Coastal plant communities along the Northern Gulf of Mexico coast are subject to chronic sea level rise (SLR) and increasingly intense tropical storms. Some species are resilient and cope with rising seas by trapping inorganic sediment and accreting organic material. When rates of SLR exceed their capacity for vertical resilience, landward (upslope) migration is necessary for long-term persistence in the landscape. Upslope vegetation, often dominated by long-lived woody species, creates dispersal and establishment barriers to migration of herbaceous marsh species, leaving the latter highly vulnerable when they are squeezed at the seaward end of their distributions. We hypothesized that disturbance to upslope vegetation opens establishment opportunities and promotes landward establishment of marsh. In April 2015, we identified four pine island-marsh complexes at Grand Bay National Estuarine Research Reserve, Mississippi, USA; two were burned and two were left unburned to serve as controls. In July 2015, we initiated a reciprocal community transplant experiment using replicate sods (containing propagule banks) excavated from the four dominant vegetation types on these marsh island complexes: salt marsh, brackish marsh, fresh marsh and pine savanna. Sods were reciprocally placed into each of the different zones, including the source zones as controls for potential transplant effects.
Results/Conclusions
Preliminary results indicate successful upslope establishment and poor survival of downslope transplants for all assemblage types. Species richness in experimental plots was highest where assemblages were migrated upslope several zones. Long-term survival may be constrained by recovering woody shrubs that are now vigorously resprouting. In addition, invasion by species from vegetation surrounding the sods is producing new mixtures of species. Competitive interactions between species from different zones may also limit expansion of downslope species that have been migrated upslope. Thus, local dispersal processes and resilience of upslope, woody-dominated assemblages may prohibit landscape resilience and fluidity by thwarting landward establishment and persistence of downslope species increasingly under stress from sea level rise.