The evolution of grassland vegetation on the Loess Plateau

Grassland is the largest terrestrial ecosystem in China, and consequently, grassland security closely mirrors national ecological security. As an important area of grassland distribution in the country, the Loess Plateau is one of the most seriously affected areas in the world in terms of soil erosion. Accordingly, with respect to the restoration and reconstruction of vegetation and ecological protection, it is of considerable significance to examine the evolution of grassland vegetation on the Loess Plateau. In this study, we systematically studied the transmutation of grassland vegetation on the Loess Plateau based on a literature review and examination of the historical data. The results indicate that grassland has been the main vegetation type on the Loess Plateau during geological history. From the Pleistocene to the mid-Holocene, grassland vegetation on the plateau underwent numerous changes in the characteristics of forest-grassland, grassland, and desert grassland in response to climate change. Coinciding with an end to the warm period during the late Holocene, there was an overall cooling and drying of the climate, an increase in the human population base, and the development of agricultural civilization. Furthermore, forest steppe on the Loess Plateau changed to dry steppe and the steppe belt migrated southward, whereas the grassland vegetation became severely damaged and reduced in area, and the distribution of desert grassland expanded. Since modern times, with the gradual development of soil and water conservation work on the Loess Plateau, ecological restoration initiatives have gradually been highlighted from the 1980s. Under the implementation of ecological projects such as the construction of the three-north shelterbelt system, the return of farmland to forest and grassland, the restoration and reconstruction of natural grassland vegetation, and a pilot project for the protection and restoration of the mountains, rivers, forests, farmlands, lakes, and grassland systems, there has been an effective control of environmental problems, such as grassland degradation and soil erosion, on the Loess Plateau. Currently, vegetation coverage on the Loess Plateau grasslands and mountains has been markedly promoted, and the degree of vegetation restoration has satisfied the requirements of the regional water resource capacity. Despite these achievements, however, this essentially represents a new phase of development in the ecological reconstruction of Loess Plateau grassland, and one that needs to be continually monitored.