Assessing climate-driven ecohydrological effects on altitudinal vegetation belt dynamics in the Bogda natural world heritage site, northwestern China

Climate change is profoundly altering altitudinal vegetation belt regimes in global mountain ecosystems, yet the ecohydrological mechanisms underlying these alterations remain poorly quantified. The Bogda Natural World Heritage Site on the Tianshan Mountains in northwestern China, preserves a complete altitudinal vegetation belt spectrum from desert steppe to alpine meadow, offering an ideal natural experimental area to disentangle climate-driven ecohydrological controls and consequences across elevation gradients. Here, using field comprehensive measurements in conjunction with stochastic ecohydrological modelling approaches, we find that soil and river properties shift nonlinearly along the elevation gradient. Soil moisture increases and soil temperature decreases with elevation, while soil pH and electrical conductivity each follow unimodal distributions peaking at the montane coniferous forest belt. River pH and electrical conductivity decrease with elevation, whereas dissolved oxygen peaks in the desert grassland zone, and suspended solids and turbidity spike at the subalpine alpine meadow transition. Aboveground biomass is controlled primarily by temperature and precipitation, whereas belowground biomass is governed mainly by soil properties. Critically, water‑carbon coupling shifts across vegetation belts, with desert and montane grasslands being water-limited, whereas coniferous forest, subalpine and alpine meadows are energy-limited. Increased rainfall frequency enhances soil moisture stability, while greater rainfall intensity promotes effective water replenishment; their combined effect elevates mean effective soil moisture and enhances carbon assimilation capacity. Accordingly, altitudinal vegetation belts do not respond linearly to climate forcing but instead shift between distinct ecohydrological regimes. These findings offer critical insights for strengthening ecosystem resilience, protecting biodiversity, and enhancing carbon sinks in global mountain systems facing climate change.