Local and management variables outweigh landscape effects in enhancing the diversity of different taxa in a big metropolis

Abstract

As the pace of urbanization accelerates, the conservation of urban biodiversity emerges as a rising concern. Urban ecological research has revealed that some green areas in cities can harbor a rich diversity of species that can be enhanced by certain landscape- and local-scale structural planning variables. However, while most studies have been conducted in large greenspaces (e.g., parks, remnants), less effort was made to understand which variables influence biodiversity within small green patches and the efficiency of management practices has been seldom investigated. Here, we explore how management practices interplayed with landscape and structural variables to influence the diversity of plants, birds, butterflies and other pollinating insects in small public gardens (0.5–2.0ha) in the center of a large metropolis (Paris, France).Small public gardens hosted significant common biodiversity and the ones that employed a conservation program (i.e., differential management) supported a higher diversity of all taxa and less urbanophile communities of birds and butterflies. Local-scale and management variables were more important in enhancing biodiversity than landscape-scale variables. Specifically, lawns rich in wild plants attracted many pollinators and bird richness increased with tree cover. Pesticides had a negative effect on bird richness, while a higher diversity of habitats and soils (i.e. mulching, peat) increased the diversity of all four taxa. We also found that bird richness could serve as a reasonable surrogate for butterflies and other pollinators. Our results highlight how planning and managing public gardens in the center of a large metropolis can benefit biodiversity, regardless of spatial context.