Resilience of a coastal ecosystem following hurricane Irma

Coastal ecosystems like coral reefs, salt marshes and sand dunes are at the front line of climate change. On the one hand, these natural systems are increasingly called upon to shield people and properties from storms and hurricanes which are growing more intense under climate change. On the other hand, these same systems are themselves threatened by the powerful and destructive storm surges and waves that accompany the strongest storms. How fast - and how completely - coastal ecosystems can bounce back (show resilience) after a major storm, and return to shielding our shorelines, therefore becomes a pertinent question, particularly in light of the highly active and damaging Atlantic hurricane season of 2017.

One such storm, hurricane Irma, brought a large storm surge to southwestern and eastern Florida, as well as to the coasts of Georgia and South Carolina, on the 10th and 11th of September. Sand dunes, an important and extensive line of coastal defence in that region and many others worldwide, suffered widespread erosion, with crucial foredunes completely wiped out in many areas. Affected dunes span urban and remote, undeveloped, areas and regions with differences in plant composition (east vs. west coast), providing a unique opportunity to investigate factors that control the ability of these ecosystems to rebound.

This study will address the role of plant functional diversity (or variation in the way plants survive, grow and reproduce) in determining dune recovery. Because differences in function will allow different species to respond to the storm impacts in contrasting ways (e.g., re-growing from roots, or re-establishing from seeds) and use different parts of the beach at different times, a greater variety of plants is expected to boost recovery. This project will also address the effects of urban development in sand dune recovery, a key issue in coastal planning. And further, it will investigate a critical management issue - (how) do washed-up plants and debris affect sand dune recovery, and does their removal in cleanup efforts potentially slow recovery? To answer these questions we will do large-scale surveys spanning 24 sites, measure the diversity of plants, track the fate and growth of individual plants, and record the recovery of vegetation and dune morphology (and so coastal protection) during 3 field expeditions in 2018. To better understand the role of debris and washed up coastal plants, we will remove these from replicated patches in a field experiment, track sediment and plant community changes over the year, and use modern statistical techniques to reveal how any effects (increased nutrients, sedimentation, buffering high temperatures?) are mediated.

We anticipate that these studies will: 1) illuminate the role of vegetation functional diversity in sand dune recovery; 2) reveal how vegetation recovery is affected by debris and dead plant material at a natural site, and how these processes might be lost from highly managed sites; and 3) provide a rare case study on the importance of biodiversity in providing reliable and resilient benefits to people.

The proposed research is poised to benefit a range of stakeholder groups. Most immediately, we expect the work to benefit environmental managers who are eager to learn from our research about the factors and processes underlying resilience in sand dunes. Our work will inform their management approach on at least three fronts: 1) it will guide practical shoreline management activities, including post-hurricane clean-ups and routine beach raking, to ensure that they do not inadvertently undermine resilience capacity; 2) it will allow managers to better predict which sites will be able to recover naturally, and which will benefit from active - though often expensive - restoration; and 3) it will, potentially, identify common interests between agencies concerned primarily with biodiversity conservation (e.g., Florida Fish and Wildlife) and those concerned with predicting and mitigating coastal flooding (e.g., NOAA) which has the potential to harmonise planning for coastal defence (which often side-lines natural processes) and biodiversity conservation; and 4) it will broadly inform coastal zone planning (and development) by identifying the consequences of development for coastal resilience processes.

We also anticipate this work will benefit the general public in multiple ways. Firstly, we will ensure that the findings are disseminated to a broad audience in the UK to increase public understanding of nature-based coastal defence and the natural dynamics of ecosystems. This will be done through dedicated social media sites, and through an exhibit at Swansea's popular Science Festival. Our exhibit will capitalise on existing expertise and equipment (a flume with a model village) developed within related projects on coastal ecosystems (CoastWeb and Resilcoast). Secondly, new management and planning approaches informed by our results will indirectly benefit the public by ensuring that beaches and dunes - highly valued by the public for recreational and aesthetic benefits - are managed in ways that encourage faster and more complete recovery and return of coastal protection services.