The Influence of landform, Terrain Shape Index and Aspect Slop on the Structural Distribution of Mixed Stands in the Arasbaran Forest by Ordination Method (Case Study: Kaleybarchay Watershed)

The forest structure and stand composition are controlled by several physiographic factors, because these factors play an important role in control the physical and chemical conditions of the environment, including access to light, soil moisture, and nutrients. In this study, the physiographic characteristics indices of the study area including landform index, terrain shape index and aspect slope index and the stand structural characteristics including density, basal area, canopy coverage, and the species important value index using the Detrended Correspondence Analysis and Redundancy Analysis studied in Arasbaran forests. The results showed that the highest altitude range (1600 to 1850 m a.s.l) had the highest amount of physiographic indices value. The Redundancy Analysis showed that the LI index had a positive correlation with the first axis and TSI and AS indices had a negative relationship with it. In addition, Caucasian oak was the most important species in terms of importance value index. Detrended Correspondence Analysis between species and sampling units showed that Caucasian oak had the smallest distance with sample units and followed by hornbeam. Correlation analysis of structural characteristics and physiographic factors showed that stand density had no significant relation with physiographic factors (p≤0.05), but the correlation of the canopy coverage area with the direction of slop in the first and second altitude ranges and basal area with the landform shape in the third altitude was significant (p≤0.05). This study showed that the trees structural distribution in the study area affected by the physiographic properties. Therefore, it suggested that the effect of other environmental factors to be investigated such as soil and climate on the forest structure.