Modelling the conversion from even-aged to uneven-aged stands of Norway spruce (Picea abies L. Karst.) with a distance-dependent growth simulator

The paper provides a conversion regime from even-aged to uneven-aged stands of Norway spruce (Picea abies L. Karst.). The conversion regime was tested by the distance-dependent single-tree simulator SILVA 2.1. The initial dat a for the simulation and the assumed site productivity were deduced using i nventory data of the north Black Forest. The conversion regime was compared to a typical future-tree oriented age-class treatment system. Thereby four variants of the conversion regime, differing in the number and diameter of the 'regeneration-funnels' (gaps in the canopy of the stand) which were cr eated during the 'graded-regeneration-phase', were compared To a basal-area oriented future-tree age-class treatment. A simulation-run of 110 years - divided into 22 periods of five years - was conducted. The analysis of the simulation-run showed that the possibilities to achieve uneven-aged structu res in single-layered, even-aged stands through 'structuring measures' duri ng thinning or target-diameter harvesting were very limited. The success of the conversion depended mainly on the success of the regeneration during t he conversion. The early creation of 'regeneration-funnels' was linked to s evere losses in increment and standing volume. As well as influences on dif ferent stand-parameters (e.g. stem-distribution) changes in structure-param eters caused by the conversion could be assessed. In particular, the modifi ed Shannon-index did react distinctly to the implementation of the natural regeneration in the regeneration-funnels. Indeed, a steady state was only t emporarily reached with the variant with the largest gaps. Finally, the res ults of the conversion experiment were subject to a critical review. Thus, the limits of the model in its current version and further research needs w ere discussed. (C) 2000 Elsevier Science B.V. All rights reserved.