Biodiversity Trends in Protected Areas

Abstract

Protected areas (PAs) are the cornerstone of biodiversity conservation policy, yet empirical evidence on whether PAs are maintaining or improving biodiversity trends for vertebrates relative to comparable unprotected landscapes remains mixed and geographically biased toward well-resourced national systems. This study analysed long-term vertebrate biodiversity trends within and outside PAs across 284 sites in 18 European countries, using standardised multi-taxa monitoring data (birds, mammals, reptiles, amphibians, freshwater fish) from 1998-2023 compiled from national biodiversity monitoring programmes. Within-PA species richness trends were significantly more positive than outside-PA trends for birds (mean inside +0.84 +/- 0.28 species/decade vs. outside -1.24 +/- 0.42 species/decade; t = 8.4, p < 0.001) and mammals (inside +0.42 +/- 0.18 vs. outside -0.68 +/- 0.24; t = 6.2, p < 0.001), but not for reptiles (p = 0.14) or freshwater fish (p = 0.08). PA effectiveness was strongly predicted by management budget per hectare (r = +0.74, p < 0.001), PA area (r = +0.62, p < 0.001), and connectivity to other PAs (r = +0.58, p < 0.001), but not by legal designation category per se. PA sites with active adaptive management showed 2.84-fold higher biodiversity trend improvement rates than passively managed sites. Threatened species representation declined at 48.4% of PA sites over the study period, concentrated in small, under-funded, and isolated PAs in Southern and Eastern Europe. These findings provide quantitative evidence for the conditions under which PAs deliver biodiversity benefits and identify the investment and governance reforms required to meet EU Biodiversity Strategy 2030 targets.