Soil Factors Affecting the Distribution of Plant Species at Different Intensities of Grazing at Kharab-e-Sanji Rangelands in Urmia

Evaluation of quantitative and qualitative changes in vegetation and soil during the grazing gradient is necessary in order to recognize the regressive changes in the vegetation and soil, and consequently to improve the range management practices. The present study was carried out with the purpose of identifying soil factors affecting the vegetation distribution with various grazing intensities in rangelands of Kharab-e-Sanji in Urmia. Systematic random sampling was conducted in late June to collect samples in three regions with low, medium, and high grazing intensities. In this regard, in each region six 100m transects and along each transect, ten 1 meters squared plots were placed. Moreover, the species present in each plot were identified and the vegetation cover percentage, density and frequency of each species were recorded. Furthermore, the samples were taken from 0-30cm depth of soil surface within each plot and the bulk density, relative humidity, EC, pH, organic matter, carbon, nitrogen, particulate organic matter and soil texture were measured. To determine the relationship between the soil factors and distribution of vegetation, the multivariate analysis (ordination) was used. Ordination of plant communities due to soil properties was performed using Canonical Correspondence Analyses (DCA¡ RDA¡ CCA). Ordination results showed that nitrogen factor in all the three grazing intensities was the most important factor influencing the distribution of species. Moreover, at the low grazing intensity level, relative humidity; with the moderate grazing intensity, bulk density and particulate nitrogen; and in the regions with the high grazing density, particulate nitrogen and particulate carbon were considered as the most important factor influencing the distribution of vegetation.