Analysis the diameter increment of Lebanon oak (Quercus libani Oliv.) under Galazani- a traditional silvopastoral system- in northern Zagros Forests of Iran

Galazani (pollarding) is a traditional silvopastoral system, which comprises disbranching and defoliation of oak trees to provide livestock fodder. This affects forest stand structure, tree architecture and growth. This study aimed to compare diameter increment between households’ forests (conventional territories) in different diameter classes and analyzing the effect of Galazani on both diameter increment and its trends. To obtain the goals, 16 Lebanon oak (Quercus libani Oliv.) trees in the Armardeh forest in the Kurdistan Province, western Iran, distributed in five family territories (as an indicator of how local owners treat their own forest) from different diameters were cut. The width of annual rings of the cross-sectional discs, which were taken from the trees, were measured via a LINTAB table equipped by a binocular with a precision of 0.01 mm. Results showed that mean annual increment (1.78 mm) was not significantly different amongst various diameters nor amongst different owners. Mean comparisons of diameter increment in the years after Galazani indicated that the increment in the first year after Galazani (1.34 mm) was significantly less than the second (2.11 mm), third (2.76 mm) and fourth (3.19 mm) years. The trend of diameter increment enhances the tree stability and supports forest structure in order to improve the tree growth. Furthermore, it is necessary to both extend Galazani rotation to at least five years and to limit its maximum allowable diameter. Based on our findings, practicing Galazani in large diameter trees (30 to 35 cm) significantly reduces diameter increment.