Is stump removal for bioenergy production effective in reducing pine weevil (Hylobius abietis) and Hylastes spp. breeding and feeding activities at regeneration sites?

Stump harvesting can help in managing forest pests, improve site preparation, and provide a source of bioenergy. However, stump removal does not remove all the roots from clear-cut areas. To investigate whether stump removal helps to manage forest pests, the effect of stump removal and its timing on the breeding and larval feeding activities of pine weevil (Hylobius abietis) and Hylastes spp. was studied. In eastern Finland, 16 commercial regeneration sites dominated by Norway spruce (Picea abies) (eight control areas, eight stump removal areas) were selected. Stumps were harvested in 2011, within the year following logging in three of the stump removal sites (short delay extraction), and in the second year after logging at five of the stump removal sites (long delay extraction). Root samples were excavated from sites three years after logging to examine the amount of roots, gnawing intensity, and density of larvae. In the control plots, gnawed root surface areas were 24% and 50% greater than those in long delay and short delay stump removal sites, respectively. After timing treatment, the estimated larval densities of both species were lower than the estimated larval densities in the control sites. In conclusion, the timing of stump extraction may partially regulate the breeding material and abundance of Hylobius and Hylastes. However, it is probable that this effect is not strong enough to substantially limit the future damage on planted seedlings.