Effect of grazing and environmental factors on the structure of Brant's oak stands of Zagros (Case study: Dalab Park, Ilam)

Species composition and structure of forest stands are subject to temporal changes as a function of anthropogenic or natural disturbances. The investigation of such changes in association to environmental factors plays an important role in analyzing of the ecosystem dynamics and in turn in ecosystem management. In this study, forest structural attributes, soil and other environmental variables were collected across 51 sample plots (each encompassing 0.1 ha) by using the random sampling method across two “grazed” and “protected” forest sites located in northwest of Ilam. Canonical correspondence analysis was used to identify patterns in stand structure of the sites and their association to environmental attributes or livestock grazing. Results showed the stand structure to be affected by the grazingand soil factors, which explained 7.7% and 6.2% of the total variation in stand structure, respectively. In addition, the occurrence of trees with high diameter classes within the grazing-disturbed class was an indication of old growth stands in such sites, in which the natural regeneration has not been taken place for a long time. On the other hand, the lower diameter classes as well as classes of lower height were predominantly observed beside the classes of higher diameter in undisturbed sites, which suggests for the existence of uneven-aged and irregular stand structure. The results of this study suggest that natural regeneration in Brant`s oak trees is mainly enabled following a preservation of such sites against grazing.