GEDI-constrained forest mapping and Potential–Realized climate limits of canopy height, biomass and structural complexity in the upper Yellow River

The upper Yellow River is a nationally important water-conservation region where forest three-dimensional structure supports carbon storage and hydrologic buffering. In this topographically complex forest–shrub–grass mosaic, watershed-scale constraints of forest structure by climate remain poorly quantified, and uncertainty in forest extent can propagate into subsequent structural mapping and attribution. We produced a GEDI (Global Ecosystem Dynamics Investigation) height-constrained hierarchical forest mask and generated 10–30 m forest cover with probability and quality-assurance layers for the upper Yellow River.

Using the Taohe River Basin as a representative catchment, UAV LiDAR benchmarks were upscaled with Sentinel-1/2 time-series metrics, topographic predictors and GEDI information to derive 30 m wall-to-wall canopy height, aboveground biomass (AGB) and canopy entropy, the latter representing vertical structural complexity. Independent evaluation indicates reliable performance (R² ≈ 0.71–0.84; canopy entropy R² = 0.836).

Forest structure–climate relationships were examined with a Potential–Realized framework. Climate-constrained structural potential was estimated using conditional upper-quantile models, and climatic limitation was quantified as the departure of realised structure from its potential. Hydrothermal thresholds are well defined: canopy height potential peaks at 2–4 °C mean annual temperature (≈ 25 m) and approaches saturation beyond 540–560 mm annual precipitation; the joint optimum for canopy height and AGB occurs under ~450–550 mm precipitation and 5–8 °C mean temperature; canopy entropy maximises near 2–4 °C, 450–550 mm, aridity index ≈ 1.2, and potential evapotranspiration ≈ 600 mm. Using downscaled CMIP6 projections and derived vapour pressure deficit (VPD), we quantify potential contraction and overshoot risk (current structure/future potential) and provide analysis-ready layers for climate-risk screening in water-source regions.