Species diversity is one of the most important indices was used to evaluate the sustainability of forest communities. In this study, the effect of complete protection (non-grazed) on plant species diversity was investigated in Bagh-e- Shadi Forest (Irano-Turanian Forest), Yazd province, central of Iran. For this purpose, sampling designed the randomized-systematic method with rectangular plots that were 40×50 meters in the 100×200 Net, Shrub species in the 100 square (10×10 meter) and Herb species in the 25m2 (5×5 meter) were sampled in the center of net inventory. In the total 60 sample plots (30 plots in the grazed and 30 plots in the non-grazed area) were sampled. In every sample plot recorded plant species and number of this plant. In order to analyze biodiversity indicators of Shannon-Wiener and Simpson as well as Margaleff evenness indices was applied. Results indicated that Gramineae, Compositae, Labiatae, Rosacae and Anacariaceae families have the highest number of species. Pistacia atlantica and Amygdalus communis were the most dominant woody plants for class of tree and Acantholimon sp. and Astragalus spp were the most dominant Shrub plants, respectively. Bromus tectorum and poa sinacia were dominant herbaceous species. Herbaceous layer had the highest richness, evenness and diversity. The differences between biodiversity indexes in the two areas were statistically significant in the tree, shrub and herbaceous layer. So the grazed and non-grazed increase tree, shrub and herbaceous diversity in Irano-Turanian forest, and complete protection (non-grazed) area have higher plant diversity compered the grazed region. Therefore, prevention of livestock grazing and irregular tree cutting in the degraded forest stands can be suggested as a suitable approach for natural restoration and increasing plant diversity.
