Vegetation restoration and ecosystem soil conservation service value increment in Yanhe Watershed, Loess Plateau

In order to explore the ecological benefits of vegetation restoration after the implementation of the Grain for Green Project(GFGP) in 1999, this study selected the Yanhe Watershed in the Loess Plateau as the study area. By using the trendline analysis, SWAT(Soil and Water Assessment Tool) Model and the evaluation approach of ecosystem services(including market value, opportunity cost, restoration cost, and shadow project approaches), the paper analyzed the vegetation restoration status and its effect on soil conservation after the implementation of the GFGP, and assessed the effect of ecosystem service value enhancement. The results showed that:(1) since the GFGP was implemented, the vegetation recovery effect has been remarkable, which was specifically reflected in the increasing trend of vegetation coverage in the Yanhe Watershed from 2000 to 2015.(2) The effect of vegetation restoration on soil erosion was obvious. Without vegetation cover, the soil is prone to erosion with the large erosion modulus. Taking 2000 as the base year when the GFGP was implemented, the soil conservation from 2001 to 2014 has increased to varying degrees, indicating that the watershed management has achieved certain outcomes over the years.(3) The vegetation cover in the watershed is dominated by medium vegetation cover, and the soil conservation is dominated by low soil conservation. There are differences in soil conservation under different vegetation cover. Among them, medium-low, medium and medium-high vegetation cover can effectively maintain the amount of soil.(4) The temporal and spatial distribution characteristics of the value of the ecosystem soil conservation services are obvious. From 2000 to 2015, the annual average soil conservation service value of the watershed was 3.64×10~8 yuan, and the monthly average soil conservation service value was 6.06×10~7 yuan during the growing season. The value of the ecosystem soil conservation service increased significantly. On the temporal scale, the precipitation is an important factor in the value of the ecosystem soil conservation service; on the spatial scale, the spatial differences in the value of ecosystem soil conservation service in the watershed is large, which is specifically manifested as the highest in the downstream, followed by the upstream, and the lowest in the middle-stream. This study not only clarified the huge ecological benefits brought by the GFGP, but also provided a certain reference role for the soil