## 5 Conclusions  
This study constructed a long-term time series Impervious Surface Coverage (ISC) dataset for the Beijing-Tianjin-Hebei region from 1985 to 2020 through spatial aggregation of 30 m GAIA data, and analyzed the spatiotemporal response relationship between urbanization and ecological environment changes. The regional impervious surface area increased dramatically from 7579.3 km\({}^{2}\) in 1985 to 37,484.0 km\({}^{2}\) in 2020, representing a total growth of 394.5% over the 35-year period, with expansion rates showing two distinct peaks around 1990 and 2010-2015. Urban centers migrated from the Beijing-Tianjin corridor toward southeastern Hebei, reflecting regional development acceleration. The forest area in high-density regions increased significantly during 1985-2005 before declining, while grassland fragmentation intensified in low-density areas primarily driven by the discontinuous urban expansion pattern characteristic of Chinese urbanization [35], exacerbated by linear infrastructure development and agricultural conversion policies [36]. The Ecological Vulnerability Index assessment revealed expanding high vulnerability areas in Beijing-Tianjin cores, which may be attributable to the concentration of urban development pressures, including population agglomeration [37], urban heat island intensification [38], and insufficient green infrastructure development relative to urbanization pace. Conversely, the 4.2% decline in low-vulnerability mountainous areas results from multiple stressors including climate change impacts on montane ecosystems [39], as well as tourism and infrastructure development pressure. While conservation policies such as ecological protection zones and afforestation programs have been implemented in the Beijing-Tianjin-Hebei region, our findings suggest that these measures may not be fully offsetting the combined pressures of climate change and development activities in peripheral areas. The declining trend indicates a need for enhanced conservation strategies and stricter implementation of environmental protection policies in low-density regions. ISC and EVI relationships showed significant spatial heterogeneity: positive correlations in areas like the Temple of Heaven (indicating successful urban renewal with ecological improvement) contrasted with negative correlations around Capital Airport (reflecting ecological degradation from rapid expansion). These findings highlight urgent needs for location-specific urban planning strategies that balance development with ecological protection. Several key research directions emerge from this study that warrant further investigation. First, the temporal resolution of vulnerability assessment could be enhanced through the integration of higher-frequency satellite data and real-time monitoring systems. The current 5-year interval analysis may miss critical short-term ecological responses to urbanization pressures, particularly during rapid development phases or following extreme weather events. Second, the transferability of our ISC methodology and vulnerability assessment framework to other urban agglomerations requires systematic validation. While our comparison with global urban products demonstrates consistency in the Beijing-Tianjin-Hebei context, application to regions with different urbanization patterns, climatic conditions, and ecological systems would strengthen the generalizability of our approach. Priority should be given to testing in other major Chinese urban agglomerations such as the Yangtze River Delta and Pearl River Delta, followed by international urban regions with similar characteristics. Finally, the development of predictive capabilities through scenario modeling would significantly enhance the practical value of vulnerability assessments. Future research should focus on coupling our ISC methodology with land use change models and climate projections to assess how different development scenarios might influence ecological vulnerability patterns under changing environmental conditions.