Vegetation-induced soil stabilization in coastal area : An example from a natural mangrove forest

Mangrove forests provide essential ecosystem services in tropical and semitropical regions by supporting their natural regeneration and other biosystem processes, offering livelihood for local communities, and contributing significantly to the natural resources. Systematic analyses on the protective role of mangrove forests and their effects on reducing coastal erosion have been carried out rarely. Mangroves form a complex ecosystem that increases substrate stabilization and dissipates wave energy favouring the deposition of fine material. This study focuses on assessing the role of white mangrove (Avicennia marina (Forssk.) Vierh.) roots in stabilizing the coastline. In a study site located in Southern Iran, a series of field and laboratory measurements were conducted on root systems that were collected from transects perpendicular to the coastline. Root samples were collected from soil cores at fixed distances from tree stems in three layers at seaward and landward positions. Moreover, Root tensile tests were conducted to estimate their biomechanical characteristics which provided the data of parameters of root reinforcement models. Also, the spatial distribution of root reinforcement and the intrinsic-variability of stabilizing components in relation to horizontal and vertical distances from the tree stem were calculated. Three models of Wu & Waldron (W&W), Fiber Bundle (FBM), and Root Bundle Weibull (RBMw) were applied. results showed that the Root Volume Ratio (RVR) and the Number of Roots (NoR) decreased with distance from the tree stem. Root tensile forces increased with root diameter. Finally, calculated root reinforcements at 0.75 m distance associated with the highest value while the lowest value was observed at 1.50 m from the tree stem. The differences between seaward and landward positions were minor. Soil detachment ratio (SDR) was approximately 10% higher at landwards positions than seaward, due to different geomorphological conditions that affected the soil detachment process. The similartity of root reinforcement values among root systems at seaward and landward positions suggest that stem density may not be an important parameter in managing mangrove forests as a coastal protection measure. Yet, RVR at different distances and NoR increasing significantly with soil depth and being different at seaward and landward positions, could improve their potential role as a nature-based solution for shoreline protection.