In a rapidly urbanising world, the ability of plant species to survive and build self‐sustaining populations in urban environments is increasingly important for biodiversity conservation. Yet, the contribution of cities to biodiversity conservation remains unclear because ecologists have studied biodiversity patterns, largely without considering the population establishment of plants and the ways in which different kinds of urban ecosystems harbour native and endangered plant species. These limitations can mislead conservation policies for cities. To better understand how urban ecosystems can contribute to biodiversity conservation, we propose a framework that links the population status (casual or established) of plant species with ecosystem novelty and highlights barriers to population establishment in different types of urban ecosystems, from natural remnants to novel ecosystems. To quantify the relative importance of natural remnants vs. human‐shaped ecosystems for the conservation of self‐sustaining urban plant populations. we re‐analyse a unique dataset from a metropolitan region in Europe with information on the population status of 1,199 plant species. Results demonstrate that urban ecosystems harbour many established native and endangered species although a considerable share (37%) of species of conservation concern are confined to natural remnants. In hybrid and immature novel ecosystems, high species numbers reflect many species with only casual populations. The role of novel ecosystems as habitats for native and endangered plant species increases as novel ecosystems mature. Synthesis and applications. General information about plant species richness in urban environments may mislead conservation policies as different kinds of urban ecosystems can play different roles in harbouring species of conservation concern. Moreover, presence/absence data can mask establishment failures of species. This proposed framework helps to distinguish between casual and established populations of plant species, and highlights barriers to population persistence in urban ecosystems, reflecting different land uses and land use histories over time. Revealing the role of natural remnants vs. hybrid vs. novel ecosystems as habitats for species of conservation concern illustrates opportunities for biodiversity conservation in all urban ecosystems and can support setting priorities for conservation.

Increasing urbanization worldwide calls for more sustainable urban development. Simultaneously, the global biodiversity crisis accentuates the need of fostering biodiversity within cities. Policies supporting urban nature conservation need to understand people's acceptance of biodiversity‐friendly greenspace management. We surveyed more than 2,000 people in 19 European cities about their attitudes toward near‐natural urban grassland management in public greenspaces, and related their responses to nine sociocultural parameters. Results reveal that people across Europe can support urban biodiversity, yet within the frames of a generally tidy appearance of public greenery. Younger people and those using greenspaces for a greater variety of activities were more likely to favor biodiversity‐friendly greenspace management. Additionally, people who were aware of the meaning of biodiversity and those stating responsibility for biodiversity conservation particularly supported biodiversity‐friendly greenspace management. Our results point at explicit measures like environmental education to increase public acceptance of policies that facilitate nature conservation within cities.

Many cities aim to increase urban forest cover to benefit residents through the provision of ecosystem services and to promote biodiversity. As a complement to traditional forest plantings, we address opportunities associated with “emerging urban forests” (i.e., spontaneously developing forests in cities) for urban biodiversity conservation. We quantified the area of successional forests and analyzed the species richness of native and alien plants and of invertebrates (carabid beetles, spiders) in emerging forests dominated by alien or native trees, including Robinia pseudoacacia, Acer platanoides, and Betula pendula. Emerging urban forests were revealed as shared habitats of native and alien species. Native species richness was not profoundly affected by the alien (co-)dominance of the canopy. Instead, native and alien plant species richnesses were positively related. Numbers of endangered plants and invertebrates did not differ between native- and alien-dominated forest patches. Patterns of tree regeneration indicate different successional trajectories for novel forest types. We conclude that these forests (i) provide habitats for native and alien species, including some endangered species, (ii) allow city dwellers to experience wild urban nature, and (iii) support arguments for adapting forests to dynamic urban environments. Integrating emerging urban forests into the urban green infrastructure is a promising pathway to sustainable cities and can complement traditional restoration or greening approaches.