Patterns and determinants of plant, butterfly and beetle diversity reveal optimal city grassland management and green urban planning

Urban landscapes are places with high interaction between humans and nature, and the benefit of maintaining their biodiversity to enhance human wellbeing is becoming clear. There is, therefore, an urgent need for understanding what influences biodiversity in cities to inform and influence urban landscape planning. We used a multi-taxa approach (plants, butterflies, and beetles) to assess the influence of the fragmented landscape of a European city, Pardubice (Czech Republic), on the biodiversity of urban grasslands. We randomly selected 40 urban grasslands and were interested in the influences of site and land-use characteristics on biodiversity. The influence of the land-use around the grasslands was analyzed along a gradient of spatial scales (i.e., the cover of land-use types within circular buffer zones of 250, 500, and 750 m around the study grasslands). We found that species richness of the three study taxa was positively influenced by the size of the grassland (measured as grassland perimeter). Butterflies were also negatively affected by increasing management intensity. Plants and beetles were influenced by the land-use type, with plant species richness positively affected by the extent of urban greenings (i.e., green areas such as urban parks, gardens, and sport grounds), and beetle species richness negatively affected by the extent of built-up areas in the grassland surroundings. Biodiversity responses to urbanization partly differed among the studied taxa, indicating different demands of specific groups, but the demands were not conflicting and instead, often complemented each other. Consideration of the three key factors influencing biodiversity identified here (grassland extent, land-use in the surroundings, and management intensity) would provide the optimal options for maintaining city biodiversity. Protecting current urban grasslands from development and restricting construction in their surroundings, restoring city wilderness areas using urban spatial planning, and setting up butterfly-friendly management regimes (e.g., mowing in mosaic) could all be future options to help enhance biodiversity in cities.