The structure of uneven-aged stands in non-economic forests of national park Risnjak in croatia

Uneven-aged stands in Croatia are mainly characterised by European fir (Abies alba Mill.), since uneven-aged structure and management are linked to ecological requirements and biological properties of this tree species. European fir, alongside with autochthonous oak species (Quercus) and common beech (Fagus sylvatica L.), belongs to a group of basic tree species in Croatia. This paper presents the condition and value of some structural elements which have an impact on natural regeneration and viability of non-economic forests. Three-dimensional digital dynamic model of selection forest and vertical stand profile with specific measured trees on the field have been made by the application of digitalisation. Basic structural indicators have been calculated: basal area and volume of wood per ha; sum of horizontal crown projections per ha in absolute and relative terms; absence of canopy density; arithmetic mean of projections and medium crown diameter. The model facilitates computing-digital monitoring of changes in stand structure and their simulation and it opens new possibilities in studying the stand structure by the application of new technologies in forest management. Too many overmature trees, complete absence of young tress in the thinnest diameter classes, as well as shortage of medium thick fir trees are indicators of disturbed natural structure. In addition to the previously stated, there is excessive crown canopy density of 88.46% and low quality and old young growth of beech in the shrubbery layer, which ultimately results in absence of natural regeneration and questionable capacity for sustainability of these stands.