3.2 Mini-patch patterns in alpine meadows might drive
multi-steady stage coexistence
The
characteristics of different mini-patches in alpine meadow ecosystems
were isolated in space and yet related in function, which imbued
ecosystems with a self-organization ability that enabled them to
maintain overall stability while permitting small-scale variability. The
mini-patches of plant communities in alpine meadows are typically
clustered (Zhang et al., 2003), which results in the formation of
mosaics of patches in which each patch reflects a certain
micro-topography and micro-climate. According to island biogeography
theory, mini-patches can be thought of as “islands” and the
surrounding areas can be thought as “ocean” (MacArthur & Wilson,
1967). The stability of
this
plant mosaic system depends on the species turnover rate, patch area,
and distance between patches
(Bueno
& Peres, 2019). While grazing is invariably disturbs to alpine meadow
ecosystems, its effect on their patch mosaics is non-homogeneous, which
facilitates habitat fragmentation
(Jessica
et al., 2017). The plant mosaic
system therefore resulted in the formation of many types of plant
communities with a range of characteristics at different stages during
the degradation succession process, with these communities serving as
the natural germplasm necessary for the recovery of damaged meadows.
Moreover, the interrelationships and permeability of the mosaic patch
system in alpine meadows can promote small-scale variability while
maintaining system in large-scale stability (Zhang et al., 2003).
The characteristics of alpine Kobresia meadows did not appear
continuously in multi-steady stages because of the positive and negative
feedback effects between various ecosystem components. However, the
alpine meadow system is an open system with the ability to self-regulate
in response to external disturbances, which is generally manifested as a
discontinuous effect in the feedback of external disturbances. This
nonlinear superposition effect typically causes a lag around an
equilibrium point or critical value in the response of alpine ecosystems
to disturbances (Liu et al., 1999). In addition, at a certain critical
value in the density of matrix media between mini-patches, infiltration
and transformation occurs that drives the plant community into new
stages
(Oborny
& Hubai, 2014). This means that the grazing disturbance pressure of the
grassland ecosystem could show a gradual and continuous change process,
but the point that leads to the regime shift among different steady
stages discontinuous, that is, only when the grazing pressure reached a
critical value, the regime shift should be occurred, so succession
process among different steady stages of alpine meadows was sudden
change, not gradual change.
Alpine meadows have high plant diversity compared to most plant
communities growing in dry and cold regions, and this is also true for
mini-patches. Therefore, the degree of degradation of alpine meadows was
best estimated by determining the frequency or pattern of mini-patches
rather than their overall richness in plant community species.
Human factors have played important role in changing alpine ecosystems
and resources in China over the past 70 years (Yang et al., 2016). The
basic cause of alpine meadow degradation at small spatiotemporal scales
is unsustainable human exploitation, and intense pasture use inevitably
leads to degradation and subsequent reduction in regional economic and
social services (Wang, 2004). Secondary effects such as rodent gnawing
and digging are not initial causes of degradation but arise from the
degradation caused by overgrazing (Zhang & Fan, 2002). Thus, while
estimating the service function of alpine meadows improves understanding
of mini-patch patterns on such meadows, the substantial problem of
managing the degradation of alpine meadows remains.