Analysing the effect of intraspecific competition on biometric attributes of Persian oak coppice trees using pair- and mark-correlation functions in Zagros forests

Background and objectives: Intraspecific competition between trees is a key interaction in shaping forest stands and makes analyzing the underlying ecological processes possible. This interaction may affect growth and spatial distribution of trees and result in a specific horizontal and vertical stand structure. For this reason, competition is known as one of the primary processes that influence population size, community structure and its diversity.  In order to understand competitive interactions of trees in forests, several methods have been developed to assess spatial scale of competition among individual trees and show the effect of competition their biometric characteristics. Therefore, this study was aimed to investigate the effect of intraspecific competition between Persian oak coppice trees on their biometric attributes in Zagros arid and semi-arid forests using spatial analysis.
Materials and methods: A 300 m × 300 m plot purely cover with Persian oaks was selected close to Yasuj city, Kohgiluye - BoyerAhmad province. The point map of all 1113 coppice trees was obtained by azimuth and distance technique. Kolmogorov-Smirnov test was primarily applied to investigate the difference between the distribution of coppice trees and homogeneous Poisson process. Spatial analysis of Persian oak coppice trees was then performed using pair correlation function g(r), O-ring function O(r), and mark correlation function k_mm(r). In mark correlation function, biometric characteristics of total height, crown height, diameter at root collar, crown mean diameter and area were implemented as marks. Moreover, Monte Carlo test was used to test the significance of the results. 
Results: Comparison with homogeneous Poisson process showed that the observed pattern of Persian oaks was significantly homogeneous (α=0.05). The results of pair correlation function g(r), and O-ring function revealed that there was intraspecific competition between Persian oak coppice trees that was significant up to spatial scale of 5 m (α=0.05).In addition, the results of mark correlation function demonstrated that total height, crown height, and diameter at root collar were very sensitive to intraspecific competition, while crown attributes (i.e. mean diameter and area) showed less sensitivity to competition.
Conclusion: In general, it was concluded that there were competitive interactions between Persian oaks in the studied pure stand that negatively affected their biometric characteristics. Competition between coppice trees negatively influenced their growth, although this negative interaction had less effect on crown attributes as the distance between coppice trees because of their low density (123.7 coppice trees ha^-1) reduced the crown competition.