Il ruolo delle aree protette nella conservazione della biodiversità vegetale e minacciata in Europa.

Biodiversity loss remains one of the most pressing environmental challenges globally, and in Europe, the Natura 2000 (N2K) protected area (PA) network plays a pivotal role in mitigating this crisis. Covering approximately 18% of the EU’s land area, the N2K network represents a cornerstone of the European Union's conservation strategy, aiming to protect priority species and habitats under the Birds and Habitats Directives. However, questions about its overall representativeness across various taxa and biogeographic regions persist. This PhD thesis explores the representativeness of N2K in biodiversity conservation through three case studies focusing on taxonomic diversity, vascular plant diversity, and forest understory plant diversity, offering a comprehensive assessment of its representativeness and performance. The first case study evaluates the impact of N2K PAs on conserving 1,769 priority species across various taxonomic groups, including mammals, birds, amphibians, reptiles, arthropods, fishes, molluscs, and vascular and non-vascular plants. Using propensity score matching to control for confounding factors related to the non-random location of PAs in the landscape the study assessed the representativeness of N2K network by comparing alpha, beta, and gamma diversity of priority species inside and outside PAs across European biogeographic regions. Results indicate that N2K PAs generally host a significantly higher number of priority species than unprotected areas. Specifically, alpha diversity was notably higher inside PAs for most taxonomic groups, except in the Boreal region. Beta diversity was also significantly higher within PAs. Similarly, gamma diversity, representing overall species richness, showed higher values in PAs, with exceptions in the Boreal and Atlantic regions. These findings underscore the uneven role of N2K across different regions and taxa, emphasizing the need for targeted expansion under the European Biodiversity Strategy for 2030 to prioritize underrepresented species and regions. The second case study focuses on the representativeness of the N2K network in conserving vascular plant biodiversity. Drawing from over 1.2 million vegetation plots in the European Vegetation Archive, encompassing 14.2 million species occurrences, the study assessed the presence of native and conservation priority species within and outside N2K sites. The findings reveal that the N2K network harbors approximately 90% of the EU’s native vascular flora, demonstrating its crucial role in conserving plant diversity. However, significant variability exists across countries and biogeographic regions. Despite this variability, N2K sites generally support a higher species richness per unit area than unprotected areas, as evidenced by species-area curves. These results highlight that while N2K is effective overall, its expansion should focus on regions and habitats where plant diversity is underrepresented, ensuring comprehensive conservation of Europe’s vascular flora. The third case study examines the representativeness of PAs (including in this case N2K sites, national parks, and reserves) in conserving forest understory plant diversity in Italy, one of Europe’s most forested and biodiverse countries. Using a dataset of 16,259 vegetation plots sampled between 1980 and 2020 in broadleaved deciduous forests, the study applied propensity score matching to control for factors related to the non-random locations of PAs and vegetation plots in the landscape. The results reveal that PAs consistently maintained higher understory plant diversity than unprotected areas. Alpha and gamma diversity showed a clear pattern, with a higher number of understory plant species found inside PAs than outside. These case studies show that while Europe's PA network is crucial for biodiversity conservation, its efficacy varies, underscoring the need for a strategic, data-driven expansion to protect underrepresented species and regions.