Resurveying the most threatened habitats

Mediterranean coastal dunes are among the most threatened ecosystems in Europe, undergoing accelerated transformations under global environmental change and anthropogenic pressures. To advance understanding of long-term vegetation dynamics in these habitats, this research was developed through three complementary steps and is based on a diachronic analysis of vegetation resurveys at both local and national scales across Italian dune ecosystems. First, within the Castelporziano Presidential Estate, which hosts one of the most well-preserved coastal dune systems in Italy, 80 historical vegetation plots, originally surveyed approximately 30 years ago across all vegetation communities of the coastal zonation, were revisited to assess temporal changes in species composition, ecological indicator values, and functional traits. In parallel, ReSurveyDunes, the first national database of resurveyed Italian coastal dune vegetation plots, was developed by integrating historical phytosociological relevés with resurveys conducted between 2023 and 2024. This database encompasses multiple dune habitats and enables long-term, national-scale assessments of their conservation status. From ReSurveyDunes 519 historical plots distributed across 11 regions, originally sampled between 1974 and 2009, were extracted and analysed to produce the first national assessment of multi-decadal trends in coastal dune vegetation, encompassing herbaceous communities of upper beach, shifting dune, and dune grassland habitats. Results revealed heterogeneous but interpretable patterns across spatial scales. In well-preserved sites such as Castelporziano, species richness and the abundance of typical psammophilous species remained stable or increased, reflecting limited anthropogenic disturbance and ongoing natural successional processes. At the national scale, overall species richness often increased, but this trend masked marked declines in habitat-specialist species, particularly in early-successional environments. These compositional changes were driven primarily by an increase in ruderal species and by species redistribution along the coastal zonation gradient, rather than by the widespread invasion of non-native taxa. Approximately one-third of revisited plots experienced transitions toward different habitat types, indicating the coexistence of inland-directed stabilisation and localised degradation in foredune zones. Together, these findings demonstrate that apparent increases in diversity may conceal structural and functional erosion in dynamic dune ecosystems. Long-term resurvey approaches, such as those implemented in ReSurveyDunes, are essential for detecting subtle ecological shifts and for guiding conservation strategies aimed at preserving the integrity and resilience of Mediterranean coastal dune habitats under intensifying environmental pressures.