Analysis and monitoring of soil arthropod communities in urban areas: a multi-taxa and multi-scale perspective

Urbanization is one of the most pervasive forms of land-use change worldwide, reshaping landscapes into often complex and fragmented mosaics of built-up and green patches. These transformations alter soil properties, microclimatic conditions, vegetation structure, and spatial connectivity, with consequences for biodiversity and ecosystem functioning. Soil and ground-dwelling arthropods are a key component of soil functioning, regulating decomposition, nutrient cycling, and trophic interactions. Their highly diverse ecological roles and different sensitivities to space make them especially useful for monitoring environmental change. In this thesis, I investigated how urbanization and land-use change shape soil and ground-dwelling arthropod communities across different Italian contexts, adopting a multi-taxon, multi-scale framework and integrating taxonomic, functional, and environmental data. In the first chapter, the research spanned four major urban systems—Turin, Milan, Florence, and Rome—and was based on standardized sampling of six groups of ground-dwelling arthropods. First, an expert-curated trait database was compiled for nearly 300 species, including information on their distribution, ecological preferences, dispersal ability, feeding habits, morphological traits, and available genetic information, providing one of the first comprehensive trait-based resources for urban arthropods in Italy. Secondly, the response of each ground-dwelling arthropod taxon and the taxonomic structure of the whole community to local habitat characteristics, urbanization intensity, and habitat isolation was assessed. The results showed that local-scale responses were highly taxon-specific, while landscape configuration—particularly habitat isolation—emerged as a stronger predictor of diversity patterns than the mere proportion of surrounding green space, highlighting the importance of green spaces fragmentation in shaping urban ground-dwelling arthropod communities. At broader scales, highly urbanized and fragmented contexts filtered not only individual species but entire taxonomic groups, leading to simplified community structures. In the second chapter, analyses focusing on terrestrial isopods in Rome revealed clear patterns of urban-driven biotic homogenization and compositional shifts, with disturbance-tolerant generalists replacing forest-associated specialists along urban gradients. Local edaphic and microhabitat conditions—such as soil pH, compaction, organic matter, and vegetation cover—consistently explained a larger share of community variation than landscape-scale urbanization alone, indicating the importance of structurally complex and environmentally heterogeneous urban green spaces. In the third chapter, analysis on soil microarthropod communities across different land-use types yielded similar results, with microarthropod diversity and soil biological quality that consistently declined with increasing disturbance and management, while structurally complex urban forests maintained values comparable to natural reference sites. Overall, this thesis demonstrates that urban biodiversity responses are strongly scale-dependent and context-specific. Landscape fragmentation constrains the entire taxonomic structure of communities, whereas local habitat and soil conditions act as immediate ecological filters. These findings emphasize the need to enhance local habitat complexity, reduce the spatial fragmentation and isolation of green spaces, and limit intensive management in order to conserve urban soil biodiversity and sustain taxonomically and functionally diverse soil communities and the ecosystem processes they support