Journal of Rangeland Science (JRS) Overgrazing is a Critical Factor Affecting Plant Diversity in Nowa-Mountain Rangeland, West of Iran Volume 11 (2021) Issue 2, April 2021 2023 11 17 Overgrazing is a Critical Factor Affecting Plant Diversity in Nowa-Mountain Rangeland, West of Iran EN Saeed Mahmoudi Former Student in Agroecology, Department of Production Engineering and Plant Genetics, Razi University 0000-0003-4271-5429 Mahmud Khoramivafa Agronomy and Plant Breeding, Razi University, Kermanshah, Iran Moslem Hadidi Academic Center for Education, Cultural, and Research, Kermanshah, Iran Nastaran Jalilian Forests and Rangelands Research Department, Kermanshah Agricultural and Natural Resources Research and Education Center, (AREEO), Kermanshah, Iran. AliReza Bagheri Department of Production Engineering and Plant Genetics, Razi University Journal Article 2023 11 17 In western Iran, mountainous rangelands provide significant resources for livestock productions. Many ecosystems that are of high environmental and economic value are threatened by climate change and social economic pressures. This is especially important for semi-arid rangelands, which have a multifunctional system. Quantifying the direct and indirect effects of grazing disturbance on plant biodiversity in the semi-arid mountainous rangelands can provide sight into the appropriate measures to restore degraded rangelands and conserve biodiversity. Here, the effects of different levels of grazing intensity (Light Grazing (LG), Moderate Grazing (MG), and Heavy Grazing (HG)) on plant biodiversity were examined in Nava-mountain rangeland in Kermanshah Province, Western Iran, in 2016. The results showed that increasing grazing intensity led to a decrease in species richness, Margalef's richness index, and Shannon-Wiener index (p <0.05). Stepwise regression analysis was used to investigate the effect of grazing intensity as (independent variables) on species diversity and richness as (dependent variable). The estimates parameter were significant (p <0.01) for species richness, Margalef's richness and Shannon-Wiener indices in the different levels of grazing intensity. In overall, grazing intensity explained 47%, 47% and 50% of the variation for species richness, Margalef's richness, and Shannon-Wiener indices, respectively. In addition, species richness and diversity were affected in response to grazing disturbance intensity and reducing grazing pressure can contribute to maintaining relatively high species diversity in Nowa-mountain rangeland.