It is important to have an in-depth mechanistic understanding of tidal marsh establishment and dynamics to ensure the long-term persistence of these valuable ecosystems. As wave forcing may be expected to impact seedling establishment, we studied the effect of water-imposed drag forces on seedling survival, morphology and biomechanical properties of three marsh pioneer species that are dominant along the salinity gradient in many areas around the world: Spartina anglica (salt to brackish), Scirpus maritimus (brackish) and Phragmites australis (brackish to fresh). Using a newly developed plant-shaking mesocosm (PSM) that mimicked water-imposed wave drag forces, the effect of wave stress on seedling survival was examined, together with impacts on morphology and biomechanical properties. After 7 weeks of exposure to wave stress, lowered seedling survival and growth for all species was revealed. Wave treatments increased the root/shoot biomass ratio to enhance anchorage and made seedlings more flexible (i.e. reduced flexural rigidity), which might be regarded as a mixed outcome between a stress avoidance and stress tolerance strategy. The different biomechanical responses between the three dominant marsh pioneer species, overall, make them less resistant to external stress. Therefore, our results indicate that the likelihood of marshes becoming established is reduced if wave energy increases. Despite the different biomechanical response of these three pioneer species to waves, the seedlings of all species were found to have low resistance to external stresses.

Loss of coastal wetland habitats has been directly linked to a decline in waterbird populations including migratory species, leading to calls to reverse this trend in part by restoring these habitats. However, distinct "sediment scarcity" has hindered coastal habitat restoration. Here, taking the Yangtze River Delta, China as an example, we put forward a feasible solution to solve the sediment shortage in habitat restoration so necessary to restore migratory waterbird numbers. Four biological indices including total wetland area, wetland vegetation area and waterbird species richness and abundance, were used to compare and assess the restorative efforts. Three solutions were adopted for the rehabilitation sites, including promoting sediment deposition and settlement through engineering intervention in Chongming Dongtan (CD) and Eastern Nanhui (EN), and using dredged sediments to nourish and create new habitats in Hengsha Eastern Shoal (HES). The mean wetland area increased 19.66 km²/yr in EN, 8.78 km²/yr in HES and 3.83 km²/yr in CD after rehabilitation. Along with the increase of wetlands and habitats, the abundance of waterbirds increased 1.3 times, 121 times and 1.5 times in EN, HES and CD, respectively. In contrast, in the site of Fengxian and Jinshan (FJ) where no any rehabilitation measure was taken after reclamation, the habitats were lost almost completely and the waterbird abundance dropped drastically. The comparison and assessment results demonstrate that proper coastal silting structures and ecological utilization of nearby dredged sediments are the feasible and effective solutions to retain sediments, restore coastal habitats and increase waterbird diversity and abundance.

Restoration has been promoted as an important strategy to reverse the decline of salt marsh ecosystems. Physical and biological processes limiting the colonization of bare tidal flats by pioneer salt marsh species are commonly recognized. Recently, the window of opportunity (WoO) concept has been proposed as a framework to provide an explanation for the initial establishment of biogeomorphic ecosystems on tidal flats under high physical stress. Understanding the thresholds for early seedling establishment and colonization is critical for the successful restoration and management of this threatened ecosystem. In this study, we investigated the WoOs for the establishment and colonization of a Scirpus mariqueter salt marsh at a large‐scale restoration site in the Yangtze Estuary. A set of field monitoring and measurements were conducted to identify the potential physical and biological thresholds that could provide a mechanistic insight on the establishment and colonization of this pioneer marsh. The results showed that the successful colonization and expansion of the S. mariqueter marsh on the tidal flat required passing both physical and biological thresholds to open WoOs for establishment and colonization. The concurrence of WoOs, that is, propagule availability in the early growing season at a suitable tidal flat elevation with a benign sedimentary regime together with the removal of competition from invasive species, is presumed to be essential for the success of S. mariqueter marsh establishment and colonization. In applying such ecological insights, the seed‐sowing field experiment proved that by surpassing these thresholds, an S. mariqueter salt marsh can be successfully restored in a cost‐effective manner. We suggest that these WoO‐related establishment and colonization thresholds as well the cost‐effectiveness of using these WoOs should be considered in future large‐scale restorations of salt marshes.

Conservation and restoration of salt marsh ecosystems are becoming increasingly important because of the many ecosystem services they provide. However, the processes controlling salt marsh establishment and persistence, especially on bare tidal flats in muddy areas, remain unclear. As muddy sediments typically experience a restriction of soil drainage, we expect that a surface drainage relief due to a heterogeneity topography, as might occur on the edge of tidal channels, can facilitate the establishment of salt marsh vegetation on muddy tidal flats. By means of a manipulative field experiment, using “Mega‐Marsh Organ” mesocosms, we investigated the impact of surface drainage and elevation relative to mean sea level on (1) the survival of Spartina anglica seedlings from three different age classes: 1‐yr, 3‐month, and 1‐week; and (2) the growth performance of mature S. anglica marsh tussocks. S. anglica seedling survival, especially in the establishment phase, was positively affected by better surface drainage, increases of seedling age, and higher elevation relative to mean sea level. That is, the survival rate of S. anglica seedlings at the end of 6th week increased from 0% (at surface water undrained, 1‐week, 0 cm elevation) to 94.44% (at surface water drained, 1‐yr, 90 cm elevation). In contrast, surface drainage did not affect the performance of large S. anglica marsh tussocks, as only increased elevation relative to mean sea level was shown to affect S. anglica tussock growth in terms of plant height, shoot numbers, and dry biomass. Based on our findings, we proposed a conceptual model to understand how surface drainage‐driven feedbacks in a heterogeneous topography may be reinforced to induce salt marsh establishment in muddy systems. Further testing of present hypothesized model would be beneficial for insights into salt marsh establishment on tidal mudflats.