Investigation on the role of sanitary cuts in survival and vitality of exposed dieback Persian oak trees in Zagros Forests (Case Study, Melahsiah Forest, Ilam Township)

  The phenomenon of decline and tree mortality of various oak species has been reported in vast areas of the world since the early nineteenth century. Overseas studies are often on thinning sanitary cuts and sanitary control methods of woodborer pests against decay of cut woods, and no considerable research has been done on pruning of forest trees to save infected trees from pests and diseases. Also, significant researches have been reported about the positive role of pruning of various fruit trees in pest control and pathogenic agents across the Iran and in the world. In recent years, relatively comprehensive researches have been done on the dieback of Zagros forests from different aspects. Given that the chemical struggle against pests and diseases in the natural ecosystems is not recommended and the biological struggle is based on the long-term research needs, so now the application of the sanitary cuts is considered as the most important strategy to control the declining of Persian oak trees. In this regard, the purpose of this study was to investigate the role of several treatments of cuttings and pruning against the dieback of Persian oak trees in the Melahsiah forests of Ilam province. To conduct this research, the effect of 10 treatments of two factors including vegetative form and cutting type were studied based on completely randomized design by factorial method. Vegetative form was studied at two levels of high and coppice and cutting type in five levels including removal of infected parts of trees, complete removal of crown, cutting from height 10 cm and cutting from 10 cm depth and control treatment (without sanitary cutting). Due to the lack of necessary conditions of parametric statistical assumptions (analysis of variance), the comparison between average two forms of vegetative forms treatment were performed by Mann-Whitney non-parametric test and the comparison between group and pair average of cutting methods by Kruskal-Wallis and Tamahan non-parametric tests respectively. The results showed that there was no significant difference between the survival and viability averages of two vegetative forms (high and coppice) in the 5% probability level. The results indicated that the difference between the mean of survival percentage of two treatments for removal of infected parts and removal of 100% crown was significant at 5% probability level and the average difference of the other treatments with the average of control treatment was not significant. Also, the results of comparing the average percentage of viability for the five treatments of the sanitary cutting factor showed that the difference infected removal parts with control treatment was significant at 5% probability level and the difference of other treatments with control treatment was not significant. Based on the results, treatments including cutting at a depth of 10 cm, cutting from 10 cm tree height and removal of 100% tree crown have not been able to have a positive effect on the improvement of survival and freshness, and therefore the implementation of these sanitary cuttings is not recommended. In general, in order to reduce the dieback damage of Persian oak trees, the implementation of sanitary cutting of selective removal of contaminated branches is recommended in similar areas with the study area.
Keywords: dieback, Ilam Province, sanitary cutting, Persian oak, Zagros forests