Prove di diradamento in acero-frassineti di neoformazione nella Comunità Montana Agno-Chiampo (VI). Risultati dopo il secondo intervento

Thinning trials in secondary growth ash-maple stands carried out in the Agno-Chiampo district (VI): results after second thinning. The second thinning results undertaken in four ash-maple stands of different age are described. In three stands a target tree management system (free thinning around few target trees) was applied. In the oldest stand one mixed thinning has been implemented. In the youngest stand 400 target trees have been preselected and numerically half reduced after a second free thinning (aged 18 yr). The basal area of this stand decreased globally with 34%. In the middle aged stand (aged 28 and 31 yr), all the target trees, previously selected, were favoured. Among them, only those seriously damaged (by logging and frost) were cut down. The overall uptake in this stand has been the 30% of basal area. In the oldest stand the second traditional thinning (aged 37 yr) was more intensive, than the previous: the 34% of basal area has been felled. The analysis of target trees diameter growth has revealed that free thinning has been efficient for the youngest stand (a constant diameter increment of 8,6 mm yr-1). Conversely, a progressive reduction of diameter increment (5,5 mm yr-1) has been found in the control plot. The reaction to thinning in the middle aged stand was inferior in terms of homogeneity and diameter increment through years (6 mm yr-1 average), this underline a less reaction of crowns. In the oldest stand, late thinnings had little incremental effect, however the general stability and specific diversity improved . The experimental results confirm the necessity to carry out the first thinning in young stands (aged 15-20 yr) with a frequency of 4-6 yr in a restricted number of target trees (100-200 per hectare). In the oldest stands the chance to improve the production of good quality timber is reduced, but timber with fairly good technological characteristics can be however obtained.