Zwiększenie efektywności inwentaryzacji lasu metodą losowania warstwowego

The purpose of the stratification is to group stands basing on the homogeneity of the measured feature. During periodic forest inventory in Poland, strata are created on the basis of age and the main species in stand within the boundary of forest district. In this work an improvement of distinguishing the strata during the forest inventory is presented. Three variants are considered: (1) distinguishing homogeneous strata in boundary of the whole forest district, not separately in forest subdistricts, (2) splitting species−aged strata into homogeneous substrata with respect to site quality, and (3) dividing strata of stands in the regeneration class with respect to stand density. Study was conducted in four mountain forest districts located in the Kłodzko Basin (SW Poland). Total area of these stands amounted to 43,052 ha, where 6,648 sample plots were established during the periodic inventory. ANOVA was used to test significance of the differences in tree volume and to assess variability reducing in distinguished substrata. Results indicated that in stands with age up to 70 years mean volume of trees on the sample plot does not differ significantly between sites, but in older stands difference was significant. Dividing age−species strata of stands older than 70 years into substrata according to site conditions influenced reduction of volume variability from 10 to 57% in newly created substrata. Dividing strata consisted of stands in regeneration class according to stand density index allowed to decrease the volume variability from 9 to 20%. Mean volume of trees in stands on similar sites does no differ significantly between subdistricts in the same forest district. Strata distinguished within the whole forest district are bigger and represented by more sample plots than on the subdistrict level, which significantly reduced standard error of volume and improved effectiveness of stratification in forest inventory.