Hydrological repair and invasive grass removal restore Rhizophora racemosa mangrove communities in West Africa

Mangrove ecosystems face significant threats from climate change and human activities. In West Benin, the invasive grass Paspalum vaginatum disrupts sedimentation and hydrology, creating anoxic conditions and nutrient imbalances. To address this, we implemented a cost-effective restoration strategy focused on hydrological repair, engaging local communities to excavate 26 artificial channels and clear 19 existing ones, restoring tidal flow to 30 ha of degraded mangrove forest. Of this, 20 ha were planted with Rhizophora racemosa propagules, while 10 ha remained unplanted due to unsuitable micro-topographic conditions. This intervention, costing $1394.3 USD per hectare, adjusted sediment levels to match natural micro-topography, enabling hydrological recovery and suppressing P. vaginatum. The return of Sesuvium portulacastrum stabilized sediments, improved nutrient retention, and facilitated mangrove regeneration. Over 24 months, restoration efforts improved physicochemical parameters, reduced ammonium and acidity, and supported the planting of 250,000 R. racemosa propagules at 25 propagules/m2 across 20 ha. At 785 days post-planting, survival reached 90%, promoting natural recolonization by mangroves along channel edges and by S. portulacastrum in adjacent unplanted areas. The 10 ha not reforested exhibited low P. vaginatum colonization, reinforcing the effectiveness of hydrological repair. This study presents a scalable, low-cost restoration model that integrates hydrological repair and pioneer species facilitation to enhance mangrove recovery. While still in early recovery, this community-driven approach establishes a strong foundation for long-term ecological restoration.