Assessing the conservation status of coastal dune systems under the EU Habitats Directive using a dual-index approach: a Mediterranean study case.

Focusing on an extensive coastal dune system in Southern Italy, a methodology for monitoring and evaluating the conservation status of coastal habitats under the EU Habitats Directive was proposed and applied. Despite the ecological significance of these environments, standardized quantitative protocols for assessing the 'structure and functions' parameter at the local level are still lacking. Building upon the belt transect framework recommended by the Italian Institute for Environmental Protection and Research (ISPRA), the assessment is enhanced through a dual-index approach. This framework integrates the Index of Favourable Conservation Status (FCSi) to evaluate local floristic quality, and introduces the novel Index of Serial Discontinuity (SDi) to capture spatial and structural disruptions within the standard dune zonation. The results indicate that the performance of the proposed indices is scale-dependent; in fact, the application of both indices revealed that they measure independent dimensions of degradation. Furthermore, by downscaling the SDi, it is possible to quantify the 'landscape-level vulnerability' imposed on each individual habitat plot by zonation gaps. Ultimately, this combined approach overcomes the well-documented limitations of traditional diversity metrics, offering a spatially explicit diagnostic tool to guide targeted management and ecological restoration strategies.