In many areas of the boreal forest, a successful natural regeneration will require some sort of site preparation. However, the economic result of regeneration of Norway spruce, Picea abies by the shelterwood method is dependent upon a number of factors. One of the most important of these factors is the value increment of the residual shelter trees during the regeneration period. Damages which lead to rot infection or growth reduction must, therefore, be avoided.
Field studies of systematic soil scarification in shelterwood stands have shown high damage rates to the root systems of the residual trees. A supplemental scarification, which leaves a treatment-free zone around each stem, is therefore recommended. The application of a supplemental scarification is limited by two questions. First, in order to avoid value reduction, how far from the residual stems should the treatment-free zone extend? Second, the treatmentfree zone will reduce the remaining portion of the site which is available for treatment. The size of this reduction will be determined by the density of the shelter trees. What is the maximum density of shelter trees which may be allowed before the treated portion of the site becomes unacceptably low? Approximate answers for these two questions are given for Norwegian conditions.
The technical feasibility of scarification in shelterwood stands has been examined. Various tractor-drawn and boom-mounted working methods have been used in both field and simulation studies. The boom-mounted methods were found to be best suited to working under these conditions. The use of boom-mounted methods unable a complete coverage of the site with a relatively low number of passes through the stand. The greater precision of boom-mounted methods also makes it easier to maintain the chosen radius of the treatment-free zones.
Key words: forest operations, shelterwood stands, soil scarification.
Correspondence: Dag Fjeld, Norwegian Forest Research Institute, N-1432 Ås, Norway
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