Predicting the evolution of coastal protection service with mangrove forest age

Although mangroves reduce the daily risk of flood for millions of people, it is still difficult to estimate the protection they provide for variable wave conditions and forest characteristics. This aspect is crucial for the promotion of conservation and restoration of mangrove forests and for the estimation of how the coastal protection service they provide will evolve over time. This paper presents evidence and a new method for the estimation of the relationship between mangrove forest age and wave attenuation. The forest under analysis is characterised by the age of the Rhizophora mangrove trees, where consideration is given to the differences in the maturity of its individual trees and the density of the forest. Environmental conditions are defined by water levels and incoming wave height and period. A set of empirical and analytical relations expressing wave attenuation as a function of the submerged solid volume fraction (SVF) are presented. Changes is tree morphology and forest characteristics with forest age, as well as the contribution of the tree canopy, are taken into account. Results indicate that, after restoration, it may take only 5 years to obtain a forest's maximum coastal protection capacity. Additionally, such capacity appears to be maintained throughout the forest's lifetime with minor variations, provided the forest is not affected by any conditions altering its health, such as extreme wave events or anthropogenic action that may modify its habitat. Our findings present a new approach to quantifying the protection provided by mangroves without requiring any calibration. These findings can also assist in planning mangrove restoration and assessing associated benefits by providing the incorporation of nature-based solutions or ecosystem-based adaptation into coastal management.

Automated summary

This study presents a new method for estimating the relationship between mangrove forest age and wave attenuation, showing that it may take only 5 years to achieve maximum coastal protection capacity after restoration. The findings suggest that this capacity can be maintained throughout the forest's lifetime with minor variations, unless affected by extreme wave events or human actions altering its habitat.