Mixed evidence that protected areas slow declines of threatened plant species in Germany

Marie Englert , Ingmar R. Staude, Marten Winter, Christian Wirth

1. A central credo of plant conservation is that the most effective way to protect native plants is to conserve the habitats in which they occur. Protected areas are therefore a cornerstone of plant conservation, and much research has focused on optimizing their representativeness across species. Far fewer studies, however, have tested whether protected populations actually persist over time. Here, we address this gap and assess whether protected areas in Germany promote persistence of threatened plant species.
2. Using a large-scale, 60-year occurrence dataset based on ~29 million records for ~2,100 plant species, together with ~7,700 local plot time series spanning almost 100 years for 1,800 vascular plant species, we evaluated protected-area effectiveness across two spatial scales. We tested (i) whether greater coverage of threatened species’ ranges by protected areas was associated with greater range retention, (ii) whether threatened species showed more favorable cover, colonization, and extinction dynamics in protected than unprotected plots, and (iii) whether these relationships differed among protected-area categories.
3. Greater protection of species’ baseline ranges was associated with higher range retention, although protected-area coverage explained little variation, and category-specific positive associations were detected only for strictly protected areas (IUCN I–III and biosphere reserve core zones) and Natura 2000 sites. At the local scale, cover trends differed little between protected and unprotected plots and were generally negative, with weak evidence for more positive trends in Natura 2000 sites. Extinction odds of threatened species were lower in Natura 2000 and IUCN IV sites, both characterized by more active management, but higher in IUCN V areas. Colonization counts were higher in Natura 2000 sites and strictly protected areas than outside protected areas.
4. Synthesis: Natura 2000 was the only protection category showing favorable effects across both spatial scales and multiple measures of persistence. More broadly, however, the effects of protection were modest and far from unequivocal or universal. Thus, our findings suggest that biodiversity targets focused on protected-area extent, like 30-by-30, whilst certainly benefiting several other attributes of biodiversity, are in themselves not a safe bet for the conservation of threatened flora.