## 3 Methods
### Ecological Environment Quality Evaluation Method  
The data used for ecosystem quality evaluation were derived from Sentinel-2 imagery collected between July and October in 2020 and 2022, with a temporal resolution of 5 days and a spatial resolution of 10 m. These data were obtained from the Google Earth Engine (GEE) remote sensing cloud platform. To assess ecosystem quality, three core indicators were utilized: vegetation coverage (FVC), leaf area index (LAI), and gross primary productivity (GPP). The specific process is as follows: the maximum value of ecological parameters for four vegetation types--forest, shrubland, grassland, and farmland--within each ecological function zone is taken as the reference value. Then, the ratio of the ecological parameter value for each vegetation type of ecosystem within the zone to its reference value is calculated, yielding the relative density of that ecological parameter for the zone. The closer the relative density is to 1, the more similar the ecological parameter for that pixel is to the reference value. The calculation formula is as follows:  
\[\text{RVI}_{\text{i,j,k}}=\frac{\text{F}_{\text{i,j,k}}}{\text{F}_{\text{max,j,k}}} \tag{7}\]  
In the formula, \(\text{RVI}_{\text{i,j,k}}\) represents the relative density of the ecological parameter of the k-th vegetation ecosystem in the j-th region of the \(i\)-th year; \(\text{F}_{\text{i,j,k}}\) represents the value of the ecological parameter of the k-th vegetation ecosystem in the j-th region of the \(i\)-th year; and \(\text{F}_{\text{max,j,k}}\) represents the maximum value of the ecological parameter of the k-th vegetation type in the j-th region of the \(i\)-th year.  
Following this method, reference values for vegetation coverage, leaf area index, and total primary productivity are determined for each region and vegetation type. The relative density values are then normalized to a range of 0 to 1 using the following formula:  
\[\text{x}^{\prime}=\frac{\text{x}-\text{min}(\text{x})}{\text{max}(\text{x})- \text{min}(\text{x})} \tag{8}\]  
In the formula, \(\text{x}^{\prime}\) represents the normalized index after processing; x represents the original index.  
Ecosystem quality, which reflects the overall health and condition of the regional ecosystem, is then computed using the relative densities of LAI, FVC, and GPP with the following equation:  
\[\text{EQI}_{\text{i,j}}=\frac{\text{LAI}_{\text{i,j}}+\text{FVC}_{\text{i,j} }+\text{GPP}_{\text{i,j}}}{3}\times 100 \tag{9}\]In the formula, EQI\({}_{i,j}\) represents the ecosystem quality in the j-th region of the \(i\)-th year; LAI\({}_{i,j}\) represents the relative density of the leaf area index in the j-th region of the \(i\)-th year; FVC\({}_{ij}\) represents the relative density of vegetation coverage in the j-th region of the \(i\)-th year; and GPP\({}_{ij}\) represents the relative density of total primary productivity in the j-th region of the \(i\)-th year.  
According to the \"National Ecological Status Survey and Evaluation Technical Specifications--Ecosystem Quality Assessment\", ecosystem quality is categorized into five levels, with the specific classification detailed in Table 2.