Mangrove area and propagule number planting targets produce sub-optimal rehabilitation and afforestation outcomes

Abstract

Mangrove rehabilitation projects often fail completely or fail to meet their objectives. This study examines village-level rehabilitation planting carried out in 13 villages (119 rehabilitation attempts at 74 sites) across two countries in southeast Asia, to assess village-level rehabilitation effectiveness, and to identify what factors influenced outcomes. Mean propagule survival across all rehabilitation attempts was 20% with a median of 10%. Sixty six percent of attempts had a survival rate of less than 20%. Mid mangrove zone projects were more successful (mean 30%) than rehabilitation projects at other elevations. Planting on mudflats, representing 32% of rehabilitation / afforestation attempts, achieved only a 1.4% propagule survival rate. The overall low success rate was due to several interrelated factors. Poor site/species matching on high and low elevation sites was common; for example, Rhizophora spp. was used alone or in combination at least 65% of the time, including on mudflats where this genus is ecologically unlikely to establish. Site selection was often driven by the desire to achieve centrally defined area or propagule planting targets, rather than survivorship targets, and thus required large, uncontested project areas. Conversely, the presence of natural regeneration, even if in small amounts, was associated with higher than average success. Therefore, it was estimated that only 16% of planting attempts were actually necessary. Highlights • Mean survival of all mangrove rehabilitation planting attempts was 20%, median 10% • Only 16% of planting attempts deemed necessary vs. natural recruitment potential • Better hydrological connection significantly improved survivorship (mid/high zones) • Area or propagule planting targets should be changed to survivorship targets

Mangrove blue carbon stocks and dynamics are controlled by hydrogeomorphic settings and land‐use change

“…This study shows that the effectiveness of carbon stock recovery following mangrove regeneration is dependent on biophysical factors such as the coastal hydrogeomorphic setting. However, mangrove restoration projects are often forced into unsuitable locations due to factors such as land‐use management, land tenure and inappropriate planting incentives, and these remain major constraints to successful mangrove restoration (Lovelock & Brown, 2019; Wodehouse & Rayment, 2019). Therefore, both land management and biophysical data should be equally incorporated for effective mangrove restoration to recover natural mangrove functions efficiently.…”

Monitoring tidal hydrology in coastal wetlands with the “Mini Buoy”: applications for mangrove restoration

“…For more detailed single-deployment approaches, Mini Buoy data could be combined with a parameterized model of WoO of the local pioneer species, including root-growth rates and stability thresholds (Balke et al, 2014(Balke et al, , 2015. Wave exposure could be included in site suitability assessments for wave exposed tidal flats; however, such sites are generally not recommended for restoration in the first place due to low success rates (Wodehouse and Rayment, 2019).…”

“…Monitoring flooding gradients and tidal currents is not only key to understanding intertidal wetland functioning but is also a prerequisite for the design and monitoring of successful restoration projects in the intertidal zone (Lewis, 2005;Primavera and Esteban, 2008;Wolters et al, 2005). Mangrove restoration projects in particular have shown low success rates due to the lack of hydrological site assessments prior to restoration (Primavera and Esteban, 2008;Wodehouse and Rayment, 2019). Here, we present the design, calibration, and application of Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Monitoring tidal hydrology in coastal wetlands with the Mini Buoy: applications for mangrove restoration

“…For more detailed single-deployment approaches, Mini Buoy data could be combined with a parameterized WoO model of the local pioneer species including root-growth rates and stability thresholds (Balke et al, 2014(Balke et al, , 2015. Wave exposure could be included in site suitability assessments for wave exposed tidal flats, however, such sites are generally not recommended for restoration in the first place due to low success rates (Wodehouse and Rayment, 2019).…”

“…Monitoring flooding gradients and tidal currents is not only key to understanding intertidal wetland functioning but is also a prerequisite for the design and monitoring of successful restoration projects in the intertidal zone (Lewis, 2005;Primavera and Esteban, 2008;Wolters et al, 2005). Mangrove restoration projects in particular have shown low success rates due to the lack of hydrological site assessments prior to restoration (Primavera and Esteban, 2008;Wodehouse and Rayment, 2019). Assessment of the local hydrology prior to planting is needed to determine whether conditions are too harsh for seedlings to survive and need to be mitigated (Albers and Schmitt, 2015) or whether insufficient flooding may lead to hypersalinity or succession towards terrestrial plant communities (Lewis, 2005).…”