Comparison between plant species richness and diversity indices along different grazing gradients in southern warm-arid rangelands of Fars

Biodiversity of rangeland ecosystems directly affects plant species diversity and vegetationcharacteristics, which contributed to ecosystem stability against environmental and biological disturbances. Heavy livestock grazing is a destructive factor lead to elimination sensitive species and reduction of biological diversity. Grazing, affects the rangeland ecosystems by changing the frequency of key plant species which guarantee stability and ecosystem performances. This study has been conducted to investigate the effect of three different grazing intensities on the diversity and richness of plant species in the arid rangelands of Khonj area in Fars Province. Three sites include light, moderate and heavy grazing intensity were selected and sampling was performed using 90 plots (1 m2) along 18 transects. The list of species, canopy coverage and number of individuals per species were recorded for each sampling unit. To evaluating diversity and richness of plant species, Margalef and Menhing richness indices, and Simpson, Shannon and Hill N1 diversity indices were calculated. SPSS software was applied for data analysis and comparison of different indices of diversity and richness among study sites was performed by Tukey test. The results of Margalef richness index showed that there was no significant difference between light and moderate grazing sites, statistically Nevertheless, heavy grazing intensity had significantly different in comparison to light and moderate grazing ones. On theother hand, no significant difference observed among Menhing richness index of diff erent grazing categories (p<0.05). Results of calculations of diversity indices, for all of three Simpson, Shannon and Hill N1 showed that there were not significant difference (p<0.05) between light and moderate grazing intensities. However sever grazing sites were significantly different from two other ones. In general, in arid rangelands such as the studied sites, heavy grazing contributes to reduction in richness and diversity of plant species and affects the ecosystem stability and should be noticed by range managers.