Effects of grazing on the relationship between some vegetation and soil phsico-chemical properties (case study: Vaz watershed)

In general, it could be supposed that the effects of soil characteristic on vegetation is different with and without a disturbance (e.g. grazing). This study aimed to evaluate the impacts of edaphic factors on vegetation distribution with and without grazing in Vaz watershed, Mazanderan province. In each of grazed and ungrazed sites, 28 one square meter plots along 4 transects (two parallel and two perpendicular to the general slope) were established. In each plot, soil was sampled within a depth of 0-30cm and the percentage covers of all plant species were measured. Electrical conductivity, pH, organic matter content, soil density, nitrogen content, relative humidity and porosity of all soil samples were measured. Redundacy analysis (RDA) was applied to correlate edaphic factors and vegetation in grazed and ungrazed sites, separately using CANOCO. The results showed that in grazed sites, soil electrical conductivity and nitrogen contents and in ungrazed area soil electrical conductivity and carbon content had significant effect on the plant distribution. Since eigenvalues of PCA axes were very low in grazed sites, it could be indirectly inferred that in grazed sites the distribution of plants was governed with grazing rather than with soil factors.