Regeneration in experimental gaps of subalpine Picea abies forest in the Slovenian Alps

In 1998, we analysed regeneration success in four 20 year old medium-sized ( 600 - 800 m(2)) and four small experimental gaps ( 100 - 200 m(2)) in subalpine Norway spruce forest in Triglav National Park, Slovenia. We assessed the influence of site ( depressions, slopes), gap size, and position within gap ( centre, gap south, and north edge) on regeneration success and interactions between regeneration density, height, height increment, direct and diffuse light, ground vegetation, soil depth, thickness of humus horizons, presence of woody debris, and microrelief. Seedling density was higher in depressions, where more seedlings developed in central positions of gaps in both gap sizes, and in microsites with deeper soils, less competition from ground vegetation and convex microsites. On slopes, a higher seedling density was found in small gaps, and at the northern edge of gaps regardless of gap size. Here, seedling density was negatively influenced by diffuse radiation and positively by soil depth. The results suggest that regeneration should be initiated from medium to large gaps in depressions and small gaps on slopes. Development of established seedlings was enhanced by higher radiation levels on both sites, therefore favourable extension of the gaps would be lateral to northwards.