Comparison of five distance sampling methods for estimating quantitative characteristics of Zagros Forests

Distance sampling methods are extensively used for forests management of Zagros region of Iran. In the present study، estimation of quantitative characteristics of sampling methods، including individual، nearest neighbor، second nearest neighbor، compound and joint point، were studied and compared. The individual sampling method was examined، using the estimators of Morisita، Byth & Ripley and Cottam et al. and the nearest neighbor method was assessed، using the estimators of Byth & Ripley and two predictors of Cottam & Curtis1 and Cottam & Curtis2. Location of total trees and shrubs of a 53 hectare forest stand at Ardal city of Chaharmahal and Bakhtiari Province was recorded. Having the actual trees density and canopy cover percentage، as well as their estimated values، the bias of each replication was obtained. Difference between the bias and the actual values (for bias test) by one-sample t-test method and analysis of variance by Games Howell test، were studied. The results showed that the differences between the distance sampling methods in respect to mean trees density per hectare were significant، except for the nearest neighbor method، using the Cottam & Curtis1 estimator، which was not significant، whereas in respect to mean canopy cover percentage، the differences were significant، except for the second-nearest neighbor and the combined methods. According to the results of this study، it is suggested to use the Cottam & Curtis1 method for estimating the density and to use the compound sampling and the second nearest neighbor methods for estimating the canopy cover percentage.