Angle sampling method for the inventory of teak plantations (Tectona grandis L. f.)

Abstract

Introduction: Sampling by fixed area plots is the usual practice in forest inventories, despite the considerable time involved. An alternative method of sampling is the angle count or Bitterlich method. Objective: To evaluate the accuracy and efficiency of the angle sampling method for the determination of dasometric variables in teak (Tectona grandis L. f.) plantations. Materials and methods: In a three-year teak plantation, 21 circular plots of 500 m2 were established. In each plot, the diameter at breast level, the height and position of each tree, the working times, the number of trees per hectare, the diameter of the average basal area, the total basal area, the average Lorey level and the total volume were determined. Angular sampling was simulated using basal area factors (BAF) of 0.5, 1, 1.5 and 2. The estimates of the variables for each BAF and fixed area plots were compared using ANOVA and the relative efficiency was determined. Results and discussion: The ANOVA did not detect significant differences (P < 0.05) in the estimation of dasometric variables between sampling types, which demonstrates that the angular method is accurate. The fixed area and shape plot required more working time (P < 0.05). The relative efficiency of the angular method was between 4.5 and 11 times higher than that of fixed area plot. The ideal BAF in young teak plantations was equal to two. Conclusions: Angular counting is accurate and more efficient for estimating dasometric variables in young teak plantations.