Stand dynamics and natural regeneration in silver fir (Abies alba Mill.) plantations after traditional rotation age

Abstract

Most pure silver fir stands on the Apennine mountains (central Italy) originated from planting and were managed according to the traditional model, with clear cutting and a 100-years rotation. In the last decades, active management has stopped in most of these stands and management goals have changed towards nature conservation purposes. The aim of this work was: (1) to analyze stand dynamics and spontaneous regeneration processes taking place with increasing age in even-aged fir plantations; and (2) to discuss if the above processes may be useful for defining management approaches addressing such conservation purposes. The study was carried out in the Vallombrosa Forest (near Florence, Italy). The relationship between fir stand age and structural parameters was analyzed using inventory data. Gap dynamics were monitored between 1983 and 2007 based on remote sensing data. A field survey of a sample of gaps was carried out. Species composition and density of seedlings and saplings were analysed in relation to gap size and within-gap position. From 1983 to 2007 the number of gaps and their total area increased, following increasing stand age. Significant relationships (p < 0.01) were found between fir stand age and number of trees per hectare (r = -0.30), quadratic mean diameter (r = 0.65) and volume per hectare (r = 0.50). A layer of trees with DBH < 15 cm (composed by 15 different broadleaf species usually mixed with fir) was observed in fir stands with lower stand density. Gap size influenced the presence of young firs (seedlings and fir < 0.5 m), which were significantly more abundant in gaps < 200 m2, but it had relatively limited influence on species diversity. Within- gap position did not affect the density of recruitments. Results indicate that the creation of small gaps (< 200 m2) in the canopy cover may simulate the natural dynamics of aged fir plantations in the Apennines and may be considered as a possible management option for their gradual transformation into mixed, naturally regenerating forests.