Forest Diptera Diversity in Southeastern Sweden: Contrasting Managed and Protected Forests

Diptera are ecologically important components of forest biodiversity and have the potential to serve as indicators of forest management effects. We investigated how forest management influences Diptera diversity, composition, and biomass across 35 sites in southeastern Sweden. Sampling was conducted using Malaise traps across six forest types representing stages of the forestry rotation cycle in spruce-dominated forests (clearcut, young 15–25 years, mid-aged 35–45 years, and old 65-85 years), as well as recently protected and old-growth forests. A total of 193 Diptera species were recorded, of which 51 were classified as saproxylic. Generalized linear mixed models revealed that richness, abundance, and biomass of the full Diptera assemblage differed significantly among forest types, with clearcuts supporting the highest values and old-growth forests the lowest. In contrast, saproxylic rich- ness did not vary significantly, while saproxylic abundance showed a non-significant tendency to be higher in young stands and clearcuts. Our results suggest that Diptera respond more strongly to structural features such as canopy openness and successional stage than to deadwood availability. Early-successional forests, particularly clearcuts and young stands, may therefore play an important role in sustaining Diptera diversity and biomass within managed boreal forest landscapes.