Plant Community Establishment in a Coastal Marsh Restored Using Sediment Additions

Abstract

A goal of wetland restoration is the establishment of resilient plant communities that persist under a variety of environmental conditions. We investigated the role of intraspecific and interspecific variation on plant community establishment in a brackish marsh that had been restored by sediment addition. Plant growth, sediment accretion, and surface elevation change in planted, not-planted, and nearby reference sites (treatments) were compared. Four perennial macrophytes were planted: Bolboschoenus robustus, Distichlis spicata, Phragmites australis, and Schoenoplectus californicus. There was 100% survival of the planted species, and all exhibited rapid vegetative spread. Intraspecific variation in stem height and cover was identified, and interspecific comparisons also indicated differences in species cover. Treatment comparisons revealed that final total cover at not-planted sites was equivalent to that at reference sites, and was highest at planted sites where P. australis became dominant. Species richness was initially highest at the reference sites, but final richness was equivalent among treatments. Soil surface elevation was greater at planted compared to not-planted and reference sites. Because of the rapid cover and increased surface elevation generated by planted species, the resiliency of restored coastal marshes may be enhanced by plantings in areas where natural colonization is slow and subsidence is high.

Large‐scale field studies inform adaptive management of California wetland restoration

“…Our results complement previous studies by demonstrating that planting fast‐growing marsh species (e.g. Salicornia pacifica ) is most effective at increasing lateral spread and introducing structure to an otherwise bare landscape (Yando et al 2019; Howard et al 2020). Fast‐growing species have also been shown to increase inter‐ and intraspecific plant survival rates (Silliman et al 2015; Howard et al 2020) and increase species richness in stressful environments (Xie et al 2019 a , 2019 b ).…”

“…Salicornia pacifica ) is most effective at increasing lateral spread and introducing structure to an otherwise bare landscape (Yando et al 2019; Howard et al 2020). Fast‐growing species have also been shown to increase inter‐ and intraspecific plant survival rates (Silliman et al 2015; Howard et al 2020) and increase species richness in stressful environments (Xie et al 2019 a , 2019 b ). Although some managers may caution against planting fast‐growing species like S. pacifica that can quickly dominate a marsh landscape, the short‐term disadvantage of lower plant diversity (Callaway et al 2003) may be countered by improved soil conditions from the establishment of these faster growing ecosystem engineers (Jones et al 1994).…”

Dieback and dredge soils of Phragmites australis in the Mississippi River Delta negatively impact plant biomass

“…Despite reduced growth on these soils, our field observations at dredge sites confirm the natural colonization of P. australis. In a brackish marsh in the Barataria Basin of Southeast Louisiana, Howard et al 60 demonstrated that transplanted P. australis to dredge sites could rapidly spread within two-years. However, further studies are needed to estimate the extent of expansion and the time it would take for P. australis to achieve substantial vegetative cover in these newly constructed sites along the MRD.…”

Phragmites australis dieback in the Mississippi River Delta, USA: Vegetation restoration

“…Our eld observations con rm the natural colonization of those sites by P. australis. In addition, (Howard et al, 2020) demonstrated that transplanted P. australis to dredge sites could rapidly spread within two-years. In our current study, we had included one dredge site, Sawdust MC South, but the unexpected addition of new dredge sediments, caused the destruction of all of our plantings.…”