LAUSR

Secondary succession in protected oak-rich temperate forests reduces variation in habitats and leads to denser, shadier sites. Long-term experimental studies of the effects of conservation management alternatives are needed for such forests. Here we present a rare follow-up study of the response of beetles (a highly diverse taxon with many red listed species) to conservation thinning, an action that could favour biodiversity. We previously harvested about 25% of the tree and shrub basal area in a treatment plot, and no trees and shrubs in a nearby matched minimal intervention plot, in each of eight oak-rich (Quercus robur and/or petrea) forest reserves. After two seasons, thinning had led to an increased number of species of both herbivorous and saproxylic beetles. In the present study, we examined the 10-year response of the beetle groups at the same sites. For herbivorous beetles, the initial positive effect of thinning on the number of species had disappeared after 10 years, presumably because of regrowth. In contrast, saproxylic beetles showed a further positive response after 10 years, increasing in the number of species by a third compared to before thinning. We found no change in species composition of either group due to the thinning, but many saproxylics were unique to thinning plots. Overall, our results suggest that in mixed oak-rich forests, saproxylic beetles seem to benefit from conservation-oriented thinning for at least 10 years.