From the sand they rise: The recolonization of coastal dune blowouts post-storm

Background/Question/Methods: Disturbances are frequently the impetus for habitat change, but this is especially true at the land-sea interface. In coastal dunes that buffer upland areas, dynamic flux is the norm, and wind events, especially major storms, have the potential to drive change by denuding once vegetated microhabitats and creating hollow blowout depressions. These blowouts are considered ephemeral, ripe for recolonization, and inherent among coastal systems, both recently storm-affected and ‘healthy’, worldwide. However, we do not understand on what timescale recolonization operates or what factors control the rate and magnitude of localized changes associated with further erosion or vegetated stabilization. Since Superstorm Sandy, October 2012, we have conducted a yearly census of blowouts created by the storm along a 3km stretch of a model barrier island coastal dune system, Island Beach State Park, NJ. We use a Trimble GeoXT Explorer 2008 to map the outermost vegetated blowout edges as a macroscale metric of extent change. We are also exploring extent shifts directionally within quadrants defined by compass direction as it relates to wind direction. Similarly, at the microscale, we are following vegetation demography and changes in substrate depth within 22 2-m radius census plots, at the interface of a vegetated foredune and a blowout within it. Thus far, we have taken census of these plots in Sept 2016, June 2017, and Oct 2017.

Results/Conclusions: After Sandy, there were 55 blowouts of various sizes and shapes within the foredunes. As of 2017, 29 of these 55 have become colonized and 26 remain unvegetated though their extents have changed. Distinctly new bowls have been created each year and fragmentation of existing bowls from colonization has also occurred. The edges of bowls have been changing location over time primarily due to vegetation encroachment via clonal growth, with negligible germination from the seedbank. Results show that the smaller the blowout, the more ephemeral it will be. Within the census plots, we see that the number of plants varies between growing seasons, but does not change within a growing season, June to October. Substrate stability and blowout extent shifts are likely coupled with wind forcing dictating where vegetation is able to root and survive. Understanding the controls on dune recolonization in a natural setting has implications for management with dictating planting locations as well so for understanding how habitats will likely change and evolve as a function of increasing disturbances related to climate change.