Effect of elevation on distribution functions of diameter, height, and canopy area of Caucasian oak

Implementation of economic and non-economic functions of forests requires efficient planning and management, which requires reliable and dedicated information from forest resources, and the optimal information obtained from the details of forest stands parameters. The probability distribution models of various tree parameters provide helpful information about the complex interactions between trees and their environment and accurately describe tree growth processes. This study aims to develop suitable distribution models for the diameter, height, and canopy area of Caucasian oak trees in the Arasbaran forest and evaluate the effect of elevation on these models.

A selective sampling plot (with 100 × 100 meters dimensions) was designed in Caucasian oak stands located in Arasbaran Forest at 38 degrees and 57 minutes of north latitude to 47 degrees and 17 minutes of east longitude at three elevations including 1200-1300, 1300-1400, and 1500-1600 meter above sea level in three replications, which was the most present for the Caucasian oak tree. The diameter at breast height, the total height, and the two diameters of all trees’ canopy were measured inside each sampling plot. Quantitative statistics and comparison of means were analyzed using ANOVA and Tukey tests in SPSS 16 software and various statistical distributions were performed in Easyfit 5.5 software. The Kolmogorov-Smirnov fit goodness test was evaluated and reported at 95% and 99% confidence levels.

The results showed that the best function for the diameter distribution at the first, second, and third elevations were Beta, Normal, and Beta distributions, respectively. Fit goodness test for tree height showed that the trees had Weibull distribution at the first elevation and Beta distribution at the second and third elevations. The canopy area of the trees showed that the Weibull distributions at the first elevation and the Beta distribution at the second and third elevations were the most suitable models to show the probability distribution of this parameter. In addition, the diameter of trees in the three elevations does not have a significant difference. In comparison, the height of trees in more elevated areas was significantly higher, and the canopy of trees was strongly affected by the increase in elevation and showed a significant difference in all elevations (p≤ 0.05).

Based on the results of the present study, elevation is an influential factor in the height and canopy area of Caucasian oak trees. It is a factor in the diversity of probability distribution functions of diameter, height, and canopy area of Caucasian oak trees in the Arasbarn forest, which can be caused by the effect of various elevations on the environmental factors such as weather, soil, humidity and also the physiological characteristics of trees. This information provides reliable results for managers and decision-makers of Arasbaran forests.