# Vegetation Dynamics and Recovery Potential in Arid and Semi-Arid Northwest China
## 2 Results
### Evolution of Vegetation Restoration Potential in Northwest China
The initial breakpoint value, representing the maximum vegetation cover threshold within the spatial window, was determined using the natural breakpoint method, thus yielding its spatial distribution. The vegetation recovery potential index was categorized into five levels ranging from low to high [34], where a higher index indicates higher potential. Figure 4e shows that the potential is low in the desert, Gobi, and saline areas; it is also low in the eastern and southern parts of northwest China, which results from the high percentage of primary vegetation cover in these areas, as well as being high in grassland-meadow areas in northwest Xinjiang and central Qinghai. These findings suggest that this area has the potential to mitigate the arid and semi-arid conditions prevailing in the region. In summary, the study area as a whole demonstrates little potential for vegetation restoration, and the mean vegetation restoration potential index of northwest China was 0.31. Based on the NDVI data from 1961 to 2019 in northwest China simulated by the LPJ model, the spatial distribution of vegetation cover in 2019 was simulated (Figure 4b), with an average cover of 34.2% in 2019, and the spatial distribution of the maximum vegetation cover was simulated (Figure 4d), with a maximum projected average cover of 35.3% in the future. This led us to estimate that there was still a 1.1% improvement in vegetation cover in the region. As a large-scale model, the simulation results of the LPJ model have obvious spatial heterogeneity, which was, in general, in line with that of remote sensing. From the map, it can be seen that the vegetation cover was higher in the northeast, northwest, and southeast of northwest China and low in the center, mainly concentrated at 0.2. The spatial distribution of simulated vegetation that could be restored by LPJ simulation was obtained by using the vegetation restoration potential index (Equation (5)), and the results are shown in Figure 4f, which is generally consistent with the remote sensing results as a whole, with an average vegetation restoration potential index of 0.14 (Table 4). \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **Very Low** & **Low** & **Lower** & **Medium–Low** & **Medium** & **Medium–High** & **High** \\ \hline FVC & \textless{}0.05 & 0.05–0.1 & 0.1–0.2 & 0.2–0.4 & 0.4–0.6 & 0.6–0.8 & \textgreater{}0.8 \\ \hline
1982 & 54.28 & 4.63 & 3.11 & 12.26 & 9.74 & 7.63 & 8.35 \\
2000 & 52.12 & 4.24 & 3.1 & 11.53 & 11.62 & 8.46 & 8.93 \\
2019 & 50 Vegetation types in northwest China are dominated by grasslands (Figure 5), with temperate deserts in the central part of the study area, forests and farmlands outside in the east, alpine grasslands at high altitudes such as in the south and central part of the study area. \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **0–0.05** & **0.05–0.1** & **0.1–0.2** & **0.2–0.4** & **0.4–0.6** & **0.6–0.8** & **0.8–1** \\ \hline IVSP (satellite-observed) & 40.47\% & 10.48\% & 10.94\% & 8.71\% & 4.02\% & 2.79\% & 22.59\% \\ IVCP (LPJ) & 68.97\% & 1.81\% & 2.48\% & 9.99\% & 7.33\% & 4.89\% & 4.53\% \\ \hline \end{tabular}
\end{table} 
Table 4: Proportion of area (%) with vegetation restoration potential index for northwest China. Figure 4: Current vegetation cover, maximum recovery cover, and natural vegetation restoration potential index in northwest China from 1982 to 2019 based on satellite-observed data and LPJ simulated data. (**(a)**, satellite-observed Current; **(b)**, LPJ simulated Current; **(c)**, satellite-observed maximum; **(d)**, LPJ simulated maximum; **(e)**, satellite-observed Ivcp; **(f)**, LPJ simulated Ivcp). area, and temperate meadow grasslands, temperate typical grasslands, and temperate desertified grasslands in the other areas. Using zonal statistics, the vegetation recovery potential index was analyzed under different grassland types.