Survival after planting without soil preparation for pine and spruce seedlings protected from hylobius abietis by physical and chemical shelters

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Abstract
In a series of 21 field experiments, established during 3 yrs between latitudes 56° and 64° N, seedlings without shelter and with four different types of shelters (one chemical, Permethrin, and three physical, Strumpan, Bema and Struten) were compared. These seedlings (Pinus sylvestris L. and Picea abies (L.) Karst.) were planted in the first spring after clear cutting without prior removal of the humus layer. The seedlings were observed continuously during one to four growing seasons after planting. It was shown that the pine weevil (Hylobius abietis L.) was the major cause of mortality during the first two growing seasons within the whole area. In all but one experiment the sheltered seedlings survived much better than the unsheltered ones. With a model based on the field observations, the survival for unsheltered and sheltered seedlings was predicted to 28% and 77%, respectively, at the end of the fourth growing season. From a practical point of view, all the shelters gave satisfactory protection and there were no significant differences between them. The silvicultural method used in these experiments shortened the rotation age and it was simple because planting was done directly after logging and heavy equipment for soil preparation was not used. In areas where nature conservation and multiple use of forests is important, such a regeneration method could be of great value.