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Biodiversity is sensitive to climate change and human activity. Grazing management practices have a profound impact on plant species–genetic diversity in grassland and woodland communities. In this study, we explored the responses of species and genetic diversity to grazing in <i>Ulmus pumila</i> L. communities in the Hunshandak Sandy Land, analyzed the relationship between species and genetic diversity, and revealed the effects of climate factors on them. We found that the dominant species were <i>Spiraea trilobata</i>, <i>Caragana microphylla</i> and <i>Artemisia intramongolica</i> in <i>U. pumila</i> communities. Plant species richness in the banned grazing (BG) and seasonal grazing (SG) communities was significantly higher than that in the delayed grazing (DG) community. Plant Simpson’s diversity index showed a downward trend with increasing grazing duration. There was no difference in allelic richness in nuclear DNA (<i>nr</i>DNA) of U (<i>U. pumila</i>) and chloroplast DNA (<i>cp</i>DNA) of NU (other dominant species besides <i>U. pumila</i>) among grazing management types. The expected heterozygosity of U in <i>nr</i>DNA and <i>cp</i>DNA was significantly affected by grazing management, and the trend was BG > SG > DG. The genetic diversity of U was lower than that of NU. The genetic diversity characteristics of U in <i>cp</i>DNA were lower than those in <i>nr</i>DNA. The analysis of molecular variance (AMOVA) showed that 98.08% of the variation in U and 95.25% of the variation in NU was attributed within populations and the differences within grazing management types were 13.35% in U and 24.08% in NU (<i>p</i> < 0.001). The species richness of communities was positively correlated with the genetic diversity of U, NU and all dominant species (U + NU) in communities. The nineteen climatic variables together explained 94.24% and 79.08% of the total variation in U and NU genetic and species diversity. The mean temperature of the warmest quarter and temperature seasonality were the main factors affecting genetic diversity (<i>p</i> = 0.046; 0.01), while the maximum temperature of the warmest month was the main factor affecting species diversity (<i>p</i> = 0.05).