Does diameter increment of Lebanon oak trees (Quercus libani Oliv.) affected by pollarding in Northern Zagros, Iran?

Abstract

Lebanon oak is one of the important oak species in the Northern Zagros forests, west of Iran, which exposed to severe pollarding in traditional silvopastoral management. The purpose of this study was to investigate the effect of pollarding on diameter increment of Lebanon oak trees. Therefore, a less-disturbed stand (0.7 ha) and a pollarded stand (1 ha) with similar physiographical conditions were selected. Full Callipering was performed in both stands and tree species; collar diameter and crown diameter for all trees (collar diameter ≥5 cm) were recorded. Moreover, total and trunk heights were measured in Lebanon oak trees as well. To evaluate the diameter increment of Lebanon oak trees, 20 and 15 tree samples were taken in the less-disturbed and pollarded stands, respectively. A pair of increment cores per sample tree was taken 100 cm above ground level, using increment borer. In the cores, annual radial increment was measured and the annual diameter increment was calculated by doubling that value. The diameter increment distribution of Lebanon oak trees in identical age classes was determined and used for comparison. The results indicated that the difference of the mean diameter increment of Lebanon oak in the same diameter classes was significant (P < 0.05) between two stands. The mean diameter increment in age classes of 57–81 years (P < 0.01) was significantly different (P < 0.01) between the two studied stands; however, in the age classes of 1–55 years, there was no significant difference (P = 0.559).