Perspectives on Maximizing Coastal Wetland Restoration Outcomes in Anthropogenically Altered Ecosystems

Abstract

When restoring coastal wetlands, approaches can vary in construction technique, planting strategy, and site placement within an anthropogenically altered landscape comprising both relict wetlands and developed habitat. Constructed marshes are often composed of discrete terraces or mounds formed with excavated sediments, or beneficial uses (BU) dredge material can be used to fill continuous areas to emergent marsh elevation. Either construction approach can be seeded or planted with native species, or colonization can occur naturally. Sites can vary in the degree of hydrological isolation due to the presence of structures (e.g., roads or buildings) that limit connectivity to other marsh areas. Data collected across multiple sites on the upper Texas (USA) coast were used to assess how coastal wetland restoration “success,” measured as emergent plant cover, biomass, and species richness, was influenced by the localized configuration of individual restoration sites and by the placement of each site within a landscape matrix of reference wetlands and developed areas. Plant biomass and cover in BU marshes were similar to reference conditions and up to 70% higher than in excavated formations, regardless of planting technique or location in the landscape. Species richness was highest at the reference sites and lowest at planted beneficial uses sites, but none of the restoration sites had species assemblages similar to reference areas. Restoration outcomes were relatively robust to anthropogenic alterations of the landscape. Individual restoration sites were highly dissimilar from each other, and although some had very low (< 20%) emergent plant cover, these sites provided habitat for aquatic wildlife. This analysis demonstrates the importance of utilizing a range of restoration approaches within the broader landscape to achieve desirable ecosystem-level restoration outcomes.