Application of survival analysis methods to assess the effects of individual characteristics, habitat and environment on survival time of oak charcoal against the charcoal disease

Charcoal disease (Biscogniauxia mediterranea) was reported in Golestan province as one of the major diseases affecting oak decline in 2011. Therefore, this study was aimed to evaluate the influence of tree characteristics, stand and site on the infection risk in oak trees in the Qoroq forest park. In this study, 192 oak trees with the average diameter of 50.9± 16.5 cm at breast height were recorded, so that the health status of the trees was evaluated in five semiannual courses from October 2013 to October 2015. Log-rank test and Cox regression analysis were used to estimate the mean survival time of the trees and the affecting factors, respectively. The Log-rank test demonstrated the highest (100.7 months) and lowest (40.2 months) mean survival time at the vegetative stage in small pole and mature trees, respectively. Oak trees at a distance of less than 10 and more than 200 meters from the road showed the lowest (51.7 months) and the highest (109.6 months) mean survival time, respectively. Nevertheless, according to the Cox regression analysis, among the variables examined only the distance from the road and distribution range had significant effects on the survival rate of oak trees. Estimation of the survival rate and the affecting factors in oak trees could be used in prevention methods to manage and decrease the charcoal disease rate particularly in Qoroq forest park. Using the survival analysis methods in epidemiological studies of the forest tree diseases, the experts will have the better and more accurate understanding on the diseases progress.