# An Analysis of Spatial Variation in Human Impact on Forest Ecological Functions
## 4 Discussion  
### Comparative Analysis of Core Human Activities Affecting FEF  
The long-term variations in forest ecological functions were influenced by both natural and human activity factors, as well as their interactions. The direct impact of natural factors on forest ecological functions was evident in the wide variability of vegetation types, forest biomass, community structure, and naturalness concerning temperature, precipitation, and elevation. Additionally, natural factors also significantly shaped the scope and intensity of human activities. For example, while afforestation was commonly used to rehabilitate and expand forest cover, the regeneration and maintenance of artificial forest vegetation depended on adequate water resources. In China, greening initiatives had not surpassed  
Figure 5: Trend analysis of impact extent of all influencing factors on FEF. the 400 mm precipitation threshold [43], and the lack of water resources post-afforestation posed a risk to the existing vegetation. We find the positive effects of temperature, precipitation, and elevation on FEF in the entire YRB. Among them, the improvement of temperature is most significant in regions VI and VII, and precipitation is crucial in the middle and upper reaches. This is consistent with the findings that precipitation has the greatest effect on vegetation cover in semi-arid regions, while air temperature in semi-humid regions [44]. The higher the altitude of a region, the less interference it receives from human activities and, therefore, the better the FEF. We also observe that natural factors have greater impacts on FEF than human activities in regions I, II, and VII. The fragility of forests tends to reduce with increasing elevation [45]. Since the challenging environmental conditions at high altitudes do not readily support a large human population, the overall impact of anthropogenic activities is greatly diminished [46]. That is why changes in FEF here are more attributable to climate rather than human factors [47]. We are sure that maintaining the natural state of vegetation and minimizing human activities to the greatest extent are beneficial to the FEF in Region I. Due to the economic backwardness and sparse population, primitive economic activities such as grazing and farming have led to the degradation of alpine meadows [48]. Excessive nibbling also slowed the regeneration and renewal of pasture grasses and reduced vegetation cover [49]. Region II has become one of the areas of serious land degradation in the semi-arid steppe region of northern China. Considering that the traditional economic development mode through agricultural sprawl is unsuitable for this region, we insist that the first imperative is to promote economic growth through new urbanization and leave more space for nature to achieve self-renewal. When it comes to Region VII, the complex terrain of the western mountainous area protects it from disturbance by human activities [33]. The abundant resource of forests, shrubs and herbs facilitates better FEF [50]. By contrast, economic activities such as farming and mining occur mainly in the densely inhabited hilly plain areas in the central and eastern part of this region. Meanwhile, ecological projects led by the government, for example, conceding farmland to forests and afforestation in barren mountains, compensates for some of the damages to FEF caused by human activities to some extent [51]. We find that as the impacts of different human activities canceled each other out, we can only capture the significant influence of natural factors on FEF, although human activities are very frequent in this area. Moreover, despite the severe uneven distribution as well as reduced precipitation in recent years, the effect of precipitation on FEF is not significant due to improved irrigation conditions. This seems to be evidence that human activities can indirectly affect FEF by influencing natural factors.