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.