Influence of topography on Brant's oak decline in Meleh-Siah Forest, Ilam Province

During the last decade, oak decline has caused critical health issues within the Zagros forests in west Iran, which is currently approaching a threatening level with effects on stand structure and stability. Identifying the influential factors on the spread of this phenomenon can thus help forest planners and administrating units to control the crisis. This study aimed to assess different aspects influencing deterioration of oak trees with respect to stands environmental characteristics in the southern part of Zagros forests. For this purpose, 12 declined stand dominated by Brant`s oak (Quercus brantii) at different conditions in both the North and South aspects as well as two altitudes and three replications were chosen within Meleh-Siah forest site in Ilam province. A transect line was randomly assigned to each of the stands, along each or which three square plots (2500 square meter) were laid. Within the plots, all individual trees were inventoried. By using a randomized complete block and factorial design, methods were used to compare the mean values of the inventoried parameters. Although the results showed no significant difference between diameter, height, crown length and basal area of the stands along gradients of aspect and altitude, significant effect of aspect on decline rate in seed based trees as well as altitude on coppice trees were observed. The degree of decline in south aspect was greater than in north aspect. In addition, lower elevations showed larger effects than higher elevations. The interaction between two factors was also significant on the decline rate.