Abstract
The source region of the Yellow River (SRYR) is an important water conservation and animal husbandry resource in China. It is of great significance to understand the patch pattern and ecological risk of alpine grassland in the SRYR for ecological environment management. This study first used 12 unmanned aerial vehicle (UAV) aerial images and eight moderate resolution imaging spectroradiometer (MODIS) vegetation index product MOD13Q1 images from July to August in 2019 to extract alpine grassland patch patterns in the SRYR, then constructed an ecological risk model based on the landscape vulnerability index and landscape disturbance index, and finally combined spatial self-reliance correlation and semi-variance analysis methods to explore the spatial distribution of ecological risks. The results showed that the patch fragmentation degree (Pi), area weighted shape index (AWMSI), and separation degree (Si) of the four grassland types in the SRYR are ordered as follows: alpine steppe > degraded meadow > alpine meadow > swamp meadow. Moreover, the greater the fractional vegetation cover (FVC), the greater the landscape dominance index (DOi), and the better the ecosystem stability. The spatial difference of ecological risk in the SRYR shows a situation of low risk in the east (ERImin=1.5355) and high risk in the west (ERImax = 70.6429). High FVC was found in low and mild low risk areas where the vegetation types are mainly swamp meadow and shrub, while low FVC was found in high and mild high-risk areas where the vegetation types are mainly alpine steppe and degraded meadow. The spatial distribution of ecological risk of the SRYR has obvious positive spatial correlation (Moran's I = 0.863), the spatial aggregation distribution is distinct, and the local space has significant high-high aggregation and low–low aggregation phenomena. The results of this study reveal that patch characteristics have good indicative significance for alpine grassland ecological protection and should be considered in future studies. In addition, the ecological risk in the SRYR is relatively high, especially in the western region, which should be taken seriously in future ecological management and governance.
Highlights
Fragile ecosystems are defined as lacking natural resilience or by being impacted heavily by an unnatural event that it changes in an unexpected or undesired way [1]
Zelnik [13] found that with the change of disturbance parameters on the Maxwell point threshold, the three trends of patch pattern are mainly perturbed by the initial disturbance degree, the greater the disturbance degree, the faster the threat to the entire ecosystem [62]
There are scholars based on indicators and models to generate a time-series ecological model used to detect key changes in ecosystem disturbances [63]
Summary
Fragile ecosystems are defined as lacking natural resilience or by being impacted heavily by an unnatural (human) event that it changes in an unexpected or undesired way [1]. Under the dual influence of global warming and frequent human activities, the changes of global landscape patterns are significant and cause many ecological risks, which leads to the formation of fragile ecosystems in many regions [3]. As an important part of the ecosystem, patches are the basic structural and functional units of the landscape [4,5]. They are ubiquitous in fragile ecosystems, which have a wide distribution and large area in the global scope
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