Urban–Peri-Urban Gradient Effects on Beetle Assemblages: Ecological Contrasts and Climatic Responses in Sibiu, Romania

Urban and peri-urban ecosystems play a growing role in biodiversity conservation, yet multi-annual comparative studies from Central-Eastern Europe remain scarce. This study presents the first three-year (2021–2023) dataset comparing ground beetle assemblages between the Dumbrava Forest (peri-urban protected oak forest) and the Sub Arini Park (semi-anthropic urban park) in Sibiu, Romania. Using standardized pitfall trapping (41 traps, 2360.9 m2 monitored area), a total of 5008 individuals, belonging to 46 species and 12 families, were recorded. Species richness was slightly higher in Sub Arini (26 species) than in Dumbrava (22 species), forest-associated species (e.g., Pterostichus niger) and generalists (P. melanarius) dominated in the Dumbrava Forest, while P. oblongopunctatus was more strongly associated with forest habitats. Diversity indices showed moderate similarity between communities (Bray–Curtis = 0.46; Jaccard = 0.62). Shannon diversity reached H′ = 2.41 in Sub Arini and H′ = 2.03 in Dumbrava, reflecting higher evenness in the urban park. Predators comprised 65–70% of all beetles, underlining their regulatory function in soil ecosystem balance. Climatic variability—milder winters and warmer summers—favored population fluctuations of forest species and the dominance of eurytopic taxa in the park. These findings demonstrate that peri-urban forests act as climatic refugia for specialists, while urban parks function as dynamic hotspots for generalist diversity. The study provides baseline data for integrating insect monitoring into regional biodiversity management and climate adaptation strategies across Central-Eastern Europe.