# The Impacts of Climate and Human Activities on Grassland Productivity Variation in China
## 4 Discussion  
The vegetation index is widely used to detect vegetation dynamics. Previous research has indicated that GPP is a more effective measure of the carbon sequestration capacity of vegetation, whereas the leaf area index (LAI) or the normalized difference vegetation index (NDVI) tends to signify the vegetation's greenness [56; 57]. Therefore, in this study, we used GPP as the vegetation indicator to research grassland variation. The results indicate that the degradation of Chinese grasslands has been effectively reversed in the past 20 years. The GPP of the grassland has shown a significantly increasing trend during 2000-2018 in most provinces (autonomous region), especially in SX, SAX, GS, and NX provinces (autonomous region), located on the Loess Plateau. These results are consistent with previous research based on remote sensing data such as the NDVI, LAI, and net primary productivity (NPP) [58; 59]. Although an overall trend of grassland recovery in China was observed, the degradation of grassland in some regions cannot be ignored, such as in the northeastern region of the IMG autonomous region and the western region of the XJ autonomous region, where there are patches of grassland degradation. Many previous studies have confirmed this finding [57; 60]. According to previous studies, climate and human activities remarkably impact grassland variation. In this study, we selected three climate factors and six socioeconomic factors as indicators to measure the impact intensity. The results show that the impacts of climate and socioeconomic factors on grassland in China had obvious spatiotemporal  
Figure 9: The individual contribution rates of various climate factors and human activity to GPP. heterogeneity. In terms of climate factors, PRE was the primary climatic factor affecting grassland in China, followed by TEM. Grasslands are mostly in northern China, and this region is controlled by arid and semi-arid climates and limited by water resources [61; 62]. Therefore, PRE is the main factor affecting northern grassland, and PRE was absolutely dominant in western XJ and parts of IMG and HB provinces (autonomous region). In recent decades, the amount and frequency of PRE have shown an upward trend [63; 64]. In addition, the grasslands of China distributed on the Qinghai-Tibet Plateau, which has a high altitude, are controlled by the plateau climate. Previous studies have shown that with global changes, the TEM on the Qinghai-Tibet Plateau has warmed significantly over the past few decades, and accelerated warming could alleviate the restriction of microthermal conditions on the vegetation growth rate [65]. Therefore, the grassland in most areas of the Qinghai-Tibet Plateau has been shown to be in a state of recovery. However, in the northern part of the IMG autonomous region, which has a temperate continental climate, the increasing TEM has an inhibitory effect on grassland restoration in the region, and previous studies have shown similar results [66; 67]. The reason for this phenomenon may be that the increased TEM leads to increased water evaporation, which accelerates the drying rate of the soil [68; 69]. How human activities affect ecosystems is often difficult to measure, and they are difficult to express on spatial and temporal scales using specific data [70; 71]. In this study, we chose six socioeconomic factors covering economic, population, livestock, and grassland conservation measures to reflect human activities, and based on the GTWR model and the LMG method, we quantified the effects and contribution of the grassland ecosystems. Grasslands are a fundamentally important source of food for livestock; however, the relationship between livestock and grassland is extremely complex. Previous studies have shown that moderate grazing can maintain a high level of ecosystem diversity in grassland ecosystems, while low or high grazing can have negative impacts [72].