1.1 Study area and sampling method
We chose 109 sampling sites located in the autonomous prefectures of Haibei, Yushu, Guoluo, Haixi, and Hainan in China (Table 1). The meteorological characteristics of accumulated temperature above 0°C and accumulated precipitation over the growing season (mainly in May to September) were respectively 659.1 to 1228.4°C and 257.5 to 693.7 mm in all of the sampling sites. The vegetation type was classified as cold, wet-rainy tundra and alpine meadow according to the Comprehensive and Sequential Classification System of Grassland, and as alpine meadow according to the passive-active degradation process hypothesis (Cao et al., 2007). However, the sampled alpine meadows were in different steady stages (Cao et al., 2007), so we classified the corresponding sample sites according to the characteristics of their plant community, mattic epipedon, and topography into seven steady-stage types of meadow: Gramineae–Kobresiameadow, Gramineae–K.humilis toK. pygmaea transitional meadow, healthy mattic epipedon in K. pygmaea meadow, thickening mattic epipedon inK. pygmaeameadow, cracking mattic epipedon in K. pygmaea meadow, eroded mattic epipedon in K. pygmaea meadow, and black-soil beach meadow (Table 1). In view of the fact that the quantitative characteristics of plant communities are prone to reciprocating changes under different grazing intensity, so we divided the meadows into five categories, namely Gramineae–Kobresia meadow and Gramineae–K. humilis to K. pygmaea transitional meadow as “A”, healthy mattic epipedon in K. pygmaea meadow and thickening mattic epipedon in K. pygmaea meadow as “B”, cracking mattic epipedon in K. pygmaea meadow as “C”, eroded mattic epipedon in K. pygmaea meadow as “D”, and black-soil beach meadow as “E”.
Table 1. Latitude, longitude, and altitude of sampling sites and their stability stages