Spatial Coupling Characteristics and Factors Influencing Soil-Vegetation Relationships in the Lower Part of the Shiyang River Basin

The relationship between soil and vegetation is an essential scientific issue in surface environment change. (1) Background: Since the implementation of the Shiyang River Basin governance plan, it has become necessary to quantitatively evaluate the impact of ecological restoration on soil-vegetation spatial coupling. (2) Methods: A coupled model and a coupled coordination model are adopted in order to investigate the spatial coupling characteristics of soil-vegetation systems. Additionally, we explore the influences of climate factors and soil properties on the level of spatial coupling and coordination. (3) Results: From 2015 to 2020, the soil-vegetation spatial coupling coordination in the lower reaches of the Shiyang River Basin was poor, and the average annual proportion of areas with medium and low degrees of uncoordination reached 79.3%. The level of spatial coupling coordination is differed under different vegetation coverage scenarios, and the bare land mainly showed low and moderate imbalances, accounting for 90.3% of the annual average area. The annual average proportions of short coverage and canopy coverage coordinated areas were 53.4% and 49.3%, respectively. In particular, vegetation in the Minqin hinterland is highly sensitive to environmental changes. With the implementation of ecological water conveyance, the spatial coupling coordination between soil and vegetation has improved slightly; however, the effect is not obvious. (4) Conclusions: Precipitation, temperature, and potential evaporation affect the level of coupling coordination between soil and vegetation, with the former having a positive effect and the latter two having negative effects. In addition, soil enriched with sulfate and sand contributed to the disharmony of soil-vegetation relationships in the study area.