2.1 | Site description
The research plots were carried out in Qinghai Haibei alpine grassland ecosystem national observation and research station (Haibei Station, 37°39.876′ N, 101°10.748′ E), with an altitude of 3227.6 m. The sample plot is a winter pasture. The grazing period is from the beginning of October to the end of April of the following year, so the plant growth season is not disturbed by grazing. It belongs to typical plateau continental climate, the annual average precipitation and temperature are 560 mm and -1.7 °C, respectively. The precipitation from May to September during the growing season accounts for about 80% of the total annual precipitation.
The plant growing season has rain and heat at the same time, and soil type is alpine meadow soil. Since the 1980s, the three pastures and grazing channel grasslands have carried relatively stable grazing intensity, and formed obvious grazing gradients in terms of surface characteristics and species composition (Table 1, Fig. 1).
The native vegetation of the alpine meadow in this area is cold mesophytic, wet mesophytic and dry mesophytic perennial Kobresia as a constructive vegetation type. The community structure is relatively complex and the species composition is rich. There are about 30 species m-2, and the dominant species are mainly includingKobresia humilis, K. pygmaea, Elymus nutants, Festuca rubra, Poa annua, Oxytripis ochrocephala, Gentiana straminea, Potentilla nivea, Saussurea superba, Thermopsis lanceolate . Coexisting species includingStipa aliena, Poa annua, Kobresia humilis, Kobresia pygmaea, Oxytropis ochrocephala, Thermopsis lanceolata, Saussurea superba, Leontopodium nanum, Gentiana straminea, Potentilla nivea, Anaphalis lactea Maxim. Among them, Stipa aliena and Poa annuabelong to Gramineae, Kobresia humilis and Kobresia pygmaeabelong to Cyperaceae, Oxytropis ochrocephala and Thermopsis lanceolata belong to Leguminous, Saussurea superba, Leontopodium nanum, Gentiana straminea, Potentilla nivea and Anaphalis lactea Maxim belong to Forb group.