Long-Term Elevational Redistribution of Vegetation Greenness Along the Dushanzi–Kuqa Transect on the Southern Flank of the Tianshan Mountains

Mountain vegetation change is commonly summarized as a mean greening or browning trend, or as the displacement of a discrete boundary; both can miss changes in the shape of the elevation profile of vegetation greenness. Here we tested whether the greenness profile on the southern flank of the Tianshan Mountains reorganized between 1989 and 2024, using a Landsat transect along the Dushanzi–Kuqa (G217) highway. NDVI and EVI2 profiles were constructed over a fixed 1000–4100 m elevation domain using only sampling locations valid in all comparison periods; profiles were mean-centered, and the early-to-recent contrast was tested with spatial-block permutations across 36 combinations of temporal window, corridor width, elevation-bin width, and index. All 36 combinations showed significant shape change (p ≤ 0.005) with cross-scenario concordance, and the contrast persisted after adjustment for cross-sensor differences. The contrast followed a consistent three-band structure, with relative decreases at 1100–1950 m, increases at 2550–3300 m, and renewed decreases at 3550–4100 m. Absolute greenness increased almost everywhere (more than 97% of 25,334 samples), but the increase was four to five times larger in the mid-elevation band than in the lower and upper bands, varied eightfold along the transect, and was organized primarily by elevation and along-transect position (spatially cross-validated random-forest R2 ≈ 0.66). The vegetation contrast was not directionally consistent with decadal temperature, soil-moisture, or snow contrasts. Greenness change along this transect was therefore an elevation-dependent redistribution of the whole profile rather than uniform greening or a single boundary displacement, and no robust directional correspondence with decadal hydroclimate contrasts was detected under the present decadal analysis.