Community types and alien species distribution in Italian coastal dunes

The present study concentrates on recent dunes (Holocene) of the Molise region (Central Italy). We focus on different plant communities along the coastal zonation with the aim of quantifying their degree of invasibility by alien plants. Vegetation data were collected following a random stratified sampling design, using a CORINE land cover map (scale 1:5,000) with the land cover classes as strata. In order to identify the major community types present in the study area, 125 sampling plots were classified through cluster analysis and ordinated with PCoA. The percentage of the flora comprised by alien species and the mean alien species richness for each community type was calculated using a one-way ANOVA to test for significant differences. Five community types were identified along a gradient of increasing distance from the sea. Despite the higher proportion of aliens, the beach and embryo dune communities showed mainly archaeophytes, or at least species introduced many centuries ago, which have clearly adapted to the particularly stressful conditions. On the other hand, mobile dunes showed lower proportion of aliens but included neophytes. In the Mediterranean macchia the lowest proportion of aliens was observed. Our results suggest that in coastal dune communities both human disturbance and environmental stress affect alien invasions. The interaction of these two factors probably plays an important role in the distribution of alien species.