tailieunhanh - Báo cáo lâm nghiệp: "Comparaison par simulation de 3 types d’unités d’échantillonnage en futaies feuillues de hêtre (Fagus silvatica L.)"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Comparaison par simulation de 3 types d’unités d’échantillonnage en futaies feuillues de hêtre (Fagus silvatica L.) (*). | Ann. Sci. For. 1988 45 3 209-222 Comparaison par simulation de 3 types d unites d echantillonnage en futaies feuillues dehètre Fagus silvatica L. 0 J. HEBERT J. RONDEUX c. LAURENT Unite de Gestion et Economie forestieres Centre de Recherche et de Promotion forestieres I. . Section Aménagement et Production Faculte des Sciences Agronomiques 2 Passage des Déportés Gembloux 5800 Belgique Summary Comparison between three types of sampling units in beech stands This study is dealing with the choice of the size and the type of sampling units which could be used in inventories of beech stands Fagus silvatica L. . Two experimental areas of 16 hectares have been considered in evenaged and unevenaged structures. Three types of sampling units were studied fixed circular plots Bitterlich plots non fixed circular plots and circular plots including a minimum of number of trees 15-20 . As regards to the estimations of basal area and number of trees per hectare there is no significative difference between plots of fixed area and plots including a minimum number of trees even if plot sizes and stand structure vary. As expected compared to the other methods the Bitterlich plots give little more precise estimations of basal area and less precise estimations of number of trees. The plots with a minimum number of trees would give higher values compared to the other types of plots but no significative difference have been observed. Numerous simulations show that in case of a fixed total cost the use of a great number of small units or of a limited number of large units has little effect on the standard error of estimations. The concept of minimum number of trees 15-20 seems to be valuable according to a compromise between precision and cost. To avoid a risk of bias in stands including large empty zones it is preferable to use plot radii suitable to normal conditions. Key words Inventory sampling units beech stands. Resume Trots types d unites d echantillonnagc placettes .