Dieback in pure stands of Brant`s oak (Quercus brantii Lindl.) in southern Zagros forests, Kohmareh Sorkhi region of Fars province

Oak decline has occurred along the Zagros forest from 10 year ago. In the current study, situation of tree decline of Brant`s oak (Quercus brantii Lindl.( of Kohmareh Sorkhi, Fars was assessed. The two affected stands by dieback in north and south aspects were identified and then two plots with variable areas were set so that 100 individual trees can be found in each plot. Moreover, two unaffected stands in the same geographical aspects were found and the same plots set as controls. Then, tree dieback severity was classified into four groups including fully health trees, sign of dieback just in upper parts of branch, dieback into the crown but less than 50% and finally dieback into the crown but more than 50%. All the oak trees within the sample plots were classified according to the four groups. Also, some tree characteristics such as origin (seed or root), coppice number, DBH, height and leaf area and dry biomass were recorded for all the trees. Also, we measured soil moisture content in all the plots. According to the results, around 11% of the trees in each affected plot belonged to the severe tree dieback group. Most of the moderate and severe dried trees were occurred in medium classes of diameter and height and their distribution follow a bell-shaped. Furthermore, soil moisture content in control plots were higher than dieback plots. Mean of leaf area and biomass of control plots were greater than those affected plots by tree dieback. Totally, there was no any significant difference in tree dieback rate between north and south aspects but it seems that moisture level is one of the key factors in tree dieback prevalence.