Comparison of three sampling methods in estimating stand parameters for a tropical forest

Abstract

Three methods — fixed-area plot sampling using 100 × 7-m, 70 × 10-m, 50 × 14-m, 28 × 25-m, and 26.45 × 26.45-m plots; angle-count sampling based on the corners of these plots with a basal area factor of 9.3; and horizontal-line sampling using the long axis of the fixed-area plots with a diameter factor of 6.0 — are compared in terms of statistical efficiency in a sampling simulation study of a 60-ha forest in Surinam. For each method, 1000 iterations of ten sample locations with an expected number of 7.94 trees per location are used to estimate number of trees, sum of tree diameters, average tree diameter, total basal area, and frequencies of trees by 10-cm diameter classes. Fixed-area plot sampling is most efficient for number of trees; horizontal-line sampling for total basal area, sum of tree diameters, and average tree diameter. The angle-count method is best for number of trees by diameter class for the larger diameter classes; the fixed-area plot method is best for the smallest trees. All three methods are most efficient with sample locations based on square sample plots. A count sampling method combining the three methods using a long rectangular plots is recommended for practical purposes if interest is in all parameters except frequencies by diameter class, so that tree diameters do not need to be measured. If interest is in frequencies by diameter class, the angle-count sample trees should be measured to give the most reliable results.