Effect of height above sea level on structure and tree species diversity in Zagros forests (A case study of Ghalaje forests in Kermanshah province)

Ecological conditions such as environmental gradients influence the structural characteristics and diversity in forests located in altitude gradients. This study aimed to investigate the effect of altitude on some structural characteristics and diversity in Zagros forests in the Ghalajeh region of Kermanshah province. To analyze the effects of diversity on structural and vegetation characteristics and their changes in different altitude gradients, a total of eight sites were selected in four altitude ranges from sea level: 1200-1475 meters (lower land), 1750-2025 meters (middle land), 1475-1750 meters (middle belt), and 2025-2300 meters (highland), identified in both northern and southern slopes. Then, in each site, three sample plots were selected as replicates, and within each sample plot, all necessary characteristics of the trees were measured and noted. The results showed that with increasing altitude, the number of species and the frequency of shrub species increased, but the density of Iranian oak trees decreased. Species such as Almond, Plakhor, and Maple were mostly present at higher altitudes. However, with increasing altitude from sea level, standing tree trunks initially increased (in the middle land) and then decreased (in the highlands). However, this characteristic was almost equal in the lower belt in both northern and southern slopes. The results of comparing the mean variables of breast diameter, total tree height, and tree dieback degrees at different altitudes from sea level were statistically different (p < 0.05).