Structural diversity of mixed beech stands in the middle stage of succession (Case study: Gorazbon District, Kheiroud Forest of Nowshahr)

To quantify the structural properties of mixed beech (Fagus orientalis) stand in the middle stage of succession, a study was carried out in the Kheiroud forest of Nowshahr in Mazandaran province. To this aim three one-ha sample plots were selected, within each of which a 30×30 m gird was established. A set of structural parameters including the diameter at the breast height, tree height, crown diameter, distance and angle among trees were measured for the closest beech to the intersection points within the grid as reference tree, as well as for other three nearest neighbors to the reference tree. The crown competition coefficient and growth space index of 0.72 and 18.57 were calculated, respectively. In addition, the average distance amongst seedlings was shown to be 60.1cm. Results also showed the average of uniform angle index, species mingling, diameter and height differentiation and neighbors distance to be 0.76, 0.7, 0.31, 0.37, 5 in plots, respectively. Based on uniform angle index (Wi) as well as the distribution pattern of beech is in its middle stage of succession, the distribution of beech trees were aggregated. This showed a high tendency to mix with the hornbeam (Carpinus betulus) trees. Furthermore, Beech was proven to have a maximum rate of inter-competition with hornbeam in the middle stage of succession, which leads to the highest frequency of neighbor distance between 2 to 4 m. According to the results, we concluded that structure of beech stands in the middle stage of succession differ from the late successional stage. This should thus be considered in the envisaged management of such forest stands in northern Iran.