Invasion rate of the alien species Acacia saligna within coastal sand dune habitats in Israel

Throughout the world, Acacia saligna is considered an invasive species that has negative impact on natural ecosystems. The aim of the present study was to quantify the rate of the biological invasion process (arrival, establishment, and spreading rates) of Acacia in Israeli Mediterranean coastal dunes, and to characterize the distribution patterns and trends within various habitats in the ecosystem. Black-and-white aerial photographs from five points in time (1965, 1974, 1982, 1990, and 1999) were analyzed using field observations, GIS (geographic information system), and remote sensing methods. The results indicate that over the 34 years studied, the area covered in Acacia grew by 166% at an annual growth rate of 2.92%. The "Arrival Stage" lasted for 20 years, and the "Establishment Stage" lasted another eight years. Since 1990, Acacia has spread over the coastal dunes (the "Spreading Stage"). Spreading was dictated primarily by optimal soil moisture regime. Acacia invaded disturbed habitats, such as sand quarries and depressions between dunes, but never shifting sand dunes.