Fig. 2. Importance of plant functional groups in mini-patches at various
steady stages
Note: A, B, C, D, and E represent Gramineae–Kobresia meadow and
Gramineae–K. humilis to K. pygmaea transitional
meadow; healthy and thickening mattic epipedon in K. pygmaeameadow; cracking mattic epipedon in K. pygmaea meadow; eroded
mattic epipedon in K. pygmaea meadow and black-soil beach meadow,
respectively; a, b, c, d represent significance among different steady
stages.
The niche breadths of Gramineae, Cyperaceae, Leguminosae, and forbs
decreased as grazing intensity increased. This succession process could
also be divided into three periods. The first period was represented by
“A” and “B” meadow in which the niche breadths of Gramineae,
Cyperaceae, Leguminosae, and forbs were highest among all of the steady
stages. The second period was the
first regime shift point in which the niche breadth of Gramineae was
superseded by the niche breadth of Cyperaceae (see the “C” and “D”
steady stages). The third stage was the “E” stage in which the niche
breadths of Gramineae, Cyperaceae, Leguminosae, and forbs all greatly
decreased. In this process we also found the shrub seemed to increase
with grazing intensity increasing, that was not because the steady stage
underwent to the shrub meadows, just because the shrub which always used
as the summer pasture had more severe degree degeneration than the
alpine meadow used as the winter pasture (Fig. 3).
Overall,
our findings showed that the steady stage of alpine meadows maintained
the highest plant community primary production relatively constantly
under no grazing intensity and under light grazing intensity. When
alpine meadows were disturbed by a high grazing intensity, their total
yield remained stable but the coefficient of variation in yields
increased, which may indicate that change the structure of the plant
community changed under these conditions to maintain a steady total
biomass.