Effects of thinning intensities in experimental plots of Black European pine in “Foreste Casentinesi, Monte Falterona and Campigna National Park” (Tosco-Romagnolo Apennine, Italy), eight years after the felling

Abstract

Different thinning intensities were compared in a 50-years-old plantation of Pinus nigra sp. located in the “Foreste Casentinesi Monte Falterona e Campigna” National Park (northern Apennine - Italy). Six experimental square plots (900 m2) were set up for comparison of two thinning intensities: heavy thinning (F: approximately 30% of basal area removed), light thinning (d: approximately 15% of basal area removed) and control (Co). The comparison concerned: (1) the periodic increment of the trees in terms of volume (Ipv), average dbh (Ipd), height (Iph) and the variation of height/diameter ratio (S) in time; (2) forest canopy cover, indirectly expressed in term of relative irradiance (I.R.). Eight years after the felling, the results highlight that F thinning: (a) increases the homogeneity of timber, as the stand volume is concentrated in dominant trees; (b) favours tree diameter increment: Ipd values increase significantly according to the thinning intensity; (c) reduces tree height increment (lower values of Iph were recorded in the F plots); (d) promotes stand stability: lower value of S are highlighted in F plots, and no significant increase of this parameter in time has been recorded. As regards canopy cover, a significant negative correlation was recorded between stand basal area after the thinning and I.R. at ground level. After harvesting, a significant difference in terms of average I.R. between thinning intensities (F, d and Co) was also recorded: nowadays, significant differences of average I.R. are observed between Co and d, whereas F shows intermediate values: the canopy gap originated from the felling has been quickly filled. Our results highlight the growth potential of Black European pine in the studied area; however, only heavy thinning shows interesting results in terms of both tree growth and stand stability.