Monitoring changes in the structural characteristics of pollarded oak stands(Case study: Kocher forest in Kurdistan province, Iran)

The purpose of this study was to monitor changes in the structural characteristics of a pollarded oak forest in Baneh county of Kurdistan province, Iran. Fifty-nine permanent sample plots were recovered for 14 years (2005-2019). In each plot, the diameter at breast height (dbh) for all trees (dbh ≥ 5 cm) was measured. Woody species less than 5 cm in dbh were recorded as regeneration in two height classes less than and greater than 2 meters by species and form (coppice and seedling). Total height and crown area for two trees in each sample plot (i.e., the nearest tree to the center of the plot and the largest tree in terms of dbh in the plot) were measured. The results showed that the difference between the beginning and the end of the studied period was significant in terms of the distribution pattern of trees in diameter classes (p<0.01); while there was no significant difference in the distribution pattern of trees in the total height and canopy area classes. The average annual increment of diameter, height and crown area in oak trees (excluding species) was 2.41 mm, 12.59 cm and 0.73 m2, respectively. A comparison of the current diameter distribution curve with the expected diameter distribution showed that the number of trees in diameter classes lower than 12.5 cm was less than the expected value, indicating poor regeneration. In order to reveal the consequences of pollarding as a traditional silvopastoral system and to make appropriate management decisions in order to improve the condition of pollarded oak forests, the use of permanent sample plots is suggested as a suitable method for studying the changes in structural indices of these forests.