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.