Monitoring the dieback of oak trees and its effect on leaf and acorn characteristics in the Zagros forests of Piranshahr, West Azerbaijan Province

This research was designed to investigate the dieback of oak (Quercus infectoria; Q. libani) trees in the northern Zagros forests in West Azerbaijan Province. Characteristics of the stand were investigated in a one-hectare sample plot with dimensions of 100 × 100 meters. To monitor dieback, inside the sample, a sub-plot with a floating surface was determined where 100 oak trees could be placed. The dieback was monitored over four years (2019-2022) using a five-level scale: 1) healthy, 2) dieback, 3) crown dieback up to 50%, 4) crown dieback exceeding 50%, and 5) tree cut down. The results showed a decrease in the number of healthy trees from 94% to 71% between 2019 and 2022, with 9% of trees ultimately being cut down. To investigate the relationship between leaf surface and the dimensions and weight of seeds of trees, 20 leaves were selected from five permanent trees, and their surface was calculated annually for three years (2019-2021). Additionally, 25 seeds were harvested, and the dimensions and weight of the seeds were determined annually. The results of calculating the average leaf area over three years showed a significant decreasing trend. Except for seed weight, other dimensions in the seed showed a significant decreasing trend during the monitoring years. Overall, the results showed that despite the absence of oak charcoal disease in the province, the trend of decreasing healthy trees and increasing trees with different levels of dieback is very worrying.