Investigating the effect of soil and topographical factors on variations of plant species diversity (case study: Sabzkesheh summer rangeland at the Mohammad-abad Katool watershed, Golestan province)

Studying plant species diversity is vital for knowing and better understanding the relationship between ecological factors and proper management principles. The existence of higher plant species diversity is an indicator of appropriate environmental conditions for deploying diverse species, which in turn lead to the sustainability of plant community in that ecosystem. The goal of current research is investigating the most important factors in the variation of the plant species in Sabzkesh summer rangelands located in Golestan province. In the first step, the data about vegetation and soil respectively in the indicator-regions were collected by random-systematic and Zigzag sampling method. After gathering data, diversity, evenness and richness calculated by using of Shannon Wiener and Pailo indices. In addition, in this stage counting plant species number per area unit was done by means of PAST software. Then, by PC-ORD 5 software major ecological groups and the most effective edaphic and topographical factors in the variation of the ecological groups of species diversity were determined through clustering and ordination analysis (Principal Component Analysis).The result showed that diversity, evenness and richness indices provided valuable information about vegetation response to the environmental variations. In this regard, factors such as elevation, pH, N, P and clay of soil had the most important role in the variation of plant species diversity of ecological groups in the studied region. Moreover, in the region under study plant-distribution-pattern with rank-abundance model indicated that the plant species of the region were compatible with Log-normal pattern therefore, the plant species in the studied region almost were out of stress.