Three decades later: a resurvey of vegetation biodiversity in Italian coastal dunes

In recent decades, global environmental changes and anthropogenic pressures have significantly altered the structure and functioning of coastal dunes across the Mediterranean, leading to shifts in coastal zonation and the loss of critical habitats. However, existing studies often provide only localized snapshots of temporal biodiversity dynamics, leaving the full extent of these changes unclear at broader spatial and temporal scales. By employing the vegetation resurvey method, we expanded the analysis of temporal trends in biodiversity across dune habitats along the entire Italian coast. We acquired data from ReSurveyDunes, the first collaborative resurveying initiative in coastal dune habitats. From this database, we analyzed 439 vegetation plots originally surveyed about 30 years ago and revisited in 2023-2024. We assessed temporal changes in species richness and composition of coastal dune communities. Preliminary findings based on ordination techniques revealed substantial variability within habitat types along the Italian coast. The analysis of temporal beta diversity revealed significant shifts in species composition and dominance patterns. The dissimilarity resulting from species gains outweighed that resulting from species losses. Although species richness increased across all habitat types, a significant decline in the occurrence and abundance of diagnostic species was observed, particularly in the upper beach and foredunes. Conversely, inner coastal dune grassland exhibited minimal changes on time. While confirming the effectiveness of vegetation resurveys in monitoring highly dynamic environments such as coastal dunes, our findings underscore the importance of obtaining reliable estimates of long-term vegetation change in these threatened habitats to establish baseline assessments for biodiversity monitoring and reporting.