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International audience; Green roofs provide many ecosystem services, but little is known about the way they contribute to urban functional connectivity. This paper has the following four objectives: (1) to compare the potential green roofs’ role to connectivity in relation to other urban green spaces, (2) to specify the green roofs contribution’s type, (3) to explore the influence of building height integration method and finally (4) to assess the impact on connectivity of simulated greening new roofs. Using a landscape graph approach, we modeled ecological networks of three species groups with different dispersion capacities in the Paris region (France). Then, we computed several connectivity metrics to assess the potential contribution of green roofs to functional connectivity. At a large scale (metropole scale), our results show that green roofs can slightly improve the global connectivity largely through the connections rather than the addition of habitat area. More than a stepping stone function, green roofs would have a dispersion flux function at a local scale. Furthermore, when the difficulty of crossing movement is exponential to the height of buildings, green roofs over 20 meters high are mostly disconnected from the ecological networks. In addition to the green roof’s height, our analysis highlights the very strong role played by buildings’ configuration. This study raises promising directions for the integration of building height into the analysis of urban connectivity. Detailed research and long-term biological data from green roofs and green spaces are needed to confirm our results.

L’adaptation des villes au réchauffement climatique passe par la recherche de solutions économiques pour être mobilisables à grande échelle. Dans ce contexte, la végétalisation des enveloppes bâties est désormais connue pour contribuer à la réduction des ilots de chaleurs et aux bienfaits de la nature en ville. Parmi les dispositifs de végétalisation existants, la colonisation des supports bâtis par les plantes spontanées est gratuite et retient l’attention. Cependant, la végétalisation spontanée est souvent associée chez les professionnels à la dégradation potentielle des constructions et les expérimentations restent rares. D’autre part, les recherches concernant la colonisation des dispositifs bâtis ne prennent pas en considération l’écoconception architecturale à destination des espèces rupicoles et rudérales. L’objet de cet article est de caractériser des situations bâties identifiées par leur capacité à accueillir le développement des plantes spontanées. La méthode employée a consisté à établir des relevés de végétaux dans leur milieu bâti. La mise à l’échelle des plantes par rapport aux ouvrages construits donne à voir les dynamiques d’interaction. Les points d’implantations ont ensuite été décrits et analysés pour en extraire des caractéristiques d’interaction entre le végétal et le bâti. Les données obtenues concernent des critères architecturaux d’implantation du végétal, des critères de caractérisation du point d’implantation du végétal sur un support bâti et une tentative d’évaluation de l’impact de ces critères sur certaines fonctions végétales. Cette étude propose ainsi une première approche destinée à l’écoconception architecturale des enveloppes dans le but de favoriser la colonisation du bâti par la végétation., The adaptation of cities to global warming requires the search for economic solutions to be mobilized on a large scale. In this context, the greening of the built envelopes is now known to contribute to the reduction of islands of heat and the benefits of nature in the city. Among the existing vegetation devices, the colonization of the supports built by the spontaneous plants is free and holds the attention. However, spontaneous vegetation is often associated in professionals with the potential degradation of buildings and experiments are rare. On the other hand, the research concerning the colonization of buildings is not addressed to the architectural ecodesign for rupicolous and ruderal species. The aim of this article is to characterize built-up situations identified by their capacity to accommodate the development of spontaneous plants. The method used was to establish vegetation drawings in their built environment. The scaling of plants compared to constructed structures shows the dynamics of interactions. The implantation points were then described and analyzed to extract interaction characteristics between the plant and the built biotope. The data obtained relate to architectural criteria for plant establishment, criteria for characterizing the plant implantation point on a built support and an attempt to evaluate the impact of these criteria on certain plant functions. This study proposes a first approach aimed at the architectural ecodesign of envelopes in order to favor the colonization of buildings by vegetation.

In a context of urban greening, vertical plantings offer a great potential to enhance urban biodiversity but it is unclear whether they act as exclusive habitats or components of urban corridors. Thus, understanding the ecological value and functioning of each system becomes critical to integrate nature into urban design and planning at the city scale. This chapter reviews studies on green walls’ biodiversity, examining the flora and fauna of different vertical planting systems and the main drivers for the establishment of communities. Perspectives for research and design are also presented to understand and explore new techniques for enhancing biodiversity on green walls and within cities.

International audience; Green roofs and walls have recently emerged as conservation tools, and they offer promising additional opportunities to enhance biodiversity in cities. However, their ecological conditions remain poorly considered when planning wildlife corridors. To discuss the role of vegetated buildings in landscape connectivity, we reviewed the ecological and technical specificities of green walls and green roofs in light of the key factors concerning urban wildlife (patch size, quality, abundance, and isolation). Green roofs and walls show limited patch sizes, distinct habitat quality at the building scale, and limited redundancy of patch quality within the landscape. We also highlight that the abundance of roof and wall patches is often low. Future research is needed to establish if walls can be vertical corridors for wildlife, thereby reducing the isolation of green roofs. We argue that creating 3D ecological connectivity within the city requires substantial modifications of the design and maintenance of existing green building systems. We suggest that research is needed to integrate the biotic and abiotic characteristics of green buildings to make them more closely resemble those of open green spaces.

National audience; La réglementation et les attentes sociétales incitent aujourd'hui les aménageurs du territoire à évaluer les impacts environnementaux de leurs projets de construction, mais également à prévoir des mesures et des actions pour créer ou restaurer la biodiversité des espaces modifiés. Des questions se posent donc aux gestionnaires sur les méthodes à utiliser et les indicateurs à employer pour évaluer la performance écologique d'un aménagement. Quelques éléments de réponse sont présentés ici, sur la base d'une étude de cas portant sur le Mont-aux-Liens, un aménagement paysager contigu à l'autoroute A19.