## 1 Introduction
The main driving factor of LPJ model is climate data, so it could reflect the variety of NPP under the pure climatic changes. These models have evaluated for a variety of conditions to test their robustness in capturing the spatial and temporal patterns of change in ecosystems' attributes such as NPP [14; 15]. However, there has been significant variability among these models' results due to differences in formulation of ecosystem processes, underlying assumptions for their formulation in these models, and the uncertainties associated with observations used in understanding these processes [16; 17]. Although the models could estimate the large-scale NPP, they have ignored the influences of human activities. For assessing NPP and its spatial and temporal trends, quite often a combination of models and observational proxies (e.g., NDVI) has been used to ensure the reliability of the results [9]. The normalized difference vegetation index (NDVI) is a simple graphical indicator to monitor the change in vegetation by using remote sensing measurements [18], which could be used as an observational proxy to study the global, regional and temporal changes in NPP. Human activities and ecological construction have also been factors affecting NPP [19]. [PERSON] et al. [20] thought that anthropogenic activity was the main force driving changes in NPP, which played an active role in the growth of regional vegetation. Meanwhile, human activities could lead to desertification, which might decrease the total actual NPP [21]. [PERSON] et al. [22] pointed out that the ecological restoration programs in Xinjiang from 2001 to 2009 could increase the NPP. In addition, the implementation of major national ecological projects in the Three Gorges Reservoir Area since 1998 has markedly counteracted the negative influences of the Three Gorges Project on NPP in this area [14]. In recent years, there have been several major afforestation projects in the Yangtze River basin, such as the Yangtze River Shelterbelt project and the project of Returning Farmlands to Forests. Through these afforestation projects, the proportion and quality of forest vegetation in the Yangtze River have been enhanced, and the NPP and carbon sequestration capacity of forests have improved [23]. In fact, [PERSON] et al. [24] pointed out that human activities and climate change jointly affected the NPP of vegetation, but at present, the quantitative analysis of the impact of human activities on NPP on vegetation is not sufficient from the perspective of spatiotemporal scale and climate disturbance. Although there have been lots of studies on NPP in the Yangtze River basin, there have been few studies on forest NPP in the basin. Therefore, the purposes of this study were: (1) to reveal the temporal and spatial evolution pattern of forest NPP and NDVI in the Yangtze River basin during the past 30 years; (2) to evaluate the influences of climate changes and human activities on the forest NPP and NDVI in the basin, and then clarify the reasons for the forest NPP and NDVI changes at regional scale. This study is of great significance to the forest water cycle and carbon cycle of the Yangtze River. Moreover, our findings will provide a basis for forest vegetation monitoring and ecological conservation efforts in the Yangtze River basin.