Protected areas enhance biodiversity across Europe: a continental and national assessment

Protected areas (PAs) are a cornerstone of biodiversity conservation, yet their effectiveness varies across taxa, biogeographic regions, and ecological contexts. Here, we evaluate the contribution of PAs to biodiversity conservation by integrating analyses at continental and national scales. To account for the non-random spatial distribution of PAs, we applied propensity score matching to control for major environmental and anthropogenic confounders. At the European scale, we analyzed the distribution of 1,769 species of conservation priority listed under the Birds and Habitats Directives, comparing alpha, beta, and gamma diversity between protected and unprotected sites. Protected sites hosted significantly higher overall biodiversity, particularly for amphibians, arthropods, birds, mammals, and vascular plants. However, effectiveness was not uniform across regions, with weaker or inconsistent patterns in the Boreal and Atlantic biogeographic regions. At the national scale, we assessed the role of PAs using understory plant diversity collected in 5,423 vegetation plots in Italian broadleaved deciduous forests between 1980 and 2020. Protected forests supported significantly higher alpha and gamma diversity of understory species, especially forest-associated taxa, whereas open-habitat species showed limited differences between protected and unprotected areas. Together, these findings highlight that protected areas substantially enhance biodiversity conservation, but with context-dependent outcomes. Extending this analytical framework to local case studies would allow for a finer-scale evaluation of conservation effectiveness, help identify region-specific gaps, and support adaptive management strategies aligned with the EU Biodiversity Strategy for 2030.