Effect of topographic factors on species diversity indices in elevation graient of Ghezel Ozen to high altitude rangelands of Kowsar County, Ardabil province

In this study, changes in species diversity, richness, evenness and dominance of rangeland plants were investigated using Shannon-Wiener, Simpson, Menhinick, Margalef and Hill indices in the elevation gradient from the near Ghezel Ozen river rangelands to the highlands of Kosar county in Ardabil province. In this elevation gradient, eight habitats were selected from the near of Qezel Ozen River to the highlands and three 100-meter transects were located in each habitat and then samples were collected from ten 1 or 25 m2 (only on site two) along each transect. Species were collected from each plot and then identified and their plant functional types were determined and, in each plot, canopy cover percentage and density of species were recorded. Diversity, richness, evenness indices and dominance of species were calculated at the total level of plants and one-way anova and Duncanchr('39')s test were used to compare the differences between the sites. The results showed that changes in elevation, slope and aspect had a significant effect on diversity, richness, evenness indices and dominance at the total level of plants, but at the level of plant functional types, elevation on forbs and grasses was not significant, but in shrubs, except Menhinick richness index, which was significant, the effect of slope and aspect had fluctuations. The results of comparing the values of the indices showed that the highest dominance was observed in the elevation class of 937-965 m and the indices of diversity, richness and evenness were observed in the elevation class of 1635-1677 m for total plants. The highest dominance was observed in slope class 30-45%, diversity and evenness indices were observed in 45-60% class and richness in 0-15% class. Moreover, the highest dominance was observed in western aspect, and diversity, richness and evenness indices were calculated in northeastern aspect for total plants. In general, it can be concluded that due to the severity of the use of low altitude rangelands, the diversity and richness of the species have decreased, while in higher altitudes, due to reduced livestock populations and improved climatic conditions, indices have mostly increased. Therefore, according to the results of this study, changes in the indices of species diversity, richness and evenness can be used as a criterion to improve the rangelands condition in the study area, as well as to adopt appropriate management plans.