Abstract: Exploring the spatiotemporal variations of vegetation on the Loess Plateau and its topographical differentiation effects is of great importance to understanding of the sustainable development modes of “Grain for Green” and the regional ecological evolution. Based on the Landsat image of the growing season from 1997 to 2018, combined with digital elevation model (DEM) data, we analyzed the spatiotemporal variations and topographic differentiation of fractional vegetation cover (FVC) before and after the implementation of the “Grain for Green” in Jixian County, Shanxi Province located in the Loess Plateau. The results showed that: (1) Ecological environment and overall FVC of Jixian County had been significantly improved from 1997 to 2018. With the implementation of the “Grain for Green”, the average annual FVC was increased from 47.87% in 1997 to 58.24% in 2018. However, FVC showed a downward trend in the county town and its surrounding areas. (2) The area with low and medium-low levels of FVC showed a decreasing trend, but the area with medium, mediumhigh, and high level FVC showed an increasing trend. The area with low level FVC (<20%) and medium-low level FVC (20%-40%) was mainly transferred out, while the area with medium level FVC (40%-60%) and medium-high level FVC (60%-80%) was mainly transferred in. FVC grade structure tended to be stable. (3) There were significant differences in vegetation restoration under different altitude, slope, and aspect conditions. The area of FVC located in the altitudes of 1000-1200 m, slopes of 15°-25°, and semi-sunny slopes was significantly increased. Our results can provide a scientific basis for evaluating the effects of regional ecological restoration and optimizing the measures of regional vegetation restoration.

Key words: fractional vegetation cover, ecological restoration, spatiotemporal variation, transfer speed, topographic differentiation.