*4.2. Soil Erosion Impact Driver Analysis*

Determining the driving factors of soil erosion helps to elucidate the driving mechanisms behind changes in soil erosion and is a key link for researchers to formulate soil protection policies scientifically and rationally. In the new form of synergistic economic and ecological development, the driving mechanism of soil erosion in karst areas has also changed.

The risk detector indicates that there is no trend correlation between rainfall intervals and soil erosion. Rainfall heterogeneity is not significant at small scales, and spatial heterogeneity of soil erosion is mainly influenced by other factors. Soil erosion in karst tends to increase with increasing vegetation cover but does not exceed a maximum of 15 t·ha−1-a−1. Erodible soil sources are extremely limited in exposed karst areas and increase with increasing vegetation cover. With 80% vegetation cover, the erosive power of rainfall and runoff on the soil is significantly reduced. The risk of soil erosion becomes less after an altitude of more than 1170 m a.s.l. and is related to the extent of human activity. Middle- and low-altitude areas are rich in water and heat resources and have a significant impact on soil erosion due to the concentration of human activities [54]. Higher altitudes have limited hydrothermal conditions and constrained human activities, which do not have a significant impact on soil erosion. Other studies have found that soil erosion in cropland > grassland > woodland. However, in this research area, it is grassland > woodland > cropland [54]. The plant roots formed a root–soil compound with the surrounding soil, which reduced soil erosion [55]. The low risk of soil erosion on arable land is due to the significant loss of soil resources caused by early over-farming. Despite recent efforts to combat soil erosion, soil resources in karst areas are difficult to recover in the short term [56]. The risk of soil erosion on arable land may appear to be low. However, once soil erosion has occurred on arable land, it would become a serious threat to the security of agricultural production. The gradual restoration of arable soil resources and the reduction of soil erosion from arable land should be the long-term goal of soil and water conservation work. The intensity of rocky desertification is negatively correlated with the risk of soil erosion. Similarly, a low risk of soil erosion does not mean a low hazard. On the contrary, the risk of erosion is much higher than that of light rocky desertification. Long-term natural restoration measures such as returning farmland to forests and grasses also aim to control soil erosion in areas of mild rocky desertification and to restore soil resources in areas of intense rocky desertification. Soil erosion risk is positively correlated with slope, and the higher the slope, the greater the increase in soil erosion risk. It is recommended to increase the vegetation cover on steep slopes to improve the stability of the soil.

The factor detector shows that slope explains 60% of the spatial variation in soil erosion. Effective measures to control soil erosion for different slopes can solve most of the soil problems. Some studies have found that sediment is mainly from sloping land [57], suggesting that sloping land above 25◦ should be converted to woodland. We recommend that conversion of land use be accompanied by the establishment of soil erosion protection zones because soils in disturbed soils are highly susceptible to erosion and soils in karst areas are difficult to recover effectively in the short term. The *q* value between LUCC and KRD gradually decreases but still plays a major role in the spatial differentiation of soil erosion. It can be seen that the impact of KRD and LUCC on soil erosion is far-reaching and long-lasting. Both karst rock desertification and soil erosion are closely related to human activities. Effectively improving people's production and living standards is also an important means of combating soil erosion. The role of vegetation cover in soil erosion shows a decreasing and then increasing trend, indicating that the rocky desertification control project in the last 20 years has achieved remarkable results. With continued ecological management, we infer that the role of vegetation cover will outweigh that of rocky desertification and land use in the coming decades. The insignificant effect of rainfall and elevation alone on regional soil erosion is related to the small scale of the study.

The results of the interaction of the factors show that the *q* value increases significantly after the interaction such as slope-rainfall and LUCC-rainfall. Rainfall is a direct driver of soil erosion occurrence and an important influencing factor for soil erosion [58]. The weak influence of rainfall alone in this study is mainly restricted by the scale of the study. The interaction of slope and rainfall increases the flow rate of the slope surface created by rainfall, intensifying scour and increasing erosion. Land use destroys the natural soil structure and weakens the soil's resistance to erosion. Land use also disturbs stable slope

flow, which in combination with rainfall increases soil erosion. During the study period, the dominant factor in soil erosion changed from KRD-slope to LUCC-slope, and finally to elevation-slope. From 2000 to 2005, karst rocky desertification was very serious and was second only to slope in its impact on soil erosion, so the interaction of KRD and slope was the dominant factor in soil erosion. As the area of rocky desertification decreased, the influence of KRD diminished. Therefore, the dominant factor became LUCC-slope. In the course of long-term natural ecological restoration, the land use structure is optimized and the dominant factor changes again to elevation-slope. In comparison with the sum of the *q* values of the individual factors, the *q* values of the interaction between elevation-rainfall increased most significantly throughout the study period. The study area is a typical plateau valley landscape with a relative elevation difference of 923 m. Differences in altitude provide a potential energetic base for rainfall runoff and therefore increase the ability to erode the soil [59].
