Epsilon Archive for Student Projects

Abstract

Understanding the underlying processes that maintain biodiversity, such as habitat amount and dispersal possibilities, is essential for successful biodiversity conservation. Forest-dwelling beetles (Coleoptera) in boreal forests are negatively impacted by clear-cut forestry, but to what extent this pattern results from a disrupted tree continuity or from changes in structural complexity is poorly understood. This thesis aims to clarify whether beetle abundance, diversity and community composition differ in relation to tree continuity and structural complexity, and how such relations differ with time since tree continuity is broken. Beetles were sampled with flight intercept traps in twenty boreal pine forests in northern Sweden. Half of the forest stands had been clear-cut and half had an undisrupted tree continuity, and both stand types included a range of structural complexity measured as dead wood volume and diversity, habitat tree abundance and richness, and basal area. Beetle abundance was significantly higher in long tree continuity stands than in clear-cut stands, a pattern primarily driven by low abundance in old clear-cut stands. Beetle diversity was positively associated with structural complexity, indicating that the abdunace and diversity of mircrohabitats on dead wood and living tree is important in determining beetle diversity at any given site. Across the forest landscape, stands with a long tree continuity hosted a wider range of beetle species than clear-cut stands. Old clear-cut stands had a higher basal area and exhibited a lower abundance of beetles belonging to a smaller but distinct species assembly, probably due to these stands growing denser and having a lower sun exposure. Young clear-cut stands had a beetle community composition that virtually was a subset of the long tree continuity beetle community. My results suggest that to maintain beetle abundance and diversity, forests with undisrupted continuity and forest harboring a wide diversity of habitats on living or dead wood should be prioritized as set-asides, and that a high abundance and diversity of such habitats should be ensured across the landscape.