# Vegetation Dynamics and Recovery Potential in Arid and Semi-Arid Northwest China
## 2 Results
### Evolution of Vegetation Restoration Potential in Northwest China  
Based on NDVI data from AVHRR remote sensing imagery, a two-dimensional pixel model was computed to obtain vegetation cover (FVC) data from 1982 to 2019; the years 1982, 2000, and 2019 were specifically chosen for vegetation cover analysis, resulting in the generation of spatial distribution maps representing vegetation cover. Figure 3 illustrates that, in general, vegetation cover in northwest China has experienced a positive trend over the years. This trend was predominantly characterized by a gradual transition from areas with low vegetation cover to those with high vegetation cover in certain regions. Additionally, there was an expansion of high vegetation cover areas from the central region towards the periphery. This notable increase in vegetation coverage was primarily  
Figure 2: Changing trends of satellite-observed NDVI and LPI-simulated NDVI in northwest China from 1982 to 2019. (**(a)**, satellite-observed NDVI 1982–2019; **(b)**, LPI simulated NDV 1982–2019; **(c)**, satellite-observed NDVI 1982–2000; **(d)**, LPI simulated NDVI 1982–2000; **(e)**, satellite-observed NDVI 2000-2019; **(f)**, LPI simulated NDVI 2000–2019). concentrated in the northeastern part of Inner Mongolia, northwestern Xinjiang, eastern and southern Qinghai, and southern Gansu. However, it is important to note that significant portions of the central northwest still exhibit low vegetation coverage. By reclassifying the fractional vegetation cover (FVC) for northwest China in 1982, 2000, and 2019 and calculating the proportion of area covered by each vegetation category, the time-varying characteristics of vegetation cover were analyzed (Table 3). Combined with the characteristics of the study area, the vegetation cover was classified into seven grades, namely, very low cover (FVC \(<\) 0.05), low cover (0.05 \(<\) FVC \(<\) 0.1), lower cover (0.1 \(<\) FVC \(<\) 0.2), medium-low cover (0.2 \(<\) FVC \(<\) 0.4), medium cover (0.4 \(<\) FVC \(<\) 0.6), medium-high cover (0.6 \(<\) FVC\(<\) 0.8), and high coverage (0.8 \(<\) FVC \(<\) 1). As can be seen from the table, the vegetation cover in northwest China from 1982 to 2019 increased in high cover and medium-high cover areas, of which the largest increase was observed for medium-high cover, which increased by 2.68%. Medium-low cover first increased significantly and then slightly decreased, increasing overall. Vegetation cover for medium-low cover remained basically unchanged and decreased for very low, low, and lower cover; specifically, from 1982 to 2019, it decreased by 3.65%, 1.12%, and 0.49%, respectively. Overall, there was a significant improvement in vegetation cover in northwest China from 1982 to 2019. Figure 3: Spatial distribution map of satellite-observed vegetation coverage in 1982 (**a**), 2000 (**b**), and 2019 (**c**). In this part, FVC calculated from NDVI data from AVHRR remote sensing images and FVC calculated from NDVI data from LPJ simulations are used to study and analyze the vegetation restoration potential of the northwest region by using the vegetation restoration potential calculation model. According to the remote sensing data, the spatial distribution of vegetation cover in 2019 in the northwest China region varied significantly (Figure 4a), with higher vegetation cover in eastern Inner Mongolia, southern Qinghai, western Xinjiang, and southern Ningxia, and an average of 21% vegetation cover in 2019 in northwest China. The maximum recovery cover of future average vegetation determined by the \"similar habitat\" method was 23.3% (Figure 4c), which meant that there was still an estimated 2.3% improvement in vegetation cover in the region. To quantify the disparity between current vegetation growth and its potential for recovery, a model for calculating the natural recovery potential index of vegetation was employed (Equation (5)).