Determination of the optimal sample plots size and shape in Arab-Dagh forests, Kalale city, Golestan province

Achieving the goals and implementation of sustainable forestry requires accurate data in order to do necessary planning and provide optimal solutions. The aim of this study was to select the optimal sample plots size and shape for estimating stand volume and tree density in Arabdagh forests, Golestan province. For this purpose, 60 ha forest area of Arab Dagh in Kalaleh city was surveyed with 100% inventory. Then, stand volume and tree density were calculated form 100% inventory and all sample plots with areas of 200, 400, 600, 800 and 1000 m2 and circular and square shapes were calculated in a Systematic Random Sampling. Also, the results were compared with stand volume and tree density obtained from 100% inventory using one-sample t-test. The results showed that the E% (square of sampling error) difference between circular plot (1.9%) and square plot (1.2%) with 400 m2 area plot is very low. Moreover,  index of circular plot (89604) and square plot (94979) with the area of 400 m2 are lower than the 1000 m2 area plot. Therefore, sample plots with the area of 400 m2 are appropriate for stand volume and tree density. Also,  index of circular plot with the area of 400 m2 is lower compared with the square plots with the same area and the differences between them are also lower. Therefore, circular plots are appropriate for stand volume and tree density. In general, the results showed that circular sample plots with the area of 400 m2 can be optimal sample plot size and shape in afforestation inventory.