Trade-off dynamics underpin distance thresholds in ecosystem service multifunctionality along alpine transportation corridors

Transportation infrastructure profoundly alters ecosystem structure and function in ecologically vulnerable regions, potentially triggering trade-offs among individual ecosystem services. More importantly, the impacts of these trade-offs on ecosystem service multifunctionality (ESM) remain poorly understood. This study developed a novel quantitative framework that incorporates trade-off dynamics into integrated multifunctionality assessment. Applying this framework to the Qinghai-Tibet highway and railway corridors from 2000 to 2020, we examined the spatiotemporal dynamics and spatial heterogeneity of ecosystem service trade-offs and ESM, focusing on carbon sequestration (CS), habitat quality (HQ), and soil retention (SR). The key findings included: 1) CS-SR synergies strengthened over time, whereas CS-HQ synergies weakened after railway construction. 2) ESM exhibited unimodal patterns with distance, reaching maximum values at approximately 4000 m for railway and 6000 m for highway, indicating a more localized impact from railway. As a regulatory factor in ESM calculation, trade-off intensity was higher within approximately 4000 m of railway but shifted to highway beyond this distance. 3) The dominant drivers varied across permafrost zones and transportation corridors, with vegetation and climate factors playing key roles; transportation distance had a stronger positive effect on highway ESM (17.09%) than on the railway in island permafrost areas; the effects of precipitation and temperature shifted in direction with increasing permafrost severity; and in continuous permafrost, significant drivers declined and vegetation index became the primary control (>85%). These findings highlight the role of trade-off based multifunctionality assessment in guiding adaptive management of alpine transportation systems.