# Exploring the Spatiotemporal Alterations in China's GPP Based on the DTEC Model
## 4 Discussion
### The Influence of Human Activities on China's GPP Dynamic Changes  
The effects of climate change and anthropogenic activities on increasing GPP trends were 1.39 and 5.67 g C m\({}^{-2}\) yr\({}^{-1}\), respectively. Anthropogenic activities had a greater positive impact on GPP than did climate change, showing that anthropogenic activities are the dominant factor in China's GPP growth. [PERSON] [45] also showed that anthropogenic activities had a stronger effect on vegetation changes than did climate change. The overall trend of change was positive, showing that China's ecological construction and protection projects have been effective [46]. [PERSON] [47] reported that China's forest area increased by 13.48% from 2001 to 2015. By 2020, the forest area had increased to 16%, with the increase obtained mainly by the conversion of shrubland and savanna types (Figure S4). According to the eighth consecutive inventory of forest resources in China, compared with the second inventory, China's plantation forest preservation area increased by 2.13 times, and the plantation forest stock increased by approximately five times [48]. This conclusion is in agreement with the regions covered in this paper where the GPP growth trend was greater than 10 g C m\({}^{-2}\) yr\({}^{-1}\). Against the background of the continuous reduction in global forest area, the average annual growth rate of China's forest coverage was the highest in the world, especially in terms of the growth of artificial forest area, accounting for approximately 41% of the global afforestation rate [49]. China's forest ecosystems have had a significant carbon sink function in the last two decades [50]. Notably, land use changes caused by human activities are also among the key factors affecting vegetation GPP [51]. Among them, the promotion of agricultural intensification techniques, such as replanting [52] and various irrigation techniques [53], has greatly contributed to the increase in GPP in farmlands in China. [PERSON] [54] noted that the grain output of farmland in China has increased by more than 35% since 2000. In this paper, by comparing the land use data from 2001 to 2020, we found that the area of cultivated land in China increased by 3%; this increase was mainly obtained by the conversion of grassland and savanna vegetation types to crops through the ecological reclamation activities of adjusting land use [55] (Figure S4). The spatial distribution of cropland coincided with regions with greater positive anthropogenic contributions (Figure 8b). However, crops are seasonal [56], and after crops and straw are harvested and consumed during the nongrowing season, carbon is no longer stored [57]. With the respiration of microorganisms in the soil and the decomposition of soil residual fertilizers, the carbon exchange process between farmland ecosystems and other systems intensifies [58]. Therefore, many scholars generally believe that the carbon sink of crops is zero [59]. The DTEC model was driven by remote sensing data to assess the productivity of terrestrial ecosystems. Therefore, this model only focuses on the carbon sequestration effect of vegetation. For issues such as carbon exchange in nongrowing seasons and soil carbon consumption in farmland ecosystems, this model's mechanism cannot be reflected at present, so we will not discuss it too much here. There were significant regional variations in the effects of anthropogenic activities on GPP. A comparison of the trends of human activity in the nine regions revealed that the difference between the extremes was 15.66 g C m\({}^{-2}\) yr\({}^{-1}\). The NC area was the most effective area for implementing vegetation construction projects [60], and the relative contribution of human activities was also the highest (82%).