AN EVALUATION OF STATISTICAL RELIABILITY IN SMS's PROPELLING INVENTORY: THE CASE FOR CONFIDENCE AND ERROR LEVELS

Abstract

This study was carried out on a randomly chosen 40-ha (800 x 500 m) forest area within the 50-ha Demography Project of the Forest Research Institute Malaysia (FRIM) in Pasoh Forest Reserve, Negri Sembilan. Out of the 40-ha study area, an area of 30 ha was used as a calibration data set and the remaining 10 ha area as a validation data set. The percentage sample or intensity of sampling was determined at various confidence and error levels, viz. from 80 to 95% confidence with ± 5 to ± 20% error in estimating tree density, basal area and volume. Results obtained from both calibration and validation data sets were used to assess the notion that the statistical reliability of the SMS's Pre-felling inventory (by the Forestry Department Peninsular Malaysia) is at 95% confidence and + 20% error
levels. At 1% sampling intensity to inventory density of trees 5 - <15cm dbh in 10 x 10 m plot, the confidence and error levels of respectively 95% and ± 15% or 90% and ± 10% would be more reliable. The 95% and ±15% levels are also true for estimating basal area and volume. At 5% sampling intensity of trees 15- < 30cm dbh (20 x 25m plot), its reliability is at 90% confidence and ±10% error limits for either tree density, basal area or volume estimation. However, at 10% sampling intensity
of trees > 30 m dbh (20 x 50 m plot), the 95% confidence and + 20% error hold true in estimating tree volume. The implications of attaching confidence and error levels to the sampling intensity are also discussed.