Comparison of crown competition and spatial pattern of Crataegus Azarolus L. in two situations of formation of type and accompanying species: Khoshkeroud and Perk forests of KhorramAbad

Abstract
Background and objectives: Competition between trees is a key factor affecting the development, structure, and dynamics of forests. Therefore, many ecologists have sought to quantify competition and related factors in the forest. The forests of Lorestan province with area 1,112,475 ha are part of the important ecosystems of the Middle Zagros, the main type of which is the Iranian oak. One of the important wood species of these forests is Hawthorn, which is often present as an accompanying species and in some areas as a pure forest. This research was conducted with the aim of comparing the crown competition and the spatial distribution pattern of Hawthorn in two forest type formation and companion species.
Materials and methods: In this study, two forest habitats Khoshkeroud (with a dominant type of hawthorn) and Perk (with a dominant type of oak) were studied in Khorramabad. After the Search in the forest and determining the areas where the density of Hawthorn species existed and the necessary conditions for calculating crown competition, areas with an area of about 45 ha were determined. In each of these forests with a relatively uniform distribution, the number of 45 Hawthorn stems that had crown overlap with at least one neighbor were identified as central trees. To identify competing trees, the crown overlap method was used, and to quantify the level of competition, the ratio of the crown size of the central tree to the neighbors was used, and to calculate the spatial patterns, the uniform angle index was used. Then information including the distance and azimuth of the neighbors, the height of the central trees, and the size of the diameters of the crowns of the reference trees and competitors were measured. Due to the non-normal distribution of the data based on the Kolmogorov-Smirnov test, the non-parametric Mann-Whitney test was used to compare the means.
Results: Due to the different conditions of the two habitats of Khoshkeroud and Perk, there is an obvious difference in the types and diversity of species in these habitats. In addition, the average distance to effective neighbors in the competition shows a big difference, if other characteristics do not have a big difference. The number of influential neighbors in the BDC index for the Khoshkeroud habitat reaches four neighbors, while in the Perk habitat; there are at most three neighbors with overlapping crowns for the central trees. Meanwhile, more than 80% of the neighbors in the Perk habitat are species other than Hawthorn, while in the Khoshkeroud habitat, other species have allocated a small percentage. In addition to the different admixture, the results of the uniform angle index also indicate the different spatial distribution pattern of Hawthorn species in the two investigated habitats. Despite the difference in admixture and spatial distribution, there is no significant difference between the results of the competition index on the reference trees.
Conclusion: Considering that the Hawthorn genus has been suggested for afforestation of degraded areas in Zagros due to its features such as edible fruit and its ability to be used as a precursor and nurse species, the results of this research can be useful in the field of afforestation and forest cultivation.