Short-term responses of soil macroarthropod community to clear felling and alternative forest regeneration methods

Abstract

We studied the influence of clear felling and new alternative forest regeneration methods on soil macroarthropods during the first 3 years after the harvesting. We focused on changes in the abundances of functional groups, and community structure at the levels of species (Coleoptera) or higher taxa. The experiment was carried out in central Finland in spruce ( Picea abies (L.) Karst.) stands on 1 ha study plots. The following five treatments were used in addition to the untreated controls: (1) selection felling (70% of the stand volume retained), (2) gap felling (0.1–0.2 ha gaps felled), (3) gap felling with site preparation, (4) retention felling (small groups of trees retained on clear-felled area) and (5) traditional clear felling with site preparation. As expected the changes in macroarthropod community were attributed to harvesting intensity (proportion of living stand volume removed): clear felling and gap fellings induced the clearest changes, while selection felling had hardly any impacts. The treatments had no effects on total numbers of macroarthropods during the 3-year study period. Clear felling and gap felling followed by harrowing had a negative effect on predators, among which spiders decreased the most, and herbivores. Gap felling without harrowing had similar but not as strong effects as the treatments with harrowing. Further, in the unprepared gaps herbivores showed signs to recover in the second growing season after the treatment. Community structure (analysed by the NMDS ordination method) was affected by the treatments both at high taxonomic level and at the species level. At higher taxonomic level, the changes were induced by clear felling and gap fellings; the alterations being, however, no larger than natural temporal variation. At the species level (Coleoptera adults), the effects on community structure were more pronounced: the set of dominant beetle species changed almost completely after clear felling and the gap fellings during the study period, but the number of species or evenness values were not affected by the treatments. Changes in community structure at both resolutions correlated clearly with harvesting intensity and subsequent vegetation change. Our study gave evidence that the total abundance of macroarthropods, species diversity as well as community structure at higher taxonomic level are relatively resistant in the short term to environmental changes caused by forest regeneration practices in boreal coniferous forests.