Using Meta-Analysis to Develop Evidence-Based Recovery Trajectories of Vegetation and Soils in Restored Wetlands in the Northern Gulf of Mexico

Ebbets, Allison L.; Lane, Diana R.; Dixon, Philip; Hollweg, Terill A.; Huisenga, Mary T.; Gurevitch, Jessica

Using Meta-Analysis to Develop Evidence-Based Recovery Trajectories of Vegetation and Soils in Restored Wetlands in the Northern Gulf of Mexico

2020

The extent to which ecological properties of restored coastal wetlands in the northern Gulf of Mexico recover to natural wetland conditions has not been synthesized. We conducted a systematic literature review and meta-analysis to evaluate whether vegetation and soil parameters at marsh sites restored through sediment addition recovered to levels found at paired reference sites. From 1342 candidate publications, we identified 25 studies (< 1 to > 30 years since initial restoration) suitable for quantitative meta-analysis. Vegetation cover was 50% lower at restored sites compared to reference sites over the first 5 years of restoration while aboveground biomass was 25% higher. On average, belowground parameters (root biomass and soil organic matter) were 44 to 92% lower at restored sites during the first 15 years of restoration compared to reference sites. Mean recovery trajectories for belowground biomass and productivity, vegetation cover, and soil parameters indicated that mean values for restored sites reached reference site conditions within 30 years following restoration. We also evaluated recovery curves for the 20th percentile of site data, which we suggest provides a valuable perspective for natural resource agencies to consider when evaluating individual projects, as it should ensure higher success rates compared with using mean recovery rates to estimate success. Understanding marsh recovery rates following restoration helps future restoration design and monitoring, but recovery rates vary across measurement endpoints. Deciding on the appropriate response(s) to use as the basis of performance measures and monitoring will influence the apparent success of marsh restoration projects.

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