Investigating the relationship between range condition of plant types and species diversity

Species diversity is one of the characteristics indicating changes in rangelands. In this regard, the relationship between range condition as a result of managerial measures and species diversity was investigated. Spearman correlation test and one-way analysis of variance were used for testing the variations of Shannon-Wiener diversity index values of plant types with their conditions. Then, by plotting rank-frequency curves and applying the frequency distribution models, the vegetation types with higher diversity were identified and their relationship with range condition was interpreted. The results showed that Shannon-Wiener diversity index had no significant correlation with range condition. Range condition had no significant effect on the amount of diversity and all three categories of condition (good, average, poor) were classified according to the mentioned index. In general, no significant trend was observed between range condition and amount of diversity. The results suggest that the high values of numerical indices of diversity are not the reason for the improvement of range condition, but their species composition and abundance should also be investigated. Drawing rank-frequency curves and matching the frequency distribution models showed that plant types with good and moderate condition, species with less abundance, were less frequently observed and its curve had a mild slope than those with poor condition, so their diversity was higher. In most plant types, the geometric series model was consistent, indicating low plant diversity and poor range condition. In general, concerning the degree of conformity of the results of the frequency distribution models with the condition of the plant types, the results emphasize the need to pay attention to the parametric indices of species diversity in rangeland health assessment.