Investigating the probability distribution functions of crown classes of coppice shoot ‎Brant's oak (Quercus brantii Lindl) in Middle Zagros

The quantitative status and probability distribution functions of crown classes of Brant's oak (Quercus brantii) stands were investigated in the Qala Gol region of Khoramabad city in this study. The number of two classes of degraded and less degraded forest was selected for this purpose by identifying the forest and obtaining samples in a selective manner, and then a square sample plot of one hectare with dimensions of 100×100 meters was planted in each class. The crown diameters of 72 coppice trees of Brant's oak in the less degraded region and 52 coppice trees of Brant's oak in the degraded area were measured. In this study, statistical distribution models such as Weibull, Gamma, Normal, Log-Normal, Beta, and Johnson Sb were utilized, and the Anderson-Darling test was used to determine the goodness of fit. The results indicated that the canopy percentage in the degraded region (11.9%) is lower than the canopy percentage in the less degraded area (37%), and the average canopy area in the less degraded stand (51.46 m2) is considerably greater (P≤ 0.01) than the canopy area in the degraded stand (22.89m2).  Based on the goodness of fit test results in the less degraded stand, the Johnson SB, Weibull, Gamma, and Beta functions were proposed as the best fit functions for the canopy classes in the degraded region, respectively. The current study demonstrates that the rate of degradation has a significant influence on the probability distribution functions of tree crown cover in coppice Brant's oak stands in the Zagros forests.