Spatial and habitat determinants of small-mammal biodiversity in urban green areas: Lessons for nature-based solutions

In an increasingly anthropogenic world, urban green areas are critical for human well-being because of the ecosystem services they offer. However, the management of these areas often prioritizes economic, architectural, and esthetic needs over ecological functionality, undermining the benefits they ought to provide. Actions to restore the functional ecological processes of urban green areas have thus become increasingly urgent. This study investigated the impact of urban green area characteristics on the community composition of an indicator animal group to inform Nature-Based Solutions (NBSs) for urban biodiversity and sustainability enhancement. We analyzed data on small mammal community composition from three Italian metropolitan cities (Milan, Florence, and Rome), focusing on the distribution pattern of synanthropic and non-synanthropic species. Small mammal surveys were carried out using hair tubes in sampled areas located along a gradient of green area size and fragmentation. Multiple Linear Mixed Models assessed the influence of spatial and habitat green area characteristics on species richness. Synanthropic species richness was positively associated with manicured urban parks, while non-synanthropic species richness was higher in woodland green areas characterized by high shrub cover. Through a Linear Mixed Model and NODF-based Nestedness analyses, we found that competitive exclusion and selective extinction/colonization processes did not significantly influence community composition. These insights emphasize the major influence of habitat composition in supporting functional communities of urban small mammals. To move toward resilient urban ecosystems, NBSs must primarily be implemented at a local scale by creating green patches with high habitat quality, and secondarily, they should be embedded in an interconnected and functional network at a city scale.