Suitable Species Diversity Abundance Model in Three Grazing Intensities in Dizaj Batchi Rangelands of West Azerbaijan

Species diversity is one of the important characteristics shows rangeland ecosystems changes, which is already under effects of management practices. Thus, this research was conducted to study species diversity variation and assess suitable distributive abundance model in three rangeland sites in West Azerbaijan. These sites were almost similar in environmental properties and differ in view point of grazing intensity (light, moderate and heavy intensities). After selecting sampling areas in each of the sites, species cover were recorded in 60, one square meter quadrates with 10 meter far from each other which established along 100 meter transects in sites and then richness, evenness and diversity (heterogeneity) indices were calculated. Thus, rank-abundance curves were plotted and four distribution models such as log-normal, geometric, log-series and Brocken stick were fitted to each of these sites and then best model was selected in 0.05 level of confidence. Means comparison test showed that richness, evenness and heterogeneity indices have significant differences (P<0.01) in sites. Highest diversity is observed in the light grazing intensity site and lowest diversity is in heavy grazing intensity site. Species rank-abundance curves point out that low-abundance species are seen lower in light grazing site and its curve have gentler slope than moderate and high grazing intensity sites thus its diversity is higher. There is lowest species number in high grazing intensity site and evenness is lowest too due to its high number of rare and dominant species. Log-normal model was fitted to light site implying on sustainable community and high grazing intensity site is fitted with geometric model which point out on distractive communities with low diversity. Overall results showed that implementing light grazing can protect species diversity and heavy intensity declines species diversity that this shows the need considering of management on implementing light grazing intensity in the rangeland.