## 3 Results and Analyses  
### Distribution and Characteristics of NPP  
Corresponding data were imported into the CASA model to estimate the NPP value of the study region, and values in July, August and September of 2016, 2017 and 2018 are displayed in Figure 5. In accordance with the value range (upper limit close to 270 gC/m\({}^{2}\)) and study period, the data, each of which equally accounted for 30 gC/m\({}^{2}\), were divided into nine groups for refining values of pixels. From Figure 5, the NPP generally decreased from July to September in each year, which might be related to the season. In August 2017, a complex variation of the color block was found in the western part of the study region, and the changes of NPP values near the epicenter were larger. One month after the earthquake, the color block in the central part and western part revealed a decline on NPP, and although the vegetation was recovering, the season was still the dominant factor. Besides, the monthly NPP changes in areas around the epicenter (central part and northern part) were relatively uniform, and the changes in areas far away from the epicenter were complex. The largest NPP ranges were found in the northeastern part and western part of the study region. From the perspective of elevation, the southern region with an altitude higher than 3000 m had diverse terrain that might affect the vegetation NPP to varying degrees when the earthquake occurred. The highest NPP value was found in the area at the altitude of 3000-4000 m, and the lowest NPP value was found in the area above 4000 m.  
As the NPP in the west and south of the study region changed significantly during the earthquake and had a broad range within adjacent pixels that existed in the high-altitude area, the area proportion represented by vegetation NPP of the whole study region was significant for evaluating the ecosystem of Jijuzhaigou Valley. Therefore, the NPP values were classified based on the number of pixels, and the area proportions are shown in Figure 6.  
Figure 5: _Cont._  
Figure 5: The overview of NPP value within the study region in 2016 (**a**), 2017 (**b**) and 2018 (**c**) (the unit of NPP value was unified as gC/m\({}^{2}\)). Figure 6: The area proportions of NPP value. The small, medium, and large annuli denote area proportions in 2016, 2017 and 2018, respectively. (The proportion less than 3.0% was not marked. The transparency of the same attribute color decreases by 20% from the inner annulus to the outer annulus). (**a**) July; (**b**) August; (**c**) September. From Figure 5(a), the areas with NPP value of 90-120 gC/m\({}^{2}\) accounted for nearly 50% of the whole study region, and the maximum value range was found in July 2017 and 2018. In addition, the NPP level in July 2018 is equivalent to that before the earthquake, indicating that the ecosystem was recovering continuously after the earthquake. The NPP value of more than 70% of the study region was 90-150 gC/m\({}^{2}\), which was consistent with the finding of [PERSON] et al. [36]. In August (Figure 5(b)), the NPP value decreased, and the area with lower NPP values became larger. The NPP values of most areas were 60-150 gC/m\({}^{2}\), and the color block indicating the maximum range did not appear. However, a larger value range appeared in August the next year, which proved that grasslands and arbor forests with higher productivity showed stronger resilience [36]. In September (Figure 5(c)), the temperature gradually decreased, and the NPP value changed greatly. One month after the earthquake, the value range peaked, while the value was smaller than 60 gC/m\({}^{2}\) in September 2018. NPP\({}_{\text{sum}}\) represented the total NPP value of the vegetation ecosystem. Owing to the diversity of the ecological system, NPP\({}_{\text{sum}}\) values are comprised of maximum (NPP\({}_{\text{max}}\)) and minimum values in the region according to zonal analysis. The NPP\({}_{\text{max}}\) value was taken to reflect the maximum intensity of vegetation productivity.