مجله جنگل ایران (May 2019)
Crown Ration Modelling of Quercus Brantii Trees in Dalab Forests of Ilam
Abstract
Crown ratio is the ratio of live crown length to the tree height. Crown ratio is a useful indicator for tree vigor, wood quality, wind firmness, stand density. It is also useful in managing many non-timber resources including wildlife habitat and recreation. The objective of the study was to model the crown ratio of oak trees and evaluate the obtained models in natural forests of Ilam province based on nonlinear regression method. For this purpose, 509 hectares of Dalab forests was selected in which 100 circular plots (1000 m2) were established as systematic-random sampling pattern with 200 m × 250m dimension. Within each sample plots, such variables as collar diameter, DBH, stem height, total height, crown area, crown length, crown diameter, basal area, tree Slenderness coefficient and crown ratio were measured. In total, 1113 oak trees were measured. Several nonlinear equations including logistics, Chapman Richard and exponential functions were used for crown ratio modelling of oak trees. These functions were evaluated in terms of coefficient of determination (R2), paired t-test, ME, RMSE, MEr and RMSEr. The results of accuracy statistics showed that all of the models are suitable. But results of R2 showed that exponential model perform better than other models. Also the results of t-test showed that there is no significant difference between of actual mean and estimated mean of crown ratio derived from exponential models. Therefore, exponential model was selected as the best one to estimate the crown ratio of oak trees in Dalab forests.
