change of species diversity in vascular plants across ecological species groups

biodiversity plays a crucial role in stability and productivity of natural ecosystem. the main goal of this research was to classify ecological groups in steppe rangeland and investigate their relationships with plant diversity indices. therefore, fifty different land unit tracts (lut) were identified in khod-neuk basin, yazd province, iran, in 2010. vegetation and soil samples were taken in the lut’s representative stands. two way indicator species analysis (twinspan) method were used to identify ecological groups on the basis of presence-absence and canopy cover of plant species. the diversity indices including species richness, shannon-wiener evenness index, simpsons’ dominance index, shannon-wiener diversity index and simpsons’ diversity index were analyzed in vascular plants based on species canopy cover data. then the relationship between land unit distribution and diversity indices was assessed using canonical correspondence analysis (cca). results showed that ecological groups were quite different in terms of species composition and plant diversity indices. so that, ecological group 2 had the lowest dominance index and the highest scores of other indices and ecological groups 1 and 5 had the lowest richness and along with ecological group 3 had the lowest species evenness values. ecological group 5 had the lowest and the highest scores of shannon-weiner diversity index and simpsons’ dominance index respectively. the second group located in the mid altitudes with high saturation percentage and low na, lime and sodium adsorption ratio (sar) had the highest diversity indices. therefore, these groups are enough to delineate rangeland into ecological units which could be used for management purposes.