Assessing quantitative changes in crown area and height of oaks (Quercus spp.) during pollarding process

The aim of this study is to investigate the quantitative changes in the biometric indices of Lebanon oak (Quercus libani Oliv.) and gall oak (Q. infectoria Oliv.) during pollarding process. In a part of the two pollarded strands in northern Zagros of Iran, in which three years had passed from its last pollarding, the name of woody species was recorded and diameter (dbh), total and crown heights, and two perpendicular crown diameters were measured before and after pollarding in a full callipering assessment of all trees (dbh ≥ 5 cm). The results showed that in the pollarding process, crown height and crown area of oak trees decreased on average 15.73 and 30.06%, respectively. In both studied species, the reduction of crown area is significantly more than the crown height. In terms of reduction in crown height and crown area, there was no significant difference between Q. infectoria and Q. libani trees. The most decrease in crown height (27.99%) and crown area (44.85%) indices on diameter classes are related to Q. infectoria trees belonging to the 35 cm diameter class and Q. libani trees belonging to the 55 cm diameter class, respectively. The results indicate a higher decrease in the crown area compares to the crown height of oak trees due to pollarding practice; therefore, it is necessary to partially compensate for this decrease in the crown area by leaving some branches during each pollarding operation, because preserving the canopy is very important for Zagros-forest ecosystems. The only way to conserve these resources is to create a participatory approach as part of the transitional forest policy.