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

Abstract

In the Apennine mountains most pure silver fir stands originated from planting and were managed according to the traditional model, with clear cutting and a 100 year rotation. In the last decades in most of these stands there has been a change towards nature conservation and active management has stopped. The aim of this work was (1) to analyse stand dynamics and spontaneous regeneration processes that are taking place with increasing age in even aged fir plantations, and (2) to discuss if these processes can be useful for defining management approaches answering biodiversity conservation aims. The study was carried out in the Vallombrosa Forest (Central Italy). The relationship between fir stand age and structural parameters was analyzed using inventory data. Gap dynamics were monitored between 1983 and 2007 on the basis of remote sensing data. Based on a field survey of a sample of gaps, 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). In the fir stands with lower stand density, a layer of trees with DBH < 15 cm had filled in the structure: fifteen different broadleaf species were recorded in this layer, usually mixed with fir. Gap size had an influence on presence of young firs (seedlings and fir < 0.5 m), which were significantly more numerous in gaps < 200 m2, but it had relatively limited influence on species diversity. Within-gap position did not influence regeneration density. Results indicate that a possible management option for gradually transforming even aged fir plantations in the Apennines into mixed, naturally regenerating systems, could be based on the creation of small gaps (< 200 m2) in the canopy cover, simulating the natural dynamics that are taking place in ageing fir plantations.