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Iran is rich in plant diversity because of its large area and topographic and climatic variations. Knowing the types of vegetation is necessary in order to better manage rangelands. In this research, using Wittaker plot for three soil types of Gomishan, i.e. New Delta/Floodplains of Atrak, NeoCaspian and Loss Deposition, the species richness was investigated, and the relationship between species richness and other factors were established. In each soil type, soil samples were taken from 0- 50 cm depth and water table level was measured in soil profiles. The factors measured were pH, EC, SAR and soil texture.
It was found that there was not significant difference between slope of New Delta/Floodplains of Atrak and Neo-Caspian soils, so their species richness was equal. However, the difference between the two types and Loss Deposition was statistically significant. Based on empirical formula of Kovda, water table was calculated to be lower than the critical level in Loss Deposition, so it had no effect on soil salinity. However, it was at critical level in other two soil types and had significant effect on soil salinity as examined by multi-factor regression relationships. Only EC had a significant effect on species richness. An equation was developed to correlate the numbers of species per area unit with EC.