In order to stop biodiversity loss, the Convention on Biological Diversity was adopted in 1992. The current Strategic Plan for Biodiversity contains 20 so-called Aichi targets that each signatory nation is expected to reach until 2020. Despite these efforts, global biodiversity loss will likely continue beyond 2020 .
Aichi target 11 explicitly refers to protected areas (PA) as a means to conserve biodiversity and calls for at least 17 per cent of terrestrial areas to be conserved through PA. In the European Union (EU), the adaptions of the Birds and the Habitats directives led to the EU-wide PA network Natura 2000 which currently covers 18 per cent of the terrestrial territory. With this, the EU formally reached the areal component of Aichi target 11, but biodiversity is still declining. To promote the successful implementation of international conservation targets, interdisciplinary research on ecological and socio-economic key factors for the establishment and evaluation of PA systems is needed.
PA network performance has seldom been assessed across the whole of Europe, yet there have been assessments for certain taxonomic groups and specific regions. According to Aichi target 11, PA networks need to be ecologically representative in order to protect biodiversity effectively. Our study therefore aims at evaluating representation of European biodiversity within the whole Natura 2000 network extent. As distribution data for many European species is not available or incomplete, we evaluate network performance on the ecosystem-level, at two different levels of detail, namely ecoregions and habitat types. First, we conducted a gap analysis, evaluating if the Natura 2000 network is representing ecoregions and habitat types adequately. While Aichi target 11 calls for 10 per cent of each ecoregion to be preserved, no targets exist on the habitat type level. We therefore assigned a target to each habitat type based on its threat status as evaluated by the European Red List of habitat types. We discovered that six ecoregions and 101 habitat types do not meet their representation target. To address these shortfalls, we simulated cost-efficient expansion of the network that strategically targets underrepresented ecoregions and habitat types.
By signing the Convention on Biological Diversity, nations pledged 25 years ago to stop biodiversity loss, but this goal is not reached yet and will likely not be reached until 2020. Evaluating and improving existing protected area networks based on systematic conservation planning principles  should be one vital component in future conservation planning efforts, ensuring that protected area networks are continuously improved to conserve biodiversity more effectively.
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