Influence of patch scarification and insect herbivory on growth and survival in Fagus sylvatica L., Picea abies L. Karst. and Quercus robur L. seedlings following a Norway spruce forest

Southern Sweden is dominated by relatively uniform coniferous forests where Norway spruce is the most common tree species. Ecological and economic con siderations have created an interest in re-establishing broadleaves in thes e forests. To study the influence of patch scarification and compare the in fluence of insect herbivory on growth and survival in beech (Fagus sylvatic a L.), Norway spruce (Picea abies L. Karat.) and oak (Quercus robur L.) see dlings, a field experiment was established. The experiment was carried out on a new clear-cut following Norway spruce, and in a Norway spruce shelterw ood. Seedlings were spring-planted in two consecutive years in untreated gr ound (control) and in patch site preparation treatment in combination with or without repeated insecticide treatment. The influence of patches on seed ling growth and survival of all species studied was low. No pronounced diff erences in photosynthetic photon flux density at seedling level and recolon ization of ground vegetation were observed between patch scarification and control. patches had higher soil water potentials than the control in the s helterwood, but this did not result in any positive growth response in the seedlings. The number of trapped pine weevils (Hylobius abietis L.) was abo ut equal in both patch scarification and control treatment. Insecticide tre atment had a significant influence on growth and survival of seedlings. On the clear-cut, herbivory by pine weevils was lower on beech and oak seedlin gs than on Norway spruce seedlings. In the shelterwood, herbivory by pine w eevils was low on all species. The conclusion is that less efforts are need ed to protect beech and oak from herbivory by pine weevil compared to Norwa y spruce. Herbivory by short-snouted weevils (Strophosoma melanogrammum For st. and Otiorhynchus scaber L.) constitutes another threat, but was about t he same on beech, oak and Norway spruce. Although the highest growth in the seedlings occurred in the open, this study shows that high survival can be achieved without using site preparation and insecticides when beech and oa k are planted under shelterwood trees of Norway spruce. (C) 2000 Elsevier S cience B.V. All rights reserved.