Untangling the role of urban ecosystems as habitats for endangered plant species.

• All populations of 213 endangered plants related to different ecosystems in Berlin. • Most populations were found in forests, grasslands and ruderal sites. • Novel urban ecosystems harbored most populations of endangered plants. • Yet population density was highest in natural remnants. • Strong arguments for broad approaches in urban biodiversity conservation. As urbanization accelerates globally, a better understanding of how cities contribute to biodiversity conservation is increasingly pressing. Previous studies reveal that cities can harbor a considerable biological richness, including endangered plant species. Yet, a key question on the urban contribution to plant conservation remains critically open, as little information is available on how populations of endangered plant species occur across different biotope types within cities and to what extent anthropogenically shaped vs. natural ecosystems provide habitats for endangered plants. We analyzed a unique dataset on the exact geographical position of 1742 populations of 213 endangered plant species in the city of Berlin. We first assessed the relative importance of Berlin's nine major biotope classes as habitats of these species. Second, we applied the novel ecosystem concept to quantify endangered plant populations for natural remnants vs. hybrid vs. novel ecosystems within Berlin. Populations of endangered plant species were generally, although unevenly, associated with specific biotope classes, with forest, grassland, and ruderal biotopes as the most important habitats. Surprisingly, novel ecosystems harbored the highest numbers of total populations, of total species, and of species that were exclusively confined to one type of ecosystem novelty. Quantifying the relative importance of biotope classes and novel vs. (near-)natural ecosystems as habitats of endangered species demonstrates that the urban contribution to biodiversity conservation is best ensured by providing a range of ecosystems. Rather than prioritizing only natural remnants, we thus argue for broad approaches to urban biodiversity conservation that include novel ecosystems. [ABSTRACT FROM AUTHOR]