Extracting Ecological Optimum and Amplitude of Fagus orientalis along environmental gradients in Kheyrud Forest, Nowshahr

The present research was performed in Patom, Namkhaneh, Gorazbon, Chelir and Baharbon districts in Kheyrud forest. Due to existence of forest typology map and extension of study area, this study was confined to beech dominated forests. A stratified sampling method based on landform is used to locate 1000 m2 circular sample plots. The number of Fagus orientalis Lipsky trees ≥ 7.5 cm in DBH within each plot is recorded along with elevation, aspect and slope of the ground. Furthermore, at the center of plot, soil samples from A horizon are taken for analyzing soil texture. Gaussian response function was used. Instead of direct estimation of Gaussian parameters, it is customary to fit an equivalent polynomial model. This can be easily fitted as a generalized linear model (GLM) with a logarithmic link function. This function showed beech has 1347 and 464-2231 m a.s.l for its optimum and ecological amplitude, respectively. North-facing slopes (optimum 43 degree) are the most suitable slope for Fagus occurrences. Beech tree can distribute from gentle to steep slopes in the study area, but this species in 39% slope has the best performance. Using generalized linear model showed Fagus can tolerate slopes from 3 to 74%. In light of sand, clay and silt, Beech tree has 25%, 43% and 35 % for optimum and 4-46 %, 25-60% for clay and 15-55 % for silt for ecological amplitude, respectively.