Mixed effects of a national protected area network on terrestrial and freshwater biodiversity

Protected areas are considered fundamental to counter biodiversity loss. However, evidence for their effectiveness in averting local extinctions remains scarce and taxonomically biased. We employ a robust counterfactual multi-taxon approach to compare occupancy patterns of 638 species, including birds (150), mammals (23), plants (39) and phytoplankton (426) between protected and unprotected sites across four decades in Finland. We find mixed impacts of protected areas, with only a small proportion of species explicitly benefiting from protection-mainly through slower rates of decline inside protected areas. The benefits of protection are enhanced for larger protected areas and are traceable to when the sites were protected, but are mostly unrelated to species conservation status or traits (size, climatic niche and threat status). Our results suggest that the current protected area network can partly contribute to slow down declines in occupancy rates, but alone will not suffice to halt the biodiversity crisis. Efforts aimed at improving coverage, connectivity and management will be key to enhance the effectiveness of protected areas towards bending the curve of biodiversity loss. ; This project received funding from the European Commission through the Horizon 2020 Marie Skłodowska-Curie Actions individual fellowships (Grant no. 101027534) to A.S., from the Jane and Aatos Erkko Foundation to A.S., O.O., T.R., J.V., L.A., M.Saa., from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 856506; ERC-synergy project LIFEPLAN) to O.O. and T.R., from the Academy of Finland, grant no. 309581 to O.O., grant no. 322266 to T.R., grant no. 330739 to M.H., grant no. 317255 to J.V., grant no. 340280 to L.A., grant no. 312650 (Project BlueAdapt) to B.W., from the Research Council of Norway through its Centres of Excellence Funding Scheme (223257) to O.O., from the Finnish Cultural Foundation to E.K., from the Helsinki Life Science Institute to M.Saa. ...