Regeneration dynamics in a Norway spruce plantation on a silver fir-beech forest site in the Slovenian Alps

Abstract

Conversion of Norway spruce ( Picea abies (L.) Karst.) plantations is a great challenge for silviculture in Europe today. While complex problems with these stands are widely recognised, methods to regenerate or convert them to mixed stands are not yet well established. The purpose of this study was to determine favourable combinations of site factors (diffuse solar radiation (DIFF) and direct solar radiation (DIR), forest ground vegetation cover, thickness of humus horizons, browsing) for development of tree regeneration within gaps of different size and age, located in a Norway spruce plantation on a silver fir ( Abies alba Mill.) and common beech ( Fagus silvatica L.) forest site. Fifteen fenced and fifteen unfenced gaps with nine plots each were placed on the north slope of Mount Krasica, in the mountain vegetation belt, on limestone parent material. From 1993 to 1998 woody seedlings and saplings were observed. A successful development of Norway spruce, sycamore ( Acer pseudoplatanus L.) and other frequently seed-bearing broad leaves was determined for the first years. Further development of seedlings was hindered by dense forest ground vegetation and browsing impact. Beech and silver fir regeneration was insufficient due to a lack of seed-bearing trees. On the basis of direct and DIFF radiation four groups of microsites were separated. This satisfactorily explained the differences in regeneration patterns among tree species. Norway spruce seedlings were most frequent in the group with high levels of diffuse and low levels of DIR, while sycamore saplings were most frequent in the group with high levels of both radiation components. Results obtained suggest that natural regeneration success and composition can be successfully influenced by managing the incidence of radiation in context with gap geometry (shape, size and orientation).