Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí lâm nghiệp đề tài: Plant community variability within potential natural vegetation units: a case study from the Bohemian Karst. | JOURNAL OF FOREST SCIENCE 55 2009 11 485-501 Plant community variability within potential natural vegetation units a case study from the Bohemian Karst P. Samonil K. Polesná P. Unar Silva Tarouca Research Institute for Landscape and Ornamental Gardening Department of Forest Ecology Brno Czech Republic ABSTRACT Based on a map of potential natural vegetation PNV actual vegetation was studied in the Mramor locality ha . A total of 188 relevés were examined using stratified random sampling. A comparison was made between trends in vegetation variability throughout the entire locality and variability within the defined PNV units. The stratification of the locality according to PNV units was only partly representative of the main trends in vegetation variability especially at ecologically distinctive sites. On the other hand in areas with a relatively limited ecological gradient the sites were oversampled . The variability of plant communities within PNV units was high. The results of this case study suggest that the need for delineation of PNV units which are homogeneous in terms of production site and phytocoenosis is overestimated. This delineation neither corresponds to the characteristics of actual ecosystems nor is necessary for the application of a PNV system. A more suitable unit for the development of such a system would be for example forest type series. Keywords vegetation classification vegetation variability potential natural vegetation oak forest Bohemian Karst Formalized sampling approaches The subjective selection of phytocoenological plots which were traditionally used for many decades is being replaced by a formalized selection process. The main reasons for this change were the requirement of a representative set of samples from surveyed territories and the desire to eliminate tautological statements of evidence . Chytrý 2000 . One of the methods widely used in this formalized approach to data collection is stratified random sampling . Hirzel
