Determining the Contribution of Species Diversity of Vegetation to Different Intensities of Grazing Using SHE Analysis1

Livestock graze is one of the significant factors affecting the structure and dynamicity of rangeland ecosystems. That is why analyzing the impact of grazing on the species diveristy indice of the vegetation appears essential. Species diversity is composed of two interrelated indices: species richness and species evenness. Evenness relates to the distribution of the species in the environment and richness stands for the number of species in the sampling plots. Considering the critical role of both indices in determining the species diversity, the ecologists are interested in analyzing the diversity indice in a way that the contribution of each of these two indices in determining the species diversity is identified. The new approach designed for so doing is called SHE Analysis. To determine the role of richness and evenness indices in diversity index in the rangelands of Nodooshan region in Yazd Province, a total of 108 random- systematic plots of 2 m2 were laid out in line with the grazing gradient. In each plot, the percentage of canopy cover by species was estimated and then the richness and evenness were counted in grazing gradient (i.e., light, moderate and heavy grazing). The results revealed that, in all three grazing intensities in the gradient, the richness indice (LnS) played a more significant role in determining the diversity compared to the evenness indice (LnE).