Determining drivers of plant community composition in a restored marsh: a complementary field and greenhouse study

Abstract

As climate change continues, tidal marshes are increasingly vulnerable to degradation or loss from sea-level rise (SLR). Restoration projects can recover ecosystem services provided by tidal marshes, but initial planting effort and continued SLR may influence the success of such projects. To test these effects on ecosystem structure, three fringing marshes were restored in Weeks Bay, Alabama by transplanting intact sods of Juncus roemerianus from a nearby donor marsh into restored marshes at varying percent efforts (0, 25, 50, 75, 100%). SLR effects were tested by installing weirs in half of the plots (+SLR) and leaving the other half as controls (-SLR). Subsequent changes in plant community structure were monitored over two growing seasons. In a companion study, intact sods of J. roemerianus were transplanted to the greenhouse facility at the University of Alabama in Tuscaloosa, AL. These sods were exposed to three inundation (-5, 0, +5 cm) and salinity (0, 4, 8 psu) levels in a full factorial experiment to gain further insight into the plant community changes observed in the field. Plant species richness increased in the field and greenhouse studies (from 1 to 25 and 8 total, respectively). In the greenhouse experiment, the increase in species richness was not affected by inundation or salinity. In the field experiment, the increase in species richness was dependent on initial cover, but was independent of inundation. This suggests that species richness and shifts in community composition were not driven by flooding and salinity associated with SLR, but by the larger propagule bank and colonization space for species other than J. roemerianus. However, the relative abundances of the species present in the field study did differ with SLR and initial planting cover. J. roemerianus and Sagittaria lancifolia increased with increasing initial effort treatments, but the relative abundance of J. roemerianus was greater within control plots while S. lancifolia was greater within weirs. Furthermore, after two growing seasons, plant cover was similar among the 50, 75, and 100% initial effort treatments, suggesting that moderate levels of initial effort can regain marsh structure and function within a few years. (Published By University of Alabama Libraries