Lessons Learned and Value of Early Post-Construction Monitoring of a Large Tidal Wetland Restoration Project

<h3>Abstract</h3> Coastal development has negatively impacted estuarine ecosystems over the past two centuries. In southern California, USA, salt marshes are valued for their high animal and plant diversity and for providing foraging and nesting habitat for species of conservation concern. Given the ecological importance of this regionally rare habitat, coastal managers have prioritized salt marsh restoration, despite its many challenges. We review lessons learned on the effect of design and adjoining landscape on early vegetation development in a 60.7 ha tidal wetland restoration project in a southern California estuary where nearly one-third of 37.6 ha of planned salt marsh was excavated to high marsh elevations. Initial planting to facilitate vegetation development in large areas of the high marsh (&gt; 1.7 m MLLW) was unsuccessful, likely due to hypersaline soils. In some areas, subsurface freshwater intrusion likely enhanced planted vegetation, which outperformed vegetation planted at comparable high elevations in other areas. In the mid-marsh (&lt; 1.7 m MLLW), vegetation development from natural recruitment exceeded that of the planted high marsh. After five years, vegetation cover in the high marsh remained low. To address this issue, the marsh plain was re-graded lower in some areas and a planting program was established to hasten vegetation development. Lessons learned pertain to the critical importance of initial wetland design, which in this project led to sparse vegetation cover and the necessity of re-grading and large-scale planting to facilitate vegetation establishment.