عنوان مقاله [English]
Current increment of forest trees is affected by inner factors, environmental factors and the time. Rate of annual growth differs in tree living periods on the basis of fluctuations range, durability and effect manner of mentioned factors. The present study was performed to findout if there is homogenity in diameter increment of Beech trees (Fagus orientalis L.) in different ages, living periods and diameter classes. For this, 30 sample Beech trees in different diameter classes were cut from Haftkhal forest project. One disk with 10 centimeter thickness extracted on dbh level of each sample tree. After Measuring the width of the rings, the regression of the age and radial increment variations fitted for each tree. Primary results show that trend and model of the tree increment change in its living periods. Statistical descriptives and growth models of the trees have Significant. difference in the same diameter classes. For decreasing the number of equations and aggregating them, stratification method was used. Sample trees stratified in ten groups upon three criteria: diameter classes, age and the mean of current annual increment (rings width on dbh level). The regression of the age and radial increment variations fitted for each group. All groups were compared by means test and increment distribution corresponding to tree age. According to the results, diameter increment models of the Beech trees are not homogenous. Thus, for estimation the Beech stand increment, trees must be divided into ten groups.