A meta-analysis of the ecological and economic outcomes of mangrove restoration

Background

Mangrove forests provide many ecosystem services to local and global communities that are both ecologically and economically important. Global mangrove loss and degradation decrease the provision of ecosystem services; however, mangrove restoration projects can reverse these effects and support critical ecosystem services. Therefore, syntheses of different restoration project outcomes are necessary to encourage global political support and investment into preserving mangroves and their vital ecosystem services.

Goals and Methods

The authors conducted a meta-analysis of studies focusing on mangrove restoration. They systematically searched for peer-reviewed literature and extracted quantitative data about restoration outcomes, factors affecting restoration outcomes, and the economic costs and benefits of restoration. They calculated the benefit-cost ratio of mangrove restoration, the natural logarithm of response ratio (lnRR), and 95% confidence intervals, in addition to other statistical tests for sensitivity, heterogeneity, and bias.

Conclusions and Takeaways

Restored mangroves provide more ecosystem services than unvegetated tidal flats and fewer ecosystem services than natural mangroves. Certain biogeochemical and ecological functions (i.e., biomass production, carbon sequestration, crab and fish production and diversity) are influenced by stand age; hence, natural mangroves outperform restored mangroves. However, both natural mangroves and restored mangroves provide similar outcomes for some critical ecosystem services, such as carbon sequestration. Restoration projects using multiple mangrove tree species perform better than monospecific mangrove restoration projects, but restoration projects aiming to improve specific ecosystem functions may benefit from monospecific mangrove restoration. Protecting these ecosystem functions through restoration could generate significant economic benefits. The benefit-cost ratio of mangrove restoration ranges from 10.50 to 6.83 under high discount rates (-2 – 8%), which is a higher benefit-cost ratio compared to the restoration of other coastal ecosystems, like coastal wetlands (0.61 – 6.68). These results demonstrate that there is a clear ecological and economic case for mangrove restoration.