Research Intention

After hurricanes, coastal freshwater swamps damaged by saltwater surge may have a different trajectory than those damaged by wind. Also, regeneration in gaps created by salinity intrusion could have an important role in shaping future coastal vegetation patterns. This study compares salinity versus wind-driven impacts of hurricanes on vegetation structure and regeneration along coastal wetland gradients after Hurricane Sandy on the Delmarva Peninsula (Delaware, Virginia, Maryland, USA).

Methods

Structural damage was surveyed along transects along coastal gradients from saltmarsh to freshwater wetland. The regeneration potentials of coastal wetland species, types and gradients were studied by conducting a seed bank assay and examining responses to various water regimes (unflooded and flooded to 8 cm) and salinity levels (0, 1, and 5 ppt). Seed bank responses to treatments were compared using general linear models. Species relationships to treatment and geographical variables were explored using Non-metric Multidimensional Scaling.

Results

After a salinity surge from Hurricane Sandy, some swamps along the Pocomoke River (MD) had elevated salinity so that individuals of some salinity intolerant species died (e.g., Taxodium distichum). Post-hurricane environments of flooding and salinity mostly suppressed the regeneration of species in these coastal wetlands, even at low salinity levels (1 and 5 ppt). Even though maritime forest was positioned adjacent to saltmarsh along the coastal gradient, maritime forest was intolerant of salinity intrusion. At the same time, both saltmarsh and fresh marsh were less affected by the salinity and flooding treatments in the greenhouse experiment. Thus, the regeneration pattern of species, wetland types and gradients were affected in different ways by post-hurricane conditions of salinity and flooding.

Conclusions

Hurricanes have the potential to drive long term changes in vegetation because of the differential effect of salinity intrusion and wind breakage on different vegetation types and their subsequent regeneration along the coastal gradient. Long-term forest composition with climate change will depends on the individualistic responses of species to these hurricane environments and the frequency and intensity of these disturbances.