Effect of spatial pattern of trees on efficiency of distance and plot sampling methods in Zagros woodlands

The spatial pattern of trees is one of the structural characteristics of forest stands that affects the efficiency of sampling methods. This study aimed at investigating the effect of spatial distribution of trees on the efficiency of distance and plot sampling methods. For this purpose, a dispersed Persian oak stand in Kohgilouye-Boyerahmad province (47 ha) and a clumped wild pistachio stand in Fars province (45 ha) were selected. Six distance and six plot sampling methods were applied on a 100 m × 100 m grid in the stands to estimate the density and canopy cover. The efficiency of methods was evaluated by statistical comparison of the results with true values, accuracy criterion, and root mean square error percent. The true density and canopy cover percent of wild pistachio and Persian oak stands were 19.4 trees ha-1 and 5.1% and 22.3 trees ha-1 and 17.1%, respectively. The results showed that between distance sampling methods, nearest individual (density: 19.5 trees ha-1, canopy cover: 5.2%) and nearest neighbour (density: 20.1 trees ha-1, canopy cover: 4.9%) methods in wild pistachio stand and line intersect method (density: 21.0 trees ha-1, canopy cover: 17.3%) in Persian oak stand were efficient. Moreover, all plot sampling methods were efficient in both stands (except square method). In general, the results showed that in contrast to plot sampling methods, the spatial distribution of trees influences significantly the accuracy and precision of distance sampling methods.