## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Year** & **Forests** & **Croplands** & **Grasslands** & **Barren** & **Waters** & **Urban** \\ \hline
1990 & 727,907 & 507,194 & 414,788 & 58,358 & 50,684 & 24,051 \\
1995 & 732,503 & 499,127 & 426,116 & 49,969 & 48,730 & 26,475 \\
2000 & 726,616 & 502,204 & 416,113 & 58,467 & 51,244 & 28,277 \\
2005 & 727,692 & 497,125 & 415,433 & 58,116 & 52,688 & 31,871 \\
2010 & 728,025 & 493,487 & 414,927 & 58,285 & 52,971 & 35,235 \\
2000 minus 1990 & \(-\)1291 & \(-\)4990 & 1,325 & 109 & 560 & 4226 \\ Percent & \(-\)0.18 & \(-\)0.98 & 0.32 & 0.19 & 1.10 & 17.57 \\
2010 minus 2000 & 1409 & \(-\)8717 & \(-\)1186 & \(-\)182 & 1727 & 6958 \\ Percent & 0.19 & \(-\)1.74 & \(-\)0.29 & \(-\)0.31 & 3.37 & 24.61 \\ \hline \end{tabular}
\end{table} 
Table 4: The land-use in the Yangtze River basin (Area, unit: km\({}^{2}\); Percent, unit: %). 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). [PERSON] et al. (10) used the Carnegie-Ames-Stanford Approach (CASA) model to stimulate the grassland NPP over the Qinghai-Tibet plateau from 1982 to 2011, and thought that the effect of human activities on the alpine grassland ecosystem obviously intensified in the latter period, so the negative effect caused by climate change to ecosystem could have been relatively mitigated or offset. [PERSON] et al. (20) thought that human activity was the main force driving changes in NPP from 2001 to 2014 in Hengduan Mountain area, China and the majority of NPP residuals were positive, possibly due to the return of farmland back to forest and natural forest protection. [PERSON] et al. (49) investigated the ecological engineering project effectiveness on vegetation restoration in the Beijing-Tianjin Sand Source Region from 2000 to 2010 based on the rain use efficiency trend in relation to the land-cover and found that the effectiveness of the ecological engineering projects differed for each subarea and was proportional to the strength of ecological engineering. [PERSON] et al. (24) considered that human activities and climate change jointly affected the NPP of vegetation. For assessing NPP and its spatial and temporal trends, quite often a combination of models and observational proxies (e.g., NDVI) are used to ensure the reliability of the results. However, [PERSON] et al. (22) concluded that human activities produced more obvious positive impact in the increasing of NPP than climate change. [PERSON] et al. (50) reported that the percentage of the warming resulting from deforestation relative to the warming when the increase in greenhouse gases concentrations was included, was higher than 60% in the tropical region. Many previous studies have revealed that the afforestation projects have increased the forest coverage, canopy density, forest NPP, forest areas and the carbon storage (51; 52). For example, [PERSON] et al. (2) reported that the magnitude of China's forest biomass C sink almost doubled during 2000-2007 due to the implementation of afforestation project. [PERSON] et al. (53) pointed out that the increased C stock in Asian terrestrial ecosystems might primarily be attributed to considerable afforestation and reforestation. Due to the implementation of large-scale afforestation and reforestation practices beginning since the late 1970s, China's forest biomass C stock has increased by 40% between the 1970s and the 2000s. [PERSON] et al. (54) analysed the distribution of the NPP using MODIS datasets and VPM (Vegetation Photosynthesis Model) from 2000-2015 and they explored that the NPP on the Loess Plateau increased significantly from 2000 to 2015 (\(p<0.05\)) since the implementation of Returning Farmland to Forest project.