Alan Vergnes

Ecological corridors also operate in an urban matrix: A test case with garden shrews

The fragmentation of landscapes, induced by the growing urbanisation, is a major cause of biodiversity loss. Ecological corridors are landscape elements that make up for the negative effects of habitat fragmentation in agricultural or natural landscapes. However, their effectiveness have been rarely assess in an urban context. To do so, we analysed shrews in woodlots, corridors and domestic gardens that are connected or disconnected from a corridor. Indeed, these mammals are very sensitive to fragmentation and could play an important ecological role even in small and isolated areas such as domestic gardens. Ninety-seven shrews, from three species were trapped. In our study, Sorex coronatus, Sorex minutus and Crocidura russula were not widely distributed and mainly occurred in woodlots, corridors and connected gardens. In gardens, shrew occurrences were mainly determined by landscape configuration with negative effects of the distance to the corridor and the distance to the woodlot, stronger for C.russula than Sorex species. At the local scale, garden management and vegetation showed a positive effect mainly for Sorex species. The quality of gardens seems good enough to permit the co-occurrence of several species of shrews and thus competition was not identified as a major process for determining the occurrence. We showed that, as in other ecosystems, ecological corridors in urban context can play an effective role for the distribution of organisms with low dispersal capabilities and should be develop in planning strategies.

Are urban green spaces suitable for woodland carabids? First insights from a short-term experiment

One consequence of the spatial expansion of cities is the multiplication of highly fragmented and diverse green spaces immediately surrounded by urban areas. Whereas the global expansion of urban areas is a growing concern for the viability of woodland arthropods, the suitability of green spaces as refuges to arthropods needs to be clarified. In order to assess and compare the survival rates of the woodland carabid Abax parallelepipedus in four types of green urban sites (remnant forest patch, urban park, woody corridor and set of gardens), we conducted a Capture-Mark-Recapture experiment based on 483 individuals collected in a forest located in a natural landscape (considered as the control site) and released into the various green spaces. Results indicated strong heterogeneity in survival probability between green spaces. Survival rates were slightly higher in the control site than in the remnant forest patch, the urban park and the corridor, which appear suitable for the survival of the species. However, it was substantially lower in the gardens. The analysis further revealed that these differences in survival are largely explained by the differences of within –site habitat fragmentation. By indicating that urban green spaces may contribute unequally to woodland carabids survival, our study highlights that the modification of local environmental conditions alone (increase of temperature, increase of soil pollution and change in food availability) could not explain the negative effect of urbanization. This study argues for the development of corridors in cities in order to favour the colonisation of green spaces by woodland carabids.

Vertical Greening Systems as Habitat for Biodiversity

Abstract 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.