Sampling
was performed in August in 2012-2013 along 100-m transects within every
sampling site that each contained eight evenly distributed 50 cm × 50 cm
quadrats. The plant community was divided into five functional groups:
Gramineae, Cyperaceae, forbs,
Leguminosae, and shrubs. In each quadrat, we recorded the coverage and
dry aboveground biomass of plant functional groups, the thickness of the
mattic epipedon, and the slope aspect, position, and angle. We also
noted the number of livestock grazing at each sampling site
(Lin, 2017).
1.2
Sample collection and preparation
The plant samples were placed in an envelope after collection and
subsequently baked at 60–80°C for 48 to 72 h to a constant weight,
which was then recorded.
An unstructured questionnaire was used to determine the area of the
pasture, the type and quantity of grazing livestock, and the grazing
time. According to the conversion ratio of 4 sheep equal to 1 yak, the
stocking capacity of the pasture was calculated (Xu, 1994), and the
stocking capacity was divided into 5 grades. The average grazing
intensities per grazing season were 0.00 sheep/ha for more than 1
year,
less than 3.65
sheep/ha,
3.65 to 7.50
sheep/ha,
8.25 to 13.00 sheep/ha, and more than 13.00 sheep/ha. In most of the
time when the alpine meadow degradation into Black-soil beach meadow
would become to no grazing in the pasture, so we investigated the
possible grazing intensity used in the past as the average grazing
intensity of the pasture.
1.3
Data analysis
The plant functional group characteristics of mini-patches were
determined by calculating the average coverage, dry aboveground biomass,
and importance value of each plant functional group in each mini-patch
(Lin, 2017). The data collected from every mini-patch were also used to
calculate the niche breadths of plant functional groups based on the
Levins index (Lin, 2017), and mean and standard error on the biomass
aboveground, the importance and the niche breadth were calculated by
performing a one-way analysis of variance in SPSS Statistics Software
(19.0). The probability of each mini-patch reaching a certain
multi-steady stage was calculated as the ratio of the environmental
characteristics in
a
single
quadrat
to the total in all quadrats. The coupling between the plant functional
groups of all mini-patch and each environmental factor was calculated
via a redundancy analysis (RDA) in R3.6.1 software.
2
Results