Comparison of the size structure of prevalent silvopastoral management in northern Zagros forests

Traditional forest management in Zagros forests is rooted in traditional ecological knowledge for livelihood needs. In this study, three prevalent models of silvopastoral management including young coppices (YC), old-age coppices (OC) and transitional structure (TS) as well as a preserved stand (PS) were compared. Trees were measured in the variable-area sample plots and stand structure of each management model was evaluated using structural diversity indices including Margalef, Berger-Parker, Shannon diversity, Simpson, and Shannon evenness. Results showed that average diameter and height of trees in OC and PS were significantly greater than both younger stands. The YC was characterized by maximum stand density, lowest basal area, an acceptable rate of regeneration, and negative exponential diameter distribution with a considerably limited size span. Positively skewed bell-shaped diameter distribution was observed in OC and TS which conversely to the YC have significantly wider size span and lower regeneration rates. Based on the indices, the maximum and minimum size diversity were observed in PS and TS, respectively while OC had the most diverse structure among the harvested stands. Due to weaknesses like limited diameter range, abundance of young individuals and low stocking level, YC structural diversity was lower than OC. Despite the lack of adequate regeneration and young stems, structural diversity of OC model was interesting. Finally, stocking in the YC stands as well as improvement of regeneration in the OC stands were suggested in order to regulate the forest structure.