COMPARING PERFORMANCE OF FIXED AND VARIABLE AREA SAMPLING PLOTS IN IRANIAN SUB-HUMID FORESTS.

In this study, two inventory methods, including use of plots with 300 m2 fixed-area and Relascope with variable-area plots were compared to evaluate biodiversity, quantitative and qualitative characteristics of Arasbaran forest stands in the North West of Iran. For this purpose, 58 sample plots were specified using 100 m×100 m regular randomized grid and tree characteristics were measured by two inventory methods. In each plot, the quantitative characteristics including diameter at breast height (DBH), basal area at breast height, tree number (density) and volume per hectare, sampling time and the qualitative characteristics such as percentage of species composition, health and origin of trees were recorded. Species richness, Shannon Weiner diversity and Simpson evenness indices were calculated for each sample plot. Independent t-test was applied for comparing the means of quantitative characteristics and biodiversity indices between the two methods. The results indicated that the quantitative characteristics are significantly different between two methods, whereas, no significant differences were observed in richness, biodiversity indices and qualitative characteristics. Average inventory duration in the fixed-area plot method (706.10 s) was considerably higher than that of the variable-area plots method with Relascope (485.91 s). The square of sampling error by inventory time (T × E%²) index was used to evaluate the two methods precisely. This coefficient was less for volume per hectare and basal area at breast height per hectare in the variable-area plot method. [ABSTRACT FROM AUTHOR]