Dieback of spruce plantations: Deadwood stands and management heterogeneity enhance beetle diversity and habitat connectivity

Forest ecosystems are important for biodiversity conservation and human societies, but are under pressure due to climate change and human interventions. This applies to natural forests as well as tree plantations. The latter are globally widespread and therefore gaining increasing importance for biodiversity conservation. However, even after dieback due to increasing disturbance frequencies, such plantations are primarily managed for economic returns, leading to growing conflicts among stakeholders. In particular, the impact of forest management on biodiversity is being discussed. This study investigates the effects of five management approaches in a landscape severely affected by spruce (Picea abies L.) dieback on beetle diversity, conservation, and community composition. We considered direct effects of management and indirect effects of environmental parameters separately in ground-dwelling and flight-active beetles. Beetle diversity was strongly affected by forest management, with non-intervention deadwood stands being most beneficial for beetles. In addition, we show indirect effects of environmental factors. In general, parameters related to salvage logging (e.g. open canopies, tree stumps) influenced beetle diversity and conservation negatively, while positive effects were found for soil nutrient availability and plant species richness. Community composition differed strongly among management categories and indicated a lack of landscape connectivity for open habitat species, as we found only low proportions of such species even on salvage-logged sites. We propose a mixture of management approaches after bark beetle outbreaks, including a substantial proportion of non-intervention deadwood stands, to increase landscape heterogeneity and connectivity. This may increase overall biodiversity while addressing the concerns of both forestry and species conservation.