Assessing Seed Bank Contribution to Landward Expansion of Coastal Wetland Communities and Responses to Fire

摘要

Land loss is a major threat to coastal wetlands of the northern Gulf of Mexico due to the impacts and interactions of sea level rise, regional subsidence, and anthropogenic changes to land cover and sediment supply. Here, coastlines are rapidly converting to open water due to an inability of coastal systems to keep pace with sea level rise via marsh migration due to barriers in the landscape, including dense shrub encroachment from fire suppression of inland communities. Fire may play an important role in promoting resiliency by in two ways, first by reducing or removing woody encroachment, allowing species to be released to migrate inland, second, by promoting primary productivity of herbaceous vegetation, which in turn, may promote vertical expansion. Where elimination of barriers is not possible (i.e., roads, industry and infrastructure), assisted migration of coastal communities landward (via translocation) may be also be a viable solution to bypass these barriers.;This research is focused on the potential contribution of seed banks in landward migration of species, the role that fire plays in compositional change, and how seed banks compare to translocated communities when introduced into new environments. Here, seed bank dynamics were assessed and compared to aboveground vegetation of naturally regenerating and reciprocally transplanted (translocated) sods through time, with and without fire. The objectives of this study were to examine: 1) richness and abundance of species in the seed bank among vegetation zones of the coastal transition gradient; 2) effect of fire on expression of the soil seed bank; 3) emergence patterns and the degree of mixing/dispersion of dominant species within the seed bank among zones; 4) similarity of species composition of seed bank to that of the standing vegetation, pre- and post-fire; 5) similarity of species composition of the seed bank to that of the inter-zonally transplanted sods, with and without fire; and 6) fire behaviors through fuel loads and fire temperatures across zones.;Results demonstrate the effect of zone on the composition, species richness and propagule density of the seed bank, and differences in similarity of the composition of the seed bank and standing vegetation. Fire did not appear to affect the composition of the seed bank. Ordinations indicate that seed bank communities are more widely distributed than standing vegetation assemblages. An overlap of communities was observed in each zone of the seed bank except salt marsh. Reciprocally transplanted sods that were burned prior to translocation were more similar to seed bank composition than no-fire transplants. Similarity, related to habitat preference, was most retained when sods were transplanted one zone away, and when transplanted upslope. A series of Procrustes analyses was conducted for combinations of seed bank treatments to standing vegetation of naturally regenerated and reciprocally transplanted plots of varying survey periods. Results showed that seed bank composition was most similar to the standing vegetation of the same survey period, and least similar for no-fire seed bank to transplanted plots surveyed 15 months after transplant. That the no-fire transplant plots were less similar to seed bank than burned transplant plot indicate that similarity between the seed bank and standing vegetation may be retained with fire. Comparisons of the Jaccard's Similarity Coefficient of transplanted plot to seed bank with and without fire showed that overall, plots that had been burned were more similar to their source plots than those that had not been burned, across all zones.;This study provides insight to zonation patterns of the seed bank across the coastal coenocline of the northern Gulf of Mexico, and compositional similarity of the seed bank to both naturally generated and reciprocally transplanted propagules, in order to understand the how these communities respond to sea level rise, how they may be managed with fire, and how plant species respond to conditions across zone, thereby the potential contribution of the seed bank to landward migration and the promotion of resiliency of coastal communities through facilitation of lateral migration in response sea level rise.