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