## 3 Results and Analysis
### Analysis of the Spatial and Temporal Evolution of Ecological Quality
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Change Level** & \begin{tabular}{c} **Change Area** \\ **(km2)** \\ \end{tabular} & **Percentage (\%)** & \
\begin{tabular}{c} **Total Change** \\ **(km2)** \\ \end{tabular} &
\begin{tabular}{c} **Total Percentage** \\ **(\%)** \\ \end{tabular} \\ \hline Improved & Significantly Improved & 1.9375 & 0.12 & & \\ Improved & 287.0625 & 17.46 & 289 & 17.58 \\ Invariability & Invariability & 1142.5 & 69.5 & 1142.5 & 69.5 \\ Degenerate & Worse & 212.375 & 12.92 & & \\ Significantly Worse & 0.1215 & 0.01 & & 212.5 & 12.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Monitoring of MRSEI changes in the Nyingchi–Gongbo’gyamda section of the Lhasa–Nyingchi Motorway from 2012 to 2020. Figure 5: Changes in the level of the MRSEI from 2012 to 2020.  
in the western and central parts of the study area. Additionally, a significant proportion (17.58%) of the area experienced improvement in ecological environmental quality, mainly located in the central and western sections, as well as the periphery of the entire study area. Lastly, there were areas where ecological quality degraded, primarily in the eastern-central part of the study area. Table 8 analyzes the overall changes in ecological quality using a transition matrix. With the exception of the \"excellent\" and \"poor\" levels, the proportion of each ecological quality level that remained unchanged was the largest. Additionally, the proportion of transitions between two or more levels was relatively small, regardless of whether the changes were \"improved\" or \"degenerate\". For each level, except for the \"excellent\" level, the proportion of improvements was greater than that of degradations. From the perspective of MRSEI level transitions, the proportions and areas of land that did not undergo transitions from the \"excellent\" to \"poor\" ecological quality levels are as follows: 33.35%/57.625 km\({}^{2}\), 75.98%/553.375 km\({}^{2}\), 54.22%/235.5625 km\({}^{2}\), 49.21%/117 km\({}^{2}\), and 44.21%/31.25 km\({}^{2}\). Among them, the land with \"good\" and \"fair\" ecological quality levels had a larger area that did not undergo any transitions. Therefore, the land with unchanged ecological environmental quality from 2012 to 2020 was mainly dominated by \"good\" and \"fair\" levels. In terms of improvements in ecological environmental quality levels, the proportions and areas of land that transitioned from \"poor\", \"fair\", \"moderate\", and \"good\" to the next higher level are as follows: 45.36%/32.0625 km\({}^{2}\), 29.61%/70.375 km\({}^{2}\), 32.1%/139.4375 km\({}^{2}\), and 12.88%/93.8125 km\({}^{2}\), respectively. It is evident that there was a significant increase in the areas for all categories. Therefore, improvements in ecological environmental quality were evident in all four levels: \"poor\", \"fair\", \"moderate\", and \"good\". In terms of degradation types, the proportions and areas of land that transitioned from \"excellent\", \"good\", \"moderate\", and \"fair\" to the next lower level are as follows: 65.39%/113 km\({}^{2}\), 10.36%/75.4375 km\({}^{2}\), 11.57%/50.25 km\({}^{2}\), and 16.4%/39 km\({}^{2}\), respectively. It can be seen that there was a higher proportion of degradation in the \"excellent\" and \"good\" categories. Therefore, the degradation of ecological quality mainly occurred in the transition from \"excellent\" to \"good\" and \"good\" to \"fair\". In summary, the ecological environmental quality in the study area was slightly better in 2020 than in 2012, with more obvious improvements in the central and western sections. The areas with significant ecological degradation were mainly located in the eastern part of the study area, where the \"excellent\" and \"good\" ecological quality levels were degraded to \"good\" and \"moderate\", respectively.