- 154 - Diaci, J.; Rozenbergar, D.; Boncina, A., 2005: Interactions of light and regeneration in Slovenian Dinaric Alps: patterns in virgin and managed forests. In: Commarmot, B.; Hamor, F. D. (eds): Natural Forests in the Temperate Zone of Europe  Values and Utilisation. Conference 13-17 October 2003, Mukachevo, Ukraine. Proceedings. Birmensdorf, Swiss Federal Research Institute WSL; Rakhiv, Carpathian Biosphere Reserve. 154160. Interactions of light and regeneration in Slovenian Dinaric Alps: patterns in virgin and managed forests Jurij Diaci, Dusan Rozenbergar and Andrej Boncina University of Ljubljana, Biotechnical Faculty, Department of Forestry, Vecna pot 83, 1000 Ljubljana, Slovenia jurij.diaci@bf.uni-lj.si; dusan.rozenbergar@bf.uni-lj.si; andrej.boncina@bf.uni-lj.si Abstract The regeneration of virgin Dinaric silver-fir beech forests is driven by small-scale disturbance. For a century, forests in this area were managed with a selection system. Due to complex reasons, the silver-fir was declining in both managed and virgin forests. Because of the more social character of beech, we tested the influence of an irregular shelterwood management system on regeneration process and sapling morphology. The three largest existing gaps (~0.20 ha) with three adjacent small gaps (~0.02 ha) were selected in virgin forest Rajhenav. An equivalent number of comparable large and small gaps was selected in the managed forests on the same site. In 2000 and 2001, we investigated light climate (hemispherical photographs), regeneration characteristics (abundance, growth and morphology), ground vegetation and humus properties in a 5 x 5 m systematic grid placed within the gaps. In large gaps of the virgin forest remnant, the results showed significantly lower light intensity, higher regeneration density of beech, lower ground vegetation coverage, and lower species diversity compared with large gaps in the managed forest. In general, the analysed factors suggested differences in climate between gaps of virgin and managed forest, although they were comparable in size. This can be attributed to higher trees, non thinned stands at gap borders, and presence of diverse advanced regeneration in the virgin forest. In both forest types, the influence of gap light asymmetry on silver-fir regeneration was detected, while there were no significant patterns for beech. Only minor differences in beech sapling morphology between managed and natural gaps were observed. The results indicated that nature-based silviculture should focus more on mimicking natural gap microclimate and less on gap patterns. Keywords: regeneration ecology, Fagus sylvatica, Abies alba, solar radiation, ground vegetation, tree architecture, virgin forest, nature-based management 1 Introduction The silver fir-beech forests of Slovenian Dinaric region cover more than 160.000 ha and represent one of the most preserved forest areas in Central Europe. They sustain many endangered and rare species, including the brown bear, wolf, and white-backed woodpecker (Dendrocopos leucotos). Moreover, the majority of the 14 Slovenian virgin forest remnants are located there (Hartman 1999). The naturalness of the forest area is a result of more than 100 years of clear-cut free forest management (Mlinsek 1972). Within this region the forests of Kocevsko were traditionally managed with a single tree selection system (Boncina et al. 2002). According to old forest management plans and forest inventories, there was a significant alternation in species dominance in the last 100 years (Hartman 1987). The reasons are partially in natural processes and partially anthropogenic, the latter representing a favouring of silver-fir through silvicultural measures and the browsing impact of ungulates. More than a hundred years ago beech dominated stand volume, until the mid- 20th century, when the proportion of silver fir increased steadily, but has later started to decline. Many indicators suggest significant dominance of the beech also in the future (Boncina et al. 2002).