China's progress towards sustainable land degradation control: Insights from the northwest arid regions

Soil erosion is a widespread environmental problem, which threatens the environmental sustainability. The northwest arid region (NAR) in China is known as one of the most severe soil loss in the world that suffering from wind erosion. Based on the Revised Wind Erosion Equation (RWEQ), the spatio-temporal change of wind erosion was identified, and the underlying drivers and influencing factors of soil erosion process were investigated. In addition, the implications of constraint effects in soil erosion control were discussed. The results showed that the wind erosion from 1990 to 2013 was substantially lessened, and the government-aided desertification prevention and control programs, as well as increasing precipitation and decreasing wind speed might have contributed to these trends. The constraint line analyses indicated that the vegetation cover had nonlinear and threshold effects on soil erosion through constraining the water condition (precipitation). Specifically, when the precipitation is below the threshold (approximately 50-100 mm yr(-1) in the NAR), the precipitation (water condition) is not sufficient to maintain a good vegetation cover (about 20-40%), therefore the vegetation cannot efficiently prevent wind erosion. However, once the precipitation exceeds this threshold, the vegetation's sand retention function will enhance and thereby reducing soil loss substantially. Vegetation cover has a lower and an upper threshold for controlling wind erosion. A plant cover lower than 10% does little to reduce wind velocity at the soil surface. The effect of vegetation on reducing wind erosion basically reaches the maximum when plant cover is 40% or above. The constraint effects of precipitation on vegetation cover in the arid region should be considered to improve the efficiency of afforestation and reforestation efforts aiming at mitigating and preventing soil loss.