Taxonomic and functional variation of Carabid beetles (Coleoptera: Carabidae) diversity in pioneer black pine and secondary broad-leaved Karst forests

Carabid beetles are widely used as bioindicators because they respond rapidly to changes in near-ground microclimate, litter and understory structure, and habitat continuity. In the Classical Karst of the North Adriatic region, forest management is shaped by two concurrent trajectories: the aging of Pinus nigra stands established during late 19th-century afforestation and the recovery of secondary thermophilous broad-leaved forests. Pine plantations, although now old and prone to biotic and abiotic disturbances, have played an important role in shaping present forest ecosystems, and their future is currently debated. To evaluate the effectiveness of pioneer pine plantations in reconstructing forest conditions, we assessed differences in carabid species composition and functional structure between the two forest types using long-term pitfall-trap data collected across multiple sites and years. We quantified taxonomic diversity through richness-based comparisons, rarefaction and additive partitioning, and examined compositional turnover using β-diversity contribution metrics and ordination with permutation-based testing. Functional structure was evaluated using distance-based functional diversity indices, functional rarefaction based on expected Rao’s Q and decomposition of functional α-β-γ components, and a ternary framework separating dominance, functional diversity and redundancy. Finally, we used indicator-oriented analyses (species-level and trait-informed) to identify taxa associated with each forest type. Overall, broad-leaved and pine stands showed limited divergence in mean richness and in conventional functional indices, whereas clearer differences emerged in turnover, site uniqueness and diagnostic species subsets. Functional rarefaction indicated that expected functional diversity may differ even when aggregate indices appear similar. Overall, results support the contribution of black pine stands to the maintenance of forest ground-dwelling biodiversity and functional structure in karst forests and suggest that conversion strategies should prioritise continuity of microhabitat conditions and microclimatic buffering rather than assuming that replacement by broad-leaved stands will automatically increase biodiversity.