Comparison of decline in Persian oak (Quercus brantii) and Wild pistachio (Pistacia atlantica) in Zagros forests

The mortality of forest species, especially in arid and semi-arid regions, has been considered the main challenge of diverse ecosystems. The aim of this study is to compare the drying status of Persian oak and Mt. Atlas mastic tree in the Zagros forests in western Iran. To carry out this study, whole forests in the Gilan-e Gharb were considered. For this purpose, the entire surface was divided into equal parts with a sampling grid of 3000 × 3000 m2. The number of 92 sample plots with an area of 0.25 ha were considered for sampling at the intersection of the lines in the forests. Sampling of all the trees in the plots was done 100%. To determine the dryness ratio of the studied trees, based on objective observations, the ratio of the amount of dried branches to the whole tree was used. The results showed that the mean total stock is 39 m3 per hectare. The volume of oak and pistachio species is 34.1 and 8.4 m3/ha, respectively. The living stock of oak and pistachio species is 3.7 and 0.05 m3/ha, respectively, while their dried stock is 13.4 and 4.13 m3/ha, respectively. The highest frequency of dryness includes pistachio with degree 2 (46.94%), and the lowest percentage includes pistachio type with degree 4 (2.9%). The frequency of drying of these species is higher in the initial stages (1 and 2), it decreases in stages 3 and 4, however, in the completely dry state, the abundance of trees increases again. The abundance of fully dried Pistachio is much less than fully dried oak. The analysis results of the frequency variance of drying degrees in oak and Pistachio species show that the frequency of these species has no significant difference with a probability of 95%. The presence of dried pistachio trees with dried Persian oak species needs to be taken seriously, which shows the fragility of these forests.