Background On the Loess Plateau of China, the check-dam farmland, which has a remarkable impact on regional vegetation restoration, may effectively promote the return of sloping cropland to forest, and check-dam farmland may also significantly improve the land use structure in the area. The objective of this study is to demonstrate the influences and causes of check-dam construction on vegetation restoration on the Loess Plateau of China under the project of returning farmland to forest and grassland.

Methods As a case study in Yulin, a representative area with enormous check dams in the Loess Hill Ravine Region of the Loess Plateau, this study analyzed the spatial-temporal changes of vegetation under various densities of check dams in different districts/counties, and illustrated the trend to recover vegetation on slopes with different gradients based on the remote sensing images of Normalized Difference Vegetation Index (NDVI) and land use which were obtained from the satellite Landsat. Some mathematical methods, e.g., linear regression analysis and Mann-Kendall test, were also considerately used here. The results were shown as follows:

Results 1) Vegetation restoration was relatively fast in the southeastern region, where check dams were densely constructed. A significant linear correlation, where R² = 0.84 and P < 0.001, existed between the density of check-dam distribution and the slope of NDVI regression equation from 2003 to 2018 in each county. The densities of check dams in the southeastern Mizhi, Suide and Jiaxian were 0.976, 1.393 and 1.217 check dams/km², respectively. In proportion, the slopes of NDVI regression equations were 0.0189, 0.0183 and 0.0205 in Mizhi, Suide and Jiaxian, respectively. 2) The most significant improvement of NDVI in the southeastern districts/counties primarily occurred in the sloping area. The NDVI increased in Jiaxian, Mizhi and Suide from 2008 to 2013 were 0.068, 0.087 and 0.028 higher than those from 2003 to 2008. At the same time, the percentages of the most significantly improved areas of NDVI on the slopes of > 15° are 50%, 41% and 38% in Jiaxian, Mizhi and Suide, respectively. 3) Check-dam construction promoted the fallow of sloping cropland in the neighboring area. The decline in grain production at the beginning of the fallow period led to a rehabilitation of sloping cropland in 2000s. Hence, the government of Yulin had a plan to add more than 40 000 hm² of new check-dam farmland to constrain the decline in grain production since 2006, realizing the continuous fallow of sloping cropland while guaranteeing food security.

Conclusions The most significant improvement in NDVI on slopes was the main reason for fast recovery of vegetation in the southeastern districts (counties). Via promoting fallowing on the Loess Plateau of China, check-dam construction accelerated the process of vegetation restoration on the sloping cropland, and consequently guaranteed the sustainable development of the “Grain for Green” Project on the Loess Plateau.