Evaluating Restoration Success Using Metric-Based Indicators of Ecosystem Recovery in Tidal Marshes along the Northern Gulf of Mexico

1. Habitat restoration is commonly used to recover ecosystem services, but due to resource constraints, post-project monitoring often fails to fully evaluate the recovery of important ecosystem functions. Metric-based indicators use simple-to-measure variables to assess ecosystem health and function, thereby providing a time- and cost-effective method to improve monitoring. 2. We used a tidal-marsh data set to develop metric-based indicators of ecosystem recovery. In 2021 and 2022, we surveyed eight restored/created and three natural reference tidal marshes in the northern Gulf of Mexico to assess the recovery of ecosystem attributes (e.g. above- and below-ground biomass, soil organic matter [SOM] and sediment total carbon [C] and total nitrogen [N]). To determine what combinations of variables best predicted recovery, we split our data into model training and testing data sets, used backwards model selection and then created and tested a metric-based indicator of ecosystem recovery. 3. Recovery of plant above- and below-ground biomass and sediment structure (i.e. SOM, C and N)-important measures of wetland carbon sink capacity and biogeochemical functioning-could be predicted through a combination of simpler to measure variables, such as time since restoration, percent plant cover and sediment bulk density. The indicator constructed from these relationships was highly effective in predicting the development of ecosystem attributes (r = 0.85, p < 0.001). 4. Synthesis and applications. This indicator approach provides an effective but simple method to assess the recovery of ecosystem attributes in tidal marshes, and it can be used to develop similar indicators in other ecosystems. By overcoming resource constraints of post-project monitoring, metric-based indicators of ecosystem recovery may serve as a key strategy to improve restoration outcomes.