The influence of different overstory removal on planted spruce and several broadleaved tree species: Survival, growth and pine weevil damage during three years

The influence of different overstory removal on herbivory by the pine weevil to seedlings was studied in a field experiment. Four overstory treatments with middle aged Norway spruce in combination with or without insecticide treatments were applied. Seedlings of the following seven tree species were planted in each of the four blocks: Acer platanoides L., Fagus sylvatica L., Fraxinus excelsior L., Picea abies L. (Karst.), Prunus avium L., Quercus robur L. and Tilia cordata Mill. The seedlings were monitored through the 2001-2003 growing seasons. Highest survival was found among seedlings planted in the overstory treatments with 15 and 20% light in the understory, whereas best diameter growth in seedlings was found in the clearcut. Overstory trees of Norway spruce decreased herbivory from pine weevil considerably among underplanted seedlings, and the pine weevils fed significantly more on planted Norway spruce seedlings than on all broadleaved tree species. The following rough preference order was obtained: (1) Norway spruce &MGT; (2) beech and oak > (3) ash, cherry, lime and maple. The influence from the insecticide treatment was minor. Therefore, during the conversion of Norway spruce monocultures into mixed species stands using overstories, the use of insecticides against pine weevil is not needed.