# Spatio-Temporal Changes in Ecosystem Quality across the Belt and Road Region
## 5 Discussion
### Advantages and Limitations of the Proposed Method  
This study proposes an objective and automatic method for ecosystem quality assessment and analyzed the spatial and temporal distribution characteristics of ecosystem quality over the B&R region at a 1 km spatial resolution scale. The method is effective in integrating the vegetation growth status derived from vegetation ecological parameters for large regional ecosystem quality assessment. One advantage of the proposed method is that the indicators selected are simple and easy to obtain and can quickly assess ecosystem quality in large regions. Another advantage is that it introduced using the PCA approach to determine the most reasonable weighting of the indicators in generating ecosystem quality results with higher objectivity and credibility. The method is different from previous studies that evaluate ecosystem quality using average weighting methods based on expert opinions [40]. However, the vegetation ecological parameters of LAI, FVC and GPP represent different characteristics of vegetation status and have different influences on ecosystem quality. Therefore, it is necessary to determine which indicator occupies a larger proportion in the evaluation of ecosystem quality. The introduced PCA weighting approach identified that the GPP was more important for determining ecosystem quality, which was reasonable because the GPP is directly related to the ability of vegetation to photosynthesize. Furthermore, the PCA weighting approach also accelerates the weighting process without requiring experts' consultation. Therefore, this improved method of ecosystem quality assessment was better in this study at dealing with multiple indicators and effectively estimating indicator weights based on the intrinsic features of the indicators compared with subjective methods, generating a reasonable result of ecosystem quality assessment in the B&R region. In addition, this study analyzed the spatiotemporal patterns of ecosystem quality over the entire B&R region and identified the changes from the years 2016 to 2020, which has not been provided by previous research. The results can objectively reflect the spatial distribution and temporal changes in the ecosystem quality of the study area. They can also provide scientific information services and give a credible reference for the sustainable development of the B&R region's regional ecology.  
However, there were also some limitations to this study, even though it achieved a reliable assessment of ecosystem quality. Firstly, this study selected vegetation ecological parameters as the indicators for assessing ecosystem quality, while not taking into consideration other factors such as human stress, social and political conditions, which could be considered in future work. Secondly, due to the limitations of data availability, this study did not consider more aspects related to natural hazards and public health emergencies like the COVID-19 pandemic, which will also be taken into consideration for future studies. Finally, the B&R region is a relatively large region for ecosystem quality assessment in that it is difficult to fully identify the ecosystem processes at play with 1 km resolution data.  
Therefore, future studies will be conducted over the regions with a significantly decreased EQI to further explore the causes of the ecosystem quality changes based on time series and higher spatial resolution remote sensing data.