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International audience; This chapter presents the results of our transdisciplinary work since 2001 on 100 wastelands in the greater Paris area, using ecological, geographical, and artistic approaches. This research subject, which we addressed with a diversity of methodologies and sensibilities, had hitherto been little studied: wastelands were unmapped and often disregarded. Our aim has been to understand the ecological, artistic, and political interrelationships of these spaces and their role as refuges for human and non-human beings.

International audience; Urbanization is one of the major threats to wild plants and pollinators, and its global increase demands a better understanding of the mechanism driving its negative impact. Urban warming and altered local environmental conditions have the potential to affect the timing of flowering and of pollinator activity. While previous evidence has shown that plant phenology tends to advance in urban areas, little is known about its effects on pollinator phenology. In this study we simultaneously assessed the response of the timing of flowering of native plants and of the flight period of wild pollinators to increased urbanization. We collected data from 12 sites along an urbanization gradient in northern France, a region under strong anthropogenic pressure. Overall, we recorded more than 70 plant species, and we sampled more than 4300 wild bees and hoverflies belonging to 154 species. Plant flowering showed a strong response to urbanization at the community level with a striking advancement of the flowering peak in sites at high urbanization. On the contrary, pollinator communities did not show any clear shift of their flight phenology along the gradient, neither regarding abundance nor diversity. Our results indicate that phenologies of plant and pollinator communities can respond differently along the same urbanization gradient. These asymmetric responses can drive modifications in the structure of plant–pollinator networks, and potentially negatively affect the fitness of both mutualistic partners.

Afin de préciser l’ambivalence, par rapport aux services écosystémiques, des délaissés urbains, réservoirs d’espèces indigènes mais aussi exotiques et envahissantes, nous avons étudié la flore des délaissés urbains de deux agglomérations de taille moyenne. Nos résultats montrent que ces espaces accueillent une grande diversité végétale, ordinaire et patrimoniale. La fréquence globale des espèces envahissantes est comparable à celle rapportée par des études effectuées sur les délaissés de métropoles, alors que leur fréquence locale, au sein des délaissés, est beaucoup plus faible. Nous discutons de ces résultats en relation avec les différences de taille d’agglomération et d’origine des délaissés., In order to clarify the ambivalence, with regard to ecosystem’ services, of urban wastelands, reservoirs of both native biodiversity and alien and invasive species, we studied plant diversity of urban wastelands in two medium-sized cities in France. Our results show that urban wastelands host a great species’ diversity, both common and rare or patrimonial. The overall rate of invasive species is similar to the one observed in large cities’ wastelands, while their local rate, within wastelands, is much lower. We discuss of these results with regard to differences in cities’ size and wastelands’ starting point.

Urbanisation leads to natural habitats being fragmented with various effects according to the species and their ecological characteristics. Paradoxically, the urbanisation process creates relatively unused environments, wastelands, habitats which could contribute to biodiversity conservation in urban regions. In this review we examined the role of wastelands in maintaining biodiversity in the city and assessed the different factors responsible for wasteland biodiversity. 37 articles were suitable for our aim. Most of the studies have been conducted in large cities in Western and Central Europe. A wasteland is defined as an abandoned site with spontaneous vegetation (i.e. wild grown vegetation). In most cases, wastelands harbour more species than other urban green spaces. The processes which affect the biodiversity of wastelands operate on two different levels. Locally, the area size, age, soil, microclimate and the vegetation structure are the dominant factors. As in other environments, the species richness increases with the size of the wasteland. Wastelands of different ages include different stages of vegetation, ranging from pioneer to pre-forest stages, and consequently harbour different communities of plants and animals. The diversity of anthropogenic soil substrates leads to different plant communities. At the landscape scale, matrix composition and geographic connectivity between wastelands influence the biodiversity of wastelands, although to a lesser extent than the local features. We show that wastelands have a real potential to contribute to biodiversity conservation in urban regions. At the city scale, they represent habitats which urban planners need to take into account and include in dynamic urban planning.