Ecotone displacement trends on a highly dynamic barrier Island: Hog Island,Virginia

Aerial photographs, recording 12 positions of the shoreline and vegetation line over a 50-yr period, were used to investigate long-term ecotone displacement trends and the relationship between ecotone displacement and shoreline migration on Hog Island, Virginia. A robust regression modeling technique, originally developed for shoreline trend detection analyses, enabled examination of the direction, magnitude, and timing of changes in long-term ecotone displacement. Measurements were obtained at 277 shore normal transects spaced 50 m apart. The results show that long-term trends in ecotone displacement and shoreline movement are nonlinear for over three-fourths of the Hog Island coast. On average, the shoreline and vegetation line experienced reversals in 1972 and 1974, respectively. Rarely did the ecotones and shorelines move in tandem or synchronously. Concavity tests indicate that most of the shoreline and ecotone are currently moving seaward and the distance between the shoreline and vegetation line is decreasing through time. Evidence exists for a decennial time lag between the reversal of the shoreline and the ecotone and vice versa. The ecotone and shoreline trends apparently correspond to tidal inlet dynamics, individual storm events, storm climate, inherited topography (e.g., dune), and vegetation type.