Short-term effects of selection, gap, patch and clear cutting on the beetle fauna in boreal spruce-dominated forests

Abstract

Even-aged management based on clear cutting has simplified the structure of boreal forests, which has adversely affected ecosystem services, including biodiversity. A potential way of combining economic, ecological and social sustainability in forest management is emulation of natural disturbance dynamics. However, ecological effects of alternative cutting methods have been little studied in northern Europe. We studied the responses of beetles (Coleoptera) to four cutting treatments – selection, gap, patch and clear cutting – compared to uncut control stands. We collected beetles one year before, and one and three years after cutting using flight-intercept window traps to assess the effects of treatment, proportion of removed trees, size of harvested gaps, and the volume of dead wood on the species richness and composition of beetles. The total number of species increased sharply in the first year after cutting in all the four treatments. Three years after cutting, the difference in species richness between controls and treatments had decreased. Both species richness and community structure formed a continuum according to treatment intensity. Selection cuts were most similar to the controls, while clear cuts differed from all the other treatments. Irrespective of the treatment, species richness of saproxylic beetles increased with the volume of dead wood, while the number of non-saproxylic species increased with gap size. Contrary to expectation, the proportion of species that were found both before and after cutting did not differ significantly between the treatments. According to an indicator species analysis, two species were associated with controls, 11 with a combination of controls and selection, gap or patch cuts, 17 with patch and clear cuts, and 38 with clear cuts. Our findings suggest that increasing harvesting intensity rapidly increases the total species richness of beetles in the studied spruce forests, but that community recovery may be faster in the less intensive treatments. In the short term, most beetle species inhabiting mature managed forests seem to tolerate cutting disturbances creating open conditions. Clear cuts hosted a large number of species, including species of conservation concern, which were missing from other cutting treatments. Even a moderate increase in the level of dead wood in managed forests is likely to enhance saproxylic diversity. If the aim of management is to preserve mature-forest beetle communities, selection or gap cutting should be used instead of clear cutting.