Influence of Dune Structure, Storm Surge Frequency and Storm Intensity on Rate and Pattern of Barrier Island Revegetation

Plants are the physical engineers of dune systems. The presence of sand accumulating pioneer grasses and dune stabilizing woody plants influences the rate and pattern of dune development. Revegetation following overwash of barrier islands is dependent on availability and establishment of plant propagules. Immediately after a storm event plants may reestablish quickly from rhizomes and basal buds, but plant establishment from seed does not become part of the revegetation process for several years. We determined the rate and pattern of plant establishment by dune-forming grasses from seeds and rhizome for each of 5 years following Hurricane Opals overwash of Santa Rosa Island, Florida. Transects were established each year at 6 sites across the island to quantify grass seedling presence and survival. Density of plants establishing from seed each year was as least partially linked to subsequent storm events and overwash (1996-2000). Overwash events associated with Hurricanes Ivan (2004) and Dennis (2005) removed much of the vegetation reestablished after hurricane Opal and removed 70% of the remaining foredunes. In the first two years following these hurricanes, LiDar data and field observation noted reduced recovery of foredune vegetation from rhizomes in areas where taller dunes collapsed and buried grasses. Similar observations were made following overwash by Opal 9 years prior. Woody vegetation surveys across the island and in dunes swales documented death of woody vegetation with all storms. Pine death was greatest in swales but saplings of pines were found in most swales several years following each major overwash event (Opal, Ivan and Dennise). Barrier island vegetation is highly resilient to storm overwash however, frequent overwash and height of dunes prior to overwash alters species frequency and abundance as well at the rate of revegetation.