N-Tree Distance Sampling vs. Fixed-Radius Plots methods for tree density estimation in central Zagros forests

N-tree Distance Sampling (NTDS) is a well-known distance sampling method which is considered as cost-and time effective compared to fixed-Radius Plots. This study was conducted across an area of 36.40 ha in Helen forest reserve in Chaharmahal and Bakhtiari Province. The study area mostly comprises of natural, old-growth Brant`s oak (Quercus brantii) stands. Here, the stands were first fully callipered. Two estimators of Moore and Kleinn-Vilcko sample plot methods were applied to derive the diagnostic measures of relative bias (RB) and relative root mean square error (RRMSE) for a number of 2 to 12 trees. For each estimator, 30 repeats with each encompassing 50 Sample points were selected. The results showed the fixed plot sampling (FPS) to be of higher performance in the clumpy-distributed trees within stands with 154.25 trees per ha. In addition, the Kleinn-Vilcko estimator was shown to be most efficient for N ≥ 5 trees. Due to its high error rate, the Moore estimator yet returned poor performances in density estimation across the study area.