Variation characteristics of plant communities in black soil shoals with different establishment years in the source area of the Yellow River

To evaluate the effects of vegetation restoration on the degraded "black soil beach" grassland in the source area of the Yellow River, we focused on the plant community characteristics of the "black soil beach" cultivated grasslands. Three cultivated Elymus nutans grasslands with different years since establishment (19, 15, 13) were selected in Maqin County, Qinghai Province. The extremely degraded "black soil beach" grassland was regarded as the control (CK) group. The results showed that: 1) the coverage of the gramineous forage and aboveground biomass in the three types of cultivated grasslands were significantly higher than those in CK (P < 0.05). However, the forbs coverage and biomass in the three types of cultivated grasslands were significantly lower than those in CK (P < 0.05). Establishing cultivated grasslands had obvious restoration effects on the extremely degraded black soil beach. 2) The coverage and biomass of gramineous forage and forbs in the grassland decreased significantly (P < 0.05) with the establishment years. The species richness, Simpson index, Shannon-Wiener index, and Pielou index of the plant community showed upward trends. 3) The principal component analysis (PCA) results showed that the dominance of Elymus nutans, Poa pratensis, and Koeleria macrantha in the plant community of the degraded black soil beach grassland improved after the establishment of cultivated grassland. In addition, the percentage of forbs dominated by A. nanschanica, A. sacrorum, and M. kokonorica significantly reduced. The research indicated that the cultivated grassland of the black soil beach in the source area of the Yellow River gradually changed to an ecological restoration grassland with an increase in the establishment time.