1. Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria, Forestry Research Centre (CREA-SEL), Viale Santa Margherita 80, I-52100 Arezzo, Italy.
2. Forest Site Science Department, Forest Research Institute (IBL), Sękocin Stary, Braci Leśnej Street No. 3, PL-05090 Raszyn, Poland.