Urban Expansion and Its Impacts on Vegetation Greenness and Productivity in the Beijing–Tianjin–Hebei Region, China

Urban expansion directly reduces vegetation via impervious surface growth, though indirect urban environmental effects may partially offset these losses. This study examines the Beijing–Tianjin–Hebei (BTH) region from 2000 to 2025 by integrating multi-source remote sensing and socioeconomic data to investigate the effects of urban expansion on vegetation greenness (NDVI) and productivity (NPP). The results show that impervious surfaces expanded from 21,747 km2 to 33,688 km2. Yet NDVI and NPP did not decline in tandem. Instead, they responded differently. NDVI exhibited broad increases—particularly in the northwest ecological zones. NPP was more sensitive to impervious surface expansion. Further analysis reveals that impervious surface coverage is the primary driver of NPP, while per capita GDP dominates NDVI. Correlation analysis confirms these relationships are consistent in direction. The combined contribution of socio-economic variables (GDP, per capita GDP, and population) substantially exceeds that of impervious surface area. This suggests that economic development, as a whole, is the dominant force shaping vegetation greenness in the region. These findings challenge the conventional trade-off narrative between urban growth and vegetation health. They demonstrate that urban expansion and ecological improvement can advance in parallel. This requires sustained greening investments and coordinated regional planning. The results offer actionable insights for carbon-sensitive land-use regulation in rapidly urbanizing regions.