Relationships between Environmental Factors and Plant Communities in Enclosure Rangelands (Case study: Gonbad, Hamadan)

Exclusion and not using of rangeland in the long term affects the composition and homogeneity of vegetation and consequently leads to the improvement of plants status. In this study, the characteristics and structural changes of the rangeland of Gonbad, Hamadan province, Iran, in 2014 (after 20 years of enclosure) were evaluated using Braun-Blanquet plot, Phytosociology and multivariate analysis by the software PC-Ord5. According to clustering diagram and Indicator Species Analysis, it was found that the studied region had 10 vegetation types and 17 Indicator Species. Detrended Correspondence Analysis (DCA) showed that in the first axis the variables: stone and gravel percentage, Electrical Conductivity (EC), clay, and organic carbon were important and in the second axis canopy cover of grasses, total canopy cover, and pH were important. Principal Component Analysis (PCA) confirmed the relationship between plant communities and environmental factors in the enclosure region. It was found that there are correlations between the echo logical units and the factors: stone and gravel (0.25), clay (-0.26), sand (0.28), silt (0.38), slope (-0.36), total neutralizing value (0.34), and plant species indicators that resulted to the separation of the units. The results showed that in the long-term enclosure, plant communities tend towards a uniform and homogeneous composition and consequently led to the improvement of the rangeland vegetation conditions. Therefore the density, composition and the class I plant species have increased.