A multitaxonomic assessment of Natura 2000 effectiveness across European biogeographic regions

: The Natura 2000 (N2K) protected area (PA) network is a crucial tool to limit biodiversity loss in Europe. Despite covering 18% of EU's land area, its effectiveness at conserving biodiversity across taxa and biogeographic regions remains uncertain. Testing this effectiveness is, however, difficult as it requires considering the non-random location of PAs, and many possible confounding factors. Here, we used propensity score matching accounting for the confounding effects of biogeographic regions, terrain ruggedness, and land cover, when assessing the effectiveness of N2K PAs on the distribution of 1,769 priority species from EU's Birds and Habitats Directives, including mammals, birds, amphibians, reptiles, arthropods, fishes, molluscs, vascular and non-vascular plants. We compared alpha, beta, and gamma diversity between matched selections of protected and non-protected areas across EU's biogeographic regions using generalized linear models, generalized mixed models, and non-parametric tests for paired samples, respectively, for each taxonomic group and for the entire set of species. While we found N2K PAs to host significantly more priority species than non-protected land, this difference was not consistent across biogeographic regions and taxa. Total alpha diversity as well as alpha diversity of amphibians, arthropods, birds, mammals, and vascular plants were significantly higher inside PAs than outside, except in the Boreal region. Beta diversity was in general significantly higher inside N2K PAs than outside. Similarly, gamma diversity showed the highest values within N2K PAs, with some exceptions in Boreal and Atlantic regions. The planned expansion of the N2K network, as dictated by the European Biodiversity Strategy for 2030, should therefore target areas in the southern part of the Boreal region, areas with high species diversity of amphibians, arthropods, birds, mammals, and vascular plants, which are currently underrepresented in the N2K network. This article is protected by copyright. All rights reserved.