Determination of optimal plot area for studying spatial structural indices in beech forests of kheyrud, Nowshahr

The quantitative description of forest structure is considered as one of the most useful working tools in modern forest management. This study aims at evaluating the optimal area of sample plot for correct and effective estimation of structural parameters of beech stands. For this purpose, a compartment with an area about 48 hectare in Gorazbon district in research forest of Kheirod, Nowshar, Iran was selected in which tree species and DBH of all trees with DBH > 7 cm were recorded. In addition, for stem mapping of trees, the location of each tree was obtained using azimuth and distance method. The square sample plots with different areas were laid out on simulated map of study area and nearest neighbor of spatial indices (spatial pattern index of Clark and Evans, mingling index, diameter differentiation index, relative mingling index) were then calculated in each sample plot. The comparison of resulted spatial indices in each of sampling schemes (1000, 1500, 2000, 3000, 4000, 5000, 7500, 10000 and 12500 m2 sampl plots) with calculated spatial indices for the whole of study area indicated that only spatial indices in sample plots with area of 12500 m2 did not show any significant difference with the spatial indices for the whole of study area. As long as the topographic and forest site conditions as well as management system do not change, horizontal structural indices could be investigated with one 1.25 ha sample plot, provided that this sample plot is not established in the margin of compartment and the forest road vicinity.