Restoring mangroves: why and what is it?

Posted on 17 February 2023

The world's wetlands are disappearing at an alarming rate even though they cover more than 12.1 million km², an area larger than Greenland is estimated to be.

Mangroves fall into the category of wetlands. Madagascar has 2% of the world's mangroves and 37% of the mangroves of the Western Indian Ocean (WIO). The Malagasy mangroves constitute the second largest area of mangroves in this sub-region (2775 km²). And yet, in 20 years (1996 - 2016), the Big Island has seen 2.3% of its mangrove area disappear. The district of Mahajanga has the largest degraded area. However, there was a gain of 1446 ha (14.46 km2) between 2016 and 2020.

Mangroves represent a natural solution for the populations and the biodiversity. They support a wide variety of animal species including crabs. Healthy mangroves can produce up to 2.5 tons per square kilometer. They are powerful carbon sinks that can store 2 to 3 times more carbon than terrestrial forests, helping to mitigate greenhouse gas emissions. They also form a barrier against erosion and rising sea levels and serve as a protection for coastal communities.

Did you know that a mangrove tree can reach 9 to 10 meters in 10 years? A relatively fast growth compared to other species such as the rosewood which take several hundred years to become large forest trees. However, it is important to note that once cut, mangroves do not grow back. Hence the urgency to preserve and restore mangroves given the vital services they provide.

Ecological mangrove restoration includes but is not limited to planting. Ecological restoration of mangroves adopts three basic principles: socially acceptable, ecologically functional and financially feasible. It focuses primarily on restoring the conditions of the area to be restored as a wetland (topographic and hydrological rehabilitation), and also focuses on controlling threats. Planting is recommended only when conditions do not allow for natural regeneration to occur, for example: there are not enough propagules (seedlings that develop from mangrove seeds while remaining attached to the mother plant) to naturally colonize the area to be restored, or conditions are not met to allow for the dispersal of these propagules.

Planting is done during the period when the propagules are mature. Setting up nurseries (land developed to produce seedlings for replanting) to produce mangrove seedlings is also an option when the flowering season and seed and propagule production are not the same as the planting season.

Here are some steps applicable to any mangrove restoration:

Know the stakeholders: who will be involved in the restoration project. This allows for ownership of the project and shared responsibility throughout the restoration process
Pre-identify the sites to be restored through participatory mapping and define together the objective of the restoration
Pre-restoration assessment of the site (diagnosis): to know the causes of degradation of the site, to verify if the environmental conditions of the site in relation to the needs of the mangroves to restore, to analyze the social and land aspects that can promote or not the restoration
Restoration action: planting, nursery, development of topographic and hydrological conditions, accompanying measures (e.g. boundary marking, information panels, dina ...)
Follow-up