Restoration of habitats for a threatened saproxylic beetle species in a boreal landscape by retaining dead wood on clear-cuts

Forest restoration measures, such as dead wood retention and creation at the time of final felling, increase the amount of dead trees and should benefit a large proportion of species dependent on sun-exposed dead wood. In this study, the value of retained dead wood and high-cut stumps was evaluated in terms of how much they contribute to the population of the red-listed beetle Peltis grossa in a forest landscape. The evaluation was based on a population estimate before and after restoration started in the study landscape. The restoration started in 1994 with 425 high-cut stumps of Norway spruce on six experimental clear-cuts and continued 4 years later with high-cutting and retention of dead trees becoming a standard measure in the 10,000-ha forest landscape. Ten years after high-cutting, adults of P. grossa started to emerge from the stumps on the experimental clear-cuts and the number of emergence holes was counted each year during the following 8 years (2003–2010). During this period, the average yearly recruitment of P. grossa from these stumps were c. 300 individuals, adding up to a total of c. 2250 emergence holes. In 2005, all clear-cuts made during 1990–2000 and random samples of young and old forest stands were inventoried in transects across the landscape. In total, 1219 emergence holes were found in 2005; all of them on the clear-cuts and none in the forest stands. Our study is the first to show that habitat restoration can increase population growth of a threatened saproxylic species on a landscape scale.