From Trees to Microhabitats Through Hierarchical Pathways Sustaining Biodiversity in Urban Mediterranean Forests

Tree-related microhabitats act as key links between forest structure and biodiversity, but these pathways may be altered in urban forests. In Mediterranean urban forests, we found that deadwood-related processes were weaker than hypothesized, while structural diversity remained the primary driver of microhabitat richness. We evaluated whether hierarchical pathways linking structure, diversity, and richness are maintained under urban conditions. A Structural Equation Model was applied to 180 plots across three Italian cities (Florence, Rome, Campobasso), assessing relationships among tree and deadwood volume, diversity, richness, and landscape variables (forest area, patch shape complexity, canopy cover). A consistent bottom-up hierarchy emerged, in which structural heterogeneity was associated with microhabitat richness through diversity-mediated pathways. However, deadwood-related pathways were positive but less consistent than living-tree-related pathways. Landscape context acted mainly as a secondary filter, although canopy cover positively influenced some richness components. Overall, urban forest microhabitat richness depended more on structural heterogeneity than biomass; patterns are consistent with the hypothesis that management, including deadwood removal, may constrain habitat continuity. Maintaining structurally diverse stands, retaining deadwood where compatible with public safety, and integrating microhabitat monitoring into spatial planning are essential to support biodiversity and ecosystem services in urban forests.