- Stump extraction for bio energy is a new forestry activity and before large-scale implementation occurs, it is important to analyse its consequences. Saproxylic beetles depend on dead trees and stump extraction will reduce the amount of habitat available for this group.
- Early warning signs of impending regional species extinctions were looked for in areas where stump harvest has only been conducted for about 3 years. In a paired design (N = 8), the beetle fauna was sampled in stumps on ordinary clear-cuts and on clear-cuts from which stumps had been extracted. Sampling in extraction clear-cuts was possible because 25% of the stump volume was retained. Samples were collected by bark sieving ten Norway spruce, Picea abies, stumps per clear-cut.
- In total, 6959 individuals of 46 species were found. Several early warning signs were seen: stump extraction reduced the number of species per stump and per clear-cut and reduced the species evenness in individual stumps.
- Species at higher trophic levels (predators and fungivores), in particular, suffered negative effects. Stump extraction reduced the number of species of fungivores and facultative predators/fungivores at the clear-cut level and reduced the relative abundance of predators at the stump level.
- These results indicate that if stumps are extracted from a high proportion of the clear-cuts in a region, the present recommendations of leaving 15–25% of the stump volume will be insufficient for preserving the beetle fauna in the stumps. Further studies are needed to identify levels of stump retention that do not lead to species loss.