Effects of gap size and within-gap position on seedlings establishment in silver fir stands

The conversion of pure conifer plantations into stands with heterogeneous structure and composition is a current silvicultural challenge in Italy. A silvicultural system aiming to the regeneration of natural forests by means of openings in the canopy cover is considered. The purposes of this study are: I) to evaluate if the creation of gaps is an appropriate way to transform homogeneous man-made stands of silver fir (Abies alba Mill.) into naturally regenerated stands; II) to analyse the influence of micro-environmental conditions in gaps of different size on the recruitment and establishment of natural regeneration of forest tree species. After three growing seasons silver fir seedlings recruitment was greater in small gaps and in the central-southern positions where PAR was lower and the shading influence of ground vegetation less relevant. The most suitable gap size for silver fir regeneration, in the southern Apennine, is 200 (300) m2, D/H = 0.5 and anyway <0.75. The silvicultural treatment proposed seems to foster natural regeneration of silver fir and other broadleaves, enhancing the development of a multi-layered forest structure and fulfilling timber production objectives without compromising ecosystem management principles.