Long-Term Vegetation Dynamics Across Distance Buffers Along the Gonghe–Yushu Expressway Corridor on the Qinghai–Xizang Plateau

Highway construction in alpine environments of the Qinghai-Xizang Plateau (QXP) raises concerns about vegetation degradation and ecosystem disruption. However, the long-term ecological dynamics along newer expressway corridors on the QXP remain insufficiently understood. This study investigated vegetation dynamics and land use/land cover (LULC) changes along the Gonghe-Yushu Expressway (G0613, 634 km) corridor from 2000 to 2025, spanning the pre-construction, construction (2011–2017), and post-construction operational periods. Using 25 years of Landsat 5/7/8/9 imagery, we analyzed NDVI trends with Sen’s slope and Mann-Kendall tests, classified LULC into four classes (Grassland, Bare land, Water body, Built-up) using Random Forest, and examined NDVI—climate relationships using TerraClimate data. The results revealed a widespread and significant greening trend, with 77.3% of pixels showing significant NDVI increases (+0.0026/year) and no significant decreasing trends. The greening was established before highway construction and continued uniformly through all periods, with no detectable distance-dependent gradient across buffer zones (0–1, 1–2, 2–5, 5–10 km). LULC transitions were limited, with Bare land and Grassland as the dominant classes in the buffer corridor. NDVI was strongly correlated with temperature (ρ = 0.748, p < 0.001), which increased by +0.068 °C/year over the study period, while precipitation showed no significant trend. These findings indicate that vegetation greening co-varied with regional warming, while no persistent distance-dependent highway-associated NDVI signal was detected at the analyzed scale. Localized roadside impacts may remain unresolved at 30 m resolution, and the long-term implications of continued warming warrant continued monitoring.