Structural and ecological changes in holm oak coppices 25 years after their conversion into high forest

Holm oak (Quercus ilex L.) is one of the most diffuse and economically important forest species in Sardinia, where it holds about 40% of holm oak cover in Italy. The forest type has also acquired a high ecological, recreational and landscape value over the last decades. Most of holm oak stands originated from overgrown coppice forests partly undergoing conversion into high forest. This study was set up in 1994 to analyse, as a function of site-index, the effects of conversion thinning on productivity, biodiversity, structural dynamics and canopy characteristics in an holm oak forest located in southern Sardinia. Two experimental permanent plots, differing in site index, stand structure and tree density, were established. The surveys were carried out in 1994-95 and 2010-11. The analysis included growth pattern, dynamics of stand structure and estimation of forest canopy attributes as leaf area index and canopy transmittance. Results pointed out the simplified stand structure, the poor biodiversity, the low LAI and high transmittance values 9 years after thinning implementation. These characteristics were more pronounced in the less productive area, characterised by substantial canopy gaps. 25 years after thinning implementation, both stands showed significant increase in the number of trees, strengthening of the clustered structure and high canopy recovery. Conversely, no significant changes in biodiversity and vertical structure were observed. Overall results contributed to a positive evaluation of the conversion practice based on periodical thinnings, even if the excessive reduction of tree density, mainly in the lower site-index area, did not allow yet the fully achievement of canopy recovery