Analysis of the Relationship between Species Diversity and Environmental Factors using Multivariate Analysis (Case Study: Sorkhdeh Rangelands of Semnan, Iran)

Species diversity is important concept in ecology and vegetation management. Protection of biodiversity and applying necessary activities for protection is one of the basic roles in modern societies. To reach to the mentioned goals, this research was performed in Sorkhdeh rangelands of Semnan province to investigate species diversity and affecting environmental factors. Totally, 230 plots established at the study area for sampling of vegetation and 29 environmental factors including climatic, topographic and edaphic factors were measured. Also, 15 vegetation types were recognized in the study area. Shanon-Weaner and Simpson diversity, Paylo evenness, Menhinick and Margalef richness indices were determined for all vegetation types using PAST software. DCA analysis showed gradient length is >3, therefore RDA analysis was appropriate to show the effect of environmental factors on the studied indices. Result of multivariate analysis showed that environmental factors had significant effect on the studied indices (P = 0.001, F = 3.233). Tow diversity indices (Shanon-Weaner and Simpson) were highly correlated with elevation, average of annual and seasonal rainfall and average of annual and seasonal relative humidity. Evenness indicator showed strong relationship with nitrogen and clay percentage. Richness indices (Menhinick and Margalef) had significant correlation with aspect, sand, CaCO3 and K of the soil. The studied indices showed no significant correlation with P and pH of soil. Results of analysis showed that 25.6% of variations in plant diversity; evenness and richness could be interoperated by environmental factors.