Western oak forests located in the Zagros Mountains, covering an area of 5.5 million hectares, make up the largest share (40%) of Iran's forests. Western oak forests have effective impacts on water supply, climate control as well as establishing a socio-economic balance. The present study was carried out to monitor the change in biometric indices in the Kocher Forest, Baneh city, Kurdistan Province, Western Iran. To achieve this goal, a 4559-ha study forest was selected and fifty-nine permanent sample plots were recovered for 14 years (2005-2019). After determining the center of sample plots, retrieval of trees in each sample plot at the end of the period (2019) was taken place using azimuth and the distance of trees to the center of the sample plot, previously recorded at the beginning of the period (2005). In each plot, diameter at breast height (dbh) for all trees (dbh ≥ 5 cm) was measured. Total height and crown area for two trees in each plot (i.e., nearest tree to the center of the plot and the largest tree in terms of dbh in the plot) were measured in 2019. The tree distribution patterns on diameter, height and crown area classes at the beginning and end of the study period were compared. The average diameter increment of oak trees (all species) was 2.41 mm/year, the average height increment was 12.59 cm/year, and the average crown area increment was 10.22 m2/year. The results showed that the difference between the distribution pattern of trees in diameter classes was significant; while, there was no significant difference in the distribution pattern of trees in the total height and canopy area classes. The use of permanent sample plots is suggested as a suitable method to study the changes in the structural indices of pollarded oak forests in order to reveal the consequences of pollarding and to make appropriate management decisions in order to improve the condition of these forests.
