## 3 Results and Analyses
### Vegetation-Earthquake Impact Assessment  
In accordance with the designed assessment system, the quantitative change of NPP before and after the earthquake was calculated by Formula (10). After normalization (Formula (11)), the \(\Delta{NPP}\) values corresponding to each seismic intensity were obtained, and vulnerability indices were calculated, as shown in Table 3.  
From Table 3, the resilience (\(R\)) one month after the earthquake was 0.642-0.693, and the resilience (\(R\)) of the whole study region was 0.671. At an intuitive ecological level,  
Figure 8: The NPP\({}_{\text{mean}}\) change caused by the three earthquake-induced geohazards in 2015 to 2019. (a) Landslide; (b) Debris flow; (c) Collapse.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{3}{*}{**Dur-quake**} & **Seismic** & \multicolumn{4}{c}{**Area Proportion for Normalized Values (\%)**} & \multicolumn{2}{c}{**Vulnerability**} & **Impact** \\  & **Intensity** & **0–0.2** & **0.2–0.4** & **0.4–0.6** & **0.6–0.8** & **0.8–1** & **Index (S)** & **Coefficient (I)** \\ \cline{2-9}  & VII–VIII & 1.93 & 15.28 & 78.99 & 3.26 & 0.54 & 0.470 & 0.168 \\  & VIII–IX & 0.97 & 12.49 & 84.98 & 1.53 & 0.03 & 0.474 & 0.146 \\  & IX+ & 1.86 & 3.26 & 5.21 & 87.81 & 1.86 & 0.669 & 0.213 \\  & VII–IX+ & 1.21 & 13.23 & 83.53 & 1.81 & 0.22 & 0.473 & 0.156 \\ \hline \multirow{3}{*}{**Post-quake**} & **Seismic** & \multirow{3}{*}{**Intensity**} & \multirow{3}{*}{**0–0.2**} & \multirow{3}{*}{**0.2–0.4**} & \multirow{3}{*}{**0.4–0.6**} & \multirow{3}{*}{**0.6–0.8**} & \multirow{3}{*}{**0.8–1**} & **Resilience (R)** & **Impact** \\  & **Intensity** & & & & & & **Index (R)** & **Coefficient (I)** \\ \cline{1-1} \cline{2-9}  & VII–VIII & 1.20 & 2.76 & 24.03 & 67.70 & 4.31 & 0.642 & 0.168 \\  & VIII–IX & 0.03 & 0.29 & 5.66 & 91.33 & 2.69 & 0.693 & 0.146 \\  & IX+ & 1.02 & 2.05 & 3.07 & 92.47 & 1.40 & 0.682 & 0.213 \\  & VII–IX+ & 0.39 & 1.32 & 13.38 & 82.23 & 2.68 & 0.671 & 0.156 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The area proportion for \(\Delta{NPP}\) value normalization, vulnerability index (\(S\)) and resilience index (\(R\)) of 3 seismic intensities and the whole study region from July to August 2017.  
resilience was determined by the natural restoration of the ecosystem, and the results had a high referential value. However, the vulnerability (\(S\)) was 0.470-0.669, with the range slightly broader than that of resilience, but the vulnerability (\(S\)) of the whole study region was 0.473 and was within the normal range. The impact coefficient (\(I\)) calculated by Formula (9) was 0.146-0.213. Also, the vulnerability and resilience indices corresponding to a single seismic intensity range remained similar, and the indices corresponding to the IX+ intensity were markedly different from those corresponding to other intensity ranges. In fact, the seismic intensity was affected by the epicentral distance and the smaller the epicentral distance, the greater the intensity [38]. The magnitude (7.0) of the Jiuzhaigou earthquake could be converted into an intensity of more than 10 by a correlation formula [39; 40], and Sichuan Earthquake Administration did not release the map of seismic intensity above 9. Therefore, it is reasonable to think that the specificity of the index is affected by the uncertain intensity boundary range.  
In the process of studying the damage degree and recovery level of vegetation before and after the earthquake, it was found that almost all (98.98%) vegetation in IX+ seismic intensity zones was damaged; the vegetation in VIII-IX seismic intensity zones was slightly less damaged (94.84%); VII-VIII seismic intensity had the least impact on NPP (82.79%). Vegetation in IX+ seismic intensity zones recovered best (93.12%) (Table 4). It could be preliminarily concluded that the higher the seismic intensity, the greater the damage degree and recovery level.