Evaluation of species diversity indices in Chaharbagh rangelands of Golestan province

This study was conducted to study species diversity changes in Chaharbagh mountain rangelands of Golestan province in five different managed sites, including non-grazing (enclosure), intermediate grazing (key), and critical (village vicinity, watering point, and pen area). Numerical and parametric diversity indexes were calculated by collecting vegetation data. One-way ANOVA results showed that exclusion and key sites were better for the Shannon diversity index (2.6 and 2.1, respectively) than critical sites; however, no differences were found in the Margalef richness index. A higher ranking of diversity site of the key site indicates that it is more diverse than the restricted site. By fitting the frequency distribution models, it was determined that the exclusion and key site were related to the log series models (stable communities), and the critical sites were related to the geometric series model (unstable communities) at the 0.05 level. Frequency-rank curve plotting indicated that high grazing sites had rare and dominant species with high numbers indicating the effect of grazing pressure; however, moderate sites and high grazing sites have high evenness. Overall, the results showed that moderate grazing preserved the vegetation diversity, and exclusion had no significant effect on increasing vegetation diversity in rangelands. This result confirms the need to pay attention to moderate grazing in the field. Among the critical sites, the village privacy site is in a worse situation, and livestock grazing intensity should be reduced due to the proven effective role of medium grazing in the region to rehabilitate sites with high grazing intensity, especially in rural areas. Reducing livestock density in critical areas by increasing the number of water sources and rest areas in the field will be one of the methods to help reduce damage to plant diversity of critical sites.