Tuyển tập những bài báo cáo nghiên cứu khoa học hay nhất được đăng trên tạp chí JOURNAL OF FOREST SCIENCE đề tài: Improving RBS estimates – effects of the auxiliary variable, stratification of the crown, and deletion of segments on the precision of estimates. | JOURNAL OF FOREST SCIENCE 53 2007 7 320-333 Improving RBS estimates - effects of the auxiliary variable stratification of the crown and deletion of segments on the precision of estimates J. Cancino1 J. Saborowski2 1Facultad de Ciencias Forestales Universidad de Concepcion Concepcion Chile Fakultat fur Forstwissenschaften und Waldokologie Georg-August-Universitat Gottingen Gottingen Germany ABSTRACT Randomized Branch Sampling RBS is a multistage sampling procedure using natural branching in order to select samples for the estimation of tree characteristics. The existing variants of the RBS method use unequal selection probabilities based on an appropriate auxiliary variable and selection with or without replacement. In the present study the effects of the choice of the auxiliary variable of the deletion of segments and of the stratification of the tree crown on the sampling error were analyzed. In the analysis trees of three species with complete crown data were used Norway spruce Picea abies L. Karst. European mountain ash Sorbus aucuparia L. and Monterey pine Pinus radiata D. Don . The results clearly indicate that the choice of the auxiliary variable affects both the precision of the estimate and the distribution of the samples within the crown. The smallest variances were achieved with the diameter of the segments to the power of Norway spruce up to European mountain ash as an auxiliary variable. Deletion of great sized segments yielded higher precision in almost all cases. Stratification of the crown was not generally successful in terms of a reduction of sampling errors. Only in combination with deletion of stem segments a clear improvement in the precision of the estimate could be observed depending on species tree target variable and definition and number of strata on the tree. For the trees divided into two strata the decrease in the coefficient of variation of the estimate lies between 10 European mountain ash and 80 old pine compared with that .
