Oriental beech (Fagus orientalis Lipsky) is one of the most important commercial tree species in the Hyrcanian region. This species is known to suffer from strong intra- and interspecific competition for above- and below-ground resources in temperate mixed stands. In the present study, a total of 26 beech trees and their surroundings trees as well as stand characteristics were evaluated for determining the interactions between them and competition index (CI) in mixed beech stand. The results showed that in mixed beech stand, there were positive correlation between CI and crown ratio and height/diameter (HD) ratio of target beech trees, but negatively correlated to crown length, crown width, crown area, and crown volume. Total height, DBH, and bole of target beech trees were decreased with increasing CI. Regression analysis showed that CI had positive significant correlation with functional group of forb richness. The target beech trees characteristics including HD ratio and crown ratio showed contrasting responses to some variables which were related to their known specific ecological strategies. This study demonstrates the different responses of target beech trees in overstory to competition in neighborhood conditions which are an important factor in retaining species coexistence and planning mixtures in temperate broad-leaved forests.
Keywords: Broad-leaved tree; Competition index; Temperate forest; Tree architecture.