develops very quickly within the enclosures from the seed bank contained in the soil. However, in order to diversify the species present on the Anse Maurice site, the choice was made to supplement natural regeneration by planting species grown up in nurseries, typical of the seaside and indigenous to Guadeloupe.

Complementary actions to the regenerative enclosures were also carried out thanks to FEADER funding and have the same objective of protecting the coastline of Anse Maurice against erosion:

• Tuff boulders have been placed at the edge of the coastal forest cordon in order to prevent the passage of motorized vehicles on the seaside and thereby limit the damage that could be brought to the vegetation and the beach by their circulation ;
• The border ditch, which delimits the car park space of the beach itself and which deserves to channel the flow of rainwater, has been cleaned up. It was full and therefore no longer played its role, causing increased rainfall erosion during heavy rain episodes.

APPRAISAL :

The main objective of the actions carried out on the site is to mitigate the decline in the coastline observed on the beach of Anse Maurice. However, the expected benefits go beyond the protection against erosion. The coastal forest provides many other valuable services:

• It plays a role in water purification, a phenomenon which has a direct impact on the quality of bathing water, and which has an impact on the state of health of marine ecosystems (coral reefs, seagrass beds and all associated aquatic fauna); 
• It provides shade sought after by beach users during the hottest hours; – It ensures ecological continuity, reinforces local biodiversity, and constitutes a favorable environment for the laying of sea turtles;
• Finally, even if this contribution remains minimal due to the small surface area of ​​the site, the forest contributes to storing carbon and thus participates in the fight against climate change.

How to join the ONF team :

• Adam Gibaud – adam.gibaud@onf.fr
• Marc Gayot – marc.gayot@onf.fr