Epsilon Archive for Student Projects

Abstract

This study examined the effect of tree stump extraction on the diversity of saproxylic insects in Norway spruce Picea abies roots. I tested if the density of saproxylic beetles was the same in the interior layer of the stump storage piles as in the exterior layer. I also tested if the beetle density was as high or higher in piles as in remaining stumps at extraction clear-cuts and to test if they could be ecological traps. I tested if species at higher trophic level as well as red-listed species could be impacted negatively by stump extraction.
A total of 110 root wood samples were collected from 6 clear-cuts and 6 extraction clear-cuts and 4 different piles in central Sweden near Uppsala, Lindesberg and Fågelfors. The clear-cuts were dominated by Norway spruce and were sampled 1 to 2 years after clear felling. Norway spruce is the most common tree species used in tree stump extraction.
Insect were reared from the sampled roots in rearing boxes for 8 weeks. Insects were also sampled after the rearing box period by pealing the bark of the roots and putting the bark in Tullgren-funnels to sample the last insects inside the bark. The sampled Coleoptera were determined to species level.
A total of 1379 beetles of 35 species were collected from the roots. Higher species richness was found inside the piles (PIN) than on the outside of the piles (POUT). Hardly any difference was found between the clear-cut (C) and extraction clear-cut (EC) in species-richness per root-sample, but a significant difference was found between the pile habitats. Common saproxylic species, like Dryocetes autographus and Hylastes cunicularius, showed increased abundance in C and EC but a decrease in the storage piles. The pest species Pityogenes chalcographus was only reared in PIN.
Predatory species higher up in the trophic levels, like the staphylinid Nudobius lentus, were found in low abundance in C, EC and in POUT but not in PIN. This could mean that the piles can be an ecological trap to species at higher trophic levels as well as for some pest species. The results of this study indicates that tree stump extraction can cause a lower diversity of saproxylic insects in Norway spruce roots and a decreased species richness if the stump piles constitutes an ecological trap. As a consequence, this can decrease the diversity and species richness in the surrounding area.