Effect of grazing on plant community composition along the gradient of the precipitation in steppe and semi-steppe rangelands

This study inspected the effects of grazing on the plant community composition along a gradient of rainfall (250-1423mm) in arid and semi-arid rangelands of Isfahan and Chaharmahal & Bakhtiyari province; in response to the question whether grazing creates more changes in plant community composition in rangelands with either low or more rainfall. Data on vegetation cover of 41 regions were gathered from previous studies and classified into light and heavy grazing intensity. Detrended Coerspondnace Analyze (DCA) was used to investigate changes in plant community composition. In order to test the interactive effect of grazing and rainfall, the scores on the Axis1 DCA introduced in General linear model as the response variable along with grazing, rainfall and their interaction as the fixed variables. The results of DCA showed that grazing by large domestic animals was the main responsible for the changes in plant community composition. Furthermore, the result of GLM revealed that grazing had the significant effect on plant community composition (p<0/05) and there was no the interaction effect of grazing & rainfall (p>0/05). The results confirmed that the hypothesis that claimed grazing by large herbivores creates more changes in plant community composition in the rangelands with lower amount of rainfall might be rejected and the same changes might be occurred in both the rangelands with low and high amount of rainfall.