Spatial patterns of coastal dune plant diversity reveal conservation priority hotspots in and out a network of protected areas

Effective conservation planning requires identifying priority hotspots to allocate resources. To preserve biodiversity, it is crucial to consider α, β and γ-diversity and protect the irreplaceable sites with high ecological uniqueness, which can host uncommon species assemblages that would be lost if only species-rich sites were protected. Coastal dunes, hosting highly specialized plant communities, are among the most threatened ecosystems worldwide. In this study, we identified conservation priority hotspots to assess the effectiveness of the network of protected areas in coastal dunes of Tuscany (central Italy), using data on plant communities collected in 506 plots. We additively partitioned γ-diversity in its α and β components, observing a significant variation at all spatial levels only for dune species. In terms of α-diversity, we found that Northern protected sites were richer in dune species, while synanthropic and alien species were equally present inside and outside protected areas of the region. By partitioning the total β-diversity into its components (replacement and richness difference), we found a prevalence of replacement for dune species, indicating the most unique sites as the ones to favor for conservation. Unique sites were identified through Local Contributions to Beta Diversity and their conservation value was determined by their species composition and the relationship with landscape variables. Unique sites with high conservation value were only partly protected, while some protected sites were altered and required restoration. Our approach proved effective for identifying the most unique sites, indicating some issues in the existing protected network, while providing valuable information on sites to prioritize for future conservation actions.