The Impact of Aspect on Forest Structural Characteristics in Zagros Forests (Case Study: Tangdalab forests of Ilam province)

Forest management achieves its management goals by considering the natural state of the forest and having enough knowledge in relation to ecological characteristics of forest species and the current state of the forest structure and monitoring changes resulting from management activities. This research was carried out with the aim of knowing the existing structural situation in Tang Dalab forest area, in two Aspect direction, northern and southern.

In the center of two northern and southern sites, a square sample plot of one hectare (dimensions 100 x 100 meters) was permanently selected and planted. All trees and Coppice shoots located in this area were numbered and specified and the structural variables of all the trees in the sample plot were measured. To compare the average of the investigated variables in both sites, after testing the homogeneity of variances and the normality of the distribution of variables, t-student test was used

The results showed that the southern stand with a density of 72 Persian oak species (Quercus brantii Lindl) per hectare was completely seedling and its forest type is Quercus brantii Lindl while the northern stand with a density of 57 trees per hectare, 82% of its seedling and its forest type was Q. brantii - C. azarolus. The results of the T-test showed that all the studied variables have a significant difference between the southern stand and the northern stand at the probability level of 1% The average diameter at root collar (DRC), diameter at 0.5m height, and diameter breast height (DBH) of trees in the southern stand were more than the northern stand. The distribution of trees in the diameter classes of the southern stand, showed that this stand has an irregularly even-aged structure. The chart of diameter distribution of this stand states that there was no regeneration in the past years in the northern stand, in addition to coppice and young Persian oak trees, in the lower diameter classes, a number of young trees of other species with small diameters were seen. The height distribution diagram of trees in the southern stand showed that the largest number of trees are in the middle of the diagram and in the height classes of 5 to 11 meters. In the northern stand, coppice trees were present in the lower height classes (less than 3 meters). While more than 80% of seedling trees have a height between 6 and 11 meters. The results of the investigation of the basal area diameter at 0.5m of the trees in both stands showed that This variable in the southern stand (26.41 square meters) due to the presence of seedling trees and higher density, it was about More than three times the northern stand (7.48 square meters).

The superiority of the southern group over the northern group showed that the aspect has a major influence on the vegetation and forest structure. in sustainable forest management planning, while monitoring the structure of forest stands during periods of time, at least ten years, it is necessary to pay special attention to the different conditions of aspect in order to preserve, revive and develop these forests.