ResearchMy research aims are to assess the influence of local and landscape parameters on urban biodiversity.
Contrasted responses of different taxa to pesticide use. We analyze the role of different pesticides (insecticides, herbicides, fungicides) on the diversity, composition and functional traits of plants, pollinators, birds and worms in urban and agricultural landscapes.
Wastelands, what social and ecological functions ? Wastelands remain unknown by scientists. In order to better understand the role of these areas in the conservation of urban biodiversity and how they are used by humans, we conducted since 2010 a transdisciplinary study to assess the sociological and ecological interactions that exist in wastelands.
Landscape connectivity in urban areas We tested different connectivity measures that take or not into account the matrix permeability with the NDVI tool (remote sensing imagery) for different dispersal capacities. We compared the networks obtained to empirical data on plant communities of semi-natural herbaceous habitats. We thus proposed an efficient connectivity measure to construct functional habitats networks in urban areas.
Urban ecosystem analysis
The preservation of biodiversity in urban areas requires to precisely describe the spatial distribution of species and locate the sites of highest interest for biodiversity, but it also requires to identify the specific mechanisms influencing the distribution of species in such highly human-perturbed environments. We described the floristic diversity in one of the most urbanized French departments, the “Hauts-de-Seine”, by carrying out floristic inventories in 1000 sites located in 23 habitats. We observed a total of 626 wild vascular plant species and established a new Index of Floristic Interest (IFI), integrating information on richness, naturalness, typicality and rarity of species, to identify sites and habitats of highest interest for conservation. We explored the relationship between site IFI and Land Use Patterns in a 200 m disc around a site and showed that close urban structures had a significant influence on the floristic interest of sites. For example, the presence of collective dwellings around a site had a strong negative impact on IFI. This information was used to define the Site Potential Value, which was then compared with the observed IFI, to identify areas (e.g. river banks) where a better management could improve the biodiversity of the department.
Invasive species impact on urban floristic diversity
In urban areas, which are prone to invasions by exotic species, plant biodiversity is already depleted due to high degrees of fragmentation and habitat destruction. Here, we explore the impact of invasive species in urban habitats, by examining the floristic differences between sites occupied -or not- by one or more of the following invasive species: Ailanthus altissima (Mill.) Swingle, Solidago canadensis L., and Reynoutria japonica Houtt. We compared the plant diversity of ‘invaded’ sites (i.e. sites containing any of the three invasive species) to that of ‘virgin’ sites (i.e. sites without these invasive species). To describe site plant diversity, we used classical parameters: species richness, mean species rarity, and proportion of native species in the site. Our study showed that, in an urban area, invasive species colonize preferentially disturbed habitat such as wastelands and elm groves. They also seem to benefit from the edges of the Seine river and slopes of railway and roads as corridors to their propagation. Our results suggests that diversity in itself, at the site scale, is not threatened by the presence of invasive species: species richness, mean species rarity and indigeneity, are generally identical in virgin and invaded sites, regardless of the invasive species considered and regardless of habitat. Although invasive species might still be a problem for urban biodiversity, the evidence for negative effects is not convincing so far at the site scale in regard of those generated by the urbanization. But it remains difficult to disentangle potential confounding factors in evaluating impacts of invasive species. Moreover, the changes created by invasive species can be slow, taking many years to play out. The study must be carried at a local scale, taking into account the abundance of each invasive species in sites to address whether invasive species are drivers or passengers. A better knowledge of the invasive effects and establishments on these zones would permit to better control the invasions and especially to reduce their extensions in the natural zones around.