## 1 Introduction  
Humans have displayed a history of deforesting and changing land use and land cover since farming began. China's environmental problems are among the most severe of any major country, because of the need for food security for its large population and the pursuit of high economic growth [1]. From the 1950s to the 1980s, China experienced severe losses of forest and grassland because of large-scale deforestation and grassland reclamation for crop production and industrial construction [2; 3; 4; 5]. This pattern of changing land use has led to severe soil erosion [6]; land desertification [7; 8]; loss of biodiversity [9; 10]; drying rivers and shrinking lakes [11]; and the frequent occurrence of dust storms, floods, and drought [1; 12; 13]. To address these problems and maintain environmental sustainability, several countrywide ecological restoration programs have been implemented [2; 14]. The Grain for Green Program (GGP), also known as the Sloping Land Conversion Program (SLCP), is regarded as the largest ecological restoration program ever implemented in a developing country [4; 15]. The GGP, originally planned for 2001-2010 (the first round), aimed to set aside 14.67 million ha of cropland (4.4 million ha with slopes greater than 25\({}^{\circ}\)) and aforest a roughly equal area of waseland by 2010 [16]. By the end of 2015, the Chinese government had achieved its ambition to increase forest by approximately 29.87 million ha, with a total investment of approximately 405.66 billion RMB (US$58.52 billion) [17]. A new round was launched at the end of 2014 [18], and the implementation region was expanded at the end of 2015 [19]. An assessment of the impact of the first round of GGP on ecosystems could provide insights into future ecological restoration, and provide input into ecological programs initiated by other countries' governments all around the world. Previous studies have evaluated the ecological changes brought about by the GGP restoration program from different perspectives, including land use and land cover (LULC) change, vegetation condition, net primary productivity (NPP), and ecosystem services, since the program was designed to convert farmland to forest and grassland, and further reduce soil erosion and desertification [20; 21; 22; 23]. [PERSON] & [PERSON] [24] detected land cover change in Ansai County and found that farmland had been reduced overall from 18.12% to 13.58% in 2004-2010, while forest increased from 14.60% to 37.95%. [PERSON] et al. [25] investigated the vegetation in Bijie Prefecture and found that it had been significantly improved, but the trend of degradation had not been reversed in the east of the region. [PERSON] et al. [26] reported that the NPP and evapotranspiration (ET) in Loess Plateau had increased by 9.3 gCm\({}^{-2}\) and 4.3 mm per year, respectively, in 2000-2010, but lost soil moisture of 2.4 mm yr\({}^{-1}\) and runoff of 0.5 mm yr\({}^{-1}\) simultaneously. [PERSON] et al. [19] stated that the transformation from non-irrigated farmland to forestland could potentially improve soil conservation by 24.89%, but the increase extent of GGP implementation decreased NPP and water yield at the sub-watershed scale. With the analysis of different ecological variables, these findings underscore the complexity and trade-offs behind the anthropogenic program implementation. Although previous studies have investigated eco-environmental change in the GGP region, most have focused on the local or regional scale, rather than the national scale. Moreover, the impact of climate change on ecosystems has often been neglected, which may cause unforeseen errors in the assessment. In this paper, we monitor and assess the ecological changes in the whole region where the GGP was implemented in China from 2000 to 2010 using remote sensing and modelling techniques along with trend analysis, based on a comprehensive assessment indicator system established to reflect changes in ecosystem pattern, ecosystem quality, and key ecosystem services.