Effects of clear-cutting and single-tree selection harvests on herbivorous insect larvae feeding on bilberry (Vaccinium myrtillus) in uneven-aged boreal Picea abies forests

Abstract In uneven-aged boreal Picea abies forests in north-eastern Sweden, the effects of clear-cutting and single-tree selection on herbivorous insect larvae feeding on bilberry ( Vaccinium myrtillus ) were studied. Abundance of geometrids and exposed folivorous larvae were significantly lower in clear-cut areas than in selection felled and uncut controls. Significantly lower total abundance of herbivorous larvae were found in clear-cuttings compared to uncut controls. Both stem and leaf damage were significantly higher in selection fellings and controls than in clear-cuttings. The dry biomass consumption per shoot and per larva were significantly higher in selection fellings and uncut controls than in clear-cuttings. Lower availability and quality of bilberry may explain the reduced abundance of larvae and the reduced consumption of bilberry by larvae in clear-cuttings. The entire tree layer is removed when the forest is clear-cut, and drastic changes in abiotic factors are probably the ultimate reason for the observed responses of both bilberry and larvae. Selection felling leaves an intact, although sparser, tree layer following harvest, and abiotic factors are probably only moderately affected. The moderate changes of abiotic factors are probably the reason for small effects on both bilberry and larvae by selection felling. Our results suggest that clear-cutting negatively affects bilberry, herbivorous larvae feeding on bilberry, and their interaction. Contrary to the negative effects of clear-cutting, bilberry, insect larvae and their interaction in selection felling seems to resemble that in uncut forest. Because exposed larvae feeding on bilberry are known to be an important food commonly used by birds during their breeding, it could be of significance that forest harvesting has only moderate effects on bilberry and larvae.