The effect of some anthropogenic disturbances on the structure of oak forests in the Central Zagros

Oak forests in the Zagros region are under continuous anthropogenic disturbances, leading to a decline in their extent and deterioration in the qualitative structure of the stands. Field-based models can predict shifts in forest structure indices due to disturbance long before forest cover is depleted. This study examines the effects of anthropogenic land uses on key structure indices of oak forests in the Central Zagros.

Forest stand structure indices in five land uses were measured by field survey on 78 sample plots in 11 forests over an area of about 24,000 ha in the rural area of Mashayekh, Central Zagros. Depending on the area, six to nine systematically randomly designated one-hectare plots were measured at the same distance in each forest. In addition, one-meter square plots were sampled for non-tree cover. One-way ANOVA and General Linear Models were used to determine discriminant indices and analyze the effects of anthropogenic disturbance, respectively.

Except for oak density, structural indices differed significantly among the studied stands. This study did not find any differences in cover, number of trees, and non-tree species under different levels of disturbance (protection and destruction). The average number of shoots per stool decreased with increasing understory cultivation and proximity to villages, while the average diameter of shoots increased, indicating that farmers were removing young trees and shoots. Different levels of grazing and distance from the road had no effect on the structural index of the forest. The implementation of the conservation program in two forests in Kavand and Doto led only to an increase in the average height of trees and not to any other structural improvement.

Long before causing a reduction in forest area or a decrease in tree density, the effects of anthropogenic disturbance on the structure of coppiced woodlands were manifested in the diameter of trees and the number of shoots-per-stool. In addition, the decadal protection of the forest stands led to an increase in the average height of the trees. This suggests that the impact of anthropogenic disturbance on forest structure precedes the depletion of forest cover. Therefore, it is necessary to consider these early indicators in forest management plans.