Efficiency of numerical and parametrical indices to determine biodiversity in mountain rangelands

Among various numeric and parametrical indices of plant species diversity, numerical ones may not provide a comprehensive description about abundance and richness of species, so application of parametric indices in addition to numerical ones would be a better approach to investigate on plant communities. For this purpose, indices of species richness, evenness and diversity were calculated for each of four plant communities of mountain rangelands in northwest of Iran. Then abundance–diversity and species ranking curves were plotted for each plant community and the best models for abundance distribution of diversity were fitted by chi-square goodness of fit test and the best representative one was selected. The results showed that there are significant differences in terms of numerical diversity among the communities and each of the indices showed higher value of diversity in every community so it was so difficult to decide on the community with the highest species diversity. Also the difficulty to explain the plotted curves species diversity and abundance ranking was obvious so the curves were not efficient to identify the distribution of species richness. So determination of species diversity by models of abundance distribution and adjustment of species distribution with expected values of distribution for plant species was implemented. The results showed the log-normal model as the best one for all locations with moderate intensity of grazing. Also the intermediate disturbance hypothesis (IDH) was supported by this model. As overall result species richness, evenness and diversity increases in intermediate levels of disturbance (moderate grazing).