Vegetation influence on stochastic coastal dune dynamics substantiated by process-based model

Coastal dunes are the highest natural features on the beach. They protect the beach communities and low-energy environments from storms by virtue of their elevation. Their formation is a result of delicate coupling between accretional and erosional processes. Here we study the influence of vegetation on dune growth and recovery under water-driven erosion utilizing a process-based coastal model under a stochastic framework. An equivalence of this model is first established with a recently developed stochastic model of dune evolution under water-erosional stress. From the model vegetation parameters: the vegetation growth time and colonization time are quantified and their relation with characteristic dune growth times is established. Vegetation causes an initial lag in dune formation due to the colonization time. Also, the dune growth under the influence of vegetation is found to be divided into two regimes, stable and mobile. Within the stable regime, the influence of vegetation on dune recovery is quantified by the colonization time, and its competition with water-driven erosion is analyzed. This leads to the development of a phase space relating to flooding frequency, intensity, dune growth, and dune establishment times. The dune state transitions from high to barren based on the competing dune recovery time controlled by vegetation and the flooding frequency. Finally, a vulnerability indicator is obtained from the transition threshold as a minimum base elevation after an overwash required by the beach for vegetation to recover and establish dunes that overcome frequent flooding.