The influence of northern and southern aspect on forest structural indicators (case study: Tangdalab forests of Ilam province)

This study aimed to evaluate the structural characteristics of natural forests and providing the possibility of studying the changes in the structural characteristics of these stands over time, in order to plan and manage the forest in the Tang Dalab To achieve this, all trees were calipered in two one-hectare plots. Additionally, the structural characteristics were measured using the nearest neighbor’s method. To measure several indices like nearest neighbor distance index (density of trees), uniform angle index Clark and Evans index (variety of location), Mingling index (species mixture), diameter and canopy differentiation indices (dimensional differences of trees), and complex structural diversity index (tree diversity) were used. The results of uniform angle (south site 0.44 and north site 0.48) and Clark and Evans indices (Southern aspect 1/07 and Northern aspect 1/09)indicated a random spatial pattern of trees. According to the Mingling index, the northern aspect has relatively moderate mixing (0.31) and no mixing (0) in the pure southern aspect). The mean distance to the neighbors was 8.12 m in the northern stand and 5.81 in the southern aspect. The results of the diameter and canopy differentiation index indicated a low difference in diameter (0.24) and canopy (0.24) in the southern aspect an average difference in diameter differentiation (0.41) and a high difference in canopy differentiation (0.51) in the northern aspect complex structural diversity index, indicated more diversity in the northern aspect (0.38) compared to the southern aspect (0.18). The indicators used in this research can be used to describe the structure and ecological characteristics of different tree species in order to increase ecosystem stability and planning to create heterogeneity in the structure of the stand and help forest managers in planning and making appropriate decisions. However, the effectiveness of these indicators in some situations is doubted by some researchers.