From clear-cuts to nature reserves: saproxylic beetle diversity and deadwood availability in Norway spruce (Picea abies L.) stands in southern Sweden

Abstract Key message Norway spruce ( Picea abies L.)-dominated production forests in southern Sweden had a significantly lower amount of deadwood and saproxylic beetle diversity compared to similar nature reserves, especially with regard to red-listed species. The species composition of beetles in reserves also differed from all young production forests. Enhanced conservation measures are essential to maintain biodiversity in production forests. Context Forests are the most important biomes globally for biodiversity, and a high diversity in structures is important for species richness. In Sweden, 87% of the forest area is used for wood supply, which may affect forest structures and biodiversity. Aims The aim of this study was to quantify the differences in the amount of deadwood and the saproxylic beetle diversity between typical Picea abies L. production forest stands of different ages and natural or near-natural forests. Methods In the current study, we sampled saproxylic beetles and amount of deadwood in stands of spruce forests in southern Sweden that represent four different parts of the forestry cycle, and compare this with nearby, recently protected spruce dominated nature reserves. In addition, we also sampled five old forest reserves in the region. Results The amount of deadwood was significantly higher in reserves than in production forests. In total, 478 saproxylic beetle species were caught and identified (in total 71,000 individuals). Overall, the highest species numbers were found in new and old reserves and 65–85 - year - old production forests, while the lowest number was found in production forests of 15–25 and 35–45 years. The odds of finding nature value indicator species and red-listed species were significantly lower in all production forest types except 65–85 - year-old ones compared to new nature reserves. This could be because clear-cutting practices did not become the main method for timber extraction until the early 1950s, meaning that some of the 60–85-year-old stands may never have been subjected to clear-cutting practices. However, old nature reserves had a clearly different composition regarding obligate saproxylic species, nature value indicators, and red-listed species compared to all production forest types. Conclusions The results bear relevance to the Swedish Forestry Act established in 1993, stating that the environmental goal and the goal of high wood production is equally important, since our forest types cover the period before and after. However, our results show that the 15–25-year-old forests are as species poor as the 35–45-year-old ones indicating that there was a lack of biologically important structures also after the change in policy.