Changes in Vegetation Greenness in the Upper and Middle Reaches of the Yellow River Basin over 2000-2015

The Grain to Green Project (GTGP), a large ecological restoration project aiming to control soil erosion and improve the ecological environment, has been implemented since 1999 and has led to great land use changes with decreased farmland and increased forest and grass, and significant vegetation variations. Understanding vegetation variations for different land use types is important for accessing the present vegetation development and providing scientific guidance for future ecological restoration design and regional sustainable development. With two land use maps and MODIS LAI data, trend analysis, fluctuation analysis, and R/S methods were applied to analyze the vegetation dynamic changes and sustainability for converted land use types from cropland and unconverted types over 2000-2015 in the upper and middle reaches of the Yellow River. The results obtained were as follows: (1) Vegetation greening was remarkable in the entire study region (0.036 yr(-1)). The increasing rate was higher in wetter conditions with AI < 3 (0.036-0.053 yr(-1)) than arid regions with AI > 3 (0.012-0.024 yr(-1)). (2) Vegetation improved faster for converted forestland, shrubland, and grassland than unconverted types under similar drying conditions. Converted shrubland and grassland had a larger relative change than converted forestland. (3) Converted land use types generally exhibited stronger fluctuation than unconverted types with small differences among types. (4) Vegetation exhibited a sustainable increasing trend in the future, which accounted for more than 73.1% of the region, mainly distributed in the middle reach of the Yellow River. Vegetation restoration exerted important influences on vegetation greening and the effect was stronger for converted types than unconverted types.